Fuel delivery problem? 1980 Chev Suburban

[fkovalski]

1980 Chev Suburban 3/4, 4WD

New 350 stock motor (7500 miles)

New TH400 trans (7500 miles)

New Rochester carb (7500 miles)



I have a sporadic, intermitting problem that feels like a fuel delivery problem. It happens so few and short time that I cannot diagnose it. I can only describe it by what it feels like and relate some possible causes of which I think it could be:



Vapor lock

Intermitting stuck bowl float valve (closed in the up position)

Collapsing fuel line hose



I have checked all of the above as well as blown out the hard pipe fuel line. The truck ran fine after dialing the new carb up until about 500 miles ago, then the symptoms as described above happened without notice only four irregular times. I am able to “goose” the pedal through the 10 sec loss of power till back to normal. BTW- the fuel pump is new. New sender and sock in the tank. It really feels like a fuel delivery problem but will not rule out others. Distributor is new as with all other engine components.

I am not asking for a cure, but rather some other brainstorming ideas that I might not have thought of. Any and all ideas and opinions will be considered.

 

[Philip]

Run a pressure test on that new pump I have had new ones bad straight out of the box before.



Now be a little more discriptive on the problem.



Does the engine die?



Does it just slow down and get sluggish?



Does it miss?

 

[kaffine krazed]

Have you checked the fuel for water?

 

[TPCDrafting]

My inlaws have a 1980 3/4 ton Burb. They had the same problem (I think) The truck would be rolling along good, then just start to hickup and spit and sputter. Sometimes it would cough it's way out of it, sometimes ya had to pull over for a while. It was vapor locking. We finally figured out the exhaust was running too close to the fuel line(s) and making the fuel real hot. Maybe even boiling it. They had duel exhaust installed the winter before and didn't have any probs till summer when we were using it to pull horses.

We put on 3" single exhaust opposite the fuel lines and it never had problems again. This truck has a 400 small block. Hope this helps.

 

[Skydiver]

20 years ago I had to pick up boats for my uncle. 78 burb. Burbs love gas. It was doing the same thing. Fuel pump was the problem. Check your carb floats if it's not the pump.

Tim

 

[fkovalski]

more info...

Thank you for the replies- More info for those who asked:

The engine does not die- it does slow down and gets sluggish.

It does not miss.

There is no water in the fuel as we dropped the empty tank to install new sender and blow the lines.

It DOES have dual exhaust with headers that were not stock. Will investigate these two items as a possible source of vapor lock.

Thanks. –frank.

 

[DaveN]

Couple other items I've seen, although I would suspect it's one of the previously mentioned problems-



1. Fuel cap not venting? Perhaps leave the cap off and go for a ride - see what happens.

2. I'm not sure of all the particulars on this one, but I know that they used to use the charcoal canisters to help with fuel vapor emissions. I'm not sure how they are plumbed, but I've heard if the charcoal canisters go bad it can somehow affect your fuel flow.

3. I've crossed the fuel delivery and return lines causing problems before. Never work on a vehicle after a few beers.



But I'm thinking the headers are the likely culprit. May need to put on some of that silver heat shielding tubing to help you out, or reroute the fuel lines.

 

[slo-ryde]

Have you checked the fuel filter? I didn't see that in your post. I spent a lot of time diagnosing the heck out of a power loss problem on a 1963 Pontiac until I took out the fuel filter. It was packed with junk, I was amazed that the car would even start. The only time it would drop power was when kicking it down into passing gear. It ran fine the rest of the time.

 

[TPCDrafting]

I think it was '81 or '82 when they started piling on all the emissions crap like charcoal canisters and such. I could be wrong though. Keep us posted, I'll be inheriting the inlaws '80 burb someday, it'll be lifted, tinted, rimmed and sold (but they don't know that yet!!!)

 

[fkovalski]

This particular model, being 3/4T has no stock emission components. We removed the A/C and all related coponent when installing the new engine and transmission. The fuel filter has been replaced numerous times. It was the first item to try (I always start with the easiest and cheapest items first. ) The fuel cap does not appear to be a problem, but will replace it as it is cheap and easy to replace. ALSO- I found two small hose lines in between the hard pipe under the body that had never been replaced. Changed those out (cheap & easy. ) If the symptom occurs again, will next install heat wrap on the headers.