My 1970 Stepside dies at 30-40 mph

[GARUMO]

I have been having problem with my truck. I thought it had something to do with gas but I really don't know now. It starts hesitating when it reaches 30-40 mph. I have replaced the carb,pump,hoses and filter from the pump up. And it continued after a week or so.
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[CC69Rat]

Does the engine cut in and out? Or does the truck just not pull and the engine RPM stays the same. (?)

[doosekoop]

check the filter and the in carb filter for black flake debris. If you find it you will either need to change filters more often or clean your tank. I had this problem with my blazer starving for fuel at freeway speeds , turns out the ethenol / alcohol added to current fuels breaks down the varnish layer from older car and truck fuel tanks.

other then that with all those changes im stumped!

good luck!!

[GARUMO]

The engine does not stay at the same rpm. It feels like it needs gas. I guess I have to clean the tank to get that out of the way and go from there. Is there any specific product I need to clean the tank? Or I need to take it somewhere to get it cleaned.
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[MagmaJct]

Does it still have point ignition? If so, check the condition of the points, and check the gap/dwell. If the dwell is set too low, there won't be enough time for the magnetic field to develop in the coil and it'll begin to misfire as speed increases. At lower engine speeds there is more time (lower RPM) so the magnetic field is fully developed for the nest spark. Good luck!

[MistaGavin]

Check your screen on the pickup line in the tank. Mine was deteriorated and occasionally would starve the engine on hard acceleration. Removed it and
Fuel flow increased. Be sure you have a inline filter.
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[GARUMO]

I have electronic ignition, but someone told that the problem could be from there. I haven't changed anything since a bought it. I'll try that as well.
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[GARUMO]

I'm also having problems when I try to crank the engine. Sometimes it wants to start and sometimes it does not even want to crank. It seems like the battery is dead. Any suggestions
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[wwotr]

Originally Posted by GARUMO

I have electronic ignition, but someone told that the problem could be from there. I haven't changed anything since a bought it. I'll try that as well.
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Damn whats that thing called in the HEI Distributors...is it "Resister",
that could be going out?

[Autoblueprint]

Originally Posted by GARUMO

It starts hesitating when it reaches 30-40 mph. I have replaced the carb,pump,hoses and filter from the pump up.

Possible exhaust restriction, click on this link and check what your engine readings are:

http://67-72chevytrucks.com/vboard/s...37#post4688437

[jhwkns]

Has it got the proper vented gas cap?
Is the H.E.I. hooked to the resistor wire from the original distributor?

[CC69Rat]

Does it have one of those in-line fuel filters on it? Could it be restricted or clogged?

Also, I had a Mallory Unilite ignotion in a 406 one time and the module in that thing would die about once a month. Something to do with a ballast resistor (?) My pop fixed it years ago. Really not sure what the ballast resistor even does but mine had some sort of problem. .. I can find out what it was. It would break down about 30-40 mph and loose power. Sometimes start, sometimes not.

[GARUMO]

I'll look into the distributor some more. I'm lost with that. Do you guys think I should just buy a new dist. Cap and rotor? I think it wouldn't hurt because I have never looked under there.
Do you guys the gap for the spark plugs and which kind should I buy?
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[Clutch442]

Take the ignition module out of the distrubutor. It's the electronic box under the rotor inside. Take it toyour local auto parts store they can check it for you. Spark plug gap is .45 with electronic ignition. I use NGK plugs but will probably get flamed for it from the ACDelco guys.