1989 YZ250WR carb set up help

[holberg]

Hi all,

This is my first post here, but I have been using the site for a while now and would just like to say to you all what a great site you guys have here.

Ok so on to the topic of my post....

I have recently purchased a 1989 yz250wr for £400, things that are not stock are
•pro circuit pipe
•prox conrod kit
•1mm oversize piston
•twin air filter

I have a running issue with this bike and that is when you get it started up and turn the throttle 1/2 open or more the engine begins to bog down, drop below 1/2 and it runs ok but doesnt want to idle and exhaust fumes smell quite heavily of unburnt fuel.

My research would suggest jets are too large and I have been having trouble tracking down what size the stock jets should be (riding in uk , not much above sea level and mostly trail riding).

The compression seems good and silencer has new packing fitted, running 32:1 premix, air screw is set at 2.5 turns out from seated which again suggests needing a smaller pilot jet.

Carb is thoroughly clean along with the tank, fuel tap and filters, needles etc look to be in good condition.

Any help or tips you guys can send my way would be great (or anything I am doing wrong please correct me lol).

thanks again guys and keep up the good work here

 

[jaguar]

bogging with more open throttle is a symptom of a lean condition. but instead of jetting you should first look for an air leak between the carb and the cylinder. also the crank seals may be blown.

 

[High Lord Gomer]

According to this:

http://www.servicehonda.com/parts/l...1989_MOTORCYCLE)/CARBURETOR_(YZ250WRW_-_1989)

Stock pilot was 60 and stock main was 340. What little experience I have had with overbores is that the increase volume of air flows better and draws more fuel, requiring even leaner jets.

I agree with my more knowledgeable friend that it sounds more like an air leak. I would also check the reeds for cracks.