Expert Carburetor Advice needed
02-27-2014, 08:30 AM
#42
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Update,
After timing adjust, IFR adjust, I can now get around 800 rpm, still a little high, smooth idle.
Now I have the dreaded part throttle stumble.
I have searched the threads some say 50cc accel pump, some say larger squirters, some say air bleeds.
It stumbles from a stop sign when you ease into it, and stumbles at cruise speed on any incline, once you get past part throttle it snaps you neck back.
I took a few days off from it, was getting frustrated, hoping to get it drivable this weekend.
Without an afr meter any suggestions?
After timing adjust, IFR adjust, I can now get around 800 rpm, still a little high, smooth idle.
Now I have the dreaded part throttle stumble.
I have searched the threads some say 50cc accel pump, some say larger squirters, some say air bleeds.
It stumbles from a stop sign when you ease into it, and stumbles at cruise speed on any incline, once you get past part throttle it snaps you neck back.
I took a few days off from it, was getting frustrated, hoping to get it drivable this weekend.
Without an afr meter any suggestions?
02-27-2014, 08:57 AM
#43
If the stumble is only momentary during transitions, increasing the squirter size will usually fix it. If it is constant lean condition at a certain low/part throttle position (meaning you can demonstrate this at a low speed cruise with a fixed throttle position), you will have to make either a low speed bleed change (go smaller) or an idle fuel restrictor change (go larger).
02-28-2014, 07:24 AM
#45
And, just keep in mind, a higher number power valve will not only come in sooner, but it often affects how rich your part throttle transitions are as well. If you use the power valve to try to substitiute getting the LSBs and IFR right, you could end up with a carb that gives really eratic a/f ratios and has inconsistent drivability.
02-28-2014, 07:50 AM
#46
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You can certainly experiment, but the vacuum gauge will not help you with a power valve. That is not how they work. If you are going to diagnose a power valve, use a wideband.
And, just keep in mind, a higher number power valve will not only come in sooner, but it often affects how rich your part throttle transitions are as well. If you use the power valve to try to substitiute getting the LSBs and IFR right, you could end up with a carb that gives really eratic a/f ratios and has inconsistent drivability.
And, just keep in mind, a higher number power valve will not only come in sooner, but it often affects how rich your part throttle transitions are as well. If you use the power valve to try to substitiute getting the LSBs and IFR right, you could end up with a carb that gives really eratic a/f ratios and has inconsistent drivability.
My air bleeds are not adjustable, I have got wires in the ifr now 10 thousandths diam. I going to try to find some smaller wires to put in the ifr and see what that does.
Thanks again.
03-09-2014, 08:12 PM
#47
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Okay this is what I have done and what I got
At this point I have tried a lot of things to get this carb to act right.
Here is what I got.
Iron block ls1/ 5.3 bored to ls1 specs
2000 ls1 stock cam
700r4 trans stock converter
dual plane intake
road demon 625 cfm 4150 style carb
70 jets front
78 jets rear
50cc accel pump
40 squirters
8.5 power valve
msd 6ls
Idles still a little high 900 rpm but smooth
If I pull off from a stop with normal press of the pedal it stumbles backfires and even goes dead sometimes. If I pump the throttle once then press it car pulls off normal.
I can hold the brake in gear and slightly depress the throttle engine will start to load up and begin the stumbling, press it a little more and it clears up.
I think I need a holley terminator efi, but my wallet says otherwise. So until I can convince wallet to change its mind I need some advice!
At this point I have tried a lot of things to get this carb to act right.
Here is what I got.
Iron block ls1/ 5.3 bored to ls1 specs
2000 ls1 stock cam
700r4 trans stock converter
dual plane intake
road demon 625 cfm 4150 style carb
70 jets front
78 jets rear
50cc accel pump
40 squirters
8.5 power valve
msd 6ls
Idles still a little high 900 rpm but smooth
If I pull off from a stop with normal press of the pedal it stumbles backfires and even goes dead sometimes. If I pump the throttle once then press it car pulls off normal.
I can hold the brake in gear and slightly depress the throttle engine will start to load up and begin the stumbling, press it a little more and it clears up.
I think I need a holley terminator efi, but my wallet says otherwise. So until I can convince wallet to change its mind I need some advice!
