Engine Issues

[hexafamily]

1972 C10, Standard 350, 700r4, dual exhaust (Heart Throb/LMC) Edelbrock aluminum manifold, factory Quadrajet, HEI distributor.

In last 6 months the engine begins to loose power when climbing moderate hills at highway speed (70-75 mph). Most recently, while leaving my son's house, I backed out of the driveway, put it in drive, accelerated and it died and would not restart. I checked the carb and could not see or hear gas being squirted when pumping the accelerator so I poured some gas into the carb, it fired right up and ran perfectly all the way home. During trips taken later, the truck runs fine, except for losing power on highway hills. Once or twice it has been hard to start.

The engine acts like its starving for gas during the times it has problems. I had the carb re-manufactured about 9 months ago, along with a new fuel pump and new steel fuel line between the pump and the carb. Fuel filter is clean. The tank, sending unit, and lines are original, although they have been cleaned. Pulled spark plugs and they all look good.

Any ideas what is going on? Help would be appreciated.

[YoungPup1977]

Can you say quadajunk....thats my first pick from your post.

[B. W.]

Is the pump mechanical or electrical? Does it run worse when it's warmed up or cold? Does it act up more when the tank is full or closer to empty? Is the condition repeatable all of the time or more intermittent? Are you running ethanol? (I know, lots of questions) Even with all of that, I believe the first thing I would do is test fuel pressure & volume. (Actually, the first thing I would do is replace the fuel filter but you said it's good) If you don't have a pressure tester, you might just want to throw a pump on it, a stock one is only about $30.00. Hate to throw parts at problems but at least it would eliminate one variable. For a mechanical pump, to test volume, UNPLUG THE ELECTRICAL CONNECTOR ON THE DISTRIBUTOR SO THE ENGINE WILL NOT RUN. Remove the line at the carb, put a hose over it, run the hose into a container & crank the engine over. There are specs for volume but if the pump is good it'll pump so much in 10-15 seconds you'll know it good. If it's just dribbling out you have a problem.

[hexafamily]

Originally Posted by B. W.

Is the pump mechanical or electrical? Does it run worse when it's warmed up or cold? Does it act up more when the tank is full or closer to empty? Is the condition repeatable all of the time or more intermittent? Are you running ethanol? (I know, lots of questions) Even with all of that, I believe the first thing I would do is test fuel pressure & volume. (Actually, the first thing I would do is replace the fuel filter but you said it's good) If you don't have a pressure tester, you might just want to throw a pump on it, a stock one is only about $30.00. Hate to throw parts at problems but at least it would eliminate one variable. For a mechanical pump, to test volume, UNPLUG THE ELECTRICAL CONNECTOR ON THE DISTRIBUTOR SO THE ENGINE WILL NOT RUN. Remove the line at the carb, put a hose over it, run the hose into a container & crank the engine over. There are specs for volume but if the pump is good it'll pump so much in 10-15 seconds you'll know it good. If it's just dribbling out you have a problem.

Thanks for the suggestions. Its a mechanical pump that I replaced and it didn't fix the problem, but I've not checked the output. I am running regular pump fuel (ethanol blend). The problem is intermittent but seems more prevalent when the truck is warm and its warm outside (over 60 deg). Tank level seems to have no effect. I'll replace the fuel filter.

[geezer#99]

Do you have a vented gas cap?

[68gmsee]

Originally Posted by YoungPup1977

Can you say quadajunk....thats my first pick from your post.

The person that posted needs help with his problem not an opinion on quardrajets. I personally have owned several and rebuilt some with no problems.

Hexa, first thing is to do the easy things first. Filters, fuel flow volume when cranking (one pint in less than 30 seconds is a good indicator), possibility of bad gas.

If above checks are okay you may have sediment plugging up the carb. Lots of good info on the net on taking them apart. A good cleaning should help.

On the problem with no fuel squirting could be a defective accelerator pump and may need to be replaced.

[TJ's Chevy]

Check the lines, what it sounds like is that there is just barely enough fuel being supplied, but under the load and rpm of running at 70 mph...the engine was to lean.

My 64 GMC had this problem, electric pump and eddy 4 barrel. Ended up being a clogged solid fuel filter so...remove the tank sending unit to make sure there is the screen filter on the end....if that is good..blow out the lines and check your filter. Also check for cracks in the rubber and metal line.

Basically check from cap to carb.

[hexafamily]

Originally Posted by geezer#99

Do you have a vented gas cap?

I have an unvented gas cap since its a '72 with the charcoal canister, but gave me an idea that maybe the vent system is not working right so I'll have to check it out!

[PGSigns]

A lot of Q-jets have the filter in the carb behind the inlet fitting. Have you replaced that one?
Jimmy