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TRX850 Possable fuel issues?

Discussion in 'Technical and Troubleshooting Torque' started by Bluey, Jan 11, 2010.

  1. Hi all, I have a Yamaha TRX 850 that stopped running on one cylinder as I pulled out onto Ferntree gully road, but ran on one cylinder long enough to get back home. Shortly after that it stopped running on the other cylinder.
    I've replaced the spark plugs and done some other mucking about, but the upshot of this is I left it on prime overnight and tried firing it up this morning. It started and ran just fine for a few minutes, then died with lack of fuel type symptoms pretty quickly.

    Not being mechanically experienced I'm looking for a helping hand. Do I pull the tank off, drain it and stick new fuel in? Or is it going to be part hunting time?

    I should be able to take pics if that would be any help.
  2. Try running it on prime again if you didn't yet, the same thing happened to me, turns out I had left off the vacuum line that opens the fuel tap. If it runs on prime you've either got a vacuum problem or kinked line, etc. There are three lines coming off the fuel tank, fuel, vacuum & overflow, make sure the vacuum line is on & intact.

    You can also take the fuel line off the carbs & make sure fuel is pumping out when it turns over...

    Did you do any work to it recently?
  3. No, no work on it recently, apart from pulling off the tank trying to figure out why it wasn't running. I'm pretty sure I got the hoses back on the right places as they didn't fit on otherwise.
    I have tried to start it on prime without leaving it on prime for a time, and I did run it on reserve when I did manage to start it. I'll try leaving it on prime tonight and start it on prime tomorrow.
  4. MV, shouldn't there be a vent hose also? Sounds like the tank is not being vented which could explain why it runs for a few min then stops.
  5. Yes, I called it the overflow, but very good point VCM!

    Try running it with the fuel cap open & see if that helps.

    I wouldn't leave it on prime overnight, just in case all your fuel leaks out.

    Let us know how you go, I had a problem that seemed like a fuel issue, it was actually a faulty coil. Drove me nuts! (It wouldn't hurt to check your spark & air filter, etc, make sure nothing blocked in that area too...)
  6. I fired it up this morning and ran it on prime with the fuel cap open, a few seconds after I switched it to reserve it stopped again. Tried firing it up on prime again and it fired and tried to run, then I could hear it fire and not quite get oomph to run.
    I have pulled the air cleaner, and spark plugs. Got new spark plugs in there now, and I think the coils are fine (screwdriver into the leads, see if it it'll spark between that and the engine block).
    I can see three hoses coming off the tank, one from forward that leads down to the right side near the rear break lever and has a cap on the end and one that go to what I assume is the pump. The last one goes forward in between the carbs, I can't quite see where it ends though.

    FURTHER EDIT: I took the fuel line to the carby on the right off and turned the bike over, no fuel gushing out, despite it being left on prime.
  7. Ok, you may have a fuel pump issue. I've never had any trouble with mine, so I've got no useful advice, sorry. (You definitely had the right line?)
  8. Ok, this morning I took the fuel pump off, and took it apart (and spilled fuel everywhere when I forgot to take the tap off prime:-s). Didn't have anything jump out at me as wrong, and the spring in it didn't seem to stick when I played with it.
    Put everything back togeather, waited for the fuel to evaporate (because I put it on prime without connecting the hose ](*,)), and fired it up. It started with full choke, ran on one cylinder, popped and banged a bit, then ran on both. I ran it till it warmed up then turned it off. Tried it on the run setting on the tap and it ran there as well.
    So yeah, whatever it was, it seems to have been fixed. I'm just puzzled as to what exactly the problem was.
    Thanks for all the help. :cool:
  9. Odd... Anyway, hopefully it's sorted now!

    BTW, if you haven't already, sign up at at http://www.motomaniac.net/trx850/forum/ it's full of really helpful people & if you sign up you can download all the manuals etc. I'm on there with the same user name.

  10. Sounds like the dreaded emulsion tubes.My trx is on its third set as they only last about 25000 k's before needing to be replaced.The other thing to check is the carby bowls for any dirt because the fuel filter in the tank is useless and mine had similar symptoms to yours when the carbs were dirty.