Backfires lean condition after carb rebuild

[sebas54]

1987 gm 4.3l merc. I/O 2 barrel carb.

After rebuilding my carb. I have experienced lean conditions. It will pop occasionally at 3500-3900 rpms and it will lose about 1 rpm when gong over wakes. I installed a spring needle and set the adjustments on the float for the spring needle. When i remove the old needle it was solid needle. Is this my problem??

 

[danond]

Re: Backfires lean condition after carb rebuild

Spark plugs show a lean condition, too?

 

[sebas54]

Re: Backfires lean condition after carb rebuild

the symptoms only started after i rebuilt the carb.

 

[danond]

Re: Backfires lean condition after carb rebuild

Yeah but you're guessing that it's a lean condition. Spark plugs will confirm it.

 

[sebas54]

Re: Backfires lean condition after carb rebuild

will the choke setting affect it if it was lean or rich?

If I take the plugs out then it will only confirm that it is running lean??

 

[danond]

Re: Backfires lean condition after carb rebuild

Yanking the plugs will confirm that it's running lean across the entire operating range (or not).

Choke will only make it more rich, not more lean. Strange thing is that at WOT (and the reason I'm questioning it) is that your carb is only able to deliver fuel through the jets at high RPM.

Assuming you rebuilt the carb properly, there's no adjustment at that RPM range other than changing jets.

The other thing needed is a timing check. The carb may be adjusted properly now and your timing was out of whack before.

 

[sebas54]

Re: Backfires lean condition after carb rebuild

I checked the timing and advance a week or two ago and it was all good. I will check it again today. These symptoms only happen under load. Can it be that I changed the solid needle to the spring needle?


Thanks so much!!

 

[sebas54]

Re: Backfires lean condition after carb rebuild

Well I figured it out. It was the spring needle with the wrong float settings. I replaced the spring needle and installed the solid needle and adjusted the float accordingly and it work great.


thanks again!!!