Yamaha TRX850 Enthusiasts Forum

Hi from Spain, TRX lovers!

I read the forum sometimes, but my poor English does not give me the courage to write ...

But now I have been encouraged to write because I have a desperate problem with my beloved TRX (red, from 1998 and 30000 km) and would greatly appreciate your help.

The bike is working well, and idle is ok and stable (1200 rpm) when the engine is cold, but when the engine is hot (90 degrees or more) idle becomes very unstable and even the engine has come to stop on occasion.

As I said, for everything else the bike is working well.

Any ideas? ... . All help will be greatly appreciated.

Greetings to everyone!

Hi,
First up, welcome. Your english is probably better than some english speaking people so don't be shy

Your problem may be a sticking choke cable, Keeping the choke on all the time. Start with the easy things first

Cheers, Alan.

pininfarelo wrote: The bike is working well, and idle is ok and stable (1200 rpm) when the engine is cold, but when the engine is hot (90 degrees or more) idle becomes very unstable and even the engine has come to stop on occasion.

Hi there, yeah do the easy things first Is it charging ok? Voltage across battery terminals when running?Battery ok?ignition coils? change plugs (check colour) & leads try a different set of coils. (got a set off ebay recently for £6 delivered thanks ddwracing)
Confirm fuel is reaching carbs. Check vacuum hoses and balance.
Starter solenoid has recently been mentioned as a possible weak link in the ignition circuit.
Then on to more checks if that don't work, carb internals for wear, pick up coils,valve clearences etc.
Good luck

Very likely carb wear, a strip and inspect of the carbs should be carried out.

Emulsion tube wear in the carbs is very common

Emulsion tube wear, although common, is unlikely to affect idling as the needles aren't in operation at that stage.
Are both exhaust downpipes the same temperature?
Are both the spark plugs tips very light brown /white?
Are the pilot jet screws still in place? From memory, there's rubber "O" rings on them to stop them vibrating out (and to seal them)

90 degrees? Do u mean 90 as in 90, or like in normal conditions (65-70). Is it always behaving like this once it reaches 90 degrees?

Weather, wet, hot? (Considering you're from a warmer place than Stockholm...)

Ignition coils, or maybe vapour lock in the carbs are my instant ideas... Coils can behave differently both due to weather and temp.


(and no need to be ashamed for your English, from one non-English to another )

dandywarhol wrote:Emulsion tube wear, although common, is unlikely to affect idling as the needles aren't in operation at that stage.
Are both exhaust downpipes the same temperature?
Are both the spark plugs tips very light brown /white?
Are the pilot jet screws still in place? From memory, there's rubber "O" rings on them to stop them vibrating out (and to seal them)

Sorry, i was talking about worn carbs in general - i'm off topic again

NWS870R wrote:

dandywarhol wrote:Emulsion tube wear, although common, is unlikely to affect idling as the needles aren't in operation at that stage.
Are both exhaust downpipes the same temperature?
Are both the spark plugs tips very light brown /white?
Are the pilot jet screws still in place? From memory, there's rubber "O" rings on them to stop them vibrating out (and to seal them)

Sorry, i was talking about worn carbs in general - i'm off topic again

Thats ok - just get back to building some luvverly frames for us

when the engine is hot (90 degrees or more)

Hola Pininfarelo

Mine only gets up to this sort of temp if it has been sitting in heavy traffic for a while. It doesn't goes above the minimum temp setting when out for a ride regardless of how hard I ride it. Why is the engine getting this hot?

Sounds like it's running very lean, strip & clean the carbs would be my first stop.

Hi friends!

First, thank all the answers! … and second to apologize for not being able to answer before ... I've had a busy days!

In response to some of the comments, actually the engine is getting this hot (90 degrees or more) only in heavy traffic or if I leave the bike at idle for quite some time ... that's when the problem occurs.

I see I have many things to see and review! ... I hope to be less busy in the coming days and start to work ...

I will report the results!.


Thank you all again!

Also check you've no cold spots on the radiator when its as hot as that - old antifreeze sludge can build up in the passageways. Putting your hand onto the radiator matrix will show up cold (choked) areas

One thing I've been thinking of to on mine, is to protect the carbs from the engine heat in some way. An easy test would be to put some kind of shield under the carbs (that is, something that doesn't burn or soaks up excessive petrol...), and to see if there's any difference?

Anoher theory is that the ignition coils can behave oddly when they are getting warm.

The carbs need some heat into carbs to prevent carb icing - a phenomenon peculiar to northern europe (or south of the southern equator) when ice forms in the air intakes as the fuel is being vaporised - then the engine stalls and you fall on your arse!
Thats why there's little coolant pipes going from the head coolant pipe to the carbs - keeps the buggas warm