This 79 FJ40 runs great for the first 15 min then stalls at idle.Any ideas what the problem could be . It'll always start up again w/ choke. Thanks Joe

If it is a 2F, the most common reason is a vacuum leak. Leaks occur at the vacuum booster, the intake gasket and cracks in the intake manifold at the bottom under the carb mounting surface. To locate the leak listen for a hissing noise at the booster, spray carb cleaner around the gasket surfaces (when the engine is cold) and see if the engine speeds up. If you take the carb off you should be albe to see the crack. You might try adjusting the idle mix and speed first, but you will want to rule out a vacuum leak as it can cause other problems.

Thanks for the help. It is the 2F engine + I tried the carb spray to check for leaks but found none. It seems so stange becouse it runs + idles perfectly for about 15 min. then acts up.

joeliz,
Keep us posted with what you find.
I am having the same problem with my 75 2F. Manifold vacuum is at 17 mmHg and it idles fine during a cold start. As it warms up to temperature manifold vacuum steadily drops to about 10, it runs rough, misfires and eventually dies. I've checked for vacuum leaks everywhere. So far I have eliminated the brake booster, carb, intake manifold, pvc valve and all hoses. I've replaced the intake / exhaust gasket (twice), I pulled the head and had it surfaced and replaced the gasket. It was recently rebuilt so all the valves and guides are still within specs. The block surface measured level. I am missing something because it still does the same thing.
I am beginning to think that there is a small crack in the block or head that is allowing the leak as the engine warms and expands.
Very frustrating! Good Luck.

Have you checked the bi metal spring on the heat control valve?
Directs hot exhaust gas to bottom of intake manifold to help atomize fuel until eng gets warm. Supposed to then close. If
it doesn't intake gets too hot, fuel vapor locks eventually burns hole or cracks manifold under the carb. Runs/starts with choke
because richer fuel mix wont vapor lock as easy and or cools the manifold. This spring is notorious for sticking open as it corrodes. Warm climates like here in Az they are somtimes secured in off posistion to avoid this prob. Good description pg 66 of Haynes manual. Hope that might help

You can get a clue about whether there is a leak and if so where it is by reading the plugs. The cylinders closest to the leak run leaner and their plugs are often noticably lighter color (light tan, white or burned) than the normal plugs (mocha brown). This won't work if you engine is burning a lot of oil or has bad compression. Try doing a tune up including adjusting your carb.

Thanks again I'm going to check out that bi-metal spring,I hope like hell it's that simple[wire it closed]. I'll be in touch.

If it is the spring check the manifold to be sure it
hasn't burned through already. Sometimes a good
welder can repair it if its not too bad.

If you find a crack in the intake man.
You can JB weld the crack if it's not too bad and you also install header to get rid of the extreme exhaust temps under the crack.
After grinding the crack area down... I have JB welded two such cracks. One was 5 years ago and it still works great.

Cory

See stalls post