HARD Starting 301!

[Mortgaged]

Hey guys, thought I'd reach out for some help on my starting issue and get your $.02.

Background: K301 on a 1964 model 70, Complete rebuild 3 years ago and I used most of Brian Millers tricks for stock puller: offset reground crank pin, shaved head, BM pulling cam, 30mm carb, mild porting work on exhaust.

The engine ran awesome since rebuild up until approx last fall. Typical Kohler quick starting (hot or cold), lots of power, no issues at all and I was very happy with the engine. Then last summer it started getting "slower" to start and got progressively worse. Typically it would just backfire with a loud bang and require lots of cranking. Starting fluid didn't seem to make any difference either. Tractor would pull start easily and once started, it would run like nothing was wrong. Nice and smooth, good throttle response, etc.

I did a bunch of research on this site and did the following: Rebuilt starter/generator, carb kit, changed points, spark plug, colder spark plug, condensor, and maybe a few others? No improvement. Zip, Zero, Nada! It was like I didn't do anything?

I then used a meter to static time the engine. The static timing showed that timing was delayed and when I opened the gap slightly (.021") to advance it to the proper spot, it actually made it worse (heavy backfiring during attempts to start). I then delayed the timing (.017" gap) and I could get it to start on it's own again, but still lots of cranking and an occasional backfire. Oh yeah, the spark is nice and fat across the plug.

At this point, I'm ready to put a stock head back on, stock carb and stock cam. I'm reluctant because the engine ran so well before slowly deteriorating over the last year, but this thing was so overpowered that I don't care about the HP drop. I just want it to run and be a daily driver.

Thoughts?

[olds45512]

Have you tried adjusting the valves? How much is the head shaved? The way you describe the backfiring reminds me of a tractor I bought a few years ago, the exhaust valve was bent and all it did was backfire repeatedly while trying to start but once running it wasn't noticeable

[J-Mech]

Did you adjust the valves? I'd pull the head. Did you do all the work yourself?

[Mortgaged]

I should have added that I checked both valve clearances and they were both set within range. I turned the engine over multiple times to check rotators were functioning normally too. Bent valve is a good idea to check, but how the heck would that have happened? Tractor is only lightly used for pulling lawn trailer, aerator, etc. No mowing or tractor pulls. Again, this seemed to be a gradual decline in starting ability.

All major engine work was performed by a highly regarded machine shop called C-Tech in Grand Rapids. They are experienced with Kohlers and helped with tips on porting and backed up the Miller mods I was looking at doing. They did the machining, (1 over on bore, checked cylinder flatness, crank pin grinding) and I assembled. The head was shaved 0.050" from high spot. Amazing how far the head was from being flat. Also it's an early 10hp head with the valve recesses (high comp.). Cam was purchased from Brian Miller.

Engine doesn't burn oil and the spark plug shows it's running a little rich which I think the Kohler's like.

[olds45512]

I've heard of cheaper valves and even factory cub valves warpig from heat, not sure what the clearances are from the valve to the head but .050 sounds like alot to shave off the head, is it possible the valve could have bent off the head? Just spit balling here because I've never shaved a head .050 so I don't know how much room there is left between the valve and head.

[ksanders]

The symptoms you describe are much like a compression release spring on the cam being broke or failing. Doesn't happen often but when it does it makes the motor hard to start due to compression not being released quick enough while starting. Almost like the battery is always borderline weak