Slant 6 hot running issues

[Trey Osborne]

Hello, I have a 1963 valiant with a 1978 super 6 engine. It runs perfect around town and for short highway drives. But if I go for more than a hour straight it won’t idle at all. If I let it sit for roughly a hour to cool down it will run perfect again. Still will run fine at speed. It’s not choke, it’s not carb, I’ve checked and adjusted timing and all the advances. Does it need one of the fuel filters with a third nipple? I think they filter the gas vapors from the gasoline. Any input appreciated thanks.

 

[slantsixdan]

it’s not carb

How do you know?

Does it need one of the fuel filters with a third nipple?

Those can help. See the fuel line mod article.

 

[AJ/FormS]

set the valves, remove the gascap an try again.
If a lash adjustment was just done, them increase the lash to .013/.023

 

[Cal Tonsley]

Could be vapour lock, make sure fuel line is routed away from exhaust or well insulated.

 

[Trey Osborne]

How do you know?



Those can help. See the fuel line mod article.

I've gone through the carb less than a year ago checked the fuel filter it's perfect. That also wouldn't make sense for it to only act that way after an hour of driving but not before.

 

[Trey Osborne]

set the valves, remove the gascap an try again.
If a lash adjustment was just done, them increase the lash to .013/.023

ok, will do. I set them to .010 and .020 before. I'll open them up.

 

[slantsixdan]

0.010" intake and 0.020" exhaust are the correct tappet clearance settings, with the engine hot. See valve adjustment procedure.

Also, carburetors are finicky, especially on today's gasoline. "Went through it less than a year ago" doesn't necessarily mean it's still fine.

 

[Trey Osborne]

Thank you for the suggestions everyone. I did the valve lash again and that didn't help. I read slantsixdan's article and did the fuel line mod. That fixed it as far as I can tell, I drove right at 100 miles today with no issues.

 

[slantsixdan]

Fingers crossed!

Take a look at tune-up parts and technique suggestions in this post. And for later (or now), carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

 

[Trey Osborne]

Fingers crossed!

Take a look at tune-up parts and technique suggestions in this post. And for later (or now), carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

thanks again! I’ve got a exhaust leak at the head so while I have everything off to fix that I’ll go through the carb since I’ll have it off painting the manifold.

 

[slantsixdan]

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions. Install tech tips here. And if your exhaust manifold fails inspection (cracked, warped, gasket surfaces no longer flat, etc), see here.

And while you are at it, consider ditching the rinky-dink, cold-blooded factory choke setup for a № 1232 Electric choke kits, which—unlike the original, is adjustable (hallelujah, praise be!).

 

[Trey Osborne]

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions. Install tech tips here. And if your exhaust manifold fails inspection (cracked, warped, gasket surfaces no longer flat, etc), see here.

And while you are at it, consider ditching the rinky-dink, cold-blooded factory choke setup for a № 1232 Electric choke kits, which—unlike the original, is adjustable (hallelujah, praise be!).

I'll get the good gasket you recommended. I'm 17 so to spend $50 on the choke upgrade doesn't make sense for me money wise. The factory setup is working just fine for me as of now.