carb bog
11-12-2012, 12:01 AM
#1
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carb bog i have a huge bog when going to wot off of idle. it is a ly6. with a small cam. i have a holley 750 im trying to play with the setup but it just seems like im wasting money on things that arnt helping.
11-12-2012, 05:38 AM
#2
Do you have a wideband? What do your AFR's look like? Also single or dual plane intake?
The bog is pretty common with the single plane intake. Some of the new carbs do better out of the box than others, but the old school Holley's need some work to get right with an LS motor.
The accel pumps are final fix for that sort of thing. More aggressive accel pump cam and bigger nozzles. But you need to get the AFR's steady with slow throttle changes first. That usually requires some adjustments to the idle air bleeds and idle feed restrictors. If you just go straight for the accel pump you will end up with a 50 cc primary pump and huge nozzles.
The bog is pretty common with the single plane intake. Some of the new carbs do better out of the box than others, but the old school Holley's need some work to get right with an LS motor.
The accel pumps are final fix for that sort of thing. More aggressive accel pump cam and bigger nozzles. But you need to get the AFR's steady with slow throttle changes first. That usually requires some adjustments to the idle air bleeds and idle feed restrictors. If you just go straight for the accel pump you will end up with a 50 cc primary pump and huge nozzles.
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11-13-2012, 08:15 PM
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no im sorry i ment what cam in the carb the yellow or brown and what about the other side? what size squirters? any info on your carb would help a lot mine is so out of tune. Also how much timing are you running
11-17-2012, 05:46 AM
#9
I don't think bigger pump diaphragm and squirters are gonna fix you problem. Just mask it and make it lazy. What size power valve if any do you have in primary transition circuit. What kind of bog do you have. A quick hesitation followed by a pop and a flame that will burn your eyebrows off, or a stumble that seems like it will never catch it's breath.
Can help diagnostic more if we know that
Beaudacious
Can help diagnostic more if we know that
Beaudacious
11-19-2012, 06:27 AM
#12
The way Ive always determined if it was a bog or stumble was have a buddy stand behind the car when you do it, if it blows smoke then it is a bog aka too much fuel. If it doesnt smoke when you do it, it's a stumble aka not enough fuel.
My car had an off idle bog, and the fix was simple. I had a stock out of the box 750 dbl pmpr. The link bar that went from front to back butterflies was straight across. Most people bend them to about 75-80 degrees so that the back butterflies open sooner. I did this to mine and it fixed the bog. Im not saying this is your problem too, but if yours is a stock 750, and the problem is a bog, give it a shot to see.
My car had an off idle bog, and the fix was simple. I had a stock out of the box 750 dbl pmpr. The link bar that went from front to back butterflies was straight across. Most people bend them to about 75-80 degrees so that the back butterflies open sooner. I did this to mine and it fixed the bog. Im not saying this is your problem too, but if yours is a stock 750, and the problem is a bog, give it a shot to see.
11-19-2012, 06:59 AM
#13
Well with my Holley 750 on a single plane, stock cam LS2 I had to reduce the primary idle air bleeds 2 steps to get rid of the off idle bog. I run a #31 nozzle in the primary and #35 in the secondary, both with pink accel pump cams, 30 cc pumps front and back. My idle mixture screws are maybe 5/8 of a turn out.
Make absolutely certain there is no slop in the accel pump linkage. The slightest throttle movement should result in a strong shot of gas from the accel nozzles. Leaky gaskets can affect this also.
Idle mixture and timing plays a part here too. You want about 20 thou of the transfer slot visible at idle on both the primary and secondary throttle plate settings. You need to pull the carb to check this. Any idle speed adjustments should be done to both the primary and secondary to keep the two open the same amount. I had to drop my idle timing to keep a reasonable idle speed with this throttle plate opening. With 30+ degrees timing at idle I had the idle screws out so far the blades were on the stops.
You can cheat a bit on the idle mixture screws, running it a bit rich will help with the bog.
Just keep in mind without a wideband you are only guessing.
Good luck.
Make absolutely certain there is no slop in the accel pump linkage. The slightest throttle movement should result in a strong shot of gas from the accel nozzles. Leaky gaskets can affect this also.
Idle mixture and timing plays a part here too. You want about 20 thou of the transfer slot visible at idle on both the primary and secondary throttle plate settings. You need to pull the carb to check this. Any idle speed adjustments should be done to both the primary and secondary to keep the two open the same amount. I had to drop my idle timing to keep a reasonable idle speed with this throttle plate opening. With 30+ degrees timing at idle I had the idle screws out so far the blades were on the stops.
You can cheat a bit on the idle mixture screws, running it a bit rich will help with the bog.
Just keep in mind without a wideband you are only guessing.
Good luck.
