carburetor problem
10-26-2010, 02:32 PM
#1
Staging Lane
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carburetor problem The season here is finished, or very close to be. After 1 summer whit a carburated LSx, i can tell that i'm very happy whit this new set-up in my 69 camaro. L92 6.0L, Msd 6012, GM intake, good comp cam, Map sensor and all other stuff run very well..
But, I have 1 problem, my carburetor did not work good.. It was installed on my 355 chevy, and the problem was the same, it's why i can say that is not the motor set-up that cause this problem. This carb came from Daytona, buy in the daytona week from a racer. It was fabricated 2002, but not use since 2004. I put it in my 355 last year, and run good for the summer 2009, but not at 100%... No link, no back fire, but not 100% satisfied( i didnot rebuild it). This summer, i run it on my 6.0L L92 engine, and run good, but not like i want. My car run whit an AFR meter, so i can tune the car on the cruise at 13.5-14:1, and WOT at 12.9-13:1.
The problem is:
When i drive the car at about 60mph, and want to go at 70, i need to push about 1/4 inch on the gaz pedal.. when i do this AFR goto 20 and motor want to stop for 2-3 second,and after, AFR go back to about 15-16 until i reach the 70 mph, very lean.. after i have reached my speed, afr go back to 13-14.
The problem is the same when i need to grow up on the highway... AFR go to about 15-16 when need more power...
During the summer, i change shooter, 31 for 35 on the primary, and no significative gain.
If i go WOT, no problem, down to about 12.8-13:1... the problem is only when i go steady and want juste a little more.... In this case, AFR go very lean. My jet are 72-76 when cold ( 10-15 degre), and go down to 71-75 this summer( at 30-35 degre).
What can be the problem? It's a 750 holley double pumper, mecanical secondairy, ported for race.
It can be the power valve? bad gasket ?
Here are some picture of my carburetor.
thanks for your help!
But, I have 1 problem, my carburetor did not work good.. It was installed on my 355 chevy, and the problem was the same, it's why i can say that is not the motor set-up that cause this problem. This carb came from Daytona, buy in the daytona week from a racer. It was fabricated 2002, but not use since 2004. I put it in my 355 last year, and run good for the summer 2009, but not at 100%... No link, no back fire, but not 100% satisfied( i didnot rebuild it). This summer, i run it on my 6.0L L92 engine, and run good, but not like i want. My car run whit an AFR meter, so i can tune the car on the cruise at 13.5-14:1, and WOT at 12.9-13:1.
The problem is:
When i drive the car at about 60mph, and want to go at 70, i need to push about 1/4 inch on the gaz pedal.. when i do this AFR goto 20 and motor want to stop for 2-3 second,and after, AFR go back to about 15-16 until i reach the 70 mph, very lean.. after i have reached my speed, afr go back to 13-14.
The problem is the same when i need to grow up on the highway... AFR go to about 15-16 when need more power...
During the summer, i change shooter, 31 for 35 on the primary, and no significative gain.
If i go WOT, no problem, down to about 12.8-13:1... the problem is only when i go steady and want juste a little more.... In this case, AFR go very lean. My jet are 72-76 when cold ( 10-15 degre), and go down to 71-75 this summer( at 30-35 degre).
What can be the problem? It's a 750 holley double pumper, mecanical secondairy, ported for race.
It can be the power valve? bad gasket ?
Here are some picture of my carburetor.
thanks for your help!
10-26-2010, 02:52 PM
#2
The 3 things that come to mind are: wrong power valve, too large of booster bleed jets and improperly adjusted or wrong accelerator pump cam.
If it were mine, the first thing I would do is measure my idle vacuum level. Then I would make sure that my power valves were appropriate. Next I would try a smaller booster bleed jet and then test drive the car to see if it improved. Lastly, I would consider the accelerator pump cam/setting.
Since you only complain about this problem at a cruise, I would most strongly suspect the booster bleed jet first if this is only a very light throttle scenario.
If it were mine, the first thing I would do is measure my idle vacuum level. Then I would make sure that my power valves were appropriate. Next I would try a smaller booster bleed jet and then test drive the car to see if it improved. Lastly, I would consider the accelerator pump cam/setting.
