Ford 861 only runs on full choke

Hi all,

I had a valve job done and just installed the head back into my Ford 861 gas. Re-installed the tank, carb, etc. but had a hard time starting it until I pulled the choke all the way to the max. Then once it started, if I let in the choke just a little bit, the engine would stop running. I tried letting it run a bit at full choke but no change after letting it warm up some.,..it still just died. If I pulled out the choke just before it stalled, it would start running again. There was not a lot of smoke, but the rpm's were probably around 800 (no tach) at min throttle so it wasn't idling. The carburetor was just rebuilt by Royse so it should be good. I tried adjusting the carburetor anyway but it made no difference. I opened the plug at the bottom of the carb, and there was plenty of gas flow. The valve cover was off at the time as I was going to adjust the tappets at operating temp until this problem.
Any ideas on what the problem is? It didn't do this before the head was removed.

Thanks in advance!
 
What position was the throttle in when you had those results?

Did you try to increase or decrease the throttle while you had it running with the choke on full? If so, what were the results?
 
(quoted from post at 19:36:37 08/15/18) What position was the throttle in when you had those results?

Did you try to increase or decrease the throttle while you had it running with the choke on full? If so, what were the results?

I had the throttle at the lowest point when starting. When it starts it is already running/idling fast, so I only experimented with briefly increasing the throttle to maybe 1/3 to 1/2 of full. The rpms increased quickly. The engine sounded alright as long as I had the choke at full. But regardless of throttle setting, whenever I reduced the choke, it would stop running.
 
(quoted from post at 19:25:51 08/15/18) Vacuum leak?
Ben

Vacuum leak is possible. I installed a "new" used manifold. Maybe there is a crack somewhere. From the archives here, it sounds like a way to test is to spray some starter fluid around the area. I'll try that. Thanks
 

The "RPMs increasing quickly" along with the need for choke makes it sound like too much air, consistent with a manifold leak.
 
I recently had the same issue on an 860 and about drove myself crazy until I found a TINY crack in the manifold near one of the studs....
 

One or more of the intake valves set too tight and blowing back into the manifold,
vacuum leak,

stopped up main jet, due to crap in fuel line breaking loose.

make sure all rockers have clearance at some point in the crank over cycle. So that no valves are being held open.

inspect intake manifold, spray wd40 on it while running to see if anypoint makes the engine rpm change. spray at base of carb as well.

Assuming it ran good before and you did not mess with timing or carb.

Since exhaust manifold is on the same side, you can NOT spray starter fluid or anything super combustible. I have even used paint as it will stop small gaskets leaks fairly well, almost permanently. Again, watch for flair up and fire.
 
(quoted from post at 15:31:53 08/16/18)
One or more of the intake valves set too tight and blowing back into the manifold,
vacuum leak,

stopped up main jet, due to crap in fuel line breaking loose.

make sure all rockers have clearance at some point in the crank over cycle. So that no valves are being held open.

inspect intake manifold, spray wd40 on it while running to see if anypoint makes the engine rpm change. spray at base of carb as well.

Assuming it ran good before and you did not mess with timing or carb.

Since exhaust manifold is on the same side, you can NOT spray starter fluid or anything super combustible. I have even used paint as it will stop small gaskets leaks fairly well, almost permanently. Again, watch for flair up and fire.


So I tried checking for a manifold leak by spraying some starter fluid all around the area of the manifold and the carb while it was running. I did that while the engine was cold to help prevent a flair up or fire. Sotxbill's warning appreciated. There was no change in the rpms or sound of engine after doing so. And I sprayed it pretty liberally. So doesn't seem to be a manifold leak. I'll next check the clearance at the rockers. I did have to make adjustments initially because I replaced some of the push rods. That might be the problem. Will update. Thanks!
 
Checked and adjusted the tappets (have a question on that but will do that in a separate post). So the valves are definitely closing. But the issue with the engine requiring full choke to run has not changed. I guess that leaves the carburetor as the last issue. Thinking as test, I can remove the carb off my 881 and install it on this 861 and see if that solves the problem.
 

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