72 C10 pickup

[robbluhm]

I need some help tracking down what could be wrong with my timing.
I have 1972 Chevy C10 Pickup with a 350 engine and I got it running after 2years of sitting and I got it running, Now here is the problem. I start it up and it runs smoth when in park or neutral and when I give it gas it runs real smooth and then when I put it in gear and step on the gas it back fires through the carbs, after I get going it runs good till I step on the gasand it back fires though the cabs again.I have adjusted the distributer and can not find a sweet spot. OH I have new cap, rotor, wires and plugs. Please help.

[silicon212]

Originally Posted by robbluhm

I need some help tracking down what could be wrong with my timing.
I have 1972 Chevy C10 Pickup with a 350 engine and I got it running after 2years of sitting and I got it running, Now here is the problem. I start it up and it runs smoth when in park or neutral and when I give it gas it runs real smooth and then when I put it in gear and step on the gas it back fires through the carbs, after I get going it runs good till I step on the gasand it back fires though the cabs again.I have adjusted the distributer and can not find a sweet spot. OH I have new cap, rotor, wires and plugs. Please help.

Once again, I am going to prescribe the following treatment:

Remove valve covers. Loosen all rocker arms and remove all pushrods. Remove carburetor and distributor, paying attention to firing order so that it may be reassembled properly. Remove intake manifold (after draining the radiator, of course).

Remove all front engine accessories. Remove radiator. Remove harmonic balancer (also called vibration damper) using the appropriate tool. Remove timing cover. Loosen and remove 3 1/2" head bolts holding cam sprocket to cam. Discard sprocket. Discard old timing chain. Remove and discard crank sprocket, again using the appropriate tool. Remove fuel pump, and remove cover plate and extract fuel pump pushrod. Set aside.

Turn your attention to the lifter valley (the area under the intake). Remove lifters, using lifter extractor (this is a tool that snaps into the groove in the inside top of the lifters that holds the retainer), as the bottoms of the lifters are sure to have a sludge/carbon buildup that will make removing them any other way difficult. Discard all old lifters.

Thread a long 5/16" bolt (the 1/2" head bolt) into the front of the camshaft - one of the three mounting bolt holes. Use this bolt to supply leverage while you slowly and carefully extract camshaft from the front of the engine, taking care not to nick the cam bearings with the cam lobes (or former cam lobes). Once cam is removed, discard it.

Using a new camshaft and new lifters, and a new timing set and all appropriate gaskets, the assembly is the exact opposite of removal. Ensure you follow all directions from the camshaft manufacturer re: assembly oil on the new cam lobes and distributor/oil pump drive gear. When adjusting the valves, ensure the #1 piston is at TDC (top dead center). Adjust any valve that is not being pushed upon by the camshaft by spinning the pushrod back and forth with your left hand (if you're right handed, right hand if you're left handed), while slowly tightening the rocker arm nut with the other hand. You want to tighten the nut until the pushrod just stops spinning, then 1/2 turn more and no more. Do this with all valves that again are not being acted upon by the camshaft. Once done, turn the engine one complete revolution and tighten the remaining valves. Ensure that all rockers are tight and then rotate the engine until #1 is at TDC _and_ both intake and exhaust valves on #6 are rocking. This is the #1 power stroke. When you reinstall your distributor, you want the rotor pointing toward the tower that will be #1 on the firing order. You want to make sure the distributor flange is flush with the intake - if it sits 1/4" or so above the intake, the oil pump driveshaft is not indexing properly with the distributor. Remove distributor and use a long flat-blade screwdriver to index the drive and reinstall distributor. The #1 tower doesn't have to EXACTLY be at the location on the distributor as what's in the shop book, but it does have to point to the location where the rotor is on the #1 power stroke.

Once engine is assembled and ready to start, before starting it up ensure two things:

#1, you have more than two gallons of fuel in the tank. You don't want it running out of gas during the break-in cycle.
#2, set the idle on the carb HIGH, as in 2000 RPM high - you can guesstimate this as long as you have some musical knowledge - 2,200 RPM on a V8 sounds like the open "D" string on a guitar.

Now, fire that puppy up, and run it to the aforementioned 2000 - 2200 RPM and KEEP IT THERE for about 20-30 minutes (this is why you need at least two gallons of gas in the tank!), monitoring things like engine temp and leaks etc. If there's leaks, or the valves are noisy (and you have oil pressure*), shut it off and tend to that issue, then start it back up and resume where you left off. * If the valves are noisy BECAUSE there's no oil pressure, don't worry about shutting off the engine - by now it's probably shut itself off (and maybe resembled an IED).

