Backfiring under a load

[govols]

I just replaced the engine in my 1995 Cobalt. Its a 5.0L Volvo Gl, with a Ford 302 block.

Not sure if any of that info is necessary, just following the adults only instructions.

When I rev the engine in neutral, it sounds great, but when its in gear it starts backfiring through the carb when I get above 1200 RPMs. I plan to have the carb rebuilt, because what can that hurt? The boat has been sitting since '09 when the block was cracked, so I assume it needs to be rebuilt anyway. I checked the timing with a gun yesterday and got it set right. All of the spark plugs and wires are firing. The engine actually runs smoother at a higher rpm, so I assume the problem is in the carb. I thought it was getting too much gas, but adjusting that didn't make it much better. Anybody have any ideas that differ from what I am thinking?

Thanks

 

[Don S]

Re: Backfiring under a load

I just replaced the engine in my 1995 Cobalt. Its a 5.0L Volvo Gl, with a Ford 302 block.

It's either running lean or you have plug wires crossed, or cap has some cross tracking in it and needs replaced or ??????

5.0L Volvo Gl that G indicates General Motors, a Ford should have had an F there. What is the FULL model number? All the letters after the 5.0?

 

[govols]

Re: Backfiring under a load

It's either running lean or you have plug wires crossed, or cap has some cross tracking in it and needs replaced or ??????

5.0L Volvo Gl that G indicates General Motors, a Ford should have had an F there. What is the FULL model number? All the letters after the 5.0?

Yeah, sorry not sure why I put Gl. Its a 5.0 FL PHUS. I double checked the plug wires, and they are all in the right place.

 

[Don S]

Re: Backfiring under a load

Check your harmonic balancer. Does it have timing marks both before and after TDC. If so, make sure you are on the Before side with your timing light, not After TDC

 

[govols]

Re: Backfiring under a load

I believe it just has one, but I will double check it and get back to you.

One more question (and this may have something to do with the problem): The fuel pump has two things coming out of it

1. the metal line that goes to the carb
2. an orange plastic line that as of now is going nowhere. I can't figure out what to do with it. Sometimes it seems to be a vacuum, and sometimes it seems to be blowing out.

Someone else took the engine down to the heads when it originally cracked, and I have put it all back together with a little help from a friend. We have no idea what to do with that line, and obviously since we didn't take it apart we have no idea where it came from.

 

[Don S]

Re: Backfiring under a load

The clear line goes to the carb/flame arrestor and only gets used if the fuel pump diaphram gets a hole in it. Then the fuel goes into the carb and not the bilge.

 

[Bondo]

Re: Backfiring under a load

2. an orange plastic line that as of now is going nowhere. I can't figure out what to do with it. Sometimes it seems to be a vacuum, and sometimes it seems to be blowing out.

Ayuh,..... Welcome Aboard,... That should be vented to the top of the carb, or possibly the flame arrester...

It'll pass gasoline, if the diaphragm rips... Safety feature...