Need Carb Help
01-21-2014, 02:24 PM
#1
Need Carb Help Sorry for the long post, but I wanted to get all the details in here.
Truck - 69 C10 SWB T56 373 gear 28" tire. Original combo was a stock LY6 with 220/230 cam, 1-7/8 headers, GMPP dual plane intake and Holley 770 street avenger. Other than a short duration lean tip in, this combo ran well for 5500miles until it spun #3 rod bearing. Idled at 950rpm, ran 25deg timing at idle plus 10 deg vac advance.
While it was torn down for rod bearing, I made some changes. Current combo is now a 6.2 iron block with LS3 flat top pistons, LS3 intake valve, mild porting on heads .015" milled, 230/242 cam, same intake and headers. Also added a larger AL radiator during teardown.
500 miles of break in was done with the 770 carb. Ran fine, idled fine but lean tip in was worse. Engine temp would creep up in low rpm 6th gear cruise, would go away shifting to 5th at same speed. Figured it was too much timing for the new compression. Swapped to Quick Fuel 750cfm mech secondaries.
Initial idle with the QF out of the box was 2400rpm. Got idle down to 1000rpm, but had the idle screw all the way out. Per QF Tech, I reset the primaries to .040" of transition slot showing and secondaries to just covering the slot. Got idle down to 1500, but still wont drop to decent idle speed without closing primaries. In addition, it diesels now when I turn it off. Not sure if this is just because of the RPM or if there is more to it. Its also heating up. Sitting in the driveway, fans running, it should be and always has run at 170F. Its now at 200F. This is with vac advance zero'd out and 8 deg of base timing.
So far I have disconnected all vacuum accessories and nothing changes. It pulls 15" of vac at idle. Sprayed carb cleaner all around the carb and manifold, no signs of leak. Retorqued intake manifold made no difference. I did pull the plugs and they were pretty carboned up (from idle tuning I guess) so I will get those replaced today, but thats not going to bring the idle down. I have an AFR gauge installed on drivers side bank. Its not showing lean and I recalibrated it recently.
I'm pretty stumped. I think if the vac leak was large enough to cause dieseling and a hot running engine, I would have been able to find it?
Truck - 69 C10 SWB T56 373 gear 28" tire. Original combo was a stock LY6 with 220/230 cam, 1-7/8 headers, GMPP dual plane intake and Holley 770 street avenger. Other than a short duration lean tip in, this combo ran well for 5500miles until it spun #3 rod bearing. Idled at 950rpm, ran 25deg timing at idle plus 10 deg vac advance.
While it was torn down for rod bearing, I made some changes. Current combo is now a 6.2 iron block with LS3 flat top pistons, LS3 intake valve, mild porting on heads .015" milled, 230/242 cam, same intake and headers. Also added a larger AL radiator during teardown.
500 miles of break in was done with the 770 carb. Ran fine, idled fine but lean tip in was worse. Engine temp would creep up in low rpm 6th gear cruise, would go away shifting to 5th at same speed. Figured it was too much timing for the new compression. Swapped to Quick Fuel 750cfm mech secondaries.
Initial idle with the QF out of the box was 2400rpm. Got idle down to 1000rpm, but had the idle screw all the way out. Per QF Tech, I reset the primaries to .040" of transition slot showing and secondaries to just covering the slot. Got idle down to 1500, but still wont drop to decent idle speed without closing primaries. In addition, it diesels now when I turn it off. Not sure if this is just because of the RPM or if there is more to it. Its also heating up. Sitting in the driveway, fans running, it should be and always has run at 170F. Its now at 200F. This is with vac advance zero'd out and 8 deg of base timing.
So far I have disconnected all vacuum accessories and nothing changes. It pulls 15" of vac at idle. Sprayed carb cleaner all around the carb and manifold, no signs of leak. Retorqued intake manifold made no difference. I did pull the plugs and they were pretty carboned up (from idle tuning I guess) so I will get those replaced today, but thats not going to bring the idle down. I have an AFR gauge installed on drivers side bank. Its not showing lean and I recalibrated it recently.
I'm pretty stumped. I think if the vac leak was large enough to cause dieseling and a hot running engine, I would have been able to find it?
01-21-2014, 03:51 PM
#2
I had the same idle screw problem you did. I ended up tweaking down the timing at idle only to set the idle speed where I wanted it.
