Yamaha TRX850 Enthusiasts Forum

OK... So I rode my bike down to the Phillip Island Moto GP earlier this year, the round trip was around 4500k's, and for some small portions of it I was pushing harder then ever (like the bit where the guy on the R1 waved my on past )... But most of the way we were just cruising along... The bike ran perfectly for the whole trip, never missed a beat except for the battery which just refused to kick over one morning... So anyway, i got back home, and replaced the battery, but now the bike is a real cow to start... I'm assuming it's not related to the battery since it's cranking over perfectly fine... I've managed to get it started only 2 or 3 times since I got back from the GP, and I've tried many more times. Most of the time it'll (almost) flatten the battery cranking over before I give up... When I did get it running, it was really rough at idle, and would stall if I didn't keep the revs up a little... I've replaced the spark plugs, and tried starting without the air cleaner, but they didn't help. It also doesn't matter whether the choke is on or not...

I'm suspecting that I might just need to rebuild the carbs (I haven't done yet, and i've had the bike for the past 35,000k's)... So I have 2 questions, Is there something relatively simple I can try before I pull it apart, and If not, Does anyone know a reliable source for carby rebuild kits?

It couldn't have happened at a worse time, I was hoping to sell the bike early in the new year to upgrade to something a little more

Any help would be greatly appreciated.

Emulsion tubes ??

you havent by chance got a leaky tap running fuel into the bores or thru the vacuum lines?
Check your oil for fuel.
Or vacuum lines perforated or loose?
Plugs clean with a good gap?
Air and fuel filters clean and flowing?
Cheers
Fung

Hi TRiXy!

Sounds like the valve clearances need to be adjusted.
Very common on the TRiXy that the effect of not starting because of too narrow (inlet) valve clearances comes all of a sudden.

Guessing greetings from Munich!

Emuslion tubes appeared to be quite good... We stripped down the carbs to check float levels, and make sure nothing was blocked up, but it all looks relatively healthy there...

Nothing wrong with fuel tap etc, I can still see the oil level in the sight glass... If anything it could do with a top up... Plugs are new, air cleaner needs replacing, but I've tried starting it without the airbox, and it doesn't help. Vacuum lines are good too...

I'm hoping it's not the valve clearances... I had them checked at 42000k's, but it's up to 70,000k's now... so that's a possibility...

Any other suggestions?

post deleted..you checked the vac tubes...I was saying the symptoms are exactly same as mine when I forgot to attach a tube on my previous rex
edit: does it start kind of better in the "prime" position?

tight inlets will make the bike increasingly hard to start, then it wont start at all.

cheers
fung

fung wrote:tight inlets will make the bike increasingly hard to start, then it wont start at all.

cheers
fung

What kind of time frame would you expect 'increasingly hard to start' to become 'won't start at all'?

I found the bike was pretty good for the ride home from melbourne, but the day after I got home it wouldn't start (I assumed it was the battery, so I bought a new one), but it hasn't started right since... I would have thought there would be a good few hundred (if not thousand) k's between starting difficulties, and not starting at all....

notice it's a 1995 model is it.. good chance it's the inlet valves.. may have stretched as it was an inherant problem on the first few yrs of production

I've just replaced my valves after checking and having no clearance at all. That check was done about.....oh...... a year ago. I'm just about to start reassembling the bike in teh next few weeks. I remember ringing a local dude here in Brisbane with a solid reputation asking about replacement valves. I was told in avery condescending tone that valves don't stretch and I was talking out my arse. Needless to say he didn't get a return call from me. Carry on..... just thought I'd tell that story.

Check teh clearances. It isn't that hard and if it isn't them then you can rule that out. Kedo have a shim set for 80 euro and you ahve plenty of choices for setting the gaps right.

Watched the TT movie (Closer to the edge) yesterday... then pulled the engine out of the bike... Figured we'd be able to check the clearances and give the engine itself a coat of paint so I can make it presentable for sale...

Hopefully the clearances aren't too far out, 'cause I don't really want to replace valves... I had thought of getting my spare set of cams welded and ground, but squashed that idea 'cause I don't want the hassle of tuning carbs, and I just want to sell it...

You know folks the yamaha valve stretch issue is not just stretch in the valve stem, it`s also pocketing that comes into play over time too.
A newly built engine out of the factory will take a few openings and closings of the valves to `bed in` fully, there WILL be minimal valve stretch at this point on virtually all engines but it will be tiny
Any valve stem that continues to stretch will actually break eventually, nearly all valves can show stretch but it occurs at initial start up and stops there, or SHOULD!
Now, as that slightly stretched valve opens and closes you will get pocketing, wear on both the valve head sealing face and the valve seat itself, this is what I believe most folk are seeing on the TRX in general.
So, when a motor is cold and parts have contracted that valve head face to valve seat could allow compression past, but if the motor is at operating temperature that tolerance could close, meaning the affects are less noticable.
All valves spin in the guides as they open and close too so if a valve head is slightly out of square to the vlave seat because of uneven stretching in the stem this will also have a detrimental affect on the performance.
How many folk have had the early TRX`s drop a valve head / break a stem?
This would be a good indicator of true valve stretch issues making themselves felt.

Also just because there is no clearance doesn't mean that doing the shims won't give you the clearance needed. After going through the process and looking at the way everything goes together I don't really think I needed new valves after all. I could have probably just done the shims and got back to where I needed to be. Having said that I think for me it was good to be able to strip the motor down to do a full inspection and rebuild as I'm planning on keeping mine for a long time and it's also prompted me to do all the little modifications I wanted to do to style the bike that way I want it. Only thing I'm saving for later is complete late model front end and different swingarm.

devlin wrote:Also just because there is no clearance doesn't mean that doing the shims won't give you the clearance needed. After going through the process and looking at the way everything goes together I don't really think I needed new valves after all. I could have probably just done the shims and got back to where I needed to be. Having said that I think for me it was good to be able to strip the motor down to do a full inspection and rebuild as I'm planning on keeping mine for a long time and it's also prompted me to do all the little modifications I wanted to do to style the bike that way I want it. Only thing I'm saving for later is complete late model front end and different swingarm.

You seem to be in Brisbane, devlin...id be interested in a photo of your machine.?..might have seen you..

Indeed, if the valve stem is within tolerances of overall length and there are no signs of wear and scoring on it`s working surface I reckon `many` of the so called strectched valves could be re-used.
If there`s been stretch and it`s not deteriorated to a head dropping / stem snapping over thousands of miles, likely it won`t.
Does Yamaha admit to the `toffee` valve issue I wonder?