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this is fred, and this is my plug fouling story.....

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It all started when I bought the bike . It is a 99wr400..

all stock just the baffle out, and air box lid off..

It had a DTM 4# 168 main , 45 pilot 1.25 turns out..

the day I bought it I took it for a ride fouled a plug..

changed the plug rode no problems..

then acc pump got dirty had to clean it..

while I was cleaning that I installed a 3.2 gallon IMS tank, and a 98 stock YZ seat...

the tank had no breather hose on the gas cap so I put the stock one on it and it had a check valve on it....

Bingo non stop fouling plugs...

I tried moving clip and lower size main 165..

with a 165 main DTM2# 45 pilot 1.25 turns out I rode a couple hours no fouling but was concered about being to lean, so I check my plug you could not tell it was even used looked like it did when I put it in..

Scared me...

plus the pipe was glowing...

so I put the 168 in my bike fouled a plug...

then I read guy's using the DVP 4#, so I tried one in the 4# clip bike didn't run well with screw at 1.25 turns so I tried adjusting till bottom ran better 3.5 turns out...

went for a ride fouled plug..

so now I'm tring YZ timing DVP 4# 178 main 48 pilot 1 turn out, and no check valve..

as soon as my jets come in, by the weekend..

if this don,t work putting stock tank and seat back on tring that..

since the gas line is so long on the IMS tank should you use special gas hose...

and have tried moving acc pump adjustment with no success, so now it is at 1/4 opened...

any advise would be nice...


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Your pilot screw has been too far out - #45 and 3.5 turns.

What I see here is jetting on both sides of rich and lean but at different throttle positions.

The DTM needle is borderline rich at 1/8-1/4 throttle. Clip #4 could be too rich mostly and #2 too lean above 1/4. Stock clip is best with DTM - #3

The #45 pilot jet allows a wide range of adjustment. 1.25 is very lean, 2.5 is getting rich. (3.5 turns is going to foul out quickly!!) Suggest you stay close to 2 turns with a #45.

Ignore the main jet while you sort this out. I rode my bike 20 miles with no main jet to see if it mattered at low to mid speeds and never fouled. With a stock US throttle stop you don't need a main jet. :)

The tank does not matter as long as the fuel line is not getting too hot or kinked. Keep the tank vent check valve off.

The DVP needle is leaner at 1/8-1/4 throttle. This will be less likely to foul. Clip #4 is a safe position, the #5 may be better after you get it working. With a #48 pilot don't turn the pilot screw out past 1 1/4 to be cautious against fouling.

The accel pump is backed out more than it should to be. This is ok for the moment but it may hesitate or bog. When it quits fouling try to adjust it to start pumping close to 1/8 throttle for better response. The specified gap is .6mm.


[This message has been edited by James Dean (edited 11-07-2000).]

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