intermittent stall

[pnut16611]

Hey everybody ! I am not a mechanic at all, more of a tinkerer. I bought an 86 last October, with a carbed sbc and it has run like a top until the last few weeks - I started having stumbling off-idle intermittently, and it`s slowly gotten worse. To start, I changed the fuel filter, with no change. But the new filter is glass, and it appeared that the fuel was boiling after an episode of rough-running. So I thought the problem is due to the increased ambient temp (over 90 most days lately), and the headers are less than six inches from the fuel line = vapor lock. So I shielded the line, and that seemed to have helped a good bit, but not eliminated the problem. Temp gauge is showing 160 avg, up to 210 sitting at a long light. Cranks & runs fine for the first twenty minutes or so, then I`ll get an off-idle stumble & start losing power. If I get off the gas & let it idle back down, it`ll smooth out. If I give it more, it`ll surge or stalls & will start right back up IF I give it a fair amount of throttle. Will run good for a few minutes and then repeat. After a stall, I popped the hood and there was little to no fuel visible in the filter - it feels like it`s running out of gas when it happens. Also, when I turn the key to off, the engine will stumble once or twice when it`s like this. Somebody educate me as to what`s going on here & thanks in advance !

 

[fast 99]

Open a fuel line after the pump. Usually at the carb. Check pressure by cranking the engine. Should be in the 5-7lb range.

If that checks out ok add a fuel hose into a small container. Crank the engine for 20-30 seconds. There should be 8 - 16 oz of fuel.

If pump fails either test, replace with a Delphi. AC or GM pump.

Toss that glass filter in the trash unless you want an insurance claim.

 

[Geoduck]

Second what Brian said about the glass fuel filter.
John, it's a Quadrajet CC carburetor I'm assuming. If so the fuel bowl is small and can heat up. A non metallic spacer between the carburetor and intake could help. GM made a heat shield that fit our trucks. Both could be had for < $100.

 

[Ricko1966]

Do you have the original 3 line bypass fuel pump on it still. If not that could be the source of your vapor lock. Also are you sure the tanknis venting correctly. Drive it with the gas cap of for 1/2 an hour,see if your problem is gone. Sounds like you put a glass filter 8n a rubber line on top of a hot engine. Great way to start a fire. I know this first hand, I now always run a steel line from the pump to the carb. If you feel the need to put in a filter besides the stock one. Plumb it in at the fuel pump and a steel line all the way to the carb. This way a fuel leak is under the truck and hopefully noticed by the puddles on the ground when you park. Instead of leaking fuel on top of a hot engine with plenty of ignition sources.