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B running rough

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Dick L View Drop Down
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Joined: 12 Sep 2009
Location: Edon Ohio
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dick L Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 3:36pm
Fuel/gas is drawn thru the power jet then up thru the discharge tube that is in the neck of the carburetor. They do twist off sometimes when they are stuck. I don't have a drawing of the MS carburetors but you can see how the fuel needs to flow with the zenith drawing. At least you have the throttle lever back. The stop screw and stop screw always needs very slight movements back and forth to get the proper mixture. When you get close an large turn will stop the engine. Once you get a feel for it you will never loose it.

If you have a smooth idle and it will speed up to full throttle without hesitation and still have the sputtering it is then time to check further.

A condenser that is shorted inside will not allow any spark. One that is open will burn points. The next thing I would do is to check timing. It can not be off far now so you could loosen the magneto and move it a little and see if you can get a better sound. I have never liked to tinker with more than one thing at a time until I have ruled out a problem with the thing I am tinkering with. Then move to the next thing that could or might be a problem.

Forgot the drawing!
Not much of a way to clean below the threads of a discharge tube without removing it.


Edited by Dick L - 25 Apr 2019 at 3:43pm
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Ranse View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ranse Quote  Post ReplyReply Direct Link To This Post Posted: 29 Apr 2019 at 11:37pm
I loaded the B up and took it to the ICD building today. This is a shop paid for by our union dues. Union members can take their own vehicles there and work on them and have access to the lift and other equipment. There's even a part time mechanic to help us. It's free to members.

I just wanted some one else to listen to this tractor other than me. I also hoped to get the new points and condenser installed. I didn't get any help there. The mechanic said he didn't know anything about a magneto.

About the only thing this trip accomplished, is they had a compression gage, and we checked the compression. Bad news there, each cylinder had about 65 psi. We tinkerer with the tractor an hour or two without accomplishing anything. The mechanic (and the others hanging out there) seems to think the tractor needs a valve job. We pulled the plugs and screwed in an air hose and blew air in the cylinders. The air would blow out the muffler. They said that meant the valves weren't sealing. I never heard of this test before, and I'm not sure I trust it. We did remove the valve cover to make sure the valves were closed.

I just thought I would put this out and see what everyone's opinion was. If the head needs to be redone, it will get it. I think I need to do the simpler stuff before I start pulling the head off. If you're going to go that far, might as well do the whole engine.
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Dick L View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dick L Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 6:04am
Without knowing that both valves, on the cylinder that the air hose is connected to, are closed with a clearance between the valve stem and rocker arm pad it will tell you nothing. If they/he made sure both valves were closed it would tell you that the valves were not sealing. No valve will seal with rocker arm pressure on the stem holding it open. With solid lifters it takes very little pressure to hold it open.
With 65 pounds of compression on all cylinders the valves can not be all that bad. If you didn't add a couple tea spoons of motor oil in each cylinder when taking a second reading on an old engine you can not be sure the lower compression is from valves or rings.     
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Ranse View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ranse Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 6:44am
We made sure we could turn the push rods on the cylinder being tested. They said that there should be no pressure on the valves in that manner. It made sense to me, but I don't know nothing.

We didn't know what the compression was supposed to be. One guy looked it up on the internet and found out it was supposed to be 100 to 115. So we assumed it was extremely low. What is it supposed to be, and is 65psi good enough?

We did take two readings, but we didn't add any oil the second time. This may be the dumb question of the day, but how does doing that tell you if it's valves or rings causing low compression?
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Dick L View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dick L Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 6:52am
If done correctly it should be 90 or above to be up to spec not knowing what pistons you have. Since it was checked to make sure the pressure was off the valve stems and air was coming out the exhaust it would mean you had a bad seal on a exhaust valve. Sounds like you had a proper test and need a valve grind.

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