Since you only complain about this problem at a cruise, I would most strongly suspect the booster bleed jet first if this is only a very light throttle scenario.
10-26-2010, 02:54 PM
#3
Don't take this the wrong way, but you need to take it to someone who knows how to tune a carb. It sounds like your accelerator pump and/or transition circuit is not kicking in soon enough or properly.
get it professionally tuned it will make a WORLD of difference.
get it professionally tuned it will make a WORLD of difference.
10-26-2010, 03:01 PM
#4
10-26-2010, 06:26 PM
#6
On The Tree
used race carb= tuning changes First off you need to understand that when you buy used carb it's buyer beware. Sometimes a "deal" is not what you think. You need to look at the metering blocks and measure all the holes. Remember a "race" carb is tuned for max effort and circletrack stuff is all about off the corner and full throttle. If you don't understand where/when fuel goes thru a carb you will be better off with a new carb. I say this because I think you are in over your head.
That being said first thing you need is to set the fuel pressure to no more than 7 lbs., no less than 6lbs. Then set the float with the car running. Now move on to the idle screws. Unless you have a real big cam the idle speed should be around 750-850rpm. Because you have an O2 sensor set the idle A/F somewhere between 14.5 and 14.8. Idle speed can be set using the front and rear throttle shafts. Unknown to many is that the rear has a set screww that can be adjusted from under the carb. Pain in the butt, we remove this screw and put it in from the top so it can be adjusted without removing the carb.
next step is the idle air-bleeds. They are used to set the A/F on rpm just below the rpm when the carb starts pulling fuel from the main jets. Usually somewhere between 1600-1800 rpm will work. I try to achieve an A/F of 14.3 -14.7 here.
Your stumble is in the transition, the acc pump circuit is not at fault. Because you have an open plenum manifold the carb gets a weaker signal so you need to richen up the carb another way.
Now we need to check the power valve the engine needs. You need a vacuum gauge to see the vacuum at idle in gear if an auto tranny. Let's say you have 10-11 inches of vacuum. You need a power valve that opens at 8.5" of vacuum. You want the power valve closed when at idle. The # stamped on them is the vacuum at which they open. I will bet you carb has a real low # power valve or it's plugged off.
Now you need to get the car up to cruise rpm. I like to tune the street cars to be 14.0-14.5 at cruise. So..... while cruising along and you try to speed up slightly as you roll into the throttle the vacuum drops and the power valve opens enriching the front jet 6-8 #'s. You might need to enlarge the power valve restrictions so the enrichment is higher.
The above is why you need to know if someone has been playing with the holes in the meetering blocks. There are idle restriction holes that play a big role here.
Long winded and just touching the tip.
Aleck
That being said first thing you need is to set the fuel pressure to no more than 7 lbs., no less than 6lbs. Then set the float with the car running. Now move on to the idle screws. Unless you have a real big cam the idle speed should be around 750-850rpm. Because you have an O2 sensor set the idle A/F somewhere between 14.5 and 14.8. Idle speed can be set using the front and rear throttle shafts. Unknown to many is that the rear has a set screww that can be adjusted from under the carb. Pain in the butt, we remove this screw and put it in from the top so it can be adjusted without removing the carb.
next step is the idle air-bleeds. They are used to set the A/F on rpm just below the rpm when the carb starts pulling fuel from the main jets. Usually somewhere between 1600-1800 rpm will work. I try to achieve an A/F of 14.3 -14.7 here.
Your stumble is in the transition, the acc pump circuit is not at fault. Because you have an open plenum manifold the carb gets a weaker signal so you need to richen up the carb another way.
Now we need to check the power valve the engine needs. You need a vacuum gauge to see the vacuum at idle in gear if an auto tranny. Let's say you have 10-11 inches of vacuum. You need a power valve that opens at 8.5" of vacuum. You want the power valve closed when at idle. The # stamped on them is the vacuum at which they open. I will bet you carb has a real low # power valve or it's plugged off.
