Yamaha TRX850 Enthusiasts Forum

I went on a ride with a big group ,started out ok speeds of about 80 - 100kph for 3/4 hour . As we pulled in for a stop the bike started to run on one cylinder . When we restarted after 1/2 hour I checked the down pipes and both started to get hot so it was firing on both cylinders but running rough . On a constant throttle it back fired thru the pipe and occasionally spat back thru the carbs. It could still accelerate ok . As the ride progressed the back firing thru the pipe got worse and running on 1 cylinder .but would still accelerate ok so I parked it and trailered it home.
I was thinking valves but they don't happen that quick unless one has let go . I put it up on the work station , tipped the tank up onto it's rear bolt to have a look see at the fuel lines / vacuum lines for kinks etc all looked ok. Started the bike ,it ran sweet as a nut so now I have to take it for another ride and see what happens . The more I think about it the more I think it may be fuel related but I can't get past why it was back firing so much . I will also get hold of a compression gauge for a test .How can I test a coil under load Any thoughts from the brains trust ?

I went and seen my car mechanic mate who is ok with bike stuff and he thinks it sounds like electrical so I sprayed the coils / spark leads with a water spray while it was idling and that made no difference . It is running great today. I will throw in a new set of plugs this week . Maybe the bike has cracked the shits cause I don't ride it enough , bit like the opposite with the missus

Yer my old bonneville did something similar a few times and I found that the coils under the seat would get a pile of crud built up on the terminals and I'd just give em a clean and ZOOM prob solved... so I'm betting its electrical..

My money would be on a coil braking down

Try swapping the coils over and if the misfire shifts to the other cylinder it's the coil or HT lead.

Mine did something very similar...running on one cylinder and backfiring, then running on two, but roughly...thought it was a coil but after fitting another one still had same problem. Then checked plugs ( should have done this fisrt ) and right plug was wet with fuel...turned out to be very worn needle jet(s) letting way too much fuel through...new jets installed...instant road rocket! Anyway, hope you get yours sorted...Rick54

Went for a ride this morning and it started to play up again . I was happy to ride home with it spitting and farting knowing now I will find the problem . Right cylinder was not firing so I pulled out the plug and tried it against the frame. Nice blue spark . I put in a spare plug and it still wouldn't fire so I changed the coil wiring and still the right cylinder would't fire . Then I noticed fuel dripping onto the work station. It was coming from the carb vent pipe .I start to think , a blocked jet While googleing for fcr41 diagrams I see a message from Rick54 with a similar problem . Thanks Rick I couldn't get out to the bike quick enough to operate on the carbs







The culprit a blocked main jet




I put it back together and went for a run , alls good so thank you to all that offered help , now its time for our Australia day BBQ with me mates if I can find any

The culprit a blocked main jet



[/quote]

That´s the slow jet huh? Would be consistent with the popping and farting as it goes lean as ´ell....

I stand corrected thank you , killer

I'd have thought Mick would've jumped off the bench and given you a pointer towards solving it..........................

bobtrx wrote: I put it back together and went for a run , alls good so thank you to all that offered help , now its time for our Australia day BBQ with me mates if I can find any

Hey BOB, Tell me you only keep that bottle of VB to put fires out with... God only knows how anyone can drink that stuff!!

Stankflapper don't be such a peasant the mighty VB has magical powers
one -- three relaxing after a days work and stare at the bikes in the shed , admiring my choice in bikes
three--five the missus's voice drifts off into the distance to become a low mumble in the back ground
and plans formulate for the next bike modification
five--ten all the worlds problems are solved and maybe I can ride as quick as Sir Casey
ten --to what ever , next day it was a good idea at the time but now I don't feel too great , no riding today

I quite liked it when I was in Aus, can`t abide `normal` lagers.

I Still reckon the stuff is incorrectly labeled weed killer. However,, if it is functioning as a Wife muffler at 3 to 5 it has at least one good point.