Engine issues.

[76chevyc20454]

Need a little help here on where to start. I have a 76 k10 with a 350, it has a edelbrock 600 on it. So last weekend I went to a offroad park and climbed some decent hills. After climbing the first one, I noticed that it was idling around 400 and shaking real bad so I figured the float bowls might have drained since I was on a hill the floats were shut. It didn't get any better. It wasn't running hot, 200 like always but after climbing the first hill it idled horrible and had a real bad hesitation when taking off, it acts like it's going to die then jumps up to about 1000. I checked fuel pressure today, it was at 5-6 at idle and dropped to around 2 when I revved the engine. I just set timing before going to 12* btdc and was running great. Drove it about 40 min there. What you guys think?

 

[1987 GMC Jimmy]

I think you may have been on the right mental track to begin with. It could just be a stuck float issue. I’d try tapping the carb with a screwdriver handle to see if you can free it up. If you’ve seen Roadkill, they had to do that when they were climbing hills in Ep. 1.

 

[76chevyc20454]

I think you may have been on the right mental track to begin with. It could just be a stuck float issue. I’d try tapping the carb with a screwdriver handle to see if you can free it up. If you’ve seen Roadkill, they had to do that when they were climbing hills in Ep. 1.

That's the first thing I tried lol. I tried rock on the trail then hammer when I got back to the camp site. Does the fuel pressure dropping when revving sound normal to you? Can't seem to find a answer.

 

[1987 GMC Jimmy]

I’d say the 5-6 is an ideal reading, but the two seems a little low. I know Holley recommends a minimum of four at redline, which sounds like a good benchmark to shoot for. Does the truck sit for long periods? Ethanol is poison for fuel pump diaphragms if allowed to sit for any protracted periods of time.

 

[76chevyc20454]

I’d say the 5-6 is an ideal reading, but the two seems a little low. I know Holley recommends a minimum of four at redline, which sounds like a good benchmark to shoot for. Does the truck sit for long periods? Ethanol is poison for fuel pump diaphragms if allowed to sit for any protracted periods of time.

I drive it maybe every other weekend or when I need to haul somthing.

 

[1987 GMC Jimmy]

I gotcha. They can also wear out, of course. Is this problem only an idle and off idle issue? It might be worth taking the outlet line off the pump and pumping into a bottle. I've been told that the volume should be about 20 oz in 8 seconds. It catches up once you get cruising? I'd look down the carb, move the throttle, and see if you get the two healthy fuel streams. I also would consider tank debris getting picked up and overwhelming the strainer sock. You can test this by running the fuel pump straight out of a fuel can. I'd probably do the fuel can test first and go ahead and check the acc. pump since it's easy. That way you're narrowed down to your pump or your carb unless the acc. pump test failed. Then do the volume test. Hopefully something won't look right, and you can get some answers. All three of those tests have worked well for me with fundamental carb diagnostics in the past.

 

[climb-101]

fuel pressure should stay constant for the most part.

 

[76chevyc20454]

I gotcha. They can also wear out, of course. Is this problem only an idle and off idle issue? It might be worth taking the outlet line off the pump and pumping into a bottle. I've been told that the volume should be about 20 oz in 8 seconds. It catches up once you get cruising? I'd look down the carb, move the throttle, and see if you get the two healthy fuel streams. I also would consider tank debris getting picked up and overwhelming the strainer sock. You can test this by running the fuel pump straight out of a fuel can. I'd probably do the fuel can test first and go ahead and check the acc. pump since it's easy. That way you're narrowed down to your pump or your carb unless the acc. pump test failed. Then do the volume test. Hopefully something won't look right, and you can get some answers. All three of those tests have worked well for me with fundamental carb diagnostics in the past.

So today I went ahead and rebuilt my carb. It was pretty dirty so it needed it regardless. Now after I put it on and started it it acted the same way. I hooked up a vacuum gauge and it read a round 15. Just for giggles I moved the dizzy around to see if adjusting timing would help and it made no difference. Don't actually have a timing light at the moment waiting for a buddy to bring one over. I'm honestly wondering if maybe the timing chain jumped.

 

[1987 GMC Jimmy]

I’d still follow through on all the aforementioned fuel tests just to rule that out completely. I’ve not been blessed with a timing chain issue, but I’m thinking you’d be pulling more hair out of your head on that one than you already are. That’s just my opinion, though. Your vacuum is definitely low, but it’s not radically low. Was the gauge a stable 15, or was it doing something else? You can check the timing chain with a light. You just need to watch the timing mark at idle, blip the throttle, and let go while having been watching, and the mark should be smooth in its movement and settle back stably. Any fluttering indicates a problem.

 

[5akman]

I have read where one of the "off road" fixes for the Edelbrock carbs is to take either some fuel resistant epoxy or a very short piece of fuel line and block the fuel vent/transfer passageway at the rear of the carb. When you pull the top of the carb off, you'll see the passageway at the rear of the carb body connecting the two fuel bowls. On rough terrain, this allows one bowl to flood while the other goes somewhat "dry". Since the bowls have normal vents, this passageway is said to be unnecessary. While this is not your current problem, you might want to address it if your back inside the carb chasing gremlins!

 

[Rusty Nail]

What happened to the 454?

 

[4WDKC]

sounds like the fuel pump cant supply enough fuel while above Idle and cant keep the bowls full. This explains the stumbling idle as its low on fuel, and why it will die if you goose it while its stumbling.

 

[76chevyc20454]

What happened to the 454?

I still have it, saving up money to rebuild it.

 

[Jrgunn5150]

sounds like the fuel pump cant supply enough fuel while above Idle and cant keep the bowls full. This explains the stumbling idle as its low on fuel, and why it will die if you goose it while its stumbling.

I concur, the pump sounds weak, draining the bowls.

 

[Snoots]

X2, fuel pump