backfire problems?

[76blazerguy]

How can i stop it backfiring? i installed an intake manifold, and it idles good, but i cant give it any gas. I installed a crosswind manifold. Its a 350 with a really small carb for the motor which is getting changed sometime soon, other than a K&N and a flowmaster exhaust its stock. Its a 76 if that give any one else any ideas. Orginally it was backfiring through the carb but adjusted the distributor a little and it now idles good, the problem occurs when i give it some gas, even in low rpm's. Also for some reason i can give it gas when in park and it wont backfire as much but when i try and test it out in drive it will do it a lot more.

 

[kilroy]

I suggest you check the following:

make sure there are no vacuum leaks
make sure the intake manifold is seated properly to the heads.
make sure the carb is properly seated to the intake.
If all that is good ensure the Distributor is not 180 out.

Kilroy

 

[Thuren]

It sounds too lean... I'd try richening up the idle mixture a bit to see what it does..

Don

 

[76blazerguy]

Im pretty sure the manifold is seated good and the carb to, i did have the distributor 180 the first time but im pretty sure thats good to, What vacuum leaks could do that? thanks for your help, any solutions are welcome because they are worth the effort

 

[Thuren]

any solutions are welcome because they are worth the effort

Did you try richening the idle yet?

 

[76blazerguy]

yea i have tried richening it im pretty sure its still a timing issue, i hope it is!! Another idea is that maybe the carb is just not getting enough fuel, as it is only a 450 cfm carb, the pump looks a little worn to round the rubber seal. could that have an effect?? see the thing that is confusing is it was running good before i went to change the intake.

 

[R72K5]

a 450cfm carb ? really ? what kind ? thats interesting,, hmmm

4bbl ?

no ?



wonder about toiming chain condition ?


lifter issue ?

valve hanging up ? try the paper suck up tailpipe test?


try a vacuum guage tester yet to see if needle does anything funky ?

rocker adjustment too tight for one of the valves ??


hmmm

good luck

 

[76blazerguy]

Yea its a old holley 4bbl, so old that its really hard to find parts for it, we are pretty sure its a 450 cfm. found the odd few numbers that say its what it says after doing hours of research online, you really think the timing chain could do that keeping in mind it ran good before? lifters or valves could do that? what is the tailpipe test do and involve apart from the obvious?

 

[diesel4me]

old Holley ??

I'm not a Holley carb expert at all(never liked them much,with a few exceptions)--the 450cfm one might have a "power valve",which is a sore spot on many older holley carbs--one backfire will blow out the rubber diaphram in it,and make it hesitate on acceleraton,backfire,and dump raw fuel in the venturi at idle...you'll have to look up your carb # and see if you can find an exploded diagram without buying a rebuild kit(maybe online??)--the power valves arent expensive,and they do make a "power valve saver" that prevents a backfire from popping them so easy--speed shops carry them(Jegs,Summit,etc)..
This is assuming the ignition timing,oplug wires,etc are all in good order and the firing order is correct..

But your carb might not use one at all,not all Holley's have one...they are rated by inches of vacuum required to open them--its stamped on it,I'd stay with the rating it came with unless your motor has a hot cam or other mods that change the factory vacuum signal to the carb......Good luck..