Ron,

Stating an educated guess you have used piston as a mechanical stop wedging something into either EX port or used a piston stop or rope down S/P hole.
Cranked on engines flywheel dog or drive collet cracking pistons dome.

That said, Never found RCMK's to start any differently than zenoahs ... 2-3 pull starts most times. Most common user caused problem is OVER CHOKING and flooding.

Nope, never used a piston stop or stuck anything inside the combustion chamber. Some of the earlier RCMK's had a bad batch of pistons but Bruce said that mine wasn't supposed to be in that shipment. What's more frustrating is that I drug my 3rd RCMK powered bost out and the same thing, no go either.
My fingers and palms are swollen from trying to get them started. Geezer wheels are looking better all the time. My plugs look OK but have got some coming into NAPA tomorrow morning. I'm going to start checking gaps on everything.

I've got a new RCMK in my Whip. I had a hard time starting it, but my issue was the ground - had to move the coil b/c of the tightness in the cowling. Created a new ground and ran it to the case (in one of the mount holes). Fired right up. They are tight at first, and I lost my first (original) recoil. Bruce told me to put some washers in as spacers. I put a zenoah pull starter on with the spacers and it seems to be okay.

I just went outside and checked the spark as it's dark outside right now and that looks good. I put them in the back of the SUV as I got tired of toting them in and out of the house. I'm leaving the plugs out for the night to let it air out.
Busy day tomorrow but I'll be thrashing on it again sometime.

Odd deal ... really clueless on the issues so many seem to be having with the RCMK's.

can only try and call it as the years of experience see fit ...
As too Ron breaking out a piston like it did ... IMO not a running failure but one of some place some how piston dome has been subjected too excessive static load stress

Ron,

I had a problem starting my RCMK, it turned out it was a sheared fly wheel key, once that was replaced no more issues.

Cheers
Jason

OK, we got one of them to fire up tonight but one wants to and well, the other I think that I found a little problem inside which is hte one hat I replaced the piston and ring in. It was a little tight pulling over at times. I pulled the sleeve and found some wear on the crank. I don't know if it's from the factory which I kind of doubt becuse I found some very fine filings where it was possibly hitting the bottom of the case. I'm not into stripping the whole thing down right now. I also found some scrapes on the piston, ring and a small but noticable nick on the very bottom of the sleeve just past the taper.

Shot 2.

This is neither here nor there at this point Ron, but I have an RCMK and installed the EZ start. It fires on the first pull every time. Best 35 bucks ever spent and no more tennis elbow.

Love the RCMK. Can't seeing buying another Zen for my next build.

Our boat club Prez, Walt Radzinski has one in his Whiplash and had me try it out. Those EZ starters are sweet for us old guys! OK, I'm only 57 but the shoulders are shot.
Can anyone get back with me on the crank? The counter-balancers appear to be scraping somewhere inside, possibly the bottom of the case. The only other thing that I can think of is that they might have been from some machining at the factory for clearance.