Now you need to get the car up to cruise rpm. I like to tune the street cars to be 14.0-14.5 at cruise. So..... while cruising along and you try to speed up slightly as you roll into the throttle the vacuum drops and the power valve opens enriching the front jet 6-8 #'s. You might need to enlarge the power valve restrictions so the enrichment is higher.
The above is why you need to know if someone has been playing with the holes in the meetering blocks. There are idle restriction holes that play a big role here.
Long winded and just touching the tip.
Aleck
10-27-2010, 10:29 AM
#7
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thanks for all your anser.. very nice! very appreciated.. ( sorry for my english )
I'm not a pro whit carburetor, only jet change, fuel level in the bowl ajustement and base tuning. It's why i ask pro, here
I made the vacuum test this week-end.
at about 700750 rpm(idle), vacuum is 8 in
at about 1000 rpm, vacuum is 11 in
and at 1500 rpm, vacuum is 15 in.
But these test was made on Park, not in gear!
I got my car remised next week, for the winter, and i will came back whit the carb, for have it chek and rebuilt whit new gasket, new power valve, new accelerator pump, buy i friend that made several LMS serie program. ( this carb didnot run during 4-5 years.
My fuel pressure is 7. i have a blue holley pump whit regulator.
What is the power valve i need? and whitch rebuild kit i need to buy?
Do i have power valve in the primary and in the secondary section? But now, my problem is only whit the primary use! No problem at WOT. I have a bit ( may be the half) this problem in harder acceleration, but it's may-be caused by the primary section.
For the primary nozzel spray,i change the 31 for 35 and did not see good difference... but the nozel spray only when push pedal, and the problem stay there during all the small acceleration ( bigger nozzel will not change the result, i think! )
For the accelerator pump cam, i thinks it's good, because a lot of gaz go out immidiately when i push pedal.. But this cam will not change anything during long acceleration!
What is the job of the bleed jet?
If , by exemple, the inside power valve is 3.5, and i put in a 6.5, what will be the difference ? the afr will be more rich during small acceleration ?
Like i can see on the link that eric1h give me ( thanks ), my car run like the power valve was plugged ! or it's a very wrong PV. For have proper AFR ratio during small acceleration ( only whit the primary part of the carb ), i need to have about 75-76 primary jet. Whit these primary jet, at cruise, AFR is about 11.5-12:1, too rich. For have a good AFR at cruise, i need 71-72 jet like i have now, but when i make small acceleration afr go to 18-19-20... very bad, the motor want to go off..
The O2 sensor connected to my AFR meter give me between 14, 14.5 and 15 at idle!
An other thing that i have remarqued, last week, i run about 1 hour on highway to go somewhere... afr at cruise was about 12.5-13:1 ( a bit more rich than normally), and when i came back home, 2-3 hours later, the afr was 14.5-15:1, and small acceleration was very hard to do... more lean than 2-3 hours ago... what can cause this? It can be the power valve that made this difference?
Thanks a lot again for all your anser!
More it go, more i think that my biggest problem is the power valve!
I'm not a pro whit carburetor, only jet change, fuel level in the bowl ajustement and base tuning. It's why i ask pro, here
I made the vacuum test this week-end.
at about 700750 rpm(idle), vacuum is 8 in
at about 1000 rpm, vacuum is 11 in
and at 1500 rpm, vacuum is 15 in.
But these test was made on Park, not in gear!
I got my car remised next week, for the winter, and i will came back whit the carb, for have it chek and rebuilt whit new gasket, new power valve, new accelerator pump, buy i friend that made several LMS serie program. ( this carb didnot run during 4-5 years.
My fuel pressure is 7. i have a blue holley pump whit regulator.
What is the power valve i need? and whitch rebuild kit i need to buy?
Do i have power valve in the primary and in the secondary section? But now, my problem is only whit the primary use! No problem at WOT. I have a bit ( may be the half) this problem in harder acceleration, but it's may-be caused by the primary section.