You say you completely cover the secondary transfer slot? That's not good. I have both primary and secondary set to 20 thou of the slot showing. 40 thou is on the top side of what is acceptable (if I remember correctly).
Zeroing out the map sensor is good. I would put both primary and secondary at 20 thou on the transfer slot then use idle timing to adjust the idle speed. I always adjust primary and secondary together.
There have been a couple of threads about dieseling and timing. I can't remember if more timing or less fixed the issue. I do know running too rich at idle will contribute to dieseling. So your fouled plugs might mean too rich. Clean them up and set the AFR to somewhere near 14.7:1 at idle. Setting it slightly richer helps with the lean tip in, but there are better ways to fix that (like idle feed restrictors and air bleeds).
Having the car run hotter usually means too little timing. Get the other stuff sorted out and worry about that later.
You say you completely cover the secondary transfer slot? That's not good. I have both primary and secondary set to 20 thou of the slot showing. 40 thou is on the top side of what is acceptable (if I remember correctly).
Zeroing out the map sensor is good. I would put both primary and secondary at 20 thou on the transfer slot then use idle timing to adjust the idle speed. I always adjust primary and secondary together.
There have been a couple of threads about dieseling and timing. I can't remember if more timing or less fixed the issue. I do know running too rich at idle will contribute to dieseling. So your fouled plugs might mean too rich. Clean them up and set the AFR to somewhere near 14.7:1 at idle. Setting it slightly richer helps with the lean tip in, but there are better ways to fix that (like idle feed restrictors and air bleeds).
Having the car run hotter usually means too little timing. Get the other stuff sorted out and worry about that later.
01-21-2014, 08:42 PM
#4
Played around with the temp gun this evening and discovered the thermostat was stuck closed, this explains the heating up. Also replaced the plugs which allowed me to lean it out some and get the idle slightly closer to where I want to be. Not going to make anymore carb adjustments until I fix the thermostat.
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01-30-2014, 02:41 PM
#8
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Just an idea.
On the quickfuel, you've got four corner idle. Where are these set? I'd recommend trying the primaries at 1 - 1.25 turns out and the secondaries out 1/4-1/2 turn or so as a baseline.
Hope this helps,
Steve
On the quickfuel, you've got four corner idle. Where are these set? I'd recommend trying the primaries at 1 - 1.25 turns out and the secondaries out 1/4-1/2 turn or so as a baseline.
Hope this helps,
Steve
01-30-2014, 07:27 PM
#11
I would take a closer look at the radiator for your heating problem. There is a lot to be said for factory radiators. GM modine radiators have aggressive fins that really cool well IMO. A lot of these aftermarket companies don't design radiators that way and you wind up with a radiator that doesn't cool well unless your going 70mph.
01-30-2014, 08:18 PM
#12
Im pulling the radiator tomorrow to see if I can find any obstructions. I dont think the radiator itself is bad. I put 500 miles on it with this combo without the temp prob and the weather was 40 degrees warmer at that time....
01-31-2014, 04:30 AM
#13
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It's your car, do it the way you want, but if the high temps didn't show up in earnest until you put the quickfuel on it, you've got black plugs, and you've got to jack with the throttle blades to that degree to get a halfway reasonable idle, i'd concentrate on the carb first. Besides, it's a lot easier than pulling a radiator...
Just remember to reset the throttle blades before you screw the mixture screws in. The default 1.5 turns out on all four corners is way too much fuel with a quickfuel double pumper.
Good luck
Last edited by LXguy; 01-31-2014 at 04:36 AM.
01-31-2014, 07:02 AM
#14
I had some of the same problem with my start up. I had a hard time getting the air out of the heads. Temp would reach 200 to 220. I screwed around bleading the air out of the engine for a while. I finally got it out and temps stabilized. My idle would not come down also , so adjusted the front and rear blades equaly open( 1/4 turn) and started the engine an adjusted the front and rear idle screws the same amount close or open which ever it needed until I got a good idle. Then I used the front idle screw to fine tune. I also started over on the idle screws and turned all four our 1 1/2 turns out and readjusted. After checking I found out I had them so far out from each other from twisting on them. I have total 25* timing at idle with map on my ls2. Also I have dieseling from time to time. Some carb people have said it can be from to hot of a plug. I am going one step cooler and give it a try ( tr6). This is from my experience with my start up. Hope some of this helps.
