Yamaha TRX850 Enthusiasts Forum

People, I need drink, drugs, therapy, a priest, whatever. Tried everything this dope can think of and still nowt.

Starts spot on, bit grumpy for a few seconds then idles sweet and responsive on throttle .
Set off, all good, lovely sweet quiet motor, feeling the love.
After exactly the same distance every time, no matter what I try she starts to cough, fart, puke and dies.
After 30 secs of cranking, boom, all is good.
Exactly the same distance later repeat, cough,,,

Valves done, carbs good, filter good, timing etc everything good.
I've changed, replaced, everything. Plugs, leads, petcock, cdi, coils, vacuum pump, all pipes, tank cap, starter solenoid, everything.
All terminals and connections are 100% clean, all earths are good.
Exhausts joints are good.

Latest thing I tried was doing away with the tank filter and fitting a clear inline one, no other filter fitted. When the bugger conked out, I could clearly see air bubbles. These went with continual cranking and she started. The tank cap seal was looking a little hard so I swapped it for a good one.

No joy, still the same.

Doooin me head in big time. Hellllllllppp meeeeeeeee

drain hole under the tank filler cap isnt blocked is it?

Con Rod wrote:drain hole under the tank filler cap isnt blocked is it?

No mate. I might leave the cap loose tonight a tad and see if that makes a difference.

Could it be some sort of vaccumm blockage coming from where it taps into the inlet manifolds itself??
Doesn't one line from one manifold go to the fuel tap and the line from the other manifold to the vaccum pump??
If you have replaced the lines, it may be the little spigots attached to the manifold blocked.

cobbadiggabuddyblooo wrote:Could it be some sort of vaccumm blockage coming from where it taps into the inlet manifolds itself??
Doesn't one line from one manifold go to the fuel tap and the line from the other manifold to the vaccum pump??
If you have replaced the lines, it may be the little spigots attached to the manifold.

Ahhh, one to check

Not that

The symptoms seem to indicate a fuel starvation issue. It sounds like the carb bowls aren't filling, or aren't filling fast enough.
Have you tried leaving the fuel tap in the PRIME position? Have you checked the little screen filter in the fuel line T-piece at the carbs?

AAAHH the sticky float gremlin

All much appreciated and sound ideas chaps, but the lil carb filter is gone and it does it on both sets of carbs I've got, which are both sound as far as I know. One set is off the bike and had new emulsion tubes and float hight set when the valves were done and the other set is off a lad who used them on his track bike and were spot on, even just rebuilt with a stage 1 kit so I'm pretty confident its not them. Its exactly like fuel starvation though, just like running out. Running on prime makes no difference either
I think I'll start investigation the safety stuff, like the stand cut out etc. Anyone got a simple drawing ?

Bummer of all this is I've done only about 50 miles since I rebuilt it and 20 of them have been trying to find this bug

can you set a simple gravity feed straight into the carbs???
This will eliminate vaccum..

As already mentioned, try with the fuel tap in Prime or bypass the tap completely and feed fuel direct to the carbs or pump.
It is possible for the rubber diaphragm inside the tap to become damaged and not work with the vacuum feed from the inlet manifold, effectively turning your fuel supply off (or in some cases permanently on).
Search this site for 'fuel tap leaking' and you'll find that this has been a common problem at times.

dicky.

As Cobba alluded to, another possibility is sticking float needles. It seems unlikely that both sides would consistently stick at the same time though.
If the bike was sitting for a while the fuel may have gone a bit gummy and some residue could be causing the float needles to stick against the seats.

To fix: open the drains on the carbs and squirt a stream of carb cleaner into the fuel inlet at the tee junction. Be generous with the stuff.
Once it's all drained out of the drain hoses, re-connect the fuel and let some of that drain through to flush out any carb cleaner residue. NB. carb cleaner can cause damage to rubber if left in contact for too long.
Then tighten up the drains, switch fuel tap to PRIME to refill the bowls and you're good to go.

dicky wrote:As already mentioned, try with the fuel tap in Prime or bypass the tap completely and feed fuel direct to the carbs or pump.
It is possible for the rubber diaphragm inside the tap to become damaged and not work with the vacuum feed from the inlet manifold, effectively turning your fuel supply off (or in some cases permanently on).
Search this site for 'fuel tap leaking' and you'll find that this has been a common problem at times.

dicky.

Took all that shit out and its just straight through now. No difference, so none of it is needed Its all turning to shit now, I'm spending that much time cranking it its cranking out

Yoozy
Can u check if the carb spigots are old. Sometimes they look ok but are not. They could be leaking after the engine heats up. Worth a try.

Have you tried your standard clocks on?.