Jump to content
Sign in to follow this  

2002 450R jetting mysterious problem

Recommended Posts

Facts:

2002 CRF450r with White Brothers Exhaust.

Less than 1,000' altitude.

80 deg F.

Fresh 91 octane gas.

Vertex piston.

APE Head w/stainless steel valves.

Hotcam Stage 2 cam.

Carb ultrasonicaly cleaned and "tuned" by a local shop.  I'm questioning their ability right now, though.

 

Bone cold, with 3 turns on the fuel screw, bike fires up no problem.  Ride in high 1st gear to mid 2nd gear for 10 minutes.  Bike dies, kick my hardest but it just won't fire.  Bike won't restart after that at all.  Almost as if the fuel screw has shut off all gas to the engine.  Confirmed that gas is getting to the carb, pulled the fuel line and it pours out of the tank.

 

Tried the fuel screw at one turn, 2, 3, and 4 and all stops in between.  No luck, although it seems to be happier in the 1-2 turn area. 

No idea what jets are inside.  

Where would be a good starting point given my conditions spelled out above?  This is a brand new engine, less than 20 minutes on the bike.  I can't keep it running long enough to get any time on it!  I don't want to take it back to the original shop.  They obviously didn't do such a good job in the first place, not gonna waste my time again.  

 

No popping on decel, but at the 1 to 1 1/2 turn area I did notice a backfire sound through the carb it sounded like.  

 

I'm all ears.  

Share this post


Link to post
Share on other sites

Fuel screw is for idle ONLY.

Set it once and only change it for dramtic changes in altitude or air moisture. 

1.5-2.0 turns is the correct place, determined by idle speed.

If turning it farther out does not raise the idle speed, it's making nearly no change.

 

You can't guess with jetting. Find out!

 

If it runs GOOD for 10 min, then stops, that is in no way a jetting problem, possibly a fuel deliver problem or a stator problem

It could be a fuel starvation problem: remove the gas cap hose next time and see what happens (lack of tank venting causing vacuum)

Jetting requirements do not change randomly.

 

It sounds more like your stator is dying.

It it happens like clockwork, then runs again when the bike is cold, it's the stator.

 

Try this: put the tank on, hook it up, but don't bolt it down. Bolt down the seat. Run the bike, ride it around.

When it dies, quickly pull off the tank and seat and check for spark.

 

I would suggest never setting foot in that shop again, if they could not figure that out in 30 min.....

Share this post


Link to post
Share on other sites

It sounds like you may have hit the nail on the head.  I was just out in the garage, and the bike starts great.  Incidentally, I swapped out the 42 jet for a 45 jet that I had.  Seems to start much better with that one in.  I'm going to ride the bike tomorrow and see if it dies again after the same amount of riding.  If it does, time for a new stator.  Not going to mess around with it anymore.  

Out of curiosity, why would the bike die when hot and be easy to start when cold if the stator was bad?  

Share this post


Link to post
Share on other sites

It sounds like you may have hit the nail on the head.  I was just out in the garage, and the bike starts great.  Incidentally, I swapped out the 42 jet for a 45 jet that I had.  Seems to start much better with that one in.  I'm going to ride the bike tomorrow and see if it dies again after the same amount of riding.  If it does, time for a new stator.  Not going to mess around with it anymore.  

Out of curiosity, why would the bike die when hot and be easy to start when cold if the stator was bad?  

 

The windings on the stator coils get hot/cold/hot etc, and are vibrated.

This makes the lacquered windings separate, which rubs off the insulation.

When the stator expands due to heat, the coils can now short to ground, killing the voltage needed to make spark.

 

This occurs most often in engines that are running too hot (Honda XL's, 2002 CRF's, Stock Japanse 'enduro's , etc)

 

The solution was proper jetting, and larger radiator or radiator fans for trail riders.

Edited by TheKoolAidMadeMeSick

Share this post


Link to post
Share on other sites

After you brought this issue up, I went out and bought a multimeter.  Learned what I was doing, then checked the two wires labeled "alternator" in the wiring diagram of the service manual.  Manual said the Ohms should be between 9-25.  Mine measured 6.2 ohms on a stone cold engine.  

I then went and measured the same two wires on my stepsons bike...which happens to be the same year, make and model as mine.  His measured 17.0 ohms.  

Looks like I found my problem.

Thanks for taking the time to post...I never would have found this problem otherwise! 

Share this post


Link to post
Share on other sites

Here's the solution to my problem...Thanks again for the help!!

 

Share this post


Link to post
Share on other sites

Excellent job.

 

This is a perfect example of how something so simple to troubleshoot can seem so difficult....until you do it once all the way through. 

 

Now, let's throw some corrosion in this guys carb, so we can get him to make a reeeeally good video on total carb maintenance.

 

OK, what's your address ??

Share this post


Link to post
Share on other sites

Oh, don't get me wrong.  Carbs still get sent out for maintenance.  Just sent "the other" 450R in the video's carb to Zip Ty racing for the mod/cleaning/jetting service.  Having read a bunch about carb stuff now, I think I'll do my own next time and see what happens.  

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×