Engine popping sound during accelerationt

[ajochum]

I have an '82 Mercruiser 260/350 that gave me fits last year as to starting. I took it to a mechanic and he gave it a general tuneup, plugs, points, etc. along with rebuilding my Rochester 1347-8292 carburetor. He had trouble with it running himself so he took it to a more experienced rebuilder. It started right up for me and I took it for a test drive, but noticed that when I accelerate, it gives a high-pitched popping sound - like a gun going off. It does it several times and almost acts like it might quit on me. However, once I get beyond that and it planes out, it runs great.
Also, after it sat for a week or so, I had trouble starting it. It just cranked. Finally, I took off the air cleaner and with the throttle in the forward position, I pushed down on the accelerator pump (dashpot?) and watched gas squirt out into one (only one) of the front barrels. After that, it started right up and continued for the rest of the evening. I'm going to give it a go this weekend, but would ask if these problems are anything that would provide hints of what might be going on. Thanks.

 

[Scott Danforth]

You should have 2 streams of fuel.

You are experiencing a "lean sneeze". Your carb needs to be rebuilt

 

[NHGuy]

And if you go back to the previous carburetor person, which I would, tell him what you found.

Hearing what you have said would make me go directly to the accelerator circuit and clean it. If he says he can't do it you might need someone with more carb skills. If he wants to help you, and hasn't been in the accelerator circuit, cut out this information and see if he will read it.
Quadrajets were the standard in GM for decades. Somebody near you can do this. Probably some old hot rodder my age or older!

There is a check ball that's removed to clear out those passages, maybe he missed it. That needs to be out and then the circuit needs to be cleared. Try to put air and cleaner backwards through the openings. Also during the repair, you take the old ball, put it in the carb and give it one slight rap with a flat punch or a nail set. This re-creates the seat for the new ball.

Try to keep the same carburetor.
There are differences from one to another that determine how they run. If your original carb ends up no good there will be some setup needed for whatever goes in it's place.
Also check and recheck for junk in your fuel filter and fuel water separator. The fuel needs to be perfect or the carb will repeatedly get messed up.

 

[ajochum]

Thanks for the replies. Two nights ago I took it for another spin. I cranked it a couple of times, but knowing how it has resisted starting, I opened the throttle, pushed the accelerator pump (think that's the right name - left of the carb) and watched several squirts of gas flow in (right side only). Started right up. The good news is that it ran perfectly. The popping has completely gone away. I'm wondering if maybe I had some moisture left in the lines from the old gas. I had just added 6 gallons of ethanol-free gas a couple of weeks ago and maybe it is now sucking the good stuff?
Anyway, I have decided to run it for a few weeks as is and get some good boating time in as our season is so short. I found an "old-timer" who used to rebuild Rochesters in the 70s and 80s and he has agreed to take a look at it. So, I'm going to run it as is until mid September, have him look it over and then reinstall and make sure all is well before I put the boat up for the winter.
Oh, and I am going to change out the fuel filter now. The guy that worked on mine said he did it, but recommends doing it again just to be sure.

 

[NHGuy]

I think that's great...just don't expect to be able to go from idle to wide open quickly. If you accelerate gradually you can minimize the lean pop that happens from your partial accelerator pump shot.

 

[Scott Danforth]

You need to get the carb cleaned. PEDIOD. That squrt only on one side will come back and bite you soon if you don't adress it