Tec H50 with Oval Bore Mikuni problem ... pics and Videos ...

For anyone still following this thread ...

I replaced the suspected bent valves with known non bent ones a couple weeks ago, ran the motor and it sounded good but the bike wasn't ready to road test yet.

Today I got her out on the road. With a 40 series TAV I didn't get her above 3200 rpm as its just too damn fast for that bike ..
She was hard to start and had a bit of black smoke that could be seen when idling. Got her out on the road and there was no stumbling or missing ... the motor would bog down when the throttle was cracked open ...
I took the UNI air filter off and black smoke and bogging went away.

So to conclude all my stumbling/missing issues were from bent valves.

The End

Wow...I just read all 27 pages of this. I recently came into one of these engines. Well, most of it anyway. I have been reading all I can to identify parts and source ones I am missing. My engine came with a brand new never built block. The factory guide heights are mis-matched. I got a box with stainless relieved valves, the billet retainers, and the 2 piece locks. Part # 36973K. So after reading all this, I have the right valves. I do not have any lifers. My camshaft is a Motorsports cam, but it's weird...the lobe side of the cam gear is machined out for weight savings, and the lobes themselves are as-cast....they were never ground. From what I know, MS cams were stock lift @ .225", but the duration was longer. I don't know about overlap. I have no springs or upper spring cups either. The yellow striped springs are presumed correct. For a while I was questioning if my crank was correct but it appears so. The rod however is not...the box is part # 36972K but the rod is for a 10hp Star. It's the same length but thicker overall, and the dipper has a hole in it. The 5hp MS rod is solid dipper and thinner overall. If you find part # 36974K, you'll often see the 5hp rod....hmm....part # issues. If anyone has a Motorsports 5hp rod, the correct Clements style one, I need it :D Also about PartsTree....the pics represent a snow blower engine but the part #'s are what you need to watch...any P# ending in "K" is Motorsports. The pic is just a general representation. It was interesting to read about the valve discrepancy though. My MS50 is my first venture into Tecumseh...I'm very excited about it and love the reading. Hope yours keeps running well!
Another thing....disappointed to hear about Clements Racing. I was looking forward to doing business with them and getting parts/setup info. Possibly sending the block and valvetrain to them for proper installation. What a shame.
Wow fisher1983 all 27 pages ... tell you what, it was a learning experience for me. I've been playing with small engines for 45 years and never had a bent valve ... now I know!

I would dare say that in the end this was a great troubleshooting thread to learn from.
Yep, read it all! Like I said, I knew nothing about this engine, and still need quite a few parts. Stuffing what's left of my brain with as much knowledge about it as possible.