Bog off! My mk3 won't run proper.

[snuckler]

Right. Hands up,I don't know what I'm doing. Bike fires up easily enough and will run ok for a few minutes. Then throttle response becomes progressively worse until it won't take any throttle without bogging down. It's a mk3 with standard air box & micron running on premix with a 220 main jet. Where to start? Any advice gratefully received, cheers.

[looey]

That's a classic crank seal failure scenario when the bike runs ok until it gets warm

I hope it's not that !

[gazbeemer]

Sticky float needle in the carb is a poss.

[snuckler]

Carb had a good going over so looking like crank seal then. Arse,didn't want to go anywhere on it anyway. Cheers for the feedback fellas.

[Eyrey1]

fuel
is tank breather blocked ?
try running it with cap open ?
take pipe off carb and put end in a can turn it on and see if after a few seconds it slows or stops coming out
try with cap shut first

[looey]

Yes try the simple stuff first.

If you dissconnect the fuel pipe from the carb and check the flow, does is flow fine for a good period of time ?.

Are you able to borrow a known good carb from a running bike ?.

Stripping the engine needs to be only once you've pretty much eliminated everything else.

I had a bike last year that stopped when running perfectly and I tried everything, but that did turn out to be a crank seal

[snuckler]

Yup will try the above first. Thanks again,appreciate it. Great to able to tap into all this knowledge.

[eddie1969]

Hi,
In my opinion a bike with worn seal wont start easy and will not idle properly
I think the main jet is too big and excessive fuel will cause spark to go
I had problems with a worn jet and jet needle.
Original jet is 190 so 210 would be already big
Good luck with it
Grtz Eddie

[snuckler]

Thanks Eddie. Think I've tried with a 210 but will give it another go. As you say could be down to wear so will have another look at the carb first. Cheers.

[eddie1969]

Hi,
My needle jet and jet needle turned out to be worn,what happens then is the mixture going far too rich,
Original is not available any more, you could try other one as i did
First thing you could try is to sink the needle one or two grooves,the mixture will be leaner then
Note that needle and main jet only come in between half and full throttle
Gr Eddie

[mudguts]

KEYSTER carb kits come with the correct needle about £25 for a kit

[eddie1969]

Hello,
At mikuni.com you can download vm carb manual,it was a good help to me
Gr Eddie

[eddie1969]

www.mikuni.com/pdf/vmmanual.pdf

[snuckler]

Thanks. Gonna order a carb kit & see how we go.