03-10-2014, 05:11 AM
#48
Adjust the accel pump so even the slightest movement of the throttle causes a strong squirt down the throat. I mean strong. There should be no slop in the linkage when at idle.
How much of the transfer slot is showing on the primary and secondary sides? Can you measure it with a flat feeler gauge?
In all honesty your nozzles are probably too big cause something else isn't right.
No mention of AFR's, do you have a wideband?
How much of the transfer slot is showing on the primary and secondary sides? Can you measure it with a flat feeler gauge?
In all honesty your nozzles are probably too big cause something else isn't right.
No mention of AFR's, do you have a wideband?
03-10-2014, 06:24 AM
#49
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Adjust the accel pump so even the slightest movement of the throttle causes a strong squirt down the throat. I mean strong. There should be no slop in the linkage when at idle.
How much of the transfer slot is showing on the primary and secondary sides? Can you measure it with a flat feeler gauge?
In all honesty your nozzles are probably too big cause something else isn't right.
No mention of AFR's, do you have a wideband?
How much of the transfer slot is showing on the primary and secondary sides? Can you measure it with a flat feeler gauge?
In all honesty your nozzles are probably too big cause something else isn't right.
No mention of AFR's, do you have a wideband?
But for now I am trying to get by with what I got.
After sleeping on it its got to be something with the transfer slots/ifr, when I hold the brake and barely press the go pedal it will shake and stumble as long as I hold it. it would seem that thats when the transfer slots are supposed to be working and they are not.
Should I try to drill out the ifr? What size bit would it be? Where would you find a small bit like that?
03-11-2014, 05:15 AM
#50
You can get sets of numbered drill bits at a hobby store or off ebay. You use them like feeler gauges to determine what size orifice is there then figure out where to go from that point.
Most of the restrictions actually have a press in brass restriction. So you need to drill those out larger and tap the hole for a brass set screw you get from McMaster Carr. You can then drill out the set screws to get the restrictions you need.
But you gotta make sure everything else is right first. There is a progression to go through.
How much of the transfer slot is showing, primary and secondary? How many turns out are the idle screws? How did you set them? Are they all the same number of turns? Float level? Power valve good? All gaskets good, carb surfaces flat, nothing leaking? Anything blocked, like an air bleed?
Most of the restrictions actually have a press in brass restriction. So you need to drill those out larger and tap the hole for a brass set screw you get from McMaster Carr. You can then drill out the set screws to get the restrictions you need.
But you gotta make sure everything else is right first. There is a progression to go through.
How much of the transfer slot is showing, primary and secondary? How many turns out are the idle screws? How did you set them? Are they all the same number of turns? Float level? Power valve good? All gaskets good, carb surfaces flat, nothing leaking? Anything blocked, like an air bleed?
03-11-2014, 07:06 AM
#51
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You can get sets of numbered drill bits at a hobby store or off ebay. You use them like feeler gauges to determine what size orifice is there then figure out where to go from that point.
Most of the restrictions actually have a press in brass restriction. So you need to drill those out larger and tap the hole for a brass set screw you get from McMaster Carr. You can then drill out the set screws to get the restrictions you need.
But you gotta make sure everything else is right first. There is a progression to go through.
How much of the transfer slot is showing, primary and secondary? How many turns out are the idle screws? How did you set them? Are they all the same number of turns? Float level? Power valve good? All gaskets good, carb surfaces flat, nothing leaking? Anything blocked, like an air bleed?
Most of the restrictions actually have a press in brass restriction. So you need to drill those out larger and tap the hole for a brass set screw you get from McMaster Carr. You can then drill out the set screws to get the restrictions you need.
But you gotta make sure everything else is right first. There is a progression to go through.
How much of the transfer slot is showing, primary and secondary? How many turns out are the idle screws? How did you set them? Are they all the same number of turns? Float level? Power valve good? All gaskets good, carb surfaces flat, nothing leaking? Anything blocked, like an air bleed?
I would not be anywhere close without you guys help thanks.
Pulled it last night it had right at 20 thou slot showing primary, none on secondary, set the slots before and marked the screws with paint. I forgot to check the turns out idle screws, I think it was 3/4 to 1 turn out front about a 1/4 on rear.
Float level I first had at bottom of sight glass, I experimented raising to the center of the glass, no change.
