This guy that lives accross the street from me owns a 230 QS, and we're having some trouble figuring out what is wrong with the machine. Here is his mods:
-Wiseco 10.25:1 piston
-Web race cam (214 grind), and springs
-ported an polished head with larger intake valve
-His box top is open with outerwear
-Cobra (?) pipe

The machine has a stock carb. He had a 127.5 main jet, needle on the 4th position. He would start the machine and it seemed to idle fine, no abnormalities. When he presses the throttle the machine starts to stumble and pops/shoots flames out the exhaust. When he put it in gear and tried to go accross the lawn it would seem to be fine for a few feet, then stumble/miss and shoot flames. I adjusted his floats to spec, and checked the plug which was black all over but WHITE at the tip. We stuck one of my 140 main jets (smallest I had laying around) and the result was largely the same, except that the machine seemed to jump with more power before starting to stumble/backfire again. I pulled the plug again, and it was a perfect tan. He recently had the machine all apart, and cleaned out the tank, carb, fuel lines. I figured I take the info I had so far and post it here, and see what you guys could come up with.

A few more things, when he first had the rebuild complete the machine ran great for like 5 hours, after broken in he said it had lots of power with none of this stumbling. Then it just stared doing this out on the trails and he had to limp back. He has checked the timing and says it's correct but I haven't checked it yet.
Any ideas? He's willing to try anything, and I'll definately help him. Thanks.

 

It sound to me like a timing or ignition problem. Did he add all of the mods at once? Did he get the correct springs(probably TI with that cam) I suppose valve flutter could cause a similar problem.

 

all mods at once. The pipe is old, but I didn't think an old possibly restrictive pipe could cause such a problem. I was thinking timing too, but I don't know anything about the 230's. If timing is not right, which way should he go with it? And about ignition issues, what would cause this? Thanks for the help.

 

A faulty CDI can cause the motor to cut out, but usually happens when it heats up. As for the timing it's just a wild guess, but it makes more sence to me that it would be too much advanced.

 

I'm hearing what you're screamin' on the timing. That's the first thing I asked him when he mentioned that the machine ran great and all of a sudden this problem arose. I'll have to check it with him again, to make sure he has TDC when checking the timing, and if he does maybe for his setup the timing is just incorrect. It still does not explain to me why it ran fine for awhile and then boom, bad timing. He says he's checked it since and it's still on, so if somehow the timing jumped or whatever, he should've been able to fix it until it happened again. We'll check the timing again, and I'll post results/findings. Thanks again for your help MBrooks.

 

check your valve lash adj. sounds like maybe your intake valve adj maybe backed out and isn't opening properly

 

ive never heard of a valve lash adj., what is that?

 

Same as valve adjustment. Most cars that list valve specs underhood will read "Valve Lash".

 

just for the record, the 230 WILL run with the timing 180 degrees off, it ticks like crazy tho, i misaligned the timing mark and cooked my rockers, if it ticks when its on the gas, and i mean knocking RE TIME IT! , luckily for me i had a spare motor. whew. i have a service manual so if you need any specs, feel free.

v581

 

Well, problem found. After checking and trying everything under the sun he picked up a timing light, and when he put it on and throttled, the light would blink off for noticeable periods that coincided with the missing backfiring. This guy is an audio/electronics pro, and went right into checking wiring first. He found an ignition plug that looked a little unseated (under the gas tank area) and pulled it apart, cleaned and pinched it for a tighter connection. It runs great! Must've had a bad connection that under throttle was vibrating. Anyways, He and myself thank you guys for your help!