Odd polini behavior

I am helping a friend set up his bike. His set up is:


DMP crank (the non stuffed version)

64 Polini

15 bing

The mesh high flow filter

Case matched

When we set up the bike we started the jetting a bit high at 96. Four stroked slightly, but I thought at least to start that would be safe, because the owner does not take it easy. Felt like it would need a 90-92, but I thought be safe for the first tank of gas. After getting it setup up rode about 10-15 miles and seemed to run good.

The next day he went to take out the bike and it would not go over 15mph. The bike is now four stroking constantly. We down jetted to a 90 and then a 88, and it now reaches 25 maybe. Feels like it would need to have something like an 82 in it.

So what could possible happen to make the big need to drop 14 jet sizes?

I thought maybe the timing had slipped and that it was full retard and just acting like it is rich. However time is still fully advanced, the sparkplug gap is stock and the spark is a nice blue.

I could not find anything wrong in the carb. The float is level, the float needle looks in perfect shape to me. We tightened the part the jet stews into (thought that could be loose and letting extra gas in.)

I am confused. If it was way to lean, then we would just have to search out an airleak, but I have no idea why it would after sitting overnight need a much much smaller jet.

Any ideas?

Re: Odd polini behavior

My guess is that the ring has seated, more efficiently using the fuel delivered too it, and thus, too rich.

Re: Odd polini behavior

but a 88 jet in 40-50 degree weather still nets 4 stroking so bad it only goes 20...

Re: Odd polini behavior

Did you try without the air filter? I know it's reed valve, and shouldn't have much blow back, but could it be super oily and clogged up?

Re: Odd polini behavior

Tried with no air filter and no better. To add to the mystery, he ran it slowly for a few blocks, acting super rich so he could not go over 25. Then just took off and ran like it should. After ripping for a few blocks he gets to the light and it stalls. It starts right back up and once again 4 strokes like crazy. What the hell?

Re: Odd polini behavior

FLOAT NEEDLE. replace it.

Re: Odd polini behavior

Sounds exactly like what my ciao was doing before.

Condenser problems maybe?

Re: Odd polini behavior

condenser. i agree.

Re: Odd polini behavior

I'm with Peter, check that float to make sure it isn't flooding the carb.

Re: Odd polini behavior

I think a 90 is pretty high. I had an intake airleak and was running a 90 with a 70cc non reed valve setup, same carb and filter... I would just keep down jetting until it stops 4 stroking. What pipe are you running? I was rocking a techno bullet exhaust. I fixed the air leak and jetting down to an 88 and it's still running rich. I'm thinking an 86 will do it.

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