I have checked and double checked for vacuum leaks, power valve is new but how do you check it?
Air bleeds are clear.
When I hold the baseplate up to the light it looks like a lot of space between the plates and bores, and they are not centered. Would that cause a problem?
Metering block is aluminum and doesn't have brass inserts.
I have seen other post about McMaster Carr, I am up to drilling and taping for air bleeds, but what do I order? There web site has a lot of stuff!
Am I just wasting time with this crappy demon?
03-11-2014, 06:58 PM
#54
You know enough to be dangerous now! It's only money. If you screw something up you buy new metering plates.
Keep good records.
Well I don't like the idea of having the secondary completely closed but that is almost certainly not your problem right now. Idle screws need to all be the same number of turns out.
You need 6-32, 8-32 and 10-32 set screws. Brass ones. You also need a pin vise and a cordless variable speed drill. Best way to drill the set screws is putting the screw in the drill, turn it slowly, then hold the drill bit. Lots of WD40 when drilling. I also bought some bottom taps for the set screws in addition to the taper taps I have in my standard set. I used a bit of blue loctite when putting in the set screws.
Here are my notes on how I drilled out my DP. I'd write more but gotta get my son from scouts.
Drilled out air bleeds and put in set screws.
• 10-32 on primary idle air bleeds
• 8-32 on all other bleeds
• Tried to match stock bleeds openings on all but the primary IAB
• Changed carb to manifold gasket
o Was open plenum gasket
o Now 4 holer with 2 composite gaskets sandwiching to metal heat plates
o Not worried about heat but got for the same price as a simple 4 holer.
At this point noticed the primary IAB was a good bit larger than the secondary. Not only the orifice, but the size of the press in bleed too.
Change was easy. Put carb body on a 2x6 on drill press table. Put drill press at 800 RPM and set stop to keep from drilling too far down. Started small and worked my way up to the bits needed for the set screw taps. One guy on the innovate forum said used 10-32 on all bleeds. This looked way too big for all the secondary bleeds and the primary HSAB. Would have left too little material, so went 8-32 on these. The primary IAB bigger than the #29 bit needed for the smaller set screw so had to go to 10-32 on this one. Good thing, the larger tap was longer so got around choke plate better. Had to use a crescent wrench to work the tap.
The set screws take the following tap drill sizes and Allen wrench sizes:
Hex Key Size Drill size for tap
6-32 #36 (0.1065)
8-32 5/64 #29 (0.1360)
10-32 3/32 #21 (0.1590)
The bleed holes only go down maybe ¼ of an inch then immediately turn 90° into the metering block. Compressed air from the metering block side of the carb blew all the crap out. Cleaned everything up with air and carb cleaner before putting it all back together again. Used blue loctite on all set screws.
Like said above, kept the equivalent air bleeds except for the primary IAB. Went down 3 drill sizes to match the secondary.
Keep good records.
Well I don't like the idea of having the secondary completely closed but that is almost certainly not your problem right now. Idle screws need to all be the same number of turns out.
You need 6-32, 8-32 and 10-32 set screws. Brass ones. You also need a pin vise and a cordless variable speed drill. Best way to drill the set screws is putting the screw in the drill, turn it slowly, then hold the drill bit. Lots of WD40 when drilling. I also bought some bottom taps for the set screws in addition to the taper taps I have in my standard set. I used a bit of blue loctite when putting in the set screws.
Here are my notes on how I drilled out my DP. I'd write more but gotta get my son from scouts.
Drilled out air bleeds and put in set screws.
• 10-32 on primary idle air bleeds
• 8-32 on all other bleeds
• Tried to match stock bleeds openings on all but the primary IAB
• Changed carb to manifold gasket
o Was open plenum gasket
o Now 4 holer with 2 composite gaskets sandwiching to metal heat plates
o Not worried about heat but got for the same price as a simple 4 holer.
At this point noticed the primary IAB was a good bit larger than the secondary. Not only the orifice, but the size of the press in bleed too.
