mikeym8414

So here's the deal,

I'm pretty green when it comes to engines and carbs so bear with me. So when I accelerate the car seems to lag, jerk, lurch or act like it wants to stall. Like its not getting enough power. Or if I kind of mash the gas a little bit there is a second or two pause where nothing happens and then...vroooooom like normal. Once I'm up to speed its fine. BUT THEN, as I let off the gas to coast or slow down for the light..or decelerate I should say...the exhaust will pop or make a backfiring sound. It doesn't ever stall out, idles fairly steady and starts right up even if it's cold. Opinions on the issue here? I did switch out plugs recently...could it be a bad plug brand new out of the package? Not really getting the misfiring signals from it but I will admit I haven't rushed to pop them out and check.

cv67

Could be a few things but would hedge a bet on a bad accelerator pump.

HeadsU.P.

A popping in the exhaust is usually a vacuum leak. Lord knows where. There are only a billzillion places. Make sure #5 plug wire is no where near #7 plug wire. They tend to crossfire because of the firing order.

ben dover

Bad quick acceleration pump.

Too rich and firing in exhaust.

Retarded timing.

cooper9811

It could be the carb, it could be timing, it could be both.

When I first got my 79 (when it was still the stock motor) I had a stumble when I started to accelerate. Adjusted timing and set the vacuum advance to use manifold and the stumble went away.

It's usually good idea to make sure timing is correct first - I would start there, then focus on the carburetor. If your engine is modified, that can also influence the timing curve you need.

There are a lot of good posts about setting timing if you search the forum. You can also email Lars Grimsrud, who participates on this forum, for some useful documentation on setting timing. His email is V8FastCars@msn.com.

This is also a good post, but as the title says, is long - still worthwhile:

https://www.corvetteforum.com/forums...long-post.html

Rescue Rogers

I had popping on deceleration and it was running lean. Check your timing again then pull your plugs and see what color they are

mongoose87

I agree. I was recently trying to reduce some gassy smell and leaned out my '72 a half turn, which does not have cats, but got some light popping when i let off the accelerator pedal on the highway. Mine is the original old engine with some of original vacuum lines left, so its possible there are some slight leaks, but I'm sure it wasn't the timing because I just did the timing according to Lars's recommendations.

As mentioned before though, it could be from a lot of things. Enriching the idle mixture could just cover up the symptom.

bobs77vet

tell us what you have done tune up wise especially related to timing and rebuilding the distributor

stingr69

The accelerator pump can cause the hole when you push down on the gas. Look for any looseness in the linkage for the accelerator pump. depends a lot on what carb you are running.

The after firing can be from a lean misfire. You snap the throttle closed and vacuum goes way high sucking a lot of air around the throttle blades. This is more air than fuel - the mixture goes soo lean it won't ignite in the cylinder causing raw fuel to be pushed out into the exhaust where it will explode on the hot surface. burble burble burble and maybe even some BANG!

pigfarmer

Had something similar yesterday in my '69. Was fine then really started to run badly. I went looking for a loose plug wire, to see if the distributor would move of if there might be a vacuum line dangling.



I found that the distributor cap wasn't fully attached - one of the clips had let go. Thought that would have fixed it but I then saw that the negative lead on the coil wasn't tight and the tach wire was wiggling around. Two seconds to fix it and I'm back in business.



Before you go nuts look for the simple stuff. Air, fuel filters. Maybe you got some crap gas - throw a can of SeaFoam into it.

mikeym8414

mikeym8414

mikeym8414

pigfarmer

Dunno if you were serious about that SeaFoam but if so there's your answer. I've had great results with that stuff over the years and never a problem, but there's a first time for everything.



I was just saying keep it simple. Too easy to create problems by "troubleshooting"



Good luck