Bike won't start - just backfires occasionally

[the Eel]

Bike won't start - just backfires occasionally. 1999 Husky WR 125.

Ran fine for about 40 miles the other day and then started losing power - eventually died and would not start. I did notice that one drain tube (there are 2) by the powervalve had popped off. I put it back on. I have spark but it won't start and just backfires every so often.

Any ideas ? The top end was just done at a shop and I rode the bike fine for about 50 miles. Then this happened ...

 

[jboomer]

Check your silencer and make sure that the packing hasn't come loose and clogged the airway. I had a '97 Yam WR250 that did this. I found that somehow the core inside the silencer had broken and allowed the silencer packing to fall and clog the exit.

 

[yardpro]

backfiring is generally a timing (ignition)problem. check to see that your timing has not advanced/retarded. Do you have sufficent compression? and are you getting fuel. A bike runs on these three things :
compression
spark
fuel
timing is also a factor but it is just the proper sequence of the above...

 

[KiwiBird]

My guess is a broken flywheel key, you'll have good spark but the timing is off so it won't start but will occasionally backfire because there is so much gas in the cylinder and pipe. Pull the flywheel off and then use valve paste to lap it to the crank and put in a new key.

Don't be fooled in to thinking it OK because the flywheel appears tight, if it has rotated it may tighten up, take it off and you'll know.

 

[the Eel]

What is a flywheel key ? And Kiwi ... if I can't get the job done, maybe I can sport you another sixer ? :)

 

[KiwiBird]

The flywheel key, also known as woodruff key, goes in a keyway in the crank and in a corresponding keyway in the flywheel. It's designed to allow the flywheel to be positioned accurately on the crank.

They break on occassions and even though the bike still has good spark it is at the wrong time so the bike won't run or sometimes will run backwards.

I probably have a puller but you should get a new key from the dealer and Sierra Nevadas will be fine thanks. Send me a email and we'll set up a night.

 

[the Eel]

Those Sierra Nevadas will do it every time. :)

 

[YZ250_#257]

Back Firing!!

You might want to check the compression. I had a YZ250 rings let go and all the bike would do is back fire.

 

[CanadianRidr]

Did you foul the plug? It's a simple start to check, try replacing the plug then giving her a kick:)

 

[the Eel]

IF I fouled the plug - does that mean I'm jetted too rich ? Reason I say this is because I did a few things recently - most notably went up to a 400 main from 390, went one more clip down from the top notch on the needle, and installed a Delta 2 reed valve / cage. The bike ran fine though the weekend before - although it was higher elevation and darn cold that day. Maybe I'm way too rich .... jetting-wise of course. :)

What do you think ?