Archive for the ‘Carburetor’ Category

I decided to trade my long-loved Husky for this CRF 450R Supermoto.  It has many nice upgrades on it, however it is definitely in need of some TLC and service.  The most attractive part of this bike is that it is TAGGED!  It may not seem like such an amazing thing, but in the state of NC, it is near impossible to tag a bike that started life as an off-road only machine.  This bike came with a clear VA title.  Once the vehicle has been titled in another state, NC will allow you to transfer it in with no problem.

The electrical was a complete mess, so I basically removed the baja designs dual sport kit and started over from scratch trying to sort the electrical all out.  Now that I have that mostly under control, I moved into the motor, chassis, and suspension.  I removed the clutch cover, and much to my suprise I found an STM slipper clutch installed on this bike.

Since the internals of this bike are unknown, I removed the entire top end down to the connecting rod.  The cylinder is on its original bore with the factory cross-hatching, the forged piston looks like it was installed recently, all top end measurements are still within factory spec.  After some cleaning, and installing a new wristpin, circlips, and gaskets, its going back together.

Inside the carb I found a clogged pilot jet which is fairly common on any FCR carb that has been sitting a while, but more disturbingly I found the needle clip position in the top position.  Perhaps this in conjunction with the clogged pilot jet was causing the popping and backfiring prior to me tearing it down.

The suspension is being serviced and re-valved by Fast Bike Industries and should be done later this week, so hopefully I can have it road-worthy by the weekend.  More pics to follow.

[View with PicLens]

This is a customer’s bike that had some serious carburetor issues.  It was having trouble starting and coming off an idle, but eventually got so bad it would not even run.  I went into the carb several times and did find some clogged orifices that once cleaned, caused the bike to run a little better, but the main problem was 2-fold:

• Bent Needle.
• Bad gas.

The WR comes with a non-adjustable needle, so I removed the bent one and installed a new yz-style adjustable needle.

It’s surprising how fuel can go bad so quickly and can even come from the pump bad.  Also, there was no “bad-fuel” smell when smelling the fuel in the tank, but I am certain it was bad because after correcting the needle and jetting, I installed my YZ tank onto the WR with fresh race fuel and it ran perfect, but when switching back to the WR tank, would not even run.

So after draining the fuel, re-jetting, and installing some new fork seals, this bike is ready to go.

Here is the jetting that worked well for me:

Elevation:  2500 ft.
Main:            175
Pilot:               42
Leak:               40  (this helps increase the initial squirt of fuel from the accelerator pump, and decrease bogging)
Air Screw:     2.0 turns out.

[View with PicLens]

A customer brought this bike in for repair because it is running terribly rich and fouling plugs.  I immediately assumed it was a carburetor issue, and I did find some clogged jets and orifices in the carb that did contribute to the rich condition, but soon found out it was something more than just the carb.  The amount of black goo coming out of this bike was more than I have ever seen on a 2 stroke.  So bad in fact that the rear tire looked like someone had sprayed it down with “wet-tire”.  Also, while testing the carb work I had done, the bike started smoking something fierce with the smoke being white and smelling like burning oil and not the typical blue premix smoke.  After doing some research on thumpertalk.com the symptoms lead me to believe it was a failing right-side crank seal.

Fortunately, for this repair you do not have to split the cases.  The clutch, water pump, primary gear and a few other misc. stuff must be removed, but nothing too complicated.  Of course, with this being a 24 yr. old bike, any disturbed gasket had to be replaced.

With the new seal installed, the problem is corrected.  There is still a lot of residual goo coming out of the pipe just from the old rich condition, but the bike does not foul plugs anymore and runs and idles the way it was meant to be.

[View with PicLens]

I got the head back from Reeves racing engines and I would have to say that he did an excellent job of cutting the valve seats and installing the new valves.  I highly recommend him and his pricing is very reasonable.  His number is listed in an older post if anyone is interested in having him do some work for you.

Here is the head assembled and ready to be installed:

Installing the head on the cylinder and re-shimmed the valve lash:

Then install cams, chain, tensioner and cap:

After all that, Its time to test it out:

So far, the top end of the bike is great.  No strange noises or vibrations. However, I do have a problem in the carburetor.  It bogs if you snap the throttle coming off an idle.  Apparently, this is a common problem on the stock Yamaha 250f’s and what I have read is that it typically is a problem with the leak jet being too large and letting fuel leak into the bowl instead of being shot into the intake from the accelerator pump.

I’m going to pick the new jet now and installing tonight.  I’ll update soon.