The Stovebolt Site Forums The Shop Area Engine Shop 1969 350 backfiring through carb and running poorly.

I have 1969 C50 with a 350 in it.

was running poorly and backfiring through the carb on heavy acceleration. Idles reasonably well.

I replaced the distributor with a MSD HEI unit as the old points distributor looked work and needed new cap, rotor, points etc.

didn't change the backfiring through carb.

I removed one valve cover today and found that the rocker on the valve second from the firewall on the passenger side is not moving as far as the rest while running.

Bad Camshaft I guess?

Hy tool, have a look under the other valve cover as well to check for the same problem on the other side. Take your distributor cap off and turn the engine with the balancer retaining bolt have some one watch the rotor and tell you when it is moving and when it stops, once you have turned it in one direction for a bit reverse the direction and make sure the rotor re-acts instantly to the change of direction, if it does not react instantly that indicates a worn timing chain/gears. Your backfiring could indicate an intake valve is still open when the cylinder is firing, or that an exhaust valve has not opened enough to let all the burnt charge out of the cylinder before the intake valve opens for the next cycle, hope that helps.

Yep, pulled the other cover.

It seems that while running #3 and #8 exhaust valves are not moving as much as the rest.

I haven't checked the timing chain condition yet, but I'm guessing this is the main issue?

Is this common?

Sounds like a worn out camshaft to me, I wonder why it would do it on 2 lobes only though?

If it is the original timing chain, I would vote for that being the problem.

I don't know if it's the original chain or not.

My thought would be, why would only two valves move less than the rest if it was the timing chain?

Hy tool,I think you probably have a camshaft problem for sure, I mentioned the timing chain as something else to check, good luck.

Sounds like the cam has some flat lobes on it. If they are exhaust valves that aren't opening correctly then it will back fire under a load.

Timing chain is probably worn, but won't have any effect on how much the rocker arms move. If a few aren't moving as much as the others then you have a cam problem.

You've got a flat camshaft on a few lobes. If the engine has over 75,000 miles, don't bother replacing the cam - - - -pull the engine and rebuild or replace it. Changing the cam would be like patching the seat on a pair of jeans with holes in the knees- - - -not worth the effort!
Jerry

Will any 350 match up if I were to swap the motor out?

Anything up to the mid 1990's is direct swap, I believe. When Chevy went to the valve covers with 4 bolts in the center and a 1-piece rear oil seal, a lot of other changes were made. All of them will bolt up to the bellhousing, but flywheels, valve cover and oil pan gaskets, and some other items are very different.
Jerry

Just changed my buddys cam in his 305 with a comp RV cam hyd. liffters it runs and sounds great.It's in a 50 1/2 ton AD.He was having the same problem.


Pete

Hy tool, I believe that 1986 was the year for the change to a one piece seal on the Chevy V8, and that would mean you would have use a flywheel other than the one on your current 350, hope that helps.

In '87 and up when Chevrolet went to fuel injection the engine was changed to a 1 piece rear main seal, the flange for the flywheel was changed also as the engine went to being externally balanced. As Jerry says the later motors will bolt up but you will find many things that are different. The dipstick on the later engine is on the right hand side, this is an easy way to identify a later engine.

Had a 68 Chev with a 327 with over 90,000 miles on it that coughed up the carburetor and miss when revved up. Ran fine at idle. One of the exhaust lobes on the cam was bad. Had a used 283 cam laying around so I put that in it. Ran fine for many years after. It doesn't take that long to change the cam. If you do change the cam put new timing gears and timing chain on.

small block chevys have been bought and installed,only after cam and timing chain and gears were installed.oil pump is good idea also.i got 327 that timing chain was so bad it had bent push rod when checked out.also had horrible head gaskets.chain was so sloppy,i could put cover bolt in with chain on outside of bolt!ive heard that 305s can run pretty good,if ya use 350 cam. gl on your bolt, tc