For the primary nozzel spray,i change the 31 for 35 and did not see good difference... but the nozel spray only when push pedal, and the problem stay there during all the small acceleration ( bigger nozzel will not change the result, i think! )
For the accelerator pump cam, i thinks it's good, because a lot of gaz go out immidiately when i push pedal.. But this cam will not change anything during long acceleration!
What is the job of the bleed jet?
If , by exemple, the inside power valve is 3.5, and i put in a 6.5, what will be the difference ? the afr will be more rich during small acceleration ?
Like i can see on the link that eric1h give me ( thanks ), my car run like the power valve was plugged ! or it's a very wrong PV. For have proper AFR ratio during small acceleration ( only whit the primary part of the carb ), i need to have about 75-76 primary jet. Whit these primary jet, at cruise, AFR is about 11.5-12:1, too rich. For have a good AFR at cruise, i need 71-72 jet like i have now, but when i make small acceleration afr go to 18-19-20... very bad, the motor want to go off..
The O2 sensor connected to my AFR meter give me between 14, 14.5 and 15 at idle!
An other thing that i have remarqued, last week, i run about 1 hour on highway to go somewhere... afr at cruise was about 12.5-13:1 ( a bit more rich than normally), and when i came back home, 2-3 hours later, the afr was 14.5-15:1, and small acceleration was very hard to do... more lean than 2-3 hours ago... what can cause this? It can be the power valve that made this difference?
Thanks a lot again for all your anser!
More it go, more i think that my biggest problem is the power valve!
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10-27-2010, 10:45 AM
#8
I would try a 6.5 power valve in the primaries. Going from a 3.5 to a 6.5 power valve will make the fuel enrichment come in sooner. This may eliminate your problem.
Here is an article from Holley:
http://www.holley.com/data/TechServi...wer_valves.pdf
Here is an article from Holley:
http://www.holley.com/data/TechServi...wer_valves.pdf
10-27-2010, 11:08 AM
#9
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thanks for the link...
If i have a 3.5 power valve , and change for a 6.5, no more fuel will be send by the power valve at idle and at cruise, but the power valve will open and give more fuel for the acceleration , when the vacuum go down of 6.5 in ? Whit a 3.5, i need to go near of WOT for have the power valve open! More the number is high, sooner the power valve will open! But power valve need to be closed at idle. It's why i need a power valve 3-4 number under the idle vacuum number! if i have 8 idle, i need PV about 4.5 ).
I'm better remake a vacuum test whit the trans in the D gear?
If i have a 3.5 power valve , and change for a 6.5, no more fuel will be send by the power valve at idle and at cruise, but the power valve will open and give more fuel for the acceleration , when the vacuum go down of 6.5 in ? Whit a 3.5, i need to go near of WOT for have the power valve open! More the number is high, sooner the power valve will open! But power valve need to be closed at idle. It's why i need a power valve 3-4 number under the idle vacuum number! if i have 8 idle, i need PV about 4.5 ).
I'm better remake a vacuum test whit the trans in the D gear?
10-28-2010, 06:57 AM
#12
Does anyone else find it is weird that his idle vacuum is so low and comes up so much with a slight increase in RPM? I haven't measured my vacuum in a while but I seem to remember a number like 23 inches at idle. What size cam are you running? Also are you running a MAP sensor, what is your idle timing and how much vac advance? A vacuum leak will make tuning your carb a tough task. Vacuum advance from a MAP sensor really cleans up the idle properties.
You didn't mention your idle screws, I assume a 4 corner idle screws? How far out are they turned?
My last question, what RPM is your motor turning at 60 MPH? Sort of need to know that to tell if you are on the idle or main circuits. Can’t believe you are into the secondaries at that point.
I will tell you my AFR ratio did exactly what yours did when cruising under 2000 RPM. AFR was good at cruise, but a slight application of throttle and things went 19:1 or 20 :1 then back down to 12:1. Mash the throttle and it as all go with no stumble. The fix in my case was going two sizes smaller on the idle air bleeds. Now I sit around 15:1 on cruise, and any touch of the throttle drops things down to 12:1 to 13:1 or so. No stumble. I have a 750 mech secondary DP also, stock LS2 crate motor, 6.5 PV. Don’t try to fix the problem with oversized primary jets or massive accel pump squirters. The fix IMO is like Stinkybutt says and getting a stronger signal to the carb.
