Yamaha TRX850 Enthusiasts Forum

Hello All,

I am new to the forum.

Looking through the forum and seeing what alot of guys (& girls) are doing with their Trexys....VERY NICE.

Have had my 98 TRX for about 18 months. Have been extremely happy with it until recently.

Hope someone can help. Over the past two months I have had trouble with Trexy cutting out while riding along.

It has happened upon start up where she only seems to fire on one cylinder and won't keep running. On other occassions it has lost power and been chugging along as though not firing properly. If I cannot clear it quickly with a few revvs I have to pull over. One time I sat on the side of the road trying to get her going. She was running very rough and would shoot flames out of the pipes (unburnt fuel I suppose). The tacho would also act strange and instead of giving a snappy response, the needle would float up to around 7000 to 8000 rpm then back down again, in time with the piss poor performance of the engine.

Other times she just completly shuts down without warning and won't restart immediately.

Needless to say this problem is of some concern, especially when travelling along a motorway doing 100 - 110 km/h and she just completely shuts down with out any notice.

It seems to be an intermitent fault. I have had it up to one mechanic who ran her on a dyno ( and ran her damn hot ), but of coarse he could not get the fault to occur.

I took it to another mechanic following a tow. He unkinked a fuel line and disconnected the side stand switch, but the problem still occurs.

I am desperate for a solution. One bloke says it may be the CDI unit, but being as intermtent as it is i'm not inclined to think so, and it's a very expensive part to buy - even a reconditioned one, so I would prefer not to buy one unless it can be confirmed.

If anyone has any ideas please let me know.

Be safe and take care.

Smithy - are you saying the tacho doesn't indicate proper revs and floats around independently of the engine...?? If so that suggests a definite CDI problem to me. It might be worth looking to see that the TPS sensor is still firm on the carb body and that the connections are clean etc.,

The rough running and over-fuelling might suggest emulsion tube problems, but that wouldn't cause the motor to spontaneously shut down unless there's just so much fuel going in that it fouls both plugs simultaneously, but you'd feel it choking up and see black smoke waaaay before then ... What's your fuel consumption like..?

See if you can borrow another CDI to have a try with - it probably wouldn't hurt to check/change the plugs either (but I don't think that's the root problem)

HTH

Greg

Hey Greg,

The tacho seems to be in time with the engine. I think the fact that the engine isn't burning fuel properly is the reason that the taco floats up and back down as the engine is having trouble burning the fuel, like it is being flooded I suppose.

When I had it serviced last, mechanic did valve clearances and dyno tune. He said air fuel/mix was perfect. When he checked it again after I noticed problem he said air/fuel mix was still perfect.

I generally get 250 - 270 km's out of a tank before I have to switch to reserve. Hasn't changed since I got it.

Have tried to borrow a CDI unit through bike shops, but they seem reluctant funnily enough. Don't know anyone locally with another TRX to swap one.

Please forgive my ignorance but what is a TPS sensor and where exactly is it. Am not the most mechanically minded bloke.

Thanks for the reply.

SMITHY wrote:Hey Greg,

Please forgive my ignorance but what is a TPS sensor and where exactly is it. Am not the most mechanically minded bloke.

Thanks for the reply.

Throttle Position Sensor - Sits on the left carb sitting on bike.
Adjusted by turning the key, unplug it....refit it.
Tacho should then read 4k....if 1k or 8k it´s off and you have to set it correctly.

Everything clean?? Tried run a carb cleaner bottle thru the system?

....i should not speculate, i´m not the best mechanic either!

I had a similar problem with mine recently, but it was just a sudden cutout, might only do it once, might keep cutting forcing me to pull over but always mysteriously came good and kept going. It turned out that it was just one of the cutout switch relays playing up intermittently (there's 2 of them in front of the battery), I just took them both out and gave them a good tap on the floor and it's been fine ever since. May not be your problem, but it's easy enough to do and it's free, so it'd have to be worth a shot.

Smithy, how many km have you got on the bike? If you could turn up here with the bike showing it's problem we could swap CDI's to diagnose....

But I'm not swapping with you and hoping mine keeps working lol... I ride it to work every day...

dirty trix, has 54000 km. Would be good to come and swap CDI's with you, but at the moment it is a fairly intermitent fault and I would probably need a different CDI for a week to sus out whether that is really the problem.

Yesterday I pulled out the battery and disconnected the 2 cutout switches as suggested by ferret. Went for a quick squirt around the block and everything seemed ok...........but fault only occurs every few days.

Pulled out the CDI and noticed the back sealed section has hairline cracks. Has anyone else noticed this on their CDI unit? Could someone who is not having any problems look at theirs and let me know.

Killerwhale, I did what you suggested with the TPS. It read 1k. How do I go about setting it correctly........lamens terms please

Thanks everyone for the ideas

SMITHY wrote:dirty trix, has 54000 km. Would be good to come and swap CDI's with you, but at the moment it is a fairly intermitent fault and I would probably need a different CDI for a week to sus out whether that is really the problem.

Yesterday I pulled out the battery and disconnected the 2 cutout switches as suggested by ferret. Went for a quick squirt around the block and everything seemed ok...........but fault only occurs every few days.

Pulled out the CDI and noticed the back sealed section has hairline cracks. Has anyone else noticed this on their CDI unit? Could someone who is not having any problems look at theirs and let me know.

Killerwhale, I did what you suggested with the TPS. It read 1k. How do I go about setting it correctly........lamens terms please

Thanks everyone for the ideas

2 screws fit the sensor, think it was torx!? ...i changed mine.
Anyway, when you turn the contact it will change tacho readings...screw it tightly when reading 4k...

It's been a week now and no problems encountered. I have tried everything suggested except adjusting the TPS sensor - don't have the right bit to undo screws.

Don't know what it was but with all of your suggestions we have obviously eliminated some sort of gremlin.

Many thanks for the help.

One question. If the bike has been tuned with the after market pipes on it etc, would adjusting the TPS sensor create from it's current position cause problems?

SMITHY wrote:It's been a week now and no problems encountered. I have tried everything suggested except adjusting the TPS sensor - don't have the right bit to undo screws.

Don't know what it was but with all of your suggestions we have obviously eliminated some sort of gremlin.

Many thanks for the help.

One question. If the bike has been tuned with the after market pipes on it etc, would adjusting the TPS sensor create from it's current position cause problems?

You have a dremel with a small cutter?? I made groves in the torx and screwed them out and replaced them with hex.