782 kt17, cant find engine miss

[danfeste]

I've tried everything I could think of to fix a miss on my 782. Its a series II and I'm unsure of hours since it was a replacement for the original series 1. When I got it I had to rebuild the carb because of bad ethanol gas. After that was done I got it started but it had a miss after running about a minute. Next I put in new Kohler points and a transducer II ignition and static timed it. No change in miss. I tried swapping coil and plug wires from my other 782, no change. New plugs, cleaned grounds, hot wire from battery to coil, cleaned gas tank out, tried good running carb, no change. Compression test showed 90 and 85. Pulled the heads and valve covers and found little valve clearance. Had the valves ground to get clearance and valves lapped. New head gaskets, intake gaskets, new breather assembly, no change. Rechecked timing, cleaned carb again, tried other spark plugs, checked compression again and still 85 and 90. Beginning to think the compression is too low and causing the miss. Any other ideas of what to try? I did the compression checks dry with throttle and choke wide open, other plug removed.

[J-Mech]

Dead miss? Or just a light miss? At idle, or WOT, or all through the RPM range?

Did you grind the valves, or just the stem to get clearance? The way you typed it, it sounds like you just ground the stem....

If it's just a light miss, I'd say that your compression has more to do with it than anything. Post a video up on a hosted site and link it here so we can have a listen to it.

[danfeste]

Light annoying miss through all rpms but more at half throttle. I brought it to the local ih dealership and they set the clearances and cleaned up the valves by lapping not grinding.

[J-Mech]

Originally Posted by danfeste

Light annoying miss through all rpms but more at half throttle. I brought it to the local ih dealership and they set the clearances and cleaned up the valves by lapping not grinding.

You can't lap the stem, you have to grind it. That was a waste of money. Should have done a valve job since you took the time to take it all apart. Might have fixed it, had it been done right.

As low as the compression is on one side, I'd say your just going to have to live with it. No idea if the low compression is in the valve train, or in the cylinder, you could do a leak down test to confirm. Seems like on the twins when one cylinder gets below 90 PSI while the other is above, they start to have issues.

I can't imagine that with all the parts that you swapped, and how much cleaning you've done in the fuel system that the issue is anything but mechanical.

[danfeste]

They lapped the valve faces not ground the faces. They ground the valve stems to get proper clearance because there was no clearance on the exhaust valves.

[danfeste]

And I'm sure the job was done right. The guy that did it has been working on cub cadets and ih tractors since 1970, and he's also a cub collector.

[ol'George]

#90 is about normal, #85 just ain't that much less. it is sure within 10%

[CubDieselFan]

Originally Posted by danfeste

And I'm sure the job was done right. The guy that did it has been working on cub cadets and ih tractors since 1970, and he's also a cub collector.

Did offer any advice on the miss or did he just do the engine work and did not hear it run.

[danfeste]

He didn't hear it run, just did the work. And he was out of the shop when I picked it up. Probably going to give him a call next week. I can't imagine 5 psi below the recommended spec would cause this problem.

[J-Mech]

Originally Posted by danfeste

I can't imagine 5 psi below the recommended spec would cause this problem.

It can if it's a valve issue.