Change was easy. Put carb body on a 2x6 on drill press table. Put drill press at 800 RPM and set stop to keep from drilling too far down. Started small and worked my way up to the bits needed for the set screw taps. One guy on the innovate forum said used 10-32 on all bleeds. This looked way too big for all the secondary bleeds and the primary HSAB. Would have left too little material, so went 8-32 on these. The primary IAB bigger than the #29 bit needed for the smaller set screw so had to go to 10-32 on this one. Good thing, the larger tap was longer so got around choke plate better. Had to use a crescent wrench to work the tap.
The set screws take the following tap drill sizes and Allen wrench sizes:
Hex Key Size Drill size for tap
6-32 #36 (0.1065)
8-32 5/64 #29 (0.1360)
10-32 3/32 #21 (0.1590)
The bleed holes only go down maybe ¼ of an inch then immediately turn 90° into the metering block. Compressed air from the metering block side of the carb blew all the crap out. Cleaned everything up with air and carb cleaner before putting it all back together again. Used blue loctite on all set screws.
Like said above, kept the equivalent air bleeds except for the primary IAB. Went down 3 drill sizes to match the secondary.
03-11-2014, 07:12 PM
#55
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You know enough to be dangerous now! It's only money. If you screw something up you buy new metering plates.
Keep good records.
Well I don't like the idea of having the secondary completely closed but that is almost certainly not your problem right now. Idle screws need to all be the same number of turns out.
You need 6-32, 8-32 and 10-32 set screws. Brass ones. You also need a pin vise and a cordless variable speed drill. Best way to drill the set screws is putting the screw in the drill, turn it slowly, then hold the drill bit. Lots of WD40 when drilling. I also bought some bottom taps for the set screws in addition to the taper taps I have in my standard set. I used a bit of blue loctite when putting in the set screws.
Here are my notes on how I drilled out my DP. I'd write more but gotta get my son from scouts.
Drilled out air bleeds and put in set screws.
• 10-32 on primary idle air bleeds
• 8-32 on all other bleeds
• Tried to match stock bleeds openings on all but the primary IAB
• Changed carb to manifold gasket
o Was open plenum gasket
o Now 4 holer with 2 composite gaskets sandwiching to metal heat plates
o Not worried about heat but got for the same price as a simple 4 holer.
At this point noticed the primary IAB was a good bit larger than the secondary. Not only the orifice, but the size of the press in bleed too.
Change was easy. Put carb body on a 2x6 on drill press table. Put drill press at 800 RPM and set stop to keep from drilling too far down. Started small and worked my way up to the bits needed for the set screw taps. One guy on the innovate forum said used 10-32 on all bleeds. This looked way too big for all the secondary bleeds and the primary HSAB. Would have left too little material, so went 8-32 on these. The primary IAB bigger than the #29 bit needed for the smaller set screw so had to go to 10-32 on this one. Good thing, the larger tap was longer so got around choke plate better. Had to use a crescent wrench to work the tap.
The set screws take the following tap drill sizes and Allen wrench sizes:
Hex Key Size Drill size for tap
6-32 #36 (0.1065)
8-32 5/64 #29 (0.1360)
10-32 3/32 #21 (0.1590)
The bleed holes only go down maybe ¼ of an inch then immediately turn 90° into the metering block. Compressed air from the metering block side of the carb blew all the crap out. Cleaned everything up with air and carb cleaner before putting it all back together again. Used blue loctite on all set screws.
Like said above, kept the equivalent air bleeds except for the primary IAB. Went down 3 drill sizes to match the secondary.
Keep good records.
Well I don't like the idea of having the secondary completely closed but that is almost certainly not your problem right now. Idle screws need to all be the same number of turns out.
You need 6-32, 8-32 and 10-32 set screws. Brass ones. You also need a pin vise and a cordless variable speed drill. Best way to drill the set screws is putting the screw in the drill, turn it slowly, then hold the drill bit. Lots of WD40 when drilling. I also bought some bottom taps for the set screws in addition to the taper taps I have in my standard set. I used a bit of blue loctite when putting in the set screws.
Here are my notes on how I drilled out my DP. I'd write more but gotta get my son from scouts.
Drilled out air bleeds and put in set screws.
• 10-32 on primary idle air bleeds
• 8-32 on all other bleeds
• Tried to match stock bleeds openings on all but the primary IAB
• Changed carb to manifold gasket
o Was open plenum gasket
o Now 4 holer with 2 composite gaskets sandwiching to metal heat plates
o Not worried about heat but got for the same price as a simple 4 holer.
