Yamaha TRX850 Enthusiasts Forum

Fired up the TRX this afternoon for the first time in a couple of months (after charging the battery for a while before hitting the starter).

Fired up eagerly enough with the choke full on, but then when I trimmed the choke back, it was idling between around 750 & 1000rpm, and would then just stop. I left it running for a few minutes with the choke on before starting to trim it back, and was running it for around 5 mins before knocking the choke off altogether (pretty normal procedure with mine), as it tends to rev quite high if I leave the choke on for any longer.

Restarted it, and took it up & down the road a few times, but it kept cutting out if I left it idling for more than a couple of minutes, and was idling at low revs when the clutch was in.

Anyone any ideas?

Cheers.

Further developments...

Decided to bring the TRX to work today, so got it warmed up before I set off with the choke out, and gradually trimmed it back while on the move.

There's some big road works near us with a big contraflow with a 30mph limit. The bike ran fine all the way up to the 30 limit, but then went seriously jerky/lumpy, and then cut out a few times, up to the point where it refused to start again, and I had to push it until I could get it off the road. Managed to get it restarted with the choke out again, and then managed to get through the road works. Again, once back on the open road, it ran fine at higher revs, but cut out a few more times when I went through towns/built up areas (30 limits/low revs etc).

The carb idle adjuster screw seems to have absolutely no effect whatsoever, so I'm thinking I might have to strip & rebuild the carbs (may as well get the needle jets/emulsion tubes done at the same time eh?).

Anyone got any other suggestions?

I had a similar problem, the bike would run ok ish until it warmed up then it got jerky and would cut out. Turned out to be a valve clearance issue so it may be worth checking them.

It's been mentioned a few times that the early model TRX's had a problem with valves stretching after 50/60,000km.. What yr is your TRX

I would start with the carbs, if the bike was running ok before you parked it up for the winter can't see the valves
been out of sink.

In my experience the cause of valve clearances closing up badly is down to the seat area of the valve itself becoming "hammered" or depressed and malshaped. I don't think it is down to the valve actually stretching. I have only witnessed this with inlet valves. The seat in the cylinder head appears to remain unaffected.

By the time the valve clearance has reduced to "naff all" I would want to take the head off the bike to investigate the condition of the inlet valve. Always worth checking valve clearances as the symptoms creep up on you gradually until the engine runs pretty roughly.

Hope this helps a little.

Mark.

cobbadiggabuddyblooo wrote:It's been mentioned a few times that the early model TRX's had a problem with valves stretching after 50/60,000km.. What yr is your TRX

It's a '96 bike, when I got it, it had about 18.5k miles on the (KMH) clock. I've since swapped the clocks to MPH (the clocks I got were showing something like 25k Miles), but I haven't done that many miles on it since doing the swap over.

dixonj wrote:I would start with the carbs, if the bike was running ok before you parked it up for the winter can't see the valves been out of sink.

I took it out in Feb for the first time, and it seemed to be running fine then, it's between Feb and now that things seem to have gone a bit astray. I was planning on refurbing the carbs later this year, so it looks like I'm going to have to bring that forward a bit, but while I'm at it, I think I'll take the head off and check the valve clearances anyway. Looks like my TRX is off the road for a while.

The carbs will need a clean Skybone, it's fuel gum in there and some of those jets are pretty fine, so it wouldn't take much to clog them up..you could just take them off and give them a good clean out and blow through and I am sure they would run well again, but a new kit would make the job so much better.
You just have deteriorated fuel that has turned to a jell somewhat and is stuck somewhere..
If you are cautious with the cleaning, just have a place that is spacious and clean as well, doing one carb at a time is good and have a set of fine wire cleaners to run through the jets...oxy acetylene cleaners are the go...or any fine wire available.
Maybe some carburettor cleaner in a new tank of fuel might help, but it's good to get to know your carbs as well.

I think I'll "kill two birds" and get the carb refurb kits anyway, so as well as giving them a good clean, I'll replace the needle jets/emulsion tubes, o rings etc at the same time. That's the plan anyway!

I thought that it might be the fuel going off, but I added some stabiliser/octane enhancer when I filled the bike up in Feb. When I started it in Feb, it hadn't been run since late Nov (and I added the stabiliser to that tank of fuel as well), when it started up and ran fine. The only change to the bike I've done between Feb & now is to fit the FZR400 headlight I acquired from the For Sale section.

As a weird aside, my speedo wasn't working either, in conjunction with it running rough. Again, the speedo was working fine when I last ran it in Feb, and the only difference between then & now is the headlight.

Finally had some time to have a look at the TRX, and there's a bit of a development...

While stripping the bike down earlier today, I noticed that one of the breather pipes had come off, and that there was oil around the pipe & inside the airbox. Slightly worried I split the airbox, but thankfully, the oil seems to be from the K&N filter after I cleaned it & re-oiled it last year.

Had a look at the carbs, and noticed that one side wasn't in the inlet rubber correctly, and the other side, the inlet rubber had actually split in half... took both rubbers off the bike, and then found that the side that wasn't seated properly was also split half way round.

Think I might have found the cause of the rough running, and the miles I've done on the bike since I got it, and then the winter lay-up, have only made things worse, culminating in the rough running. The air leak from the rubbers would certainly go towards explaining things, lets hope new rubbers sorts it out and I can start on Phase 2... tidying the bike up and getting it back on the road.

New rubbers ordered BTW.

Might be worth a look at the fuel tap as well.
Being laid up with the bike on its side stand (I'm guessing) the vacuum diaphragm may be leaking down .
Easy fix with a kit.

Fitted the new inlet rubbers a few weeks back (needed to wait for a pair of the carb side retaining clips), but didn't get the chance to fire it up until this weekend.

Fired the bike up, and thankfully, it ran sweet as anything. Excellent stuff. Took it up & down the street to try it out, and the bloody speedo still isn't working (even with a new cable). Ordered another new cable, but need to take the front wheel off at some point and have a look at the speedo drive.

When that's done, check it over and get it MOT'd.