title edited , please keep them family friendly
 

So I just picked up a 78 C10 2 weeks ago. Test drove it, no problems. Now when I go over 45mph it surges/jumps heavily and seems as thou it is not getting fuel. I have to push in the clutch and try to rev the engine to keep it from dying. Sometimes it works sometimes it doesn't. When I press the gas she doesn't rev or get any fuel almost like its out of gas, but I know its not.

I've replaced the ignition mod, sparkplugs, cap and rotor coil and the fuel filter near the tanks. Not sure what else to check. I was told the fuel pump is only about 6 months old, but again it only does it at high loads over 45mph.

Its a 78 4 speed 350.

Re: WTF is going on with my truck?
 

Is there is a fuel filter in the carburator? I know Quadrajets have a filter right where the fuel line goes in.

If you have rust and junk in the tank it may clog a new filter rather quickly, did you notice rusty fuel when you replaced the filter?

If definitely sounds like a fuel problem to me, but I am no mechanic.

High loads seems to support the fuel issue. The pump or filter is letting enough fuel by to get the truck to run at lower RPM's and loads, but not at higher RPM's and loads.

One more point - a new part doesn't mean a good part. It's becoming more and more common to have a new part be bad right out of the box.

Re: WTF is going on with my truck?
 

I actually had the opposite problem w/my 81 when I was driving it w/a 305. Under 45 it would jump and studder. Turns out the rocker arms were broken on #3 cylinder and one of the push rods was seized up. Not to say it's the same w/yours but that was mine. Try what 71swb4x4 suggested and if not try pulling the valve covers. Hope it's nothing major... that's what led to my frame off :lol:

Re: WTF is going on with my truck?
 

Carb is a holley 650cfm. Is the fuel pump in the engine bay or in the tanks? Trucks not with me atm and I've been told both. No rust or crap in the fuel when filter was replaced.
Posted via Mobile Device

Re: WTF is going on with my truck?
 

the fuel pump is mechanical on these trucks and runs off the cam
it is on the pass side of the block.
i'd check for some other fuel filters that could be on the line. something older between the carb and the fuel pump.

could be the holley...

Re: WTF is going on with my truck?
 

also could be something with your spark. id check all your wires and pull the cap off and make sure theres no moisture in there. is your advanced set right?

Re: WTF is going on with my truck?
 

check timing, make sure the floats are set right. check the vacuum advance. is more when cruising or on the gas?

Re: WTF is going on with my truck?
 

Happens when i'm on the gas I can't even get up to cruse at 50+. Timing is spot on, floats were checked Sunday and are good. Plugs were changed out sunday as well along with cap and rotor. No moisture.

I'll probably pull the fuel pump and replace it to rule that out.

Re: WTF is going on with my truck?
 

that really sounds more like a fuel filter than anything...

Re: WTF is going on with my truck?
 

Fuel filter or fuel pump is what it sounds like to me, starving on the big end.

Re: WTF is going on with my truck?
 

I've only found one fuel filter, which is near the passenger side tank.
Posted via Mobile Device

Re: WTF is going on with my truck?
 

I had a similar problem and it turned out the short rubber fuel line on the suction side of the fuel pump was collapsing.

Re: WTF is going on with my truck?
 

Does the truck have dual tanks? If it was sitting for awhile, you may have some old gas and/or you've sucked something up that is clogging the fuel filter. I'd start with the filter and check it carefully to see if anything is clogging it.

Re: WTF is going on with my truck?
 

Yes there is dual tanks, I replaced the filter near the pass tank and there was no crap in the fuel.
Posted via Mobile Device

Re: WTF is going on with my truck?
 

Good Morning,

I like the collapsed line idea. Also check the fuel tank pickup tube sock in each tank. They can become plugged up as well. In '78 the factory did not use a filter near the tank. The fuel filter would of been inside the carburetor.
With a mechanical pump you should always put the filter between the pump and carburetor not before the pump. Mechanical pumps push much better than pull.

God Bless, Terry

Re: WTF is going on with my truck?
 

i had the same problem with my 78 cheyenne 292 were your fuel line goes into your carb theres a small filter behind it pull it out and look at the small gasket on the filter theres one with a rubber gasket and a small hole and one with a paper gasket and a big hole but the exact same paper gasket. if you have one with the small hole rubber gasket go to ur local pars store and find the other one.. there the same size.. that was my problem runs like a dream now!! who ever replaced the filter last prob never noticed a diffrence

Re: WTF is going on with my truck?
 

rubber gasket is black paper gasket is brown!! be carefull not to strip your filter housing when ur putting it back in.. i did it to mine and its a real pain

Re: WTF is going on with my truck?
 

carb is a holley 650 thou, no filter in the carb as far as I can tell. The only filter is right after the tank, I know its not OEM so there is no filter right before the carb like my 66 gto rochester tripower has

Re: WTF is going on with my truck?
 

So I just replaced the fuel pump and still have the same issue. The line from the pump to the carb was good and the pcv line from the fuel line to the pump was good as well.

Not sure what else it can be....drop the tanks and check the socks and blow air through the fuel lines?? Where is the Y joint for the fuel lines? Could that be bad or going bad? I thought about bypassing that Y joint and running one tank to find out if thats it.

The carb does have a small metal filter and it was clean....

Re: WTF is going on with my truck?
 

Hey man you may have already found your problem i dunno but before we tore my engine down it was spittin and sputterin when i gave it half or more throttle like it was out of gas. but when time came for a new engine i wanted to take mine apart just for the heck of it and that problem before was the timing chain was really loose. hope that might help

Re: title edited , please keep them family friendly
 

If it was the timing chain thou then wouldn't it happen all the time not just after 45 or a higher load?

Re: title edited , please keep them family friendly
 

Plug wires will break down especially under a load. It will be worse on a manual trans vehicle because there is no slippage in the converter to let it rev a little. I read your original post and you replaced everything but the wires . I would definitely give them a shot . I have had several vehicles act like yours and the wires were the answer most of the time .
Frank

Re: title edited , please keep them family friendly
 

Wires look great though, not a cheap brand, MSD brand.

Re: title edited , please keep them family friendly
 

when you start giving it gas does it backfire or pop at all through the carb?

also do you know if its starts to get hotter when your trying to give it gas

Re: title edited , please keep them family friendly
 

It does backfire sometimes, maybe 20% of the time. Not sure if it gets hotter as my temp gauge is inop. It can't be too hot though cause it can be sitting overnight and only have it warmed up for a minute or 2 and it will do it. Engine can't be over 180.