In short, you have a camshaft/lifter issue. Been there, done that, have multiple T-shirts.

[bobss396]

I'd explore the cheap and easy route first. It sounds like you might have a sticky intake valve or a gummed up lifter. Add a pint of Marvel Mystery oil to the oil, drive it around as best as possible for a week. Not beating on it, just slow and steady maybe around the neighborhood for 15 minutes or so or until the engine is fully warmed up.

Pour some of the Mystery oil down the carb while its running. Crack the throttle by hand so it won't stall out. It'll smoke like crazy, but around a cupful should be all you need to do. Take it out for a ride afterward to clear out the plugs and combustion chamber.

Since the thing does idle smoothly, I don't think that you have any internal issues.

Bob

[silicon212]

Originally Posted by bobss396

I'd explore the cheap and easy route first. It sounds like you might have a sticky intake valve or a gummed up lifter. Add a pint of Marvel Mystery oil to the oil, drive it around as best as possible for a week. Not beating on it, just slow and steady maybe around the neighborhood for 15 minutes or so or until the engine is fully warmed up.

Pour some of the Mystery oil down the carb while its running. Crack the throttle by hand so it won't stall out. It'll smoke like crazy, but around a cupful should be all you need to do. Take it out for a ride afterward to clear out the plugs and combustion chamber.

Since the thing does idle smoothly, I don't think that you have any internal issues.

Bob

Bob, I've had a few cars with bad cams, they all ran the way his runs - very smooth at idle, smooth with unloaded acceleration, popping and spitting under load.

[bobss396]

I know that it could be a cam, but engine woes are hard to diagnose unless the car is sitting in front of us. So I'm giving him a possible easy out in case the thing is just mucked up. Maybe your cam replacement tutorial will come in handy after all.

Bob

[robbluhm]

It was running good when it was parked about 2 years ago. I am going to change the valve cover gaskets, is there any way to tell a sticking valve with the covers off?

[silicon212]

Originally Posted by robbluhm

It was running good when it was parked about 2 years ago. I am going to change the valve cover gaskets, is there any way to tell a sticking valve with the covers off?

I've never seen a valve "stick" open without an ancillary cause, such as a broken valve spring or a bent valve stem. Either one of these is mechanical damage necessitating the need for mechanical repair work. I've seen lifters stick and cause problems with valve lash, which would cause a valve not to open properly, this is usually a clicking, ticking or hammering noise depending upon the degree of severity. If this is the case, then Marvel Mystery Oil or a quart of automatic transmission fluid in the oil can clean out the carbon that's inside the lifters causing them to stick.

If you can spin the pushrods without any effort on any valve that's fully closed, soon after the engine is shut off, this could indicate sticky lifters or worn (excessive leakdown) plungers.

Another possibility is a worn timing chain (excessive slack causing a dull knocking sound, resembling a rod knock, from the engine front while idling), or a broken timing sprocket (aluminum sprocket with nylon teeth, nylon cracks and breaks off due to age and the slack chain beating at it). I'm still, however, sticking with the camshaft theory. At any rate, it's a valvetrain issue.

[bobss396]

I'm staying out of this one from here on, good luck to you and hope everything turns out ok.

Bob

[alblogg]

Originally Posted by robbluhm

I need some help tracking down what could be wrong with my timing.
I have 1972 Chevy C10 Pickup with a 350 engine and I got it running after 2years of sitting and I got it running, Now here is the problem. I start it up and it runs smoth when in park or neutral and when I give it gas it runs real smooth and then when I put it in gear and step on the gas it back fires through the carbs, after I get going it runs good till I step on the gasand it back fires though the cabs again.I have adjusted the distributer and can not find a sweet spot. OH I have new cap, rotor, wires and plugs. Please help.

What kind of carb are you running?

[jveik]

lol i had that exact problem with my old 350 before i started restoring my truck and it would run better without the no. 1 plug wire hooked up. if i gave it a bunch of gas over about 2500 rpm it would just bog and backfire, and when i took the heads off, i had a total of 3 burnt exhaust valves, one of them on the no.1 cylinder. im sure that the cam was bad as well...

[rob_bluhm]

Sorry for the long delay on getting back to yall. The prob was the distributor was off time, so I hooked up a timing light and checked the timing and it was way off, so I set it at 8 degrees before top dead center and it runs like a champ now. thanks for your input

[silicon212]

Mmm, that crow tastes good!

Glad to see you got it going.