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Uber Guru

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RE: Carb Bog


Just wondering if you checked the accelerator pump nozzle fuel stream . Is it a nice solid stream or does it sputter out of the nozzle. Because if you have a worn out accelerator pump diaphragm It would give you a bog. Just wondering because you are saying it's an old carb. 

 

Ian



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Canadian Poncho Superstar!

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beaucarlo wrote:

did you check this little khown adjustment on a holley 4 barrel....from under the carb there is a secondary throttle plate adjustment..a small screw that should be turned 1/4 times to provide a little fuel to prevent a stumble (google Holley carb adjustment--good info)



-- Edited by beaucarlo on Thursday 20th of July 2017 12:54:02 PM


 Lloyd, as per Bobs suggestion: I know this won't have much to do with a bog, but if you do go to the trouble of removing the carb, take that secondary idle limit screw out from the bottom, and re-install it from the topside. It should be a 3/32 Allen screw. This way you can always adjust it from the top, by just opening the carb up fully to fit the key in and turning the screw.

Another tuning hint for a good baseline, carb off, is to make sure your primary butterfly's only cover as much transfer slot to make little squares. Then do not touch the primary idle speed screw again, adjust the idle speed with the secondary from then on. Does your carb have 4 corner mixture screws?

As others, I have to believe in the wisdom of concentrating on getting the ignition right first, then move to the carb. Ignition being a good spark, correct initial timing, and a working mech and vac advance system (if it has one). Do you have a good ignition switched power source to the distributor? What distributor do you have? Sounds like you have a lack of proper advance just off idle. Does the mech system move freely? Will the vac can pull in with some vac applied? Does it advance running when you plug in the vac hose to the can (with the timing light)? Set the initial to 16 advance disconnected and plugged, re-connect and see what it advances to. I think it should go up to at least 28 at idle. Then rev it to at least 2500 and see if you can get at rough number. Cheers.



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We now know why Mark is a superstar.

Great tip Mark.

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Cliff



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Yes in this case I think they threw on an old carb they had laying around on, the choke wasn't even assembled properly.

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The stream from the accelerator jet seemed pretty steady.



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cdnpont wrote:
beaucarlo wrote:

did you check this little khown adjustment on a holley 4 barrel....from under the carb there is a secondary throttle plate adjustment..a small screw that should be turned 1/4 times to provide a little fuel to prevent a stumble (google Holley carb adjustment--good info)



-- Edited by beaucarlo on Thursday 20th of July 2017 12:54:02 PM


 Lloyd, as per Bobs suggestion: I know this won't have much to do with a bog, but if you do go to the trouble of removing the carb, take that secondary idle limit screw out from the bottom, and re-install it from the topside. It should be a 3/32 Allen screw. This way you can always adjust it from the top, by just opening the carb up fully to fit the key in and turning the screw.

Another tuning hint for a good baseline, carb off, is to make sure your primary butterfly's only cover as much transfer slot to make little squares. Then do not touch the primary idle speed screw again, adjust the idle speed with the secondary from then on. Does your carb have 4 corner mixture screws?

As others, I have to believe in the wisdom of concentrating on getting the ignition right first, then move to the carb. Ignition being a good spark, correct initial timing, and a working mech and vac advance system (if it has one). Do you have a good ignition switched power source to the distributor? What distributor do you have? Sounds like you have a lack of proper advance just off idle. Does the mech system move freely? Will the vac can pull in with some vac applied? Does it advance running when you plug in the vac hose to the can (with the timing light)? Set the initial to 16 advance disconnected and plugged, re-connect and see what it advances to. I think it should go up to at least 28 at idle. Then rev it to at least 2500 and see if you can get at rough number. Cheers.


 Thanks cdnpont, it seems to get better with adding more advance. Its a HEI Gm distributor which looks newer. Hooking up the vacuum advance doesn't seem to make any difference . The carb only has two idle mixture screws. 



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