A couple of other hints I have picked up along the way. The power valve should be selected off a vacuum reading at cruise, not idle. A bad power valve gasket essentially bypasses the power valve making things too rich at idle. The idle mixture screws are only for setting the mixture at idle. Any throttle off idle and it is idle feed restrictors and air bleeds. The primary throttle blades should be set so there is I think 20 thousands of the transition slot showing. Adjust the idle RPM by turning the secondary blades and by adjusting the timing. If your cam is so big that you can’t get the primary blades that far shut, you may need to drill a hole in the blades.
Holley says the idle screws should be turned to maximize the idle vacuum. With the creation of wide band O2’s I have to wonder if that is true anymore. I turned mine to get 15:1 AFR.
Like everyone said you need to measure all the orifices in your metering block and check them against the numerical carb listings Holley publishes. You want to know if someone went all happy on your carb with a drill. But not to worry, if any of them are too large. You can drill and tap them for a brass set screw then drill that to whatever restriction you need. Press in air bleeds can be drilled out and replaced with set screws also. Very easy to do. It can be a little tricky measuring the restrictions, make sure you get all the way into the metering block holes to measure the actual restriction.
Oh, and as for the AFR fluctuating with time and temp, that could just be the nature of a carb. FI does a much better job of compensating for changes in temp and air density. However I would really look into your idle vac. If your cam is anywhere near stock then that just doesn’t seem right to me. Maybe someone will correct me on that. But a vacuum leak will cause inconsistent results.
10-28-2010, 08:12 AM
#13
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Thanks Pop N wood, thanks for your anser, and here are mine
1st thing i want to remember, this carb was on my chevy 355 and the problem was the same, but a little bit less important. ( the 355 was very low in vacuum , and the LS have a good vacuum for booster brake)
For my vacuum, idle, 1000 rpm, and 1500 rpm, i thinks it's normal to have difference! faster run the motor whit trottle plate closed, higher is the vacuum! No ?
But this week end, i will remake a test whit trans in D postition. Whitch rpm i need to know? only idle at 700 rpm? As i can read, i'm better take vacuum at cruise at about 3000 rpm ? i can take the number that i will have on my msd software?, in PSIa ? how to convert this number in ''in HG'' ? because power valve number are in ''in HG'' Or i'm better to take 3 feets ose and have my gauge on the wiper ?
I also have 14.5-15 AFR at idle.
I run a comp cam #54-469-11 recommanded by a comp cam tech.
I also run a map sensor, for timing advance.
Idle vacuum is about 3 ( not in HG ), by memory, it give total of 22-23.
For the idle screw, you can not see it on the picture? i see only 1 each side on the primary section.
At 60 mph, motor run about 3000 rpm, and is only on the primary section... secondary is needed only at 100mph and more, i think.
Ok, in your case, drop 2 size of your air bleed jet fix the problem ? Happy to read this.. Can you let me know what are the air bleed, because i can see 8 small jet, inner, outer, primary, secondary !! i'm not a pro in carb I will se also, what is my actual power valve this week-end.
For the vacuum leak, i will put new gasket when chek for the power valve, and chek for the air bleed jet!
What is the job of the air bleed? more the jet is big, leaner will be the acceleration? if i drop down 2-3 sizes, the acceleration will be more rich?
Thanks for all again!
1st thing i want to remember, this carb was on my chevy 355 and the problem was the same, but a little bit less important. ( the 355 was very low in vacuum , and the LS have a good vacuum for booster brake)
For my vacuum, idle, 1000 rpm, and 1500 rpm, i thinks it's normal to have difference! faster run the motor whit trottle plate closed, higher is the vacuum! No ?
But this week end, i will remake a test whit trans in D postition. Whitch rpm i need to know? only idle at 700 rpm? As i can read, i'm better take vacuum at cruise at about 3000 rpm ? i can take the number that i will have on my msd software?, in PSIa ? how to convert this number in ''in HG'' ? because power valve number are in ''in HG'' Or i'm better to take 3 feets ose and have my gauge on the wiper ?
