Yamaha TRX850 Enthusiasts Forum

This morning, in my bid overtake a chump in his stupid Focus ST-somethingorother, my bike stumbled around 5 - 5.5 k rpm (under load in 4th). It felt like Yam two strokes do when they're cold, like it just didn't want to pull through it. I chalked it up to the fact it was bloody freezing this morning yet the bike had been run (not hard, just short-shifting) for a good 20-odd miles up to this point and was showing the usual 65°-ish on the gauge. Any ideas what could've caused it?

ps Still got past the chump though.

water in the fuel ,could be spark plug shorting ,did it feel like it was running on one pot when it did it and then chimed back in on two?? does the bike live outside ?

steve speed wrote:water in the fuel ,could be spark plug shorting ,did it feel like it was running on one pot when it did it and then chimed back in on two?? does the bike live outside ?

The bike does live outside, sadly, under a cover. It felt like it just hit a limiter and sounded like an IL4 bouncing off the limiter.

yes but did it clear its throat then run ok ??if it did i would still go with water in the fuel ,,you can get a product from halfords called dry fuel just tip it in the tank and it will clear it ,, and change your petrol station for a bit and see how that goes

It felt it would've if I'd kept at it but I just shifted up and it pulled ok in top. It had done it earlier in my journey when I opened it up in top and it stumbled around the same point so I backed off. I'll get some dry fuel gubbins and give that a whirl- thanks Steve

its as you give it some that it happens,, this would still point to water being dragged up ,,if you want you can empty the float bowls , if you look on the bottom of the carbs you will see a black pipe going to the bottom of the carb and a screw at the side of it, undo the screw and this will empty the float bowl try and catch it in a jar so you can see if there is water in there,,do this to both carbs , you will still need dry fuel as it will be in the petrol tank as well ,,good luck

steve speed wrote:its as you give it some that it happens,, this would still point to water being dragged up ,,if you want you can empty the float bowls , if you look on the bottom of the carbs you will see a black pipe going to the bottom of the carb and a screw at the side of it, undo the screw and this will empty the float bowl try and catch it in a jar so you can see if there is water in there,,do this to both carbs , you will still need dry fuel as it will be in the petrol tank as well ,,good luck

Yep, sounds like water or even a bit of dirt, especially as when you shut the throttle and changed up it cleared. Had that with my KTM recently. Draining the float bowls a couple of times should sort it. Problem is that getting to one of the carb drains is a right bastard and involves pulling the tank and the airbox. Make sure you close the drain screw fairly positively (not as easy as it sounds without stripping the shitmetal phillips head bolt or breaking the float bowl cover, natch), as if it starts to leak fuel all over your rear tyre and exhaust pipes, that would be rather unfortunate.

Steve is much more clevererer than me, but you may not be able to easily see the contamination when you drain the carbs. If you are bored or the problem recurs afterwards, it may also be worth pulling the float covers and cleaning up the bowl and jets. Only problem being the arseache involved in getting the cables disconnected.

Note that if it is contamination, it's more likely to be caused by wet cleaning than rain - careful with the hose or (esp.) the jetwasher.

2 likely causes, damp leads or coils breaking down

cover the leads in self amalgamatting tape
if they still do it try a new set of coils

Possibly condensation sometimes as well what with our great weather, hot and sunny one day then rain and freezing the next.

Dave E

idl1975 wrote:Note that if it is contamination, it's more likely to be caused by wet cleaning...

Wet what? My bike's only ever seen a sponge in anger once since I got it

It peed it down all the way home last night but I did mix a little acetone in with the fuel and then went and filled up. The bike behaved, but I didn't really get a chance to open it up cos the traffic was mental. Why do people lose the ability to drive when it's raining? It's only water, ffs.

It may only be water, but oil and crap float on it, lifts it to the surface, and spotty OIK, Salesperson, white van man and Dickhead stil think they can drive like normal; Yet another fatal.

Dave E

swollen plug.
Moisture gets in your exhaust, and if the engine was stopped with the exhaust valve open, the ceramic coating on the spark plug absorbs the moisture. It doesnt take long.. A wet weekend can ruin a plug (old not brand new). All it does it make the plug start acting crazy when its firing a lot. Like it would at high RPM..
Took me ages to diagnose that one for my bike. Hope this helps.

PS: mine was cyl2.. The bastard one to change.

I mixed a few cc of acetone in with my fuel when I filled up the other night. I had to bring the car to work yesterday so didn't get a chance to try the bike. I brought it in today though, and it ran fine, right through to the red in top*, so I'm chalking it up to water in the fuel (for now).

* I bloody love this bike