YZ85 keeps cutting out

[oliver85]

I have a 2004 Yamaha yz85. It runs fine most of the time but some times at high revs it will suddenly cut out. I don’t think it’s a fuel problem because if I dip the clutch I can hear the un-burnt fuel back fire in the exhaust. Then when the engine has stopped I let the clutch out again and it will fire straight back up or if I’m stopped kick straight up

I hope that makes sense

Does any one on what might be wrong with my bike?

[oliver85]

can some one help me please?

[Racer808]

can some one help me please?

Sounds like a needle position problem. We have a 08, stock is 2nd clip from top, I tried first clip and it was too much, so I stuck a small washer on the needle to make it 1 1/2. I think i still need a different needle, but it seems to be working fine for now. Try messing with your needle and jetting. Whats your elevation? They come jetted really rich.

[Zoeller_208]

Have you checked the carb bowl? I had a CR85 that would cut out at high rpm's and it caused me to wrecked a few times then I pulled the bowl and cleaned it and it ran great.

[oliver85]

it does run rich so i might try moving the needle down a slot and clean the bowl and see it that helps,

but its strange how as soon as the engine has stopped turning it will start right up again

[Zoeller_208]

I know it seems strange but it most likely will fix your problem.

[oliver85]

I have cleaned the carb out and moved the needle down so it’s now on the top clip instead if the 2nd top and it still cutts out

What should I try next?

Could it be a problem with my CDI box or a faulty spark plug?

[Paul-P]

do if have a br10 plug in there, try an 8 or 9 i bet it will go away.

[oliver85]

i know it has a b8 sumert, dont know the full name, but it already has an 8, im going to try a new plug and see if that helps

[Zoeller_208]

i know it has a b8 sumert, dont know the full name, but it already has an 8, im going to try a new plug and see if that helps

If it's not the plug I bet it is unfortunately the CDI.

[oliver85]

If it's not the plug I bet it is unfortunately the CDI.

i hope its not because i aint got the money to buy a new CDI at the mo

spent all my spare cash on my aprilia mx50 as ive just turned 16 and needed a road bike

[Zoeller_208]

You can probably find one cheap on eBay just make sure whoever you buy it from someone with good feedback.

[Racer808]

If it's not the plug I bet it is unfortunately the CDI.

Make sure the plug you are using is the BR type, BR9 or BR8, no R in it and it will fry the CDI

[oliver85]

Make sure the plug you are using is the BR type, BR9 or BR8, no R in it and it will fry the CDI

its not got an R its a B8 then some other numbers/letters , so my CDI is probable f*ucked then

[Zoeller_208]

I found a couple of CDI's on eBay really cheap. I can send/post the link if you want.

[DLHamblin]

its not got an R its a B8 then some other numbers/letters , so my CDI is probable f*ucked then

Not necessarily. Try a BR8EG or BR9EG in it. Also, the cutting out a high rpm; make sure your tank vent line isn't clogged or the vent line valve connected wrong. This would cause the bike to starve for fuel. After a minute or two it would have enough to start back up.

[oliver85]

ok i'll try ang get a new plug and see if that solves the problem before i change the CDI

its got a B8HS plug in it now

[j-bo]

More than likely, it's NOT the CDI.

As far as a non-resistor plug "frying" the CDI, that's hogwash. Any 8 series plug is fine.

Have you soaked the carb to clean it? High RPM is the main jet circuit.

[DLHamblin]

ok i'll try ang get a new plug and see if that solves the problem before i change the CDI

its got a B8HS plug in it now

I am not sure what the difference is but the B8HS seems to be an outboard motor engine plug for boats?? At least thats what seems to be listed for it? It shows a 12.7mm reach for the B8HS where the correct plug (BR8EG or BR8ES) has a 19 mm reach.

I'd definitely put the correct plug in first before doing anything else.

[oliver85]

the last owner most have put the wrong plug in then

ive put a spare BR8ES in it now from another bike and it runs great!

thanks very much to all the people that have helpped me