Bike looses power when hot


10 replies to this topic
  • R_Little

Posted August 17, 2013 - 06:12 PM

#1

At first I thought it was a bad gas tank vent.  Bike starts 1st kick and runs hard and good  for about 3-4 miles.  Then it starts  loosing power and backfiring like it is running lean.  If I don't shut it down right away it starts to get hot and in poor light I can see the header pipe turning red.

 

There is no indication that the coolant is overheating and the rads are hot like usual..I assume the water pump is working but maybe I should check. There is oil in the bike and it is clean.  Plenty of gas in the tank and the petcock flows.

 

It will idle almost normaly but when I hit the gas it just has no power.

 

If i let it cool it will start and run normally

 

I'm suspecting some sort of electrical component failing under load?

 

Any ideas?

 

Thanks


Edited by R_Little, August 17, 2013 - 06:12 PM.


  • Krannie McKranface

Posted August 17, 2013 - 08:04 PM

#2

You have a lean condition. 

It could be many things.

You did not bother to mention year, hours, tuning, jetting as it sits now, so......

 

If you have been riding the bike for an extended period of time with the stock jetting, most likely, you have a failing stator: the bike runs WAY TOO HOT stock, and slowly kills the stator.



  • R_Little

Posted August 19, 2013 - 10:12 AM

#3

2000 WR400 with 444 kit.  Mild head work.

 

Rebuilt about 5 yrs ago..piston /Rod etc.

 

Have not touched the jetting in years.....i think it is 168 main JD red and 42 pilot.

 

Valves recently checked and needed .001 adjustment on exhaust  one after 3 yrs riding.

 

Bike Starts 1st kick and pulls hard right off idle....this bike is as fast as any dirt bike I have ever rode.   FMF Q keeps it quiet too.

 

The loss of power is sudden....goes from super hard and snappy to wet blanket in a second....like it is running out of gas or someone stuffed a rag in the airbox....the red header suggests to me it is lean.

 

But how does it go from jetted perfect to "clogged" main jet and then run perfect again?

 

Stator, maybe...any other ideas?



  • Krannie McKranface

Posted August 19, 2013 - 01:04 PM

#4

Replace your pilot jet with a brand new one



  • R_Little

Posted August 20, 2013 - 06:16 AM

#5

Replace your pilot jet with a brand new one

 

I think you are right.

 

I started the bike last nite...one kick no choke 80deg out.  Starts right up.

 

Rode it around the yard...fine,,,nice and barky.

 

Parked it to check oil.

 

Started it later....turned off the gas and power  started to fall off immediately.  Turned gas on and it pulled again for a bit.

 

Turned fuel screw in 1/4 turn and lost power...turned it out and it ran okay for a while then lost power.

 

So I guess it is fuel related......prolly a clogged pilot as you say.  Maybe very sensitive to float hight a little low too.

 

Anyway got the carb out and  the slide looks good. bowl clean but I guess that pilot is partially blocked.

 

The only thing that baffles me is why did it run fine when cold if it was lean and lousy when it warmed...I'd expect the exact oposite.



Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • R_Little

Posted August 20, 2013 - 04:53 PM

#6

Well the float bowl and all the jets had a slight film of ethanol dust on everything.

 

Cleaned it as best I can.  Will order a new pilot.

 

The ac pump is working fine.  It is tuned for a quick short squirt.

 

What I did find was one maybe two vent hoses clogged with mud.

 

This leads me back to the intial suspicion that the float bowl level was dropping.

 

I'll put it back tomorrow and see what happens.



  • Krannie McKranface

Posted August 20, 2013 - 05:34 PM

#7

Well the float bowl and all the jets had a slight film of ethanol dust on everything.

 

Cleaned it as best I can.  Will order a new pilot.

 

The ac pump is working fine.  It is tuned for a quick short squirt.

 

What I did find was one maybe two vent hoses clogged with mud.

 

This leads me back to the intial suspicion that the float bowl level was dropping.

 

I'll put it back tomorrow and see what happens.

Apump should squirt all the way into the head, for 1.0 seconds on a full 'whack'.



  • R_Little

Posted August 21, 2013 - 06:01 AM

#8

Apump should squirt all the way into the head, for 1.0 seconds on a full 'whack'.

 

I think I set it to .8 sec as best as I can measure .8sec.  Just clearing the slide.

 

Before I modded the AC linkage the darn thing would spay for like twice that and spray about 20ft.   When blipping the throttle in tight woods it would load up with gas and stall from all the fuel in the intake tract. Then it would not want to start.

 

I added a stop screw to the back of the ac linkage to limit the stroke....it was worked great for 10 yrs.

 

What do you think about the clogged carb vents?

 

I think that may be the issue....it seem to run like the float level was slowly dropping as I was riding. I suspect that it why it was not running lean when it was cold.

 

How critical are the carb vents on an FCR?  One maybe two were clogged but all four seem to vent the float bowl.

 

Thanks
 


Edited by R_Little, August 21, 2013 - 06:03 AM.


  • Krannie McKranface

Posted August 21, 2013 - 12:53 PM

#9

You need to run the two carb vents above the carb and under the tank, or they will clog, or worse, suck up water and dirt.....which they will do every single time you stall it. 

The over flows obviously still run down.

Don't eliminated the vent hose for the starter motor either, as the starter is otherwise air tight, and needs to vent moist air out to prevent corrosion. 



  • T-bar

Posted October 10, 2013 - 08:40 AM

#10

Did you ever find the cause of your issue? I have an 01 wr426 doing the exact same thing and I am stumped. Carb has been professionally soaked and cleaned and rebuilt, AP is fine, floats are good, I have tried every needle/jetting combination from lean to rich and and nothing works. I replaced the intake boot that was cracked, new uni filter, new ignition coil. Valves were checked and adjusted. Cam timing is good. Bike still pulls like crazy for a couple miles when stone cold, then suddenly starts popping and bogging anywhere above 1/4 throttle and won't even redline. Doesn't matter how slow and gently I apply throttle either. Bike starts up and idles fine though. Should I buy a new stator?

  • T-bar

Posted October 10, 2013 - 08:42 AM

#11

I'm thinking it has to be something that's expanding or warping due to heat? It has nothing to do with load either as it will do the same thing on the stand in neutral.




 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.