rmc_olderthandirt

~SPONSOR~
Apr 18, 2006
1,533
8
I have a 1997 Yamaha WR-250 that I just can not get jetted properly using OEM parts.

My primary objective is to get it so that it will quit fouling plugs every ride. It does OK if I am on it, riding hard like when I am riding an enduro. When I ride easy, such as when I am riding with my wife or nephew, I will foul a plug every time. I don't dare take off without bringing a spare plug along.

I have already changed the main and needle jets to the smallest size I can get from the dealer. I have the needle in the top most clip position, which lowers the needle as far as possible. I am running synthetic oil, 40:1 mix ratio. The plug is a BR8EG.

What surprises me the most is that I have made what I would think are dramatic changes in the jetting and I have not noticed any significant change in how the bike runs. It can be a bitch to start, especially hot. It will idle reasonably well, but if I let it idle to long it will foul the plug.

I have tried looking at the JD jetting website for an after market solution but they don't offer anything for my bike and the carburetor is different than what the YZ models used.

I have tried various float levels. The Clymer manual I have for my bike has totally bogus specifications for the float level, there is no way the number they provide is correct.

What do I do now?

Rod
 

TWRT

Member
Sep 13, 2001
249
0
Is it possible you have a main seal leak on the clutch side? This will allow trans oil to leak into the crank area and cause it to run rich.
 

jsantapau

Member
Nov 10, 2008
340
0
check your reeds first and the idle and starting of the bike will have to do with the pilot jet not the jet needle and main jet, I would bring back the settings to stock(wondering if the settings are too lean now and when you get the pilot sorted out it would get dangeous) and start using smaller pilot jets till the air screw makes a difference and it starts easily cold with choke and hot with no choke.
 

SpDyKen

LIFETIME SPONSOR
Mar 27, 2005
1,237
1
You may have the smallest jets the dealer had, but you can get way smaller jets from either Yamaha, or several other sources.

Read all of the "two stroke jetting" threads you can find here. (Do a search.) No one here can know, for sure, if you are dealing with a jetting problem, or a mechanical problem. You will have to determine that through the process of elimination.

You can get your bike to idle and run at low rpm's all day long, without any plug fouling, if you're diligent.

There are some good links and information in this thread, though the poster does not seem to be listening to the good advice given, very well.
http://www.dirtrider.net/forums3/showthread.php?t=169940&page=1&pp=10
 

FNG

Member
May 2, 2008
97
0
Matt90GT said:
You say you are riding slow. no mention of changing the pilot jet. Go smaller there.

Typically any bike will be close on jetting stock, usually you can go down 2 sizes on a main and 1-2 sizes on a pilot depending on state of tune. How many hours on the top-end? How many on the reeds? Clean the Power valve lately? Have you completely cleaned the carb? Removed the float and needle/seat and thoroughly cleaned the seat? You may have a leaky needle/seat causing a rich condition on the bottom end which will clean out if you hammer it.

How about the last time the packing was replaced in the silencer?
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Change the float valve and seat. When no matter what you do, and it does not make sense, its puking too much fuel in your cylinder. Even if it seems to be stopping the fuel, change it. That is a high wear, and chemically abused part.
 

Top Bottom