Also to add, octane to comp ratio can also make one diesel. Some cam grinds can increase cranking cylinder pressure and at idle.
Do you have a catch can for the radiator. As it goes thru some hot cold cycles it will continue to fill the radiator and get the air out if you keep some fluid in the catch can and get all the air out.
Also to add, octane to comp ratio can also make one diesel. Some cam grinds can increase cranking cylinder pressure and at idle.
Do you have a catch can for the radiator. As it goes thru some hot cold cycles it will continue to fill the radiator and get the air out if you keep some fluid in the catch can and get all the air out.
Last edited by homemade87; 01-31-2014 at 07:14 AM.
01-31-2014, 07:45 AM
#15
With the street avenger carb, right? (according to the timeline above)
It's your car, do it the way you want, but if the high temps didn't show up in earnest until you put the quickfuel on it, you've got black plugs, and you've got to jack with the throttle blades to that degree to get a halfway reasonable idle, i'd concentrate on the carb first. Besides, it's a lot easier than pulling a radiator...
Just remember to reset the throttle blades before you screw the mixture screws in. The default 1.5 turns out on all four corners is way too much fuel with a quickfuel double pumper.
Good luck
It's your car, do it the way you want, but if the high temps didn't show up in earnest until you put the quickfuel on it, you've got black plugs, and you've got to jack with the throttle blades to that degree to get a halfway reasonable idle, i'd concentrate on the carb first. Besides, it's a lot easier than pulling a radiator...
Just remember to reset the throttle blades before you screw the mixture screws in. The default 1.5 turns out on all four corners is way too much fuel with a quickfuel double pumper.
Good luck
02-08-2014, 01:05 PM
#18
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EDIT: Found this in this old thread that might help.
"The Performer RPM has a 10/32 threaded hole on one of the front runners to bolt MSD box on. You would think this would be a blind threaded hole, but it goes through into the runner. If you don't use it to bolt the box on, it needs a 10/32 screw in it. Just a thought, Ron"
Youd thing that would respond to spray testing, but maybe not...
https://ls1tech.com/forums/carburete...-shut-off.html
There's also some good info about electric fans backfeeding voltage to the 6LS box.
Here's another bit I've seen people have trouble with the 6ls related to vacuum advance and the presence (or not) of a MAP sensor..
".....the MSD box adds whatever timing values are in the vacuum advance table....even if there is no MAP sensor connected. You wind up with a constant 20* of timing on top of whatever was set in the main timing table. Therefore, I have all values in the vacuum advance table zero'd out.....and just use the "mechanical" (so to speak) timing."
What is your A/F ratio at idle?
Milled heads/flat tops? What's your CR? Sound like it might be high.
Pump gas?
"The Performer RPM has a 10/32 threaded hole on one of the front runners to bolt MSD box on. You would think this would be a blind threaded hole, but it goes through into the runner. If you don't use it to bolt the box on, it needs a 10/32 screw in it. Just a thought, Ron"
Youd thing that would respond to spray testing, but maybe not...
https://ls1tech.com/forums/carburete...-shut-off.html
There's also some good info about electric fans backfeeding voltage to the 6LS box.
Here's another bit I've seen people have trouble with the 6ls related to vacuum advance and the presence (or not) of a MAP sensor..
".....the MSD box adds whatever timing values are in the vacuum advance table....even if there is no MAP sensor connected. You wind up with a constant 20* of timing on top of whatever was set in the main timing table. Therefore, I have all values in the vacuum advance table zero'd out.....and just use the "mechanical" (so to speak) timing."
What is your A/F ratio at idle?
Milled heads/flat tops? What's your CR? Sound like it might be high.
Pump gas?
Last edited by LXguy; 02-08-2014 at 01:17 PM.
02-08-2014, 01:24 PM
#19
EDIT: Found this in this old thread that might help.
"The Performer RPM has a 10/32 threaded hole on one of the front runners to bolt MSD box on. You would think this would be a blind threaded hole, but it goes through into the runner. If you don't use it to bolt the box on, it needs a 10/32 screw in it. Just a thought, Ron"
Youd thing that would respond to spray testing, but maybe not...
https://ls1tech.com/forums/carburete...-shut-off.html
There's also some good info about electric fans backfeeding voltage to the 6LS box.
