Urgent 91 RM 250

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Aug 18, 2003
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#1
Hi,I have a 1991 RM 250,and it spooges oil out the pipe and is loading up pretty bad from 1/2 to full throttle but runs good down low,I was told the stock main jet size was a 370,and the bike had a 340 in it when I took it apart so I put a 330 in it and it still runs really bad from 1/2 to full throttle unless I really hang in it and blow it out,I also have the needle clip on the leanest setting. I called around and most people said that a 370 sounded to rich and I got looking around and almost all 250's except a 01 CR is running like a 160-180 range jet.I have a 183 jet do you think it would be safe to make that jump? My bike is bone stock,and the carb is a mikuni tm or tmx but I think it is a tm.Also I run my premix at 32:1.Any help would be greatly appreciated as I would like to have it going reliably by tomorrow.Thanks
 

Rcannon

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Nov 17, 2001
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#2
You cannot really make jetting changes to your bike because "the other bikes use"

There are too many variables involved to do that. Try a 320.
 
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#3
Also it may not be my jetting at all I am told,is it possible that my powervalve could be causing this? Sticking possibly? Do you know the stock setting on the preload adjustment on the left side of the cylinder? Is there any type of restrictor plate on the exhaust or the powervalve I have heard there was on some models any help is greatly appreciated.
 

bigc

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Jun 3, 2003
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#4
I am not sure about the suzuki,but is there a power valve cover you can take off?If there is take it off start the bikeand see if it opens when you rev it up.The main jet is for 3/4 to wot,the bigger the more gas you will get.I would check the reeds mabye damaged letting in to much gas.perhaps the float level is too high in carb.It sounds to me you could have an electrical problem bad stator maybe.Not enough spark at high revs to burn the gas.If you put that 183 main jet in you will more than likely seize your engine by it being to lean .Only make changes on the main one size at a time.
 

Studboy

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#6
My friends is having a similar problem to yours on his 91 RMX250.
So far here are things that we have done:
New Topend and gaskets. Double Checked.
New Reeds.
New Right side crank seal.
New gas. Premium, 32:1 Mobil 1.
New plugs.
Cleaned carb 10+ Times. Attempted adjusted float heights and jetted the bike up to 6 sizes leaner on the main with absolutely no difference. Tried the other carb we have for the bike. Maybe a little bit better but not much. Also tried the choke plunger out of the other carb.
New Filter properly oiled.
Repack silencer.
Triple checked everything.
The newest thing: Spent $400 to have a new stator installed and absolutely no difference.

The bike runs like the choke is on. It runs like absolute crap, smokes and spooges like crazy and it doesn't have any response or power. The bike does start on the first kick and idles. The exhaust doesn't smell like tranny oil and we definately do not have a coolant leak.

This bike is driving us crazy. We keep throwing money and time at it and it really isn't funny anymore, we absolutely can not figure it out.

What else could cause this mess? My friend would give you a kidney to know. :)
 

storytime

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#7
Did any of you check the sparkplug and the sparkplug cap?
Plug should be of the resistor type and the cap should be in good condition without any cracks or defects.
The resistor plug would be my first guess if you have checked float level, right side crank seal and did you clean the filter? Did you take the rag out that you stuffed into the airbox to avoid dirt getting into the intake track?
 
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Oct 23, 2002
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#8
RM250M,
I have a '92 Rm250 that had a similar problem. According to Eric Gorr's book, these year Suzukis are jetted too rich from the factory. I found that the problem was in the slide. The stock slide has a 3.5 cutaway, and it should be closer to 4.5. I would try a 320 main jet. I called and talked to Eric and he explained how to file the slide . You may want to do the same. It made a huge difference(combined with a RAD Valve)! It now runs clean and crisp throughout the rev range. You may want to think about getting a RAD valve. This is absolutely the best mod I have done to my bike. Good luck!
 
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Feb 23, 2003
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#9
I had a 91RM250 up until the spring of this year. Spent a lot of money getting it n shape in 2000, but it was a solid bike. I wish I had my jetting settings for you, but i sold the bike, manual and all. I know the main jet was a 340, cause i found a receipt for that. not sure about the rest. I had it dyno'd and with the shorty silencer i made, it had 42HP. not bad for an old girl!! visit http://ca.geocities.com/willysrm250 for some pics!

i've tried FMFracing jetting settings on my 02 RM250, and they worked awesome. For your info, they recommend the following for a 91 - 55pilot, 360main, 60 needle with the clip in #3.

as for the bike not responding, my wife's yz80 had a similar issue....her reeds were damaged but more importantly, the silencer tube was crushed from a fall and it wasn't running due to that. I spent so much time on that bike, monkey'd with the carb etc.... then found out it was the silencer causing the headaches.

Hope you get the 91 rolling, it was a fun bike to own.

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Studboy

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#10
We finally got the RMX running. As it turns out it was the clogged spark arrestor that was causing the problem. :(
 

kbob

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Nov 27, 2001
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#11
the jets you are comparing to other bikes are different they are for a keihin carb and you also can't compare to other bikes because they may have modifications such as pipes, reedvalves or porting which can realy change jetting.some suggestions pull the fly wheel and see if the seal is leaking on that side. chek the orings in the head see if they are blown. the rings on the piston may also be bad or like previously stated could be bad reeds.i beleive your adjuster should be set at half turn, just pull the cover off the cylinder on the left side of the cylinder and check to see if the powervalve moves free.