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SSchulz

Jetting 01 YZ426

11 posts in this topic

Would appreciate some help here guys. My plug is running dark black in color. I get 3-4 rides before the bike starts getting hard to start. Bike runs great except for slight popping when letting off the throttle. Jetting is stock with BK mod done recently. Using 92 octane gas. Riding at 750' MSL. Can some suggest how to setup my carb to get a nice tan color on my plug?

Thanks

Scott

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I see the classic signs of recurring plug fouling problems with your machine. When you did the BK mod, were you able to get the squirt duration and timing within the specs of this mod? I mean, is the squirt duration ~.3 seconds and begins where it just misses the slide? That's a starting point. Are you keeping your air filter clean and not over oiling it? A dirty air filter causes richness and a black plug is an indication of richness or oil fouling. If you have oil fouling, you have a much more serious problem to solve. You also could suck some filter oil into the carb air jets causing richness there. CDI units have been faulty causing plug fouling as have defects in the carb itself. You are going to have to go one step at a time and eliminate each possibility. Good luck.

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I’m not sure what you mean by “nice tan color” on your plug, mine are always black just about everywhere, but if you look real closely at the insulator I guess it may be tan. I don’t really know. I don’t pay attention, IMO you should jet your bike to run the best, as far as you are able to determine. If you can’t decide if you are too rich or lean then I guess a plug reading would help.

If the bike is progressively harder to start after 3 or 4 rides what happens after five or six? Do you change the plug and then it starts easily again? If so, that is weird, and is indicative, IMO, of some other weird stuff going on aside from your jetting.

The popping at decel means you are lean on idle and maybe pilot circuits, or have an exhaust leak.

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BKs two mods have cured my bike of the plug fouling problems, and the second step was to increase the octane of your fuel. I have had great success with running a combo of 92 octane pump gas and VP 108, giving me a 100 octane gas and my plug has lasted for 3 races and still looks great!

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Been out of town the last few days. Thanks for the suggestions. I did check my air filter and I did have it oiled up pretty good. Will try running it a little drier. After doing the BK mod I have the timing set to just miss the slide with .3 sec on the duration. I have been changing the plug when the bike starts getting hard to start so not sure how long my plug is really lasting. I will also try opening the air screw in 1/4 turn increments to see if that helps (is this located on the side of the carb)? What does the screw on the bottom side of the carb adjust?

Thanks

Scott

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SSchulz: There is no airscrew. The screw on the bottom of the carb towards the front of the bike is the fuel screw. Backing it out adds fuel, making the idle and low-throttle circuit richer.

[This message has been edited by mikeolichney (edited September 20, 2001).]

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Originally posted by Taffy:

Hick

according to patrick burns write up the PAJ MAY BE TO BLAME and that for a couple of years folks have been dishing out the wrong info.

maybe?

Taffy

You mean the popping on decel? That makes sense, I’ve not had that problem since I went to the adjustable PAJ, and the popping occurs at high rpm low throttle settings...

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Thanks. Didn't mean to say air screw. Since mine is popping slightly on decel I might richen (open the fuel screw slightly). Would raising the needle up a notch lean things a bit?

Thanks

Scott

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Hick

according to patrick burns write up the PAJ MAY BE TO BLAME and that for a couple of years folks have been dishing out the wrong info.

maybe?

Taffy

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SSchulz:

By raising up the needle I assume you mean raising the clip on the needle and thus effectivly lowering the needle. Yes this will lean it up a bit but expect to turn out the fuel screw even a little more to get rid of the decel pop. Decel pop has always occured on my bike due to a lean fuel screw setting. I've never messed with the pilot jet so I don't know how the pilot relates to the fuel screw exactly.

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