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XR50 Fouling Plugs, A Lot!

6649 Views 4 Replies 4 Participants Last post by  firepower354
I have a 2000 xr50 that my son has ridden for 4 years and it recently began fouling plugs. In one weekend it fouled about 7 or 8 plugs. The plugs look black and wet when I pull 'em out so I figured there was too much fuel getting through, so I dropped the needle down a few notches. Plugs were still getting fouled, so I dropped it down all the way. Still fouling plugs and the plugs look the same.

My son raced the bike this year and so I made a few modifications:

1. removed exhaust baffle & spark arrestor

2. cut funnel off of air box to allow better air flow

3. increased timing slightly

4. removed choke

He raced the bike quite a few times after I made these changes and I never had a spark plug problem until just recently. I don't think it ever fouled a plug prior to these recent occasions. It was pretty cold when this started happening, though that may not have anything to do with it.

I appreciate anyone's help. I can't keep cleaning/buying plugs! ;-)

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how long ago since you changed a piston and rings? does it blow smoke when he revs it a bit ?
No smoke when it revs or runs. I've not done any piston/ring work, but it hasn't shown any other signs of problems there.

I definitely think its running rich, but I"m not sure how to address it other than dropping the needle all the way like I've done.

What's the stock setting for the fuel mixture screw? Also, what's the compression I should be getting on a stock 50 with 8 to 9 years on it?
Did you jet up when you did the mods? Could have been running lean so long it cooked guides, seals, rings. Should have some smoke if that were it, though.

If something changed that drastic, playing with the carb ain't gonna help unless it's just a sticking needl & seat.
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