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3 Arm Wiper Setup
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Ford 6R80 6 spd
More Tech...
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Off idle bog
- Thread starter Madgyver
- Start date
77bronk
Full Member
Had that same problem with my holly carb . Rebuilt it several times . Still could never get it to go away. Finally said screw it bought an edlebrock . Bolted it up added the fuel line and runs great with no tuning . Could never figure out the right off idle bog mine had .
Powervalve numerically too low.
blubuckaroo
Grease Monkey
You're going to have to give us more info if you want help.
You've been here a long time and should know how that works.
Yes, but seriously, pull the powervalve and tell us what number power valve you have got. Makes a big difference and few carbs are rebuilt/built with the proper one.
OK Not sure I can get this point across in a post. But seems like there were about 3 holes in the arm off the power diaphragm . Seems to me like if you increased it stroke. Or let me say it a 2nd time . The little linkage rod If you could get all the slack out of it. Or I'll say Get or bend that rod to push earlier & It helped on old carbs I worked on.
Of Course timing up a degree or 2..
Clean Air filter.
Vacuum advance in the dist.
& Advance the push pump ..I've gone blank on what it's called .. Maybe accelerator Pump. It can't be lazy.
.. Maybe some of that will help.
................
..................
..... I'm taking that you've been driving it for years & It's just came up with a dead spot.
....... In this case I'd think you need to look inside .. at the Rubber or leather on the acc. pump & See that it's not got an edge bent back. & Just replace the Power Piston pump. Seems like there were several of these but just slightly different. so buy them all & don't forget what you original looked like.
Of Course timing up a degree or 2..
Clean Air filter.
Vacuum advance in the dist.
& Advance the push pump ..I've gone blank on what it's called .. Maybe accelerator Pump. It can't be lazy.
.. Maybe some of that will help.
................
..................
..... I'm taking that you've been driving it for years & It's just came up with a dead spot.
....... In this case I'd think you need to look inside .. at the Rubber or leather on the acc. pump & See that it's not got an edge bent back. & Just replace the Power Piston pump. Seems like there were several of these but just slightly different. so buy them all & don't forget what you original looked like.
Rustytruck
Bronco Guru
- Joined
- Feb 24, 2002
- Messages
- 10,872
Make sure vacuum advance for distributer is on a ported vacuum port. If there is full manifold vacuum on the port at idle you have the wrong port. If you move the vacuum line for the vacuum advance recheck the timing at idle.
Don't know about the Summit carbs but one MAJOR reason to have an off idle bog with a Holley Carb is maladjustment of the Idle screw/ throttle plate / transfer slot .
When the choke is in the off position and the throttle resting against the idle adjustment screw the transfer slot is supposed to form a " square " - the length of the slot is equal to the width of the slot .
The transfer slot aids in the transition from idle to light/partial throttle.
Of course depending on your exact problem and how much throttle and rpm and etc - it could be a timing advance issue or accelerator pump issue or a vacuum leak.
When the choke is in the off position and the throttle resting against the idle adjustment screw the transfer slot is supposed to form a " square " - the length of the slot is equal to the width of the slot .
The transfer slot aids in the transition from idle to light/partial throttle.
Of course depending on your exact problem and how much throttle and rpm and etc - it could be a timing advance issue or accelerator pump issue or a vacuum leak.
TDubya
Sr. Member
I've developed a similar issue with my Holley, except mine stumbles from cruise (1500-2500 rpm) to half throttle if I don't ease into it. I'm hoping it's an issue with our winter fuel in California. I bumped the initial timing a couple degrees and went from 87 to 89 octane and it seemed to fix it. I know it's not the same issue, but I hope this helps.
- Joined
- Jul 1, 2011
- Messages
- 1,890
basically what gr8scott said. Off idle bogs are usually caused by not enough accelerator pump shot check adjustment if all is good there you may need a different pump cam or even a larger pump nozzle.
Power valve opening point is usually not a issue just off idle as the accelerator pump is used to cover the lean out during the opening the throttle blades the power valve doesn't act fast enough to cover that lean out.
Power valve opening point is usually not a issue just off idle as the accelerator pump is used to cover the lean out during the opening the throttle blades the power valve doesn't act fast enough to cover that lean out.
That is certainly the theory that I always operated with, too. But there may be a couple of other variables that are at play.
I run a fairly lean set of jets to cover the altitude range from 5000 ft to 10,000ft. The off-idle acceleration has always been spot on. I once had to replace a powervalve when the vacuum diapraghm died. The accelerator pump squirt was good and healthy, and the float levels and seats were good and new. Stupidly I threw away the old powervalve before recording what number it was. I mean, the powervalve is a powervalve. How much effect could it have, right? Using the rule of thumb that a the correct powervalve should be numerically half the measured engine vacuum, I got one a on the low end of the spectrum.
The results were horrific. Pressing the accelerator resulted in a flame-out bog. I mean a big bog. So to test a theory I started installing progressively higher powervalves. 6.5 was good but there was a definitely little stumble on acceleration while driving down the street. Then an 8.5 seemed to fix most of that, but there was still a small stutter in there. With a vacuum of 16 in/Hg that should have more than done it. But maybe the altitude? Don't know. Then to continue the experiment I swapped in a 10.5 and the Action Bronco got its mojo back. 10.5 is way up there.
So, yes, the powervalve should not have that big an effect, but there it is. Maybe the annular discharge ventures on the 4100 empty out the fuel well faster than most carbs. Maybe the lean jets can't supply enough gas and the accelerator pump can't cover that. Whatever the mix of variables, the powervalve tuning did the trick and having one too small definitely affected the off idle behavior. Just sayin'.
I run a fairly lean set of jets to cover the altitude range from 5000 ft to 10,000ft. The off-idle acceleration has always been spot on. I once had to replace a powervalve when the vacuum diapraghm died. The accelerator pump squirt was good and healthy, and the float levels and seats were good and new. Stupidly I threw away the old powervalve before recording what number it was. I mean, the powervalve is a powervalve. How much effect could it have, right? Using the rule of thumb that a the correct powervalve should be numerically half the measured engine vacuum, I got one a on the low end of the spectrum.
The results were horrific. Pressing the accelerator resulted in a flame-out bog. I mean a big bog. So to test a theory I started installing progressively higher powervalves. 6.5 was good but there was a definitely little stumble on acceleration while driving down the street. Then an 8.5 seemed to fix most of that, but there was still a small stutter in there. With a vacuum of 16 in/Hg that should have more than done it. But maybe the altitude? Don't know. Then to continue the experiment I swapped in a 10.5 and the Action Bronco got its mojo back. 10.5 is way up there.
So, yes, the powervalve should not have that big an effect, but there it is. Maybe the annular discharge ventures on the 4100 empty out the fuel well faster than most carbs. Maybe the lean jets can't supply enough gas and the accelerator pump can't cover that. Whatever the mix of variables, the powervalve tuning did the trick and having one too small definitely affected the off idle behavior. Just sayin'.