Here's another bit I've seen people have trouble with the 6ls related to vacuum advance and the presence (or not) of a MAP sensor..
".....the MSD box adds whatever timing values are in the vacuum advance table....even if there is no MAP sensor connected. You wind up with a constant 20* of timing on top of whatever was set in the main timing table. Therefore, I have all values in the vacuum advance table zero'd out.....and just use the "mechanical" (so to speak) timing."
What is your A/F ratio at idle?
Milled heads/flat tops? What's your CR? Sound like it might be high.
Pump gas?
"The Performer RPM has a 10/32 threaded hole on one of the front runners to bolt MSD box on. You would think this would be a blind threaded hole, but it goes through into the runner. If you don't use it to bolt the box on, it needs a 10/32 screw in it. Just a thought, Ron"
Youd thing that would respond to spray testing, but maybe not...
https://ls1tech.com/forums/carburete...-shut-off.html
There's also some good info about electric fans backfeeding voltage to the 6LS box.
Here's another bit I've seen people have trouble with the 6ls related to vacuum advance and the presence (or not) of a MAP sensor..
".....the MSD box adds whatever timing values are in the vacuum advance table....even if there is no MAP sensor connected. You wind up with a constant 20* of timing on top of whatever was set in the main timing table. Therefore, I have all values in the vacuum advance table zero'd out.....and just use the "mechanical" (so to speak) timing."
What is your A/F ratio at idle?
Milled heads/flat tops? What's your CR? Sound like it might be high.
Pump gas?
Heads milled .015" stock LS3 flat tops. Should be around 11:1
93 octane.
I don't think dieseling is the problem itself. The cylinder head temps are getting too hot and causing the run on when the car shuts off. I cant figure out why the engine is heating up. It didnt do this before.
02-12-2014, 06:32 AM
#20
Update:
Pulled the plugs after ~1hr and they were all carboned up again. I run an internally regulated Aeromotive pump that is designed for use with Holleys. QF instructions say it is setup for 6.5psi (I run at ~7psi) but they indicate you will just need to adjust the floats if you run more. I call QF and they are adamant that it will have fuel delivery issues and run like crap over 6.5psi. So I call Aeromotive and they don't recommend adding an external regulator to this pump.
Faced with the option of spending more money either on new pump w/ regulator or selling QF and buying Holley Ultra, I decided to do some more diagnostics. Lowered floats on QF to bottom of sight glass. Monitored FP as it warmed up. Pressure stayed between 6.8psi and 7.3psi. Truck still got hot and dieseled. Immediately after turning it off, I pulled the QF and confirmed fuel puddles in the intake manifold.
I tore down the QF and found a piece of packing foam? on the primary needle. Wasn't in the seat, but very suspect. I think I am going to run it one more time with the QF just to see if that was the issue. Assuming its still a FP issue, I will put the holley back on to make sure it cleans up and runs right.
As to why it still ran hot with Holley last weekend, my guess is that I didn't let the engine cool/clear out. I went straight from QF to Holley, so the intake was still soaked.
Pulled the plugs after ~1hr and they were all carboned up again. I run an internally regulated Aeromotive pump that is designed for use with Holleys. QF instructions say it is setup for 6.5psi (I run at ~7psi) but they indicate you will just need to adjust the floats if you run more. I call QF and they are adamant that it will have fuel delivery issues and run like crap over 6.5psi. So I call Aeromotive and they don't recommend adding an external regulator to this pump.
Faced with the option of spending more money either on new pump w/ regulator or selling QF and buying Holley Ultra, I decided to do some more diagnostics. Lowered floats on QF to bottom of sight glass. Monitored FP as it warmed up. Pressure stayed between 6.8psi and 7.3psi. Truck still got hot and dieseled. Immediately after turning it off, I pulled the QF and confirmed fuel puddles in the intake manifold.
I tore down the QF and found a piece of packing foam? on the primary needle. Wasn't in the seat, but very suspect. I think I am going to run it one more time with the QF just to see if that was the issue. Assuming its still a FP issue, I will put the holley back on to make sure it cleans up and runs right.
As to why it still ran hot with Holley last weekend, my guess is that I didn't let the engine cool/clear out. I went straight from QF to Holley, so the intake was still soaked.