Hi Everyone,

My 1979 Corvette had a newer 400 SB with a Edlebrock Carb. The car starts, runs, and drives fine, The problem is after the car warms up it starts to bog or hesitate whenever I step on the gas harder than normal. This will continue until I take it up on the highway and even then it does it until I pass 60 MPH then it will accelerate OK with out the hesitation.
I left it at a friends house for a night so he could show his wife and talk to her about buying the car. When I got it back the idle was turned up high. When it is in park the tach. reads 1400 rpms. I asked him about it and he said that's all he did to the carb. I am worried about trying to adjust the carb. myself since I know very little about carb. adjustment and I do not want to make the problem any worse.
When I bought the Vette it came with a manual carb. installed under the hood. It is hooked up but I have never needed to use it and I did check it tonight to be sure it was not pulled out. I checked the choke because like I mentioned the car runs great until the engine warms up then it runs terrible.

Thank you for any input you may have.

Jeff

Note: I also have side pipes that run directly from the headers. I do not know if that makes a difference. It has never back fired and the car has alway ran great after they were installed. It is just since he messed with the idle that it has been hesitating or bogging.

 

Try turning the idle back down again.. What may have happened is that by turning the main idle up, he exposed the transfer slots, which can easily cause a bog or hesitation.

 

Have you checked fuel pressure? Gunk in your fuel filter?

 

Thank you! I will do both right now and let you know what happens.

Thanks,

Jeff

 

hes turned the idle up to compensate for something else. see if the acc pump is squirting gas into the carb. get the idle correct first, then get a vacuum gauge. adjust the idle air control screws in front and get it to read as high a vac as poss 15-20hg is good. and start reading the numbers. then work from there. once you get the vac going adjust the idle then adjust the vac then the idle.
once this is all done drive it, you will probably still have the bog and this will be due to the secondaries opening too soon. that is done with the secondary adjustment screw on the side. you want to tighten it 1/8 turn drive it test it keep going till the bog is gone but dont over tighten the spring.

note-these are basic operating procedures for a carb that is in good shape and not needing a rebuild.

also look for a crushed or collapsed fuel filter too.

 

It it runs fine and then acts up after the engine reaches operating temp you should suspect the HEI module located under the rotor. You will probably see signs that the rotor is shorting to the distributor shaft (rust like build up on the advance weights). When the rotor begins to fail a stray spark can kill the module.

If it ran good before I'd replace rotor and module and this is a simple DIY fix.

 

Thank you for all the tips. I have done a few of the tips you have suggested and I cannot believe the increase in power/torque. The power increase is still when it is cold but I still have to do a couple more of the tips you have suggested. I did buy a new fuel filter today and will install it tomorrow to see how that works, if that does not do it I will keep on trying until I get it right.
I also have a mechanic coming to the house Friday to do a tune up as well as go over the carb. to check all the settings. I will most surly show him your tips.

Sincerely,

Jeff (Zenvette) Fuerst