At this point noticed the primary IAB was a good bit larger than the secondary. Not only the orifice, but the size of the press in bleed too.
Change was easy. Put carb body on a 2x6 on drill press table. Put drill press at 800 RPM and set stop to keep from drilling too far down. Started small and worked my way up to the bits needed for the set screw taps. One guy on the innovate forum said used 10-32 on all bleeds. This looked way too big for all the secondary bleeds and the primary HSAB. Would have left too little material, so went 8-32 on these. The primary IAB bigger than the #29 bit needed for the smaller set screw so had to go to 10-32 on this one. Good thing, the larger tap was longer so got around choke plate better. Had to use a crescent wrench to work the tap.
The set screws take the following tap drill sizes and Allen wrench sizes:
Hex Key Size Drill size for tap
6-32 #36 (0.1065)
8-32 5/64 #29 (0.1360)
10-32 3/32 #21 (0.1590)
The bleed holes only go down maybe ¼ of an inch then immediately turn 90° into the metering block. Compressed air from the metering block side of the carb blew all the crap out. Cleaned everything up with air and carb cleaner before putting it all back together again. Used blue loctite on all set screws.
Like said above, kept the equivalent air bleeds except for the primary IAB. Went down 3 drill sizes to match the secondary.
Thanks for all that info I may try to sneak out from work tomorrow and run over to mcmaster carr.
One quick question, I have read where you can put wire in the ifr to reduce size, is this possible with the IAB also?
03-18-2014, 05:06 PM
#56
If it were mine, I woud drill the IFR to .031". Take it out for a ride. I suspect this will improve the problem. If it improves, but does not eliminate the problem, go to .033". Let me know how that works. NOTE: after you change the IFR size, you will have to re-adjust your fuel mixture screws slightly.
03-18-2014, 07:35 PM
#57
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If it were mine, I woud drill the IFR to .031". Take it out for a ride. I suspect this will improve the problem. If it improves, but does not eliminate the problem, go to .033". Let me know how that works. NOTE: after you change the IFR size, you will have to re-adjust your fuel mixture screws slightly.
grabbed a pack stuck one in there now no bog! Now I can work on that part throttle stumble at cruising speed.
Thanks for the IFR numbers I didnt know how much to drill out.
Do I need to worry about the air bleed when I drill out the IFR?
03-18-2014, 07:55 PM
#58
That is actually a very good question to have asked. Yes, you will want to try to maintain the ratio. But, it i will be very tough to quantify without a wideband to verify. As you have correctly summized, the bleeds and the IFRs have an important relationship. As I experimented with mine, I generally found that the changes to the IFR tend to effect the lower RPMs and just over idle more while the LSBs tended to effect the higher speed cruise AFRs more. When you increase the IFR to get rid of the off idle stumble it may richen up your cruise across the board. Increasing the LSBs can clean this up.
03-19-2014, 05:16 AM
#59
This is why it is hard giving tuning advice or even troubleshooting advice over the internet. Your car sounded way to far out to just be a tuning issue. Like I said, there is a progression on these things and sometimes you just have to be there to stumble over them.
By the way, you live within bicycle distance of both Summit and McMaster Carr? How fortunate is that. I suppose there is a White Castle's around the corner too?
By the way, you live within bicycle distance of both Summit and McMaster Carr? How fortunate is that. I suppose there is a White Castle's around the corner too?
04-04-2014, 01:34 PM
#60
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This is why it is hard giving tuning advice or even troubleshooting advice over the internet. Your car sounded way to far out to just be a tuning issue. Like I said, there is a progression on these things and sometimes you just have to be there to stumble over them.
By the way, you live within bicycle distance of both Summit and McMaster Carr? How fortunate is that. I suppose there is a White Castle's around the corner too?
By the way, you live within bicycle distance of both Summit and McMaster Carr? How fortunate is that. I suppose there is a White Castle's around the corner too?
I am back from Disney World and ready to get back to work!
So I took my bicycle to Mcmaster Carr picked up brass bleeds and taps, stopped by Summit got afr meter and going to install that this weekend.
Question I have is the placement of the o2 sensor. I am using the stock LS1 exhaust manifolds and I put a plug in the bung from the stock sensor, can I put the sensor in that location? I have no cats.