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Fresh rebuild with a miss at 6000???? 09 xp.

mx100

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Jun 16, 2010
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Livingston, MT.
Nephew has an 09 that he recently lost compression in the mag side. Tore it down and it looks really lean. Mag piston scored up real bad. Stock motor with can and stock jetting. The good cylinder/piston looked lean also.

New pistons along with different cylinders and got it running again. Now it has a miss at 6000 rpm if you hold it there for a second. If you thumb the throttle it will come thru it and go to 8000 and pull hard. From a dead stop if you peg it full throttle it will pull to 8000 and run great. Only hesitates at 6000 until you work the throttle. Annoying.
It never did this before the loss of compression. Any idea's? Thx.
 
B
Sep 24, 2009
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Yakima Wa
My guess as far as the 2 burndowns & running lean would be the DPM solenoid stuck in the closed position. It might also cause the miss.
 

mx100

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Only had 1 burn down, and during the rebuild, we cleaned, wd-40 and tested the DPM. Seams to work fine, but who knows. I will pull one off a good running sled and give it another try.
Could a stuck DPM make it run lean? I thought it would run rich if that happen? Thx.

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B
Sep 24, 2009
605
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Yakima Wa
They are supposed to default to full rich when they fail, & they usually do for a while, but if you don't replace the solenoid it will eventually stick full lean & burn down the engine. Had it happen to 3 different sleds, 01, 06 & 08. I don't do the wd-40 trick anymore. If I question the solenoid, I change it.
 

mx100

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Livingston, MT.
Another question, when do the Rave valves open? Could they possibly be hanging up a little bit around that 6000 RPM? They never got cleaned during the rebuild.

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mx100

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Got it fixed.

First we tried a brand new solenoid on the DPM . Still had the mess at 6000. Then we swapped a complete DPM unit off of a good running sled and it ran fine. So we pulled the original DPM black plastic housing apart and cleaned everything. We found a little restriction in one of the vent lines that wasn't allowing good airflow. We cleaned it up and put it back on with the new solenoid, and it has been running great ever since. Not sure how we missed cleaning that vent line on the first go-around, it would flow air, but had a little restriction in it.

Could this little bit of restriction possibly make the sled run lean, causing the original burn down?

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mx100

Active member
Lifetime Membership
Jun 16, 2010
234
29
28
Livingston, MT.
Got it fixed.

First we tried a brand new solenoid on the DPM . Still had the miss at 6000. Then we swapped a complete DPM unit off of a good running sled and it ran fine. So we pulled the original DPM black plastic housing apart and cleaned everything. We found a little restriction in one of the vent lines that wasn't allowing good airflow. We cleaned it up and put it back on with the new solenoid, and it has been running great ever since. Not sure how we missed cleaning that vent line on the first go-around, it would flow air, but had a little restriction in it.

Could this little bit of restriction possibly make the sled run lean, causing the original burn down?

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eddy

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Burn Down

A slight restriction in a DPM vacuum line going to the float bowl would not cause a lean condition (on that cylinder). As stated above the DPM system fails rich.
Question begs to be asked: If the line in the DPM manifold was clogged on one side could that provide "double" the vacuum to the other side causing a lean condition?
 
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