Yamaha TRX850 Enthusiasts Forum

Hi,
I need some help.

My TRX does not start after standing for 2 weeks. The engine turns over well on the starter but the engine does not fire at all. If the petrol tap is then set to prime and the drain screw on right hand carburetor float bowl opened to allow some fuel to flow out, then the bike starts as soon as the starter button is pressed, it then runs well. Opening the drain screw on the left hand carburetor (i.e. before the right hand bowl drain is opened) does not have the same effect.

If the bike stands for a week or so the problem does not occure.

The problem started last winter after the following was undertaken: Valve gaps set, carburetor overhaul (new seals fitted, dynojet stage one needles and jets fitted, float heights adjusted (the fuel levels were quite a bit low). I presume that messing with the carburetors has caused the issue.


Once running the bike ticks over and runs well all day.

I have checked the following:
-Contents of the float bowls after the bike has been standing for 2 weeks, there is no dirt or water present
-Carburator breathers; all are clear
-Fuel pump and tap: Both are functioning well



Has anybody had the same problem?

Other than the dynojet kit the bike is satandard

sounds like maybe a vacuum leak between the intakes and fuel tap? Check your hoses................

Hello bagmaker. Thanks for the idea.
Actually I have already checked the vacuum hoses from the inlets to the petrol tap and to the petrol pump, both are ok. If the hoses were not good, then there would also be problems during normal running or starting after a short stand i.e. not just after standing for a couple of weeks.

What I can not clearly fathom is why the bike makes no attempt to fire at all until the right hand bowl is run through with petrol.

Just some random ideas for you, I don't have any real suggestions:

-How old is the fuel in the tank? I have found on my dirt bikes that if the fuel is not fresh, it seems to go off really quickly in the float bowls and is a pig of a thing to start. Draining the float bowls first (usually just by tipping the dirt bike on it's side first) makes a huge difference.

-How old are the spark plugs? I found on my TRX that after I flooded it badly once, I had trouble with starting even after a good run until I put new plugs in.

Perhaps a mix of older fuel and flooded plugs is just enough to cause trouble?

Hi goose202
Thanks for the ideas.

The fuel is new, the bike gets used regularly and there have been quite a few tanks of fuel through since the problem started happening. You mentioned about old fuel causing this kind of problem, it is almost as if the fuel in the float bowls is going off, once the right hand bowl has been drained through and replaced with new fuel then the problem disappears, although why this only works with the right hand carb I can´t imagine.

The two week old fuel drained out of the carbs is totally clean, no dirt and no water.

The plugs are also quite new, maybe a few thousand KM old, and I am not sure if old plugs would work with new fuel and not with the 2 week old fuel, that said it is an easy thing to try so I will change them. (I will see if the doc can fit some double joints to my wrists to make this easier)

I have also left the fuel tap in the prime position, just to see if having a constant head of fuel to the carbs has an effect.
At the moment I don´t usually leave the bike standing for more than a week so testing is a spasmodic long affair.

Thanks again for the ideas, it helps to think about other potential causes.

Regards

Where the fuel float valve needles replaced as well?? Maybe your not getting a good enough seal on the float and it's weeping through ever so slightly and flooding the RH carby ???
Check your air cut off valve while at it as this is starting to become a common issue now the TRX is gracefully aging out of it's teens and into it's 20's.
You can buy kits for these plus new plastic covers which seem to deteriorate and no shot of Botox will take those cracks and wrinkles out... $50 for both kit and cover , money well spent to save you the stress of the tuning problems they cause and should be good for another 15-20 years.

Keyster carby kits are around $110 for 2 and comes complete with float needles , needle jets ( emulsion tubes) and jet needles , seals and gaskets and o rings. ( but no cut off valve parts)
As a precautionary measure , just dump the 3-500mm of oil that lives in the bottom pan on the engine and just check it doesn't smell of fuel...