Yamaha TRX850 Enthusiasts Forum

so the saga continues the fuel cap has been replaced and seals much better than it did before so think its unlikly to be water getting into the fuel but thats what it acts like surging and popping hesitateing etc.......
so far
new plugs fitted
Carbs balancend
new petrol cap
compression was spot on
no air leaks

thinking i may have to start wacking new bits on to eliminate electrical items but would rather know which one and only replace that one as you can imagine......
maybe coils under load?
I have noticed i seems to start off cold ok then when its done say 10 miles ish it starts and gets progressivly worse............ ideas?

Coils can heat up in use and cause problems they are easy to get at on a trx feel them at the start of a run and when your poor running starts stop the bike and feel for any change. pick up coils can heat up as well. but from your description of the problem it sounds more like an over rich mixture as it gets worse as the motor heats ignition faults feel different to fuel problems in the way the bike reacts to throttle inputs stuttering rather than surging

don`t buy any new bits borrow a meter and check the resistance and continuity of the coils and pick up coils against the values listed in the manual.and then pull the carbs apart (have some new emulsion tubes and needles in stock if your bikes done a high milage

Hope this is of some help Vicar

emulsion tubes were replaced with factory pro ones couple of years ago so dont think it will be them tbh....
I had similar problems with the bike a few years back when the battery terminals were loose and it gave me the same sort of symtoms as i have now hence my thinking electrical. Also the fact that i stripped and cleaned the carbs before fitting the new fuel cap as i was thinking water was getting into the tank causeing the issue so drained and cleaned it and the carbs..........

I shall test the coils but if they look ok and give the right results is it possible that they are ok but when heated up they might not be ?

I had an electrical problem on SRX once, the bike would run great cold then as it warmed refuse to run, cool down and be OK. I traced it to a faulty pick up coil in the end which was breaking down as it got hot. you may need to check all your resistances when the engine is hot and giving you agro. you probably kenw that, but it is worth bearing in mind.

I had a lot of problems with bad running with my TRX recently, was all down to carbs, is worth checking that your choke is not jamming on, check your emulsion tubes and jets If you are still struggling get it checked out on a dyno, they can have tank and body work off and check it on the rolling road. Much easier than doing a bit bolting it all back together and then trying and trying - very frustrating while summer is slowly trickling away

well spent the morning rebuilding the carbs checking it all out setting float heights etc then went for a ride which as soon as i was about 2 miles down the road it started to run on one cyclinder at first on and off then when i got near where i was heading it died so had to push it for a mile up an incline so im going to get me some coils now

I had a similar issue with mine and I changed the plugs and one was causing a misfire.

Well i was having issues before i changed the tank cap and at that time i put in some irdium plugs so its unlikly to be them but will check them anyway soon as the mrs returns from holiday and i can get my bike back at home as she has the car with her

well these were iridium plugs too and they didnt last a month.

thats odd heard nothing but good things about them myself

I did have the same problem. In my case it was the choke. The right cilinder choke was stuck.... After use the choke doesnt go in it "orginal" position. The fuel mixture was to rich.
So the sparkplug gets black and after some miles its was going to misfire.

Sorry for my bla bla English

Goodluck with it

thanks ive just got a pair of coils and an orginal trx toolkit on ebay for £46 inc postage so will finally be able to get the plugs out easier if all the storys about the orginal spark plug spanner being just the job are correct

pwmotorsports wrote:thanks ive just got a pair of coils and an orginal trx toolkit on ebay for £46 inc postage so will finally be able to get the plugs out easier if all the storys about the orginal spark plug spanner being just the job are correct

just found this therad - sounds to me like coils as well

good luck with the original spark plug spanner. I found it to be worse than useless

did you find anything helpfull to get the plugs out I would rather take a long walk off a short pier than mess about as long as i did last time with them

pwmotorsports wrote:did you find anything helpfull to get the plugs out I would rather take a long walk off a short pier than mess about as long as i did last time with them

proper spark plug socket on extention

what size socket is it as the bike is still a few miles away going to pick it up over weekend and want to get suitable socket think its 12mm from memory but cant recall