The Stovebolt Site Forums The Shop Area Engine Shop carb

i just changed my carb, i went back with rochester carb same as what i had, but now it back fires through the carb, it didn't before maybe the timing was off ,,whats up ? i did see that the choke writing was upside down compared to the old one ,, does that matter ???

thanks

could it be the air mixture? ? or could it be gas, because when i primed it all i had was mixed gas, , ,lol it shouldnt matter really,

Thansk

A backfire through the carburetor occurs when there is a passage open from a cylinder to the carburetor when the cylinder fires.

This is generally caused by:

(A) ignition timing out of correct adjustment
(B) valve timing out of correct adjustment
(C) burned or sticking intake valve.

Before throwing rocks at your carburetor, I would suggest at least a compression test, and checking the ignition timing.

Jon.

If nothing had been touched in the engine when you last parked it until now, I would be suspect to a faulty accelerator pump.

oh in a new carb?? i guess it could be ,, i got it running now don't know if there is any back firing now or not ,,the only thing now is when you give it gas there is a hesitation ,, sounds like a acc pump ??

thanks

A hesitation when giving it the gas could be a defective accelerator pump BUT:

It could just as easily be defective timing, a defective advance mechanism, or a host of other items.

Again, before tearing into the carb, would check compression, ignition, etc.

Jon.

Ok i will do these things, ,i am taking it to a guy tue and see what he does, , i keep doing the same thing over and over maybe he will do something different, , but i will tell him about the compression

Thanks

i took apart my New carb that i just bought ,, and i swap the acc pump out with my old carb and its all better now go figure ,,i am going to make them give me a carb kit ,, i am still going to take it to these guys tue to get them to check it over ,, i feel like i keep doing the same things over and over

i will get back to the road tube after that

Every carb kit I buy for a Rochester does not have the recharge check ball retainer pressed into the pump/plunger far enough(this is on the very bottom of the plunger). This allows the ball to fall to far down/away from it's seat. Gas flowing past the ball sucks it UP against it's seat on the pump stroke. If the ball is to far away from the seat the gas just flows by it. In that case it flows back into the bowl not to the nozzle.
It is a little hard to see but there are four slots in the bottom of the plunger. If you look between the slots you will see the recharge ball. With the plunger held in the upright position you will see the ball is down from the seat. the correct clearance between the ball and the seat should be about .020". On most replacement plungers the clearance is more like .060".
I put the accelerator plunger in my vice and push the retainer further into the plunger. There is a stop so you can't go to far.
This always works for me.

ohh ok so when they rebuild this carb they didnt do this ,, thats why when i reused my old one it was already seated ??

i been looking , so were is a good place to get a crab ??

thanks

i am getting ready to order a carb ,, just checking if there is any other carb that will work ?? like a 2 barrel ??? something that will bolt on

thanks

has anyone bought anything from rockauto ??

Yes, quite regularly.
They are fast and they carry a lot of parts.

so good stuff then ?? thanks

i got my carb fro rock auto its great,, the only thing is i need to adjust the fast idel i am guessing i need to this with choke i dont see any other way ,, we drove it to town it was great i let it set for a 1 or so and come out it was idling way to fast it came down though but still it was too fast being that hot

If this is on your 1958 Biscayne, it probably has an automatic choke - right?

yeah temp choke ,, does the choke spring expand or contract when it heats up i took it apart and dont know how it goes back

thanks

i played with the choke a little ,, running pretty good , i did notice that now after the new carb it shifts a lot better real smooth why ???