I also have 14.5-15 AFR at idle.
I run a comp cam #54-469-11 recommanded by a comp cam tech.
I also run a map sensor, for timing advance.
Idle vacuum is about 3 ( not in HG ), by memory, it give total of 22-23.
For the idle screw, you can not see it on the picture? i see only 1 each side on the primary section.
At 60 mph, motor run about 3000 rpm, and is only on the primary section... secondary is needed only at 100mph and more, i think.
Ok, in your case, drop 2 size of your air bleed jet fix the problem ? Happy to read this.. Can you let me know what are the air bleed, because i can see 8 small jet, inner, outer, primary, secondary !! i'm not a pro in carb
I will se also, what is my actual power valve this week-end.For the vacuum leak, i will put new gasket when chek for the power valve, and chek for the air bleed jet!
What is the job of the air bleed? more the jet is big, leaner will be the acceleration? if i drop down 2-3 sizes, the acceleration will be more rich?
Thanks for all again!
10-28-2010, 09:13 AM
#14
Man, big cam. I have never set up a cam that large so hopefully people who know more than me will jump in.
Here is a picture of air bleeds. One is for the idle circuit and the other the main circuit.
At 3000 RPM you are probably in the main circuits. Air bleeds meter the amount of air getting drawn into the emulsion tube. A larger bleed allows more air to come in, emulsion tubes mix the air with the fuel going into the booster. My understanding is if you didn't have air bleeds and emulsion tubes, the amount of gas getting sucked into the venturi would increase with air flow making the mixture vary with airflow. so the air bleeds sort of even out the mixture with changes in airflow. I have read other descriptions that say the airbleeds just alter the timing of when the carb switches from the idle circuits to the main jets.
At any rate you can play with the size of the airbleeds to see what that does. Higher end carbs have screw in airbleeds. If yours are pressed in then you need to figure out another way of adjusting them. I know you can adjust the idle feed restrictors in the metering block by putting a small piece of wire in the restriction. you can get different sized wire from old guitar strings or piano wire. Not sure how you would secure this in an airbleed. The other option is drilling out the press in bleed and tapping it with a 8/32 or 10/32 set screw then drilling that to the size you want
This link has some pretty good pictures and a much more complete description of what I am trying to tell you
http://www.google.com/imgres?imgurl=...26tbs%3Disch:1
By the way, my work blocks pictures so I can't see your pictures till I get home. don't tell my boss.
Here is a picture of air bleeds. One is for the idle circuit and the other the main circuit.
At 3000 RPM you are probably in the main circuits. Air bleeds meter the amount of air getting drawn into the emulsion tube. A larger bleed allows more air to come in, emulsion tubes mix the air with the fuel going into the booster. My understanding is if you didn't have air bleeds and emulsion tubes, the amount of gas getting sucked into the venturi would increase with air flow making the mixture vary with airflow. so the air bleeds sort of even out the mixture with changes in airflow. I have read other descriptions that say the airbleeds just alter the timing of when the carb switches from the idle circuits to the main jets.
At any rate you can play with the size of the airbleeds to see what that does. Higher end carbs have screw in airbleeds. If yours are pressed in then you need to figure out another way of adjusting them. I know you can adjust the idle feed restrictors in the metering block by putting a small piece of wire in the restriction. you can get different sized wire from old guitar strings or piano wire. Not sure how you would secure this in an airbleed. The other option is drilling out the press in bleed and tapping it with a 8/32 or 10/32 set screw then drilling that to the size you want
This link has some pretty good pictures and a much more complete description of what I am trying to tell you
http://www.google.com/imgres?imgurl=...26tbs%3Disch:1
By the way, my work blocks pictures so I can't see your pictures till I get home. don't tell my boss.
10-28-2010, 09:58 AM
#17
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my air bleed are screw!,i can change it easy!
1 is for the idle, and 2 is for the main!
I see somewhere that a HP carburator arrive whit 35 for the idle, and 75 for the main... I will unscrew this jet and chek the size... In my case, i must go 2 size smaller, like 73 ( if i have 75), if i need to change the main air bleed!
