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Discussion Starter #21
Thanks again, pulling the weak side carb tonight so I can get at it, I'll let you know what I find, planning on removing the abs altogether.
 

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Discussion Starter #22
Thanks, I'll have it apart in a little while, hoping to get to a conclusion on this one. Many thanks for your help!
 

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Well I put all the covers back on and actually was cutting grass. Ran about 20 minutes and was just finishing around trees of side yard when I lost power.I was hoping it was fuel because I'm running a small temporary tank. Not so. It was running but my temperature gauge on the exhaust indicated the left cylinder was again dead. I have a fuel filter so it shouldn't be a plugged carb jet. After stopping it I could not get restarted. Had spark. Pulled valve cover on right. Good valve movement and clearance. Did compression. 110 on left and now only 70 on the right. Think I'm going to throw a different engine on to test the mower. With the tecumseh on a bench I guess I'll pull the right head at some point.
 

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Id get a pair of inline spark testers and hook them up to see if one coil is cutting out on you. If it is i would inspect the ground wire leading to it and insure its not bare, hitting metal accasionally, and grounding the coil. If not replace the coil.

If spark is not the issue i believe those are twin carbed (a bit overkill if you ask me) once again inspect the wires for the fuel solenoids (anti backfire) be sure they are not bare. If you want to disable them just pull them out and cut the plungers off flush. They will become fancy looking bolts after that. If that does not fix the problem i would clean the carbs or replace them.
 

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38... If it ran well for those 20 minutes, and then power fell off, I'd suspect something making one of the valves fail to seat properly. Could be a sticky guide, closed up due to heat, something on the seat, gummy rockers, etc., or something simple or not.
I guess it could even be a head gasket that was/is on the verge, and 20 minutes of work was more than it wanted to do right now. Perhaps check cold compression to see if things closed up with the reduction in temperature?
tom
 

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38... If it ran well for those 20 minutes, and then power fell off, I'd suspect something making one of the valves fail to seat properly. Could be a sticky guide, closed up due to heat, something on the seat, gummy rockers, etc., or something simple or not.
I guess it could even be a head gasket that was/is on the verge, and 20 minutes of work was more than it wanted to do right now. Perhaps check cold compression to see if things closed up with the reduction in temperature?
tom
In hindsight I should have retorqued the head bolts. I don't recall doing that. Certainly not the one that's under the pushrod guide. They were pretty easy to loosen. It is a blown head gasket.
 

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Discussion Starter #27
UPDATE! OK, so I removed the weak cylinder carburetor, disassembled the float assembly and blew out the fuel inlet with compressed air, no obstruction present - at least none that I could see, might be on the ceiling at this time - if there actually was one. None the less, no obstruction now.

I removed the anti-backfire solenoid and tested it with a 12v trickle charger: it seemed to work perfectly, but that is when provided a solid and consistent 12 v dc source. I don't know that the tractor is providing a constant 12v feed so I think I will replace the abs solenoid with suitable bolts just to take that out of the equation - I'll get the bolts tomorrow and probably do both carbs.

Then I'll reassemble and test.

One thing I'm not sure of: when I installed the new coil on the weak cylinder I used feeler gages to set the air gap measuring from the center of the coil to the magnet. Is the center the place to take the measure or should it be measures at the outer sides of the coil assemble (between the outer sides and the magnet. ??
 

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Discussion Starter #28
YEEESSSSSSS!!!! It runs again, and better than ever.!! Apparently there was a problem with the weak side carburetor - never did find any trash or debris but after reassembling with new o-rings on the venturi inlet tubes (see below) it starting running great. I left the anti-backfire solenoids in place as they tested good. And I did replace one coil but I don't believe that had anything to do with the problem.

It was not uneventful though as in my exploratory efforts I somehow lost the little springs that go under the venturi fuel inlet tubes, and worse, didn't realize they were missing!! I put it all back together more than once and it wouldn't run at all. Finally after studying the parts diagrams I realized that the carb in the diagram had springs and mine didn't. So, after looking all over the garage floor I found one, but couldn't find the other one. I looked at Jack's Small Engine's diagrams and found the springs and some o-rings I thought would be a good idea and ordered them and they'll be here Wednesday - in the meantime, using my one spring as an example, and one of my o-rings, I found springs (too long) at Ace hardware, and O-rings in the plumbing section of Lowes. I trimmed the spring down to the right lenght and replaced my o-rings with those from Lowes and now it runs GREAT, more power than ever! So when the new parts come in I'll either put them on, now that I know more about what I'm doing, or possibly save them for later. I also got an extra coil - I'm convinced the original coil was not the problem so I'm keeping one old one and one new one on hand as spares.


Thanks to everyone for your input, I've learned a lot, and at this point I'm feeling like something of an expert on taking this tractor apart and putting it back together again!! I've replaced all the belts, the transaxle input shaft gears, and now the coils and carburetors!! Again, thanks to all of you for your help!!
 

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When I was doing my carbs I knew about the springs but I had not pulledd the nozzle from carb. It was sitting in container. I thought that a bug had whizzed past me but it was the nozzle and spring launching. I immediately found nozzle on floor but like you I had to use a substitute spring. Week or so later I actually found the spring.
I'm just finishing up the heads. I decided to lap the valves. Now I'm looking for the assembly grease that I bought last January.
 

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Discussion Starter #30
"lap the valves" : is this just a reconditioning of the valve seats? or is it a performance enhancement?
 

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Mike, lapping the valves is a method of insuring the surfaces that meet when the valve closes are sealing to each other. Valve grinding compound - grease with an abrasive mixed in - is used when lapping. The compound is smeared onto the valve, on the seating area. The valve is inserted into the guide, and while pressed gently against the valve seat in the block or head, the valve is rotated back and forth, lifted, rotated a bit, re-inserted and moved back and forth more. The valve is lifted and rotated to get all the surfaces to have fun with each other. Once you have gone around a full turn or so, remove the valve, wipe of any remaining compound on both surfaces, and inspect.
A valve that is lapped to its seat will have a 'ring' on the valve that is bare, clean metal. It will go all the way around, and have a nice even finish. Same for the valve seat. Clean both, oil the guide, and install the valve when done.
Lapping can improve valve sealing, and is commonly done to engines that have some hours on them, and will in most cases improve compression. When done on flathead engines, the tip of the valve stem must be ground to accommodate the changed geometry of the valve-tapped-cam lobe. The stem will move closer to the tappet when closed, and take up clearance as it wears. Lapping will remove even more seat material, and close the clearance. OHV, you just have to re-adjust the clearance between rocker arm tip and valve stem.
tom
 

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got mine back together.Ran fine for a short test run. Need to replace air cleaner assembly and test again.
Murphy's law and chance. So I decided another start test before air cleaner stuff. Left side not running. I have inline testers on each cylinder for test shorting. During test sound changed and left carb started spitting back. I pulled left valve cover. Exhaust rocker off the pushrod. To fix I pulled both plugs for easy crank rotation. Fixed and hopefully got set nut tight enough. Installed plugs. Fire it up and test shorts I find left cylinder now runs. Right does not. Pull its valve cover. Clearance might be .008 so redo to .004. Compression test it. Over 100. Fire up and no change. Left runs. Right doesn't. Then i think. I know I just happened to switch sides on the first plug replace. Just because of how I picked them up. So I swapped the plugs. Now right runs. Left does not. Got a new plug for left side. Now both sides run. The failed plug was a new ngk. I had e3s that fit it but decided to go ngk.
 
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