Yamaha TRX850 Enthusiasts Forum

Hi, I am new to the site and hope that somone can help me.Ive had my Trx for six years now with no problems until now.It is a 1997 uk model.I started it in the garage around x-mas time and it was a little rough but cleared very quickly.It got worse each time I started it.Very rough idle with back fires and pop back coming back into the carbs and it would not clear with a blip of the throttle anymore.I took it out for a short run and much to my horror the head gasket went.I have rebuilt with all gen Yam gaskets.No bent valves.New stem seals.Re-seated the valves.Springs ok.A few noisy shims but not two bad.Cams and timing mark on the rotor set ok.I still have the same crappy tick over with pop back and back fire.I have tried plugs,coils,cdi unit,starter circuit relay,pick up coil,stator.Ive used the volt meter all over the thing.The only thing I can think that it could be now is the carbs need some t.l.c.They are dyno jetted.Needles and tubes are quite worn.The bike used to run quite rich but now seems very lean and hot.Number two cylinder seems to get quite hot and smokes when I stop the bike.Any ideas guys.

The cylinder smokes when you stop the bike,from the exhaust you mean?
Are you certain the head is now sound,torqued down properly etc?
Your head gasket could have been letting go for some time,had you been noticing coolant level dropping,white smoke from the exhaust or a drop off in performance,moisture in the oil tank(white,waxy emulsion)?
It`s most likely that your carbs need a good fettling and balancing by the sound of things,does the bike clear it`s throat and run better while being ridden with the throttle off it`s stop?
Twenty questions eh but it`s important to diagnose the problem before it exacerbates any more that may be lurking in the background.

Are you 100% the valve timing is ok?

Also, Dynojet can be a pig to setup - even on stock pipes.

If your carb internals are shot I'd advise using Factory Pro emulsion tubes with stock Yam needles - the sharp taper on the Factory Pro needles can give rough running at low/medium throttle

Straightline Racing in the UK sell them - mention Carpe Tdm for some discount

Hi guys,thanks for your ideas.The exhaust on the off side only smokes when you turn it off.I have double checked the valve timing,all seems ok.The head is in good condition and porked down to the correct nm in the correct two stage way and in order of tightening.I am only running it on the stands at the mo and only short running times as I dont want to do any damage.It doesnt clear with a blip of gas like it first did.Im going to take both of your advise and treat the carbs to a re-furb but I cant see why that would cause it to back fire norm thats unburnt fuel going past the ex valves and igniting.2 ngt I will see what the induction is like with carbs off.May be it is a valve problem.I dont know.Its getting on my nerves now. Thanks.

jafferstrx850 wrote:Hi guys,thanks for your ideas.The exhaust on the off side only smokes when you turn it off.I have double checked the valve timing,all seems ok.The head is in good condition and porked down to the correct nm in the correct two stage way and in order of tightening.I am only running it on the stands at the mo and only short running times as I dont want to do any damage.It doesnt clear with a blip of gas like it first did.Im going to take both of your advise and treat the carbs to a re-furb but I cant see why that would cause it to back fire norm thats unburnt fuel going past the ex valves and igniting.2 ngt I will see what the induction is like with carbs off.May be it is a valve problem.I dont know.Its getting on my nerves now. Thanks.

Have you checked fuel delivery and for air leaks? All fuel hoses properly connected at tap and pump, no leaks, and your carb/airbox and carb/intake diaphrams aren't split/loose? Simple example, if the vacuum hose to the tap perishes and leaks or comes off, it won't run very well.

how old is the petrol ? is there any chance it might have water in the tank ? if so put about 20cc of acetone in the tank and run that though , or if theres not much in there tip it out and use some fresh petrol

Wow,what a great site this is.Thanks for the further ideas.The fuel is new.I will try all the hoses again to make sure of any air coming from them.I stripped the carbs down today and the dyno needles are the worst worn needles ive ever seen and the tubes are shot as well.New diaphragms on the way as well,no holes in the old ones but look quite stretched.I got the emulsion tubes from a very helpful guy called Andy @ NRP Carbs and Diaphragms,Manchester.01618328646.Just over £14 each plus p & p.They also do carb repair kits and diaphragms for Trx/Tdm,s.I hope this will cure what has been a challenge and headache to find.I will post results so if anyone else has the same trouble it may be of some use to them.Thank you all for your help.P.s. nice to know that the Trx fan base is still strong. Martin.

Yep NRP are very good,here`s a link to them folks:

http://www.nrp-carbs.co.uk/index.htm

Those emulsion tubes are a good price.

jafferstrx850 wrote:Wow,what a great site this is.Thanks for the further ideas.The fuel is new.I will try all the hoses again to make sure of any air coming from them.I stripped the carbs down today and the dyno needles are the worst worn needles ive ever seen and the tubes are shot as well.New diaphragms on the way as well,no holes in the old ones but look quite stretched.I got the emulsion tubes from a very helpful guy called Andy @ NRP Carbs and Diaphragms,Manchester.01618328646.Just over £14 each plus p & p.They also do carb repair kits and diaphragms for Trx/Tdm,s.I hope this will cure what has been a challenge and headache to find.I will post results so if anyone else has the same trouble it may be of some use to them.Thank you all for your help.P.s. nice to know that the Trx fan base is still strong. Martin.

You've probably read this already, but one theory is it's the slide wearing or locating poorly in its channel which causes the needle to damage the needle jet, so possibly replace the slides as well. That may just be people who've spent too much time with Amal round-slide carbs , but it could certainly help. I replaced them on mine when I cleaned up my carbs.

Ok thanks for that il check when I do the re-furb.

Boy all those bits n pieces are gunna add up. Wouldn't a set of fcr's be just as cheap???

Thanks for eveyones tips and help.The carb rebuild did the trick.

cobbadiggabuddyblooo wrote:Boy all those bits n pieces are gunna add up. Wouldn't a set of fcr's be just as cheap???

where can you get fcr's and how cheap are they?
Cheers

PM'd you a msg on some on offer on e bay over your side of the world at present... great investment.. with a set of pipes that breathe to complement you can bolt on 15 h/p if set up right from std and depending on what choice of intake upto 90h/p is possible..