I must change 2 air bleed for the main in the primary, or i need to change all 4 air bleed for primary and secondary?
I thinks i'm better to begin whit the 2 primary, fix my small acceleration problem, and after, if i also have problem whit acceleration using the secondary section, i will change it too.
So, i will retake a vacuum test for the power valve whit trans at D, chek the power valve if it's ok, and after, drop de size of my primary main air bleed jet!
Whit this, may-be i will fix my problem!
Thanks for the link... a lot of information...
1 is for the idle, and 2 is for the main!
I see somewhere that a HP carburator arrive whit 35 for the idle, and 75 for the main... I will unscrew this jet and chek the size... In my case, i must go 2 size smaller, like 73 ( if i have 75), if i need to change the main air bleed!
I must change 2 air bleed for the main in the primary, or i need to change all 4 air bleed for primary and secondary?
I thinks i'm better to begin whit the 2 primary, fix my small acceleration problem, and after, if i also have problem whit acceleration using the secondary section, i will change it too.
So, i will retake a vacuum test for the power valve whit trans at D, chek the power valve if it's ok, and after, drop de size of my primary main air bleed jet!
Whit this, may-be i will fix my problem!
Thanks for the link... a lot of information...
Last edited by marco_chevy; 10-28-2010 at 10:08 AM.
10-29-2010, 01:35 PM
#18
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[QUOTE=marco_chevy;14050181]my air bleed are screw!,i can change it easy!
1 is for the idle, and 2 is for the main!
I see somewhere that a HP carburator arrive whit 35 for the idle, and 75 for the main... I will unscrew this jet and chek the size... In my case, i must go 2 size smaller, like 73 ( if i have 75), if i need to change the main air bleed!
I must change 2 air bleed for the main in the primary, or i need to change all 4 air bleed for primary and secondary?
I thinks i'm better to begin whit the 2 primary, fix my small acceleration problem, and after, if i also have problem whit acceleration using the secondary section, i will change it too.[QUOTE]
I probably ought to stay out of this, but I just can't help myself, LOL. First of all I hope you just got mixed up when you posted the bleed sizes. It should read 75 for the idle bleed (the outside one) and 35 for the main bleed (the one closestto the center) If they ARE like you posted, somebody has mistakenly put them in the wrong positions. The next thing that I noticed is your advance curves, both RPM and MAP. If these are the curves you are actually running, I don't see how you are running as well as you say you are. The cam you mentioned is (if I remember right) around 216-220 @ .050 on a 112 LA. You should have an RPM curve similar to this 0 RPM (cranking speed) 12-15*...800RPM (idle speed) 18-22*...2000RPM 28-32*...and, depending on who you believe, from 3000RPM up...anywhere from 32-36*. These are not exact numbers, only ballpark. Your vacuum curve is also not working. (MAP) Here's why. Someone has convinced you to put 20* in your MAP curve to
"make it idle better". Unfortunately, you have it coming in at 4psia, which is somewhere around 20" of vacuum, which you probably cannot achieve even going down the road at cruise speed! I have never subscribed to this method of getting a decent idle speed because as soon as you engage the clutch or put it in gear or put any load on the engine, you instantly lose several degrees of timing. If you had a MSD 6010, I would suggest putting a #3 or #4 or even #5 pill in it and trying it for awhile until you get it sorted, but, again, unfortunately, the MSD 6012 has some weirdo pills shipped with it for some reason. Maybe you could borrow from someone with a 6010. Since everyone hates the pills so much, maybe someone will send you theirs,LOL !! Personally, I think you need to get your advance curves in order before you start messing with the carb....however, that link above has some very good advice on bench setting the carb to get you started. Just my .02 cents worth. Ron
1 is for the idle, and 2 is for the main!
I see somewhere that a HP carburator arrive whit 35 for the idle, and 75 for the main... I will unscrew this jet and chek the size... In my case, i must go 2 size smaller, like 73 ( if i have 75), if i need to change the main air bleed!
