Choke Plate Screw Vanished - Farmall H

At this point I wanted to get it off that cold pasture and to the garage. I opened the gas valve just a tiny bit, started the tractor and drove it about a quarter mile to the garage. It died in front of the garage when I slowed down, and once again I saw the carb was dripping gas.

I went to work checking the carb, and tapped on it thinking the float may have been stuck. Thats when I noticed the choke lever would come partway out. Removing the air intake, I found the choke screw was gone, and nowhere to be found. Although this is an updraft carb, I do believe it was sucked into a cylinder.

I have since replaced that screw, (put locktite on it). I also opened the fuel bowl and cleaned it out, but did not do a complete rebuild because the local dealer did not have the full kit.

The engine is now running, and after some carb adjustments, seems to be running ok, except it seems to have a bit of vibration to it.

I have been rather worried ever since. Did the screw get embeded in a piston? Does it need to be removed? Was a valve damaged? Was the cylinder wall scored or did a ring break? And my biggest question is what caused that loud knock? Could that just have been the result of liquid gas getting sucked into the cylinders, or was it that screw? I am not going to feel comfortable using the tractor until I learn more what happened, especially considering that screw may still be in the intake manifold or somewhere and waiting to destroy the engine. It still amazes me a metal screw could be sucked upward that far.

Someone in an archived message said that they put a thin brass screen in the carb intake (at manifold) to prevent these screws from getting sucked into the engine. Is this something I should do, or is the locktite enough? (I also thought about putting some JB Weld on the screw head, but I'd never be able to get it out again).

One other thing. When I opened the carb, I found the float bracket was broken on one side (by the hole, on the side that pinches together), and the float pin was barely holding. This is not a part my dealer said they had and doubted they could get. I had a local machine shop use a TIG welder and weld a washer to it. I think this should be ok, but can these brackets be gotten?

I'd appreciate any advice. Thanks.

It looks like anything is possible from what you said. I know that knock was very noticable, but it's gone now. I doubt there's a hole in the piston or anything else because it runs pretty well. It just has that vibration, which I suppose could be a bent valve. Like you said, I need to do a compression check.

I noted that from some of the archived replies on here, that some people have removed those screws thru the sparkplug hole using something with grease or gum on the end. I am assuming that would mean to get the piston to the top, right? How I'll know which cylinder it is, is another question, unless the plug shows damage. Guess I'll just have to play around with it and carefully look at everything in the process.

On the other hand, I am wondering if the vibration could be carburetor related. Seems that after I opened it, it needed quite a bit of adjustment. At first it was surging like crazy.

If the screw did blow out the cylinder and got into the exhaust manifold, should I run the tractor for a short while with the muffler off, so it comes out all the way? I'm sure it could not climb to the top of the muffler. It's no big deal to take the muffler off, because I never clamp it. (I cant get it in my garage door with the muffler on).

If it is still in there, and as to your question of which cylinder to look in -- you're going to do a compresion check anyway, so you're going to have all the plugs out. Couldn't hurt to have a peek in each one, but do the compression test, and look for the screw first in any cylinder that comes up with low compression. Turn the engine by hand until that piston comes up to the top. If the screw is still in there, but you can't see it, try blowing a little compressed air in through the plug hole and see if you can blow it around to where you can see it. Then you can get it out with a magnet or a dab of rease on a stick, Worst case is you'll have to pull the head to fix the valve and you can take the screw out then, if it's still there.

That's all best case. Worse relates to what somebody mentioned up above about possibly a gear tooth chipping off and jamming, causing you to stop so abruptly. My neighbor lost a tooth on the pinion in the rear end of his pickup last summer. That's a lot tighter quarters than the tranny and diff on your H. Still, that broken tooth got caught up and grenaded the rest of the pinion. It bound up so tight that it snapped his rear driveshaft. Anyway, after we got all that fixed, he ran it only a short time before he got a low-end knock in the engine. We opened up the bottom and found the rod bearing on #1 had spun and #2 was about ready to go. 3 through 6 looked okay, but 7 and 8 were messy, too. Bottom line, the abrupt stop bent his crank. I hope that isn't the source of your knock and vibration, but it's something to keep in mind.

If it were mine, I'd check out the top end first. Fix anything there and then, if the vibe and knock are still there, drop the pan and have a look at the bearings in the lower end. If the crank was damaged in the stop, then it's a whole other can of worms about what to do.

If the latter is the case (and I hope it's not) and you get it fixed, you'll likely want to lift the deck and look your gears over. Sometimes those broken gear teeth will sit harmlessly in the bottom of the gearcase, other times they'll get swept back up and do more damage the next time they get caught.

Sorry about your troubles, and I hope the problem turns out to be something simple. Keep us posted.