Thread: What would cause this??

Hi all, new to jet skis and have been loving it up until now. My first ski, a 99 STX 1100 developed a missfire/lack of power while riding the other day. I removed the plugs to check them and attached is a pic of what I found. Ok, no worries, fouled plug. Replaced them the next day and went for a ride, going great for about 20 minutes then it starts missing again. Pull the plugs, same deal. Trimmed the end of the plug leads as I read that sometimes when they play up this may help. Brand new set of plugs and again within 20-30 mins same thing. Always the same plug, cylinder 3. When testing spark there is spark there, checked resistance on coils, all seems ok. What else could be causing this? Its a hard, carbon type build up, doesnt seem like fuel/oil. Any ideas?

What oil are you using in what fuel? TCW3 oil is required. Normal unleaded should be okay with stock compression. Is the motor stock?

Are you pre-mixing or does it have the auto oiler on it? 40 to 1 if pre-mixing. Auto oiler may need a fix up?????

Looks very very rich too. Plugs should be a nice light tan colour. Carb. rebuild may be needed??????

thanks for replying. using valvoline 2 stroke outboard oil, tcw3 spec. just running regular unleaded fuel. auto oiler still hooked up and motor is stock. has good compression, 125 on all 3 cylinders. is there a way to test oil system or carbies? again thanks for help.

Engine sounds okay with good compression numbers.
My best guess is that it's running very rich and fouling the plugs. You probably need to have the carbs (Mikuni?) rebuilt.
Sorry, but that's about all I can suggest.

Anybody else out there with ideas????????????

Just another thought. Is the choke staying on making it rich??????????

Umm, hasnt got a choke, i think it has been removed as it has a primer system fitted. Can any one suggest anyone on the coast who is good with these things? Have heard good things about JetSki doctor, think im gonna have to bite the bullet and take it in.

It has the later model carbs, the CV ones. Would it be worth getting them rebuilt (if thats the problem) or would i be better off replacing them with with the carbs of the earlier models (non CV) or something after market?

Jet Ski Doctor (Taka) is your man for that ski for sure. He'll sort you out on the carbs. or whatever it is.

Just dropped the ski in to Taka, now I guess we wait and see what the verdict is. Thanks again for your help.

Just thought I would post an update on the ski. Taka has looked over it and and believes the issue is possibly due to water he found in #3 carby. Jet Ski Doctor's Blog / Service, Repair, Parts