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Post Info TOPIC: Carb Bog


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Carb Bog


I have a 350 engine with a 4150 vacuum secondaries 600 CFM. Car stumbles or bogs when you give it some gas, worse when it is cold. Choke is working proper, set accelerator pump to specs and it seemed worse. Increased the shot and it was better but not enough adjustment. The engine is stock would I need to increase the accelerator pump size? Timing seems to be on.confuse



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Poncho Master!

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Classic example of late ignition timing.

I would try advancing it a couple of degrees at a time to verify.

Thanks
Randy

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Sherwood Park
Alberta, Canada

1981 Parisienne 400



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Thanks I will give it a try. I have never run into timing affecting the stumble, but of course I always ran lots of advance in the "old" days on my Chryslers. 



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A Poncho Legend!

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Often you will get a backfire though with not enough advance.

No backfire?

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1966 Strato Chief 2 door sedan 283 "survivor"


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No backfire, starts great,doesn't knock on regular gas or run on after you shut it off. I will buy a timing light and check it tonight.



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Can you still buy timing lights out there. I am still on my old trusty timing light that i have had since the early eighties. 



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1957 Pontiac Pathfinder Deluxe sedan restored 261 six

1974 Chevrolet Caprice Estate wagon low milage original 400 V-8



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Yes bought a timing light, it at 10 degrees before TDC



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I'd be looking for a vacuum leak and adjusting the idle mixture.



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72 Nova SS,   66 Beaumont Sport Deluxe,   09 Pontiac Solstice GXP Coupe



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Thanks I will check again for a vacuum leak, I have tried enriching it but maybe I didn't go far enough.



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Poncho Master!

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Sounds like you didn't try bumping up the initial?

Thanks
Randy



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Sherwood Park
Alberta, Canada

1981 Parisienne 400



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It was at 10 before TDC, I don't want ping or dieseling 



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Poncho Master!

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It's not uncommon to have incorrect or slipped timing marks so I usually never use a timing light.

I set it to idle best, stert easy and not hesitate or ping.

Advanced timing doesn't directly cause dieseling.

It can indirectly cause dieseling if the timing is so late the throttle has to be open excessively to maintain an idle.

If advancing causes the Engine idle to rise enough to cause dieseling the timing was obviously late.

If advancing causes the Engine idle to increase the timing was obviously late.

No one wants their Engine to ping or diesel but optimum timing is close to pinging.

Maybe retard it a few degrees and check out the cold stumble.

Thanks
Randy











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Sherwood Park
Alberta, Canada

1981 Parisienne 400



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sure its not to rich, I find most carbs are set at three jets too much for stock tight convertors.



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Also check your float levels . Make sure your getting fuel in the rear bowl. I have seen new carbs with float levels set wrong. Could be starving for fuel. Does not hurt to check. Like randy said timing. Would not hurt to ad a few degrees. You can always put it back. 

 

Ian



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Thanks Randy I will give it another try with the timing, I have checked and have no vacuum leaks and have tried playing with enriching and leaning out and doesn't make any difference. I forgot to mention that is does have a one inch spacer on the carb so don't know how much that would change flow characteristics      



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Guru

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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

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bob lewis


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as a quick experiment , rev her up to about 1200 lay your hand over the air horn does the rpm go up or down, rich is down, I have to play with the holley in the Camaro every time I drive it , finicky to a carter



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20170720_132141.jpg



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bob lewis


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I set the timing to 20 before TDC and tried a bigger accelerator pump nozzle 25 to 35 no bog when it is warmed up now, still a bog when it is cold, so will have to keep tuning.



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20 initial timing? That's a ton of advance.

Is there a chance your balancer has slipped and the mark is moved?

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1966 Strato Chief 2 door sedan 283 "survivor"


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I wanted to see if it made a difference in the bog, seemed to help and gave it a bit more snap. I don't know if the balance slipped?



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Thanks for the tip beaucarlo  where did you get that spec sheet?



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Guru

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i searched Holley carb adjustments....in the list there is a section -Rebuild and Adjustment Manual for Models 2010,2300,4010..Holley- from the manual i took a picture

with my cellphone to post it.......the trouble with this adjustment is you have to remove the carb to adjust...if you have a bigger cam some people suggest turning the 

screw 1 1/2 turns then adjust the 4 idle screws using a vacuum guage and a tach



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bob lewis


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The engine is stock, the carb looks old and may have been thrown on it to just to sell it. I have never had so much trouble with a carb or tuning it before.



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Guru

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sounds like you recently bought your car.....a carb gets blamed for alot of issues...start with a good basic tuneup...including a compression test....make sure the timing is to spec. ,vacuum advance is operating,no vacuum leaks, no cracked hoses correct pcv valve(new hose)last to set is the carb i don,t know your engine size-maybe you have the wrong carb or jet size....sounds like you are close...


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bob lewis
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