Starting to think I need race gas....

[Micahdawg]

Something ain't right about my new 2001 RM250. From idle to 1/4 throttle the bike chops around and kind of makes a knocking noise. From 1/4 throttle to WOT it runs much better, but feels like it's got a wierd dead spot in the mid range. Not like it falls on it's face, but like it doesn't want to pull that well right in the middle.

The plug is a BR8EG and jetting is 162 Main, 52 Pilot, Needle at 3rd, and air screw .5 out. Also at 500ft. Gas is 32:1 Klotz on 93 octane.

Yesterday I took the bike out and tried to mess with the air screw. Once it got warmed up and really started jerking on the low end I came to a stop. I was sitting there at idle and the bike was just going BAA, baa, BAA, baa, BAA, baa....up and down chopping. I turned the airscrew in so that it was almost totally closed and it smoothed out right away. Then I went to take off and it just seemed like it was rich (a little less responsive on the bottom.

I still get spooge on my rear fender and everytime I yank the plug it is as dry as it can be. The porcelain is NOT a rich smooth carmel color, but kind of dry ashy light tan color with NO real oil deposits.

At this point I'm wondering if it's not a jetting issue, but a preignition issue. Maybe the knocking and chopping down low is detonation? This is gonna suck if I have to use race gas all the time.

Micah

 

[jumpingjoe628]

Try taking the carb out and checking the piolet jet for any obstructions or if it came unscrewed. For that matter see if everything is tight in there. Usually pinging will be felt when you are putting a load on the bike. My bike will ping on 93 octane when riding at mid to full throttle but is fine at idle. Most air screws like to be at least one and a half turns out. You can try and lower the clip to the next position and try that too. Unless you have some head work done to it you probably won't need race gas, but as a last resort you can give it a try. It is important to try one thing at a time to really find out what is causing the problem.

 

[Micahdawg]

I just gave the carb a good cleaning and inspected the jets and such. On a good note, at least the carb is not dumping gas anymore while sitting unstarted with the petcock open.

The cylinder has been ported too. I don't know what was done to it, but I found out that the original owner did his own home brew top secret port job?!? I really just want to yank the top end and see wtf has been done as it wouldn't shock me to find the head has been shaved too.

What compression reading would be too high for pump gas? From the feel of the kicker...it has got a LOAD of compression.

Also, is the air screw serving any purpose past 1/4 or 1/2 throttle. Like if i had it almost shut to be rich on the pilot, would it even matter on top end?

Micah

 

[RM_guy]

From your other thread I wouldn't doubt if the original owner milled the head for race gas. My head was machined for 94 octane pump gas and I get 210 psi compression.

 

[Bullwinkle58]

Since your air screw is only 1/2 turn out, you need a smaller pilot jet. That should cure the midrange "dead spot," and off idle reponse.