Planet Minis

monkeybike_mike

A friend of mine has a '73 Honda ST90 that wasn't running so I took it apart , did a bore up on it - now 100cc - mild cam - longer duration - 20mm carb , stock pipe. I put it back together , the coil that was in the bike had several shorts in the cable to the plug . I cut the cable back and used an NGK splice kit to fix the cable. The insulation on the stock cable was like tar unlike the new cable that had a nice white dense insulator. I put everything back together had spark but it wouldn't run. I checked the cam timing and it was off a tooth , fixed that , it would fire but pop and back fire . The bike also seemed to run hot. Once you got it off idle it would pull good at full throttle. The carb dosen't sit level , I don't think the coil is as good as it could be. What are your thoughts on the popping and miss fires?

monkeybike_mike

Any ideas ?!?

nola_fiddy

I would re-check the electrical. I had a similar problem on an xr75 and it was the stator that was causing the mis-fire. I was running hot and fouling plugs and not getting the power I should have. I changed the coil and spark plug cap and wire. Still had the problem. I checked and rechecked the carbuerator over and over. Still had the problem. I even went as far as converting over to a CDI. Still had the problem. The only thing left was the stator. Couldn't find a new one - so I rewound the old one and presto!

(Along the way I made sure the valve clearance was good and my rings and piston were good etc.)

Good luck.

dirtbkr188

Try installing a new set of contact points, and make sure they are properly adjusted.