backfire on start up when cold

[1956olds]

86 5.7 4 bbl carbs,rebuilt three seasons agnly when it first starts one pop and done,any ideas? could it be just from last seasons fuel,i treat it with startron and store inside heated so i wouldnt think it would be the problem.I also installed newer vernalifts this winter ,it had been plumbed straight through with no mufflers before and it was just too noisy,so it may have done it but i couldnt hear it.Thanks Glen

 

[1956olds]

anybody?Is this normal?

 

[Bob & Sue]

It's not normal if it were me I would start by checking to see if the carb is leaking into the engine by pulling all the plugs out to see if one is wet when engine has been sitting at least 24 hours you can put a napkin in each cylinder then crank engine over to see if it has gas on one of them, if it's leaking whichever intake valve is open will have gas in it causing it to detonate if it leaks enough fuel you can do a lot of damage like a rod through the pan, if thats ok then check your timing, if all is ok you may have some other issues like worn timing belt. Just my opinion on where to start.

 

[vernh59]

That may be a "lean pop." You may have a gasket leaking at the carb or maybe stale gas. If it keeps running I think I would let it run and check for a vacuum leak at the manifold/ carb joint.