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question about jetting

723 Views 7 Replies 6 Participants Last post by  Ninjame
Hi everyone! Well I am back with another issue with the 89 zx-10. Got it running with help from the dealer. Here's the deal, after pulling the plugs and checking they are very carboned up. The mechanic says that the jetting was not replaced, but he recommended maybe readjusting the jets to run leaner. Now, I have a full Muzzy header system on the bike. Would it be best to go with a jet kit or try and adjust stock jets? I have been reading about something called the "Flow Commander" and it sounds like it might be something worth trying. Anyhow I am at wits end with the beast as this last time I rode it I got at least 300-400 miles before the plugs fouled out and it would only run on 2-3 cyclinders. Can anyone offer any advice? Would be greatly appreciated. Thanks!
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+100 I'm with JimmyD. I'd also suspect oil as the culprit if it indeed has factory jets installed. What mechanic suggested "adjusting" the jets? Unless thats his term for changing the jets I'm lost. Most bikes are set to run lean from the factory to comply with EPA emissions requirements and installing the aftermarket pipe normally makes it just a shade leaner. I don't see how the bike is running too rich with this unless you have severely restricted air flow on the intake.
Ditto that aftermarket pipes will run lean with stock jets. You may want to actually look at the jets and see what they are to get a starting point. They may not be stock jets.

A jet kit is probably a good idea as you will get a selection of jets and save $$ from having to keep ordering more jets.

I think a rough ball park starting point for adding a full race header would be to go one size bigger on the pilot jet and one or two sizes larger on the main. See what that does and adjust from there.

If you are actually running rich (and not oil fouling) it sounds like somebody already installed some big jets and maybe overshot the mark. If it's oil, you need new valve guide seals.
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