Yamaha TRX850 Enthusiasts Forum

I've been trying to get my bike back on the road for a few months now. I thought I had dirty pilot jets from standing over the winter so I took the carbs to bits and cleaned them.
My bike will run for a bit but then slowly loose revs and die, I can keep it idling with the throttle but then it revs to about 3.5k rpm and won't settle again. Its getting to the stage where it struggles to start once its cut out. The exhausts seem to be blowing a bit of smoke, I'm guessing this could be unburnt fuel?

While cleaning the carbs I noticed a few things that might be the actual culprit, when I took my tank off fuel came out the fuel tap even thought the manual said it shouldn't, over the course of a night with my tank stacked against the wall with the fuel tap in the air I lost around 6 liters of fuel, so I assume my fuel tap or pump is knackered and letting fuel flood the engine? Should fuel only come out when vacuum is applied?

I then looked at my oil and the sight glass is full, I let a bit of oil out and it was very runny and smelt like fuel. Could excess fuel be getting in my oil?

I also read emulsion tubes can have these side effects as well?

I'm not sure what I need to replace or how to test if it is the tap or pump?

Has any one had these issue before?

Thanks

Suspect the vacuum fuel pump.

I've had fuel still trickelling from the fuel tap once, if you service the tap..you might find the small O ring in the shut off mechanism needing a clean.
Otherwise sounds like your carbs might need a clean out as it's the float fuel valve that will let unwarranted fuel leak through the carbs and down onto the inlet valves and then past the Pistons to the sump.
Do you have an inline filter ?

Hi skull-candy18!

Sounds like a known problem - don't start the engine till you have changed the oil 'cause yours contains a lot of fuel (as you already wrote)!

The cause of this is most probably a combined failure of a leaky membrane in your fuel tap (at least) and (maybe additionally) leaky float needle valve in your carburettor.

While at it, also check the little filter on the inlet side of the carbs.

Telediagnosing greets from Munich!

So my repair list will be:

Sort the leaky fuel tap with new seals
Fuel pump
Fuel filter
Float needles
Change oil and oil filter.

Do I need to change Emulsion tubes as well?
Anything else I need to look at?

*I have just taken the carbs to pieces and cleaned the pilot jets as this was what I thought would cause poor idling. I must say the the carbs were pretty darn clean inside, I only had to give it a quick wipe with carb cleaner to get them spotless.


Any good places to buy all this from in the UK?

You can get Mikuni carb seal kits on ebay and elsewhere, this will most likely fix most of the problem.
The float needle itself is probably not the cause of the problem (unless the floats are very out of place), just the seal.
The fuel tap itself would be next to fix, there are other threads on here about fixing leaking taps.
The inline, almost internal, fuel filter in the carbs is a bit of a bugger. Many have removed it and fitted a traditional in-line filter that is easier to access and inspect.
I doubt that there is anything wrong with the fuel pump, leave it until you sort the seals in the carb.
Replacing the emulsion tubes, if they are worn, will help the bike running smooth at part open throttle. Worn tubes manifest as surging problem at around 3k to 4k RPM when putting around town on constant throttle. Standard emulsion tubes will show wear after approx 35k km. FactoryPro and others have replacement kits.

As above, emulsion tubes cause poor slow speed running and Tickover but they don't leak fuel! If you look down them, if they are worn they will be oval.

Dave E

I fitted a Viton seal kit from Litetek in Thailand - run by a Brit. Cheaper than genuine Mikuni and work a treat - they even do a kit for FCRs

http://litetek.co/

http://www.trx850.com/phpBB_forum/viewt ... =5&t=10962

Indeed, I have also just fitted a set of seals from Litetek - only £13.39 delivered. I also bought some Keyster emulsion tubes from here which have dramatically improved fuel economy and roll-on smoothness. They'll pay for themselves in no time if you actually use the bike. My tubes were not exactly ovalled, more the hole that the needle blocks up was worn bigger in all directions. No wonder it would stink like the choke was stuck on.. This was with 34K miles on the clock, and a 136 Dynojet main jet with the needle clip in the top position(!), a standard setup with 142 mains and the clip in the middle will be even worse.

My fuel tap also used to piss fuel out all the time, but I don't think much/any made its way into the oil. I rebuilt it with a Tourmax kit but it still dribbles a bit, I put a small clamp on the hose before taking it off the vacuum pump to stop it leaking.

I wonder if your issue might be the choke sticking on? The mechanism for the choke looks to be utter pants, just waiting to gum up and not slide properly any more..

Remove inline strainer from teepiece.
install inline filter.
improve upper revs fuel flow.

Ordered the carb seal kit.

Would this solve the leaky fuel tap?
http://www.ebay.co.uk/itm/MS-Fuel-Tap-P ... 259ee43362

Yes, this looks right - but, years ago, there were membranes on sale which were mirror-inverted

But in the meantime they should've fixed it, so there's no real issue to expect on this side.

Confirming greets from Munich!

Finished this yesterday and I think it's fixed now.
Ran it for 15 mins and had a quick ride up the drive way.

Best get it booked in for its MOT now.

Thanks for the help.