I must change 2 air bleed for the main in the primary, or i need to change all 4 air bleed for primary and secondary?
I thinks i'm better to begin whit the 2 primary, fix my small acceleration problem, and after, if i also have problem whit acceleration using the secondary section, i will change it too.[QUOTE]
I probably ought to stay out of this, but I just can't help myself, LOL. First of all I hope you just got mixed up when you posted the bleed sizes. It should read 75 for the idle bleed (the outside one) and 35 for the main bleed (the one closestto the center) If they ARE like you posted, somebody has mistakenly put them in the wrong positions. The next thing that I noticed is your advance curves, both RPM and MAP. If these are the curves you are actually running, I don't see how you are running as well as you say you are. The cam you mentioned is (if I remember right) around 216-220 @ .050 on a 112 LA. You should have an RPM curve similar to this 0 RPM (cranking speed) 12-15*...800RPM (idle speed) 18-22*...2000RPM 28-32*...and, depending on who you believe, from 3000RPM up...anywhere from 32-36*. These are not exact numbers, only ballpark. Your vacuum curve is also not working. (MAP) Here's why. Someone has convinced you to put 20* in your MAP curve to
"make it idle better". Unfortunately, you have it coming in at 4psia, which is somewhere around 20" of vacuum, which you probably cannot achieve even going down the road at cruise speed! I have never subscribed to this method of getting a decent idle speed because as soon as you engage the clutch or put it in gear or put any load on the engine, you instantly lose several degrees of timing. If you had a MSD 6010, I would suggest putting a #3 or #4 or even #5 pill in it and trying it for awhile until you get it sorted, but, again, unfortunately, the MSD 6012 has some weirdo pills shipped with it for some reason. Maybe you could borrow from someone with a 6010. Since everyone hates the pills so much, maybe someone will send you theirs,LOL !! Personally, I think you need to get your advance curves in order before you start messing with the carb....however, that link above has some very good advice on bench setting the carb to get you started. Just my .02 cents worth. Ron
10-29-2010, 05:51 PM
#19
Cam is much bigger than that.
Brand COMP Cams
Manufacturer's Part Number 54-469-11
Part Type Camshafts
Product Line COMP Cams LSr Series Hydraulic Roller Camshafts
Summit Racing Part Number CCA-54-469-11
UPC 036584195313
Cam Style Hydraulic roller tappet
Basic Operating RPM Range 2,000-7,000
Intake Duration at 050 inch Lift 231
Exhaust Duration at 050 inch Lift 247
Duration at 050 inch Lift 231 int./247 exh.
Advertised Intake Duration 281
Advertised Exhaust Duration 297
Advertised Duration 281 int./297 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.617 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.624 in.
Valve Lift with Factory Rocker Arm Ratio 0.617 int./0.624 exh.
Lobe Separation (degrees) 113
Manufacturer's Part Number 54-469-11
Part Type Camshafts
Product Line COMP Cams LSr Series Hydraulic Roller Camshafts
Summit Racing Part Number CCA-54-469-11
UPC 036584195313
Cam Style Hydraulic roller tappet
Basic Operating RPM Range 2,000-7,000
Intake Duration at 050 inch Lift 231
Exhaust Duration at 050 inch Lift 247
Duration at 050 inch Lift 231 int./247 exh.
Advertised Intake Duration 281
Advertised Exhaust Duration 297
Advertised Duration 281 int./297 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.617 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.624 in.
Valve Lift with Factory Rocker Arm Ratio 0.617 int./0.624 exh.
Lobe Separation (degrees) 113
10-29-2010, 11:05 PM
#20
Staging Lane
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Join Date: Mar 2010
Location: quebec, Canada
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rojs234..... like i already wrote, this carb was on a 355 chevy from last summer, and problem was the same... for solve temporary the problem, i put 2 size up in primary jet... but run at 12.5:1 at cruise.
Thanks Pop N Wood for the spec, it's exactly this cam, recommanded by a comp cam Tech whit all my specification and application.
Thanks Pop N Wood for the spec, it's exactly this cam, recommanded by a comp cam Tech whit all my specification and application.