Big bog with holley double pumper
Thread Starter
Heel & Toe
Joined: Nov 2009
Posts: 16
Likes: 0
Big bog with holley double pumper
Hi all,
Just put a slightly used but stock Holley 650 double pumper (4165) on my semi stock Vette. It runs great until I open the secondaries, there is a very bad bog. Tried to adust air/fuel mixture and ignition timing but didn't fix the problem.
Is there something I'm missing to do, did it happen to anyone else?
Ken
Just put a slightly used but stock Holley 650 double pumper (4165) on my semi stock Vette. It runs great until I open the secondaries, there is a very bad bog. Tried to adust air/fuel mixture and ignition timing but didn't fix the problem.
Is there something I'm missing to do, did it happen to anyone else?
Ken
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
Hi all,
Just put a slightly used but stock Holley 650 double pumper (4165) on my semi stock Vette. It runs great until I open the secondaries, there is a very bad bog. Tried to adust air/fuel mixture and ignition timing but didn't fix the problem.
Is there something I'm missing to do, did it happen to anyone else?
Ken
Just put a slightly used but stock Holley 650 double pumper (4165) on my semi stock Vette. It runs great until I open the secondaries, there is a very bad bog. Tried to adust air/fuel mixture and ignition timing but didn't fix the problem.
Is there something I'm missing to do, did it happen to anyone else?
Ken
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
First, what is your timing ?
Then, as Ben Lurkin said, tear the carb down and verify/set it up to original Holley specs using HOLLEY parts.
Assuming your timing is correctly set, and that all the carb parts are identical to your holley carb list, check and adjust accelerator pump cams.
Remember that pump response must be instantaneous to the movement of the throttle. Holley web site shows the correct procedure for adjustment. ( Videos and .pdf files ).
If it backfires or hesitates, then goes, try bigger cams and /or bigger discharge nozzles.
First try a cam that will activate the pump sooner, like a red / orange / green one.
If it's not enough, then try #0.035 discharge nozzles. Once you get a small puff of black smoke when you floor the gas pedal,
then you have done enough ! Double pumpers like a big initial shot.
This procedure is much easier and accurate when you own a wideband AFR meter...
Then, as Ben Lurkin said, tear the carb down and verify/set it up to original Holley specs using HOLLEY parts.
Assuming your timing is correctly set, and that all the carb parts are identical to your holley carb list, check and adjust accelerator pump cams.
Remember that pump response must be instantaneous to the movement of the throttle. Holley web site shows the correct procedure for adjustment. ( Videos and .pdf files ).
If it backfires or hesitates, then goes, try bigger cams and /or bigger discharge nozzles.
First try a cam that will activate the pump sooner, like a red / orange / green one.
If it's not enough, then try #0.035 discharge nozzles. Once you get a small puff of black smoke when you floor the gas pedal,
then you have done enough ! Double pumpers like a big initial shot.
This procedure is much easier and accurate when you own a wideband AFR meter...
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Very important question, that. IME mild SB's with auto transmission aren't typically at their happiest with mech 2nds.
Also, as mentioned by others, at first thought this sounds like insufficient fuel delivery upon opening the 2nd bores. That said, I wouldn't do any adjusting to the carb until you know the ignition system and timing are dead on.
Also, as mentioned by others, at first thought this sounds like insufficient fuel delivery upon opening the 2nd bores. That said, I wouldn't do any adjusting to the carb until you know the ignition system and timing are dead on.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
That assumes he's going lean upon throttle application. This is usually accompanied by a lean backfire. He may want to investigate a rich bog. This carb has a 50cc secondary pump so I doubt it is a lean issue unless there's a pump problem and he's getting a backfire.
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