The Stovebolt Site Forums The Shop Area Engine Shop Need help! Out of ideas!

'59 Apache 3600. 235ci w/4spd. Rebuilt engine, bored out, stock grind cam, orig intake w/Fenton headers and glass packs. Rochester carb (rebuilt)
Runs fine when cold until it warms up then starts to idle a bit rough but still not too bad. After about a 20 minute run at hwy speeds when coming to a stop the engine stumbles real bad and will usually die unless I keep it throttled up. After stumbling around a while if I keep feathering the gas around at low speeds it will get better again.
Just finished resto last fall w/ new plugs, points, cap, rotor, coil, vac advance on dist, fuel pump, and rebuilt Rochester carb.
Since then I've replaced all of those parts again with no improvement. Actually seems to be getting worse.
I do have the hot air kit on the bottom of the intake. I did have a vacuum leak at the intake but that is fixed now. Checked and rechecked timing and carb adjustments. Truck runs great above idle!
I'm out of ideas...

Sounds like the valves need adjusting. They might be recessing in the seats from no lead gas. If the clearance is too small when it gets hot & the parts expand they are not closeing tight.

Might look at a fuel issue. Is the gas cap vented? It should be. There's been more than one person have issues with their truck either dieing or stumbling when the gas cap would vent reating a vacuum on the tank.

I would also consider possible fuel percolating in the carburetor when flow is reduced after a heat producing drive.
What can you do to help keep the fuel cool before the carburetor and isolate the carb bowl from manifold heat?
Tie that heat valve open in hot weather--can you test this possible boiling problem by cooling the carb bowl when it performs at it's worst?--cool with a water spray in a spray bottle--maybe refrigerant.
Our modern fuel has so introduced some bad habits due to the lowered boiling point.

Wrenchbender; I've adjusted the valves so many times I had to get a new valve cover gasket. They are adjusted to where they quit ticking when running with motor warmed up.

Roy; fuel cap is vented. Ran with cap off, same issue.

Enginenut; tried the old trick of clothespins on fuel line, no help.

What about the fuel lines & pickup in the tank?

This question is probably clutching at straws: did you check the surfaces on the rocker arms that press against the valve stems? They sometimes have a groove worn in them and that makes adjustment difficult.

All fuel lines and pickup/sending unit new. Tank flushed, cleaned, sealed. Frame off resto completed last fall.
Rocker arms and shaft new also because when I put the motor together I failed to put the plug in the oil passage to the rockers which caused my oil to flow out on the lifters instead of going up to the rockers. Hence the new rocker assy. I did however drive it for 200-300 miles before finding the problem.
(I wondered why I kept having to adjust the valves)You can laugh now! Rookie mistake! I'm more familiar w/ V8's.
Maybe I damaged valves/ head running w/o oil?

valve guides galled up from not having any oil and the valves are hanging up>

Really sounds like you have a fuel issue. My bet is that the idle speed circuit in the carb is still partially clogged even though you've done a rebuild.

I agree with the fuel side. How many fuel filters do you have? What do they look like? Some tank seal products react to new fuel compounds. Take another look for any crud in the fuel pump and filters and also the carb filter. Good luck.

Logic says fuel issues but it also says fuel issues like insufficient delivery to the carb would NOT allow high speed/load running without missing and dying out until the load /speed was reduced.---I hear you saying rough running at idle and low speed after runing down the road normally.
A hot carburetor loses it's ability to provide an accurate idle mixture.
Also a look in the carburetor bowl may reveal some small particles that will plug or partially plug the low speed orifices---sometimes they move around and cause intermittant trouble.Look in that bowl.

k10- Have 1 glass fuel filter right before the the carb. Looks clean.. It was also replaced recently with no change.

Rebuilt carb again today, let soak several hours in Chem-dip then sprayed with brakleen and carb cleaner. Paid special attention to holes and passages, poked with weld wire..
Took out for a jog ... Minor improvement but problem still exists.

When I read your post for the first time without reading any replies, my first thought was valve adjustment problem....just my 2 cents,
Scott