1996 RM250 Problem

[RayRay]

It keeps fouling plugs, it has a brand new top and bottom end around 220 compression. It has a fmf pipe, the settings that keep fouling plugs are as follows:

main-175
pilot-48
stock needle on the top notch(lowest position)
air/fuel 1 1/2 turns

These are all stock settings as far as I know

It runs good for around 20-30 minutes of moderate riding then fouls the plug, it has a very oily plug after fouling.

Reeds are flat with no spacing.

Do I need to lower my jets? if so what is recommended?

and yes I've searched this site for a solid week with no concrete answers.

Thanks

 

[IndyMX]

You aren't going to get anyone to give you a definitive answer on what jet sizes to use. It's a trial and error sort of thing.

You do know you are way too rich though. So, best bet it is to get a handful of jets, and start working on it.

There are good jetting guides on here that will give you the basics on how to jet. Just follow that, and find what works for your bike and conditions.

Keeping in mind the whole time, that what works now, in the winter will be all wrong come summer.

 

[_JOE_]

Also check the float height as well as the inlet needle/seat.

What kind of riding do you do? If you do more low speed trail riding you might want to try going up one heat range on the plug as well. Poor fuel/oil quality can also aggrivate things.

 

[RayRay]

Also check the float height as well as the inlet needle/seat.

What kind of riding do you do? If you do more low speed trail riding you might want to try going up one heat range on the plug as well. Poor fuel/oil quality can also aggrivate things.

It's kind of a mixture on the riding, my main concern was why would it be too rich and fouling plugs when these are stock settings on a rebuilt motor.

Is it common to change jetting after a rebuild?

This bike was in pieces when acquired so I'm not sure if I got the right carb or not. It seems to be the "T" model but it has the "V" model carb.

VIN says it's a "T" model though

 

[whenfoxforks-ruled]

Is the plug black? Open the radiator cap and rev it, see any bubbles? Top of the needle, there are no more grooves showing above the clip? How much tension is in the power valve spring? What is the premix ratio? Have you ever changed the float valve? Does the air screw do anything to raise the rpm, when adjusted all the way out or in? Vintage Bob

 

[RayRay]

Is the plug black? Open the radiator cap and rev it, see any bubbles? Top of the needle, there are no more grooves showing above the clip? How much tension is in the power valve spring? What is the premix ratio? Have you ever changed the float valve? Does the air screw do anything to raise the rpm, when adjusted all the way out or in? Vintage Bob

The plug looks like if you had a cup full of premix and dipped it in it. It's just getting too much fuel that's not being burned off.

No more adjust on the needle

The power valve only opens in higher gears, I thought it was a little tight, could this be the problem? Lower gears are nothing but torque

40:1 premix

nothing done to the float, I'll try the other things you mentioned and get back to you.

Thanks!

 

[whenfoxforks-ruled]

By cutting back the amount oil from 32:1, its not helping your rich condition. Reducing the oil is backwards, its too much fuel. While I am pretty confident putting the factory recommended mix is not the fix, it is a step in the right direction. And the motor will run a ton better!

 

[RayRay]

By cutting back the amount oil from 32:1, its not helping your rich condition. Reducing the oil is backwards, its too much fuel. While I am pretty confident putting the factory recommended mix is not the fix, it is a step in the right direction. And the motor will run a ton better!

So I need to run 32:1 and see how it does?

 

[1998RM250]

The plug looks like if you had a cup full of premix and dipped it in it. It's just getting too much fuel that's not being burned off.

No more adjust on the needle

The power valve only opens in higher gears, I thought it was a little tight, could this be the problem? Lower gears are nothing but torque

40:1 premix

nothing done to the float, I'll try the other things you mentioned and get back to you.

Thanks!

So the bike will not "get on the pipe" through the lower gears? What does it do, bog? I kind of had the same problem after a rebuild and I ended up needing new crank seals and having to lower my pilot jetting. Also check the a/f screw on the carb and make sure it didn't get turned all the way in like mine did somehow.

 

[RayRay]

So the bike will not "get on the pipe" through the lower gears? What does it do, bog? I kind of had the same problem after a rebuild and I ended up needing new crank seals and having to lower my pilot jetting. Also check the a/f screw on the carb and make sure it didn't get turned all the way in like mine did somehow.

No, I just have it adjusted too much, it runs great in the lower gears it's just straight torque but smooth engine and power. I'm going to set it correctly I was just wondering if that had anything to do with it running rich before I install the carb back with smaller jets.

 

[_JOE_]

What? How do you get it to work differently in lower gears?

 

[whenfoxforks-ruled]

That made my head hurt. I read it twice, and still sounded like it runs good, like a 4 stroke, but could be better?

 

[Rich Rohrich]

It's kind of a mixture on the riding, my main concern was why would it be too rich and fouling plugs when these are stock settings on a rebuilt motor.

The stock jetting specs from the OEM are usually on the rich side for the sake of safety. The expectation is the rider will tune the bike for the fuel being used and the riding conditions.