Yamaha TRX850 Enthusiasts Forum

Hi

My TRX is backfireing on one of the cylinders. This only happens when it is cold. When it heats up it disappears. It aslo runs fine and engine sounds very good. I smell petrol in that exhaust. I reasenly serviced it...new plugs, oil and filters. I think it might be the carburetors. Any ideas?

Jean

What mileage is on the engine?

Could be emulsion tubes, but if it clears up when warm I'd say unlikely.

Could be valve clearances closed up.

Could be a bad plug, coil, cap, HT lead or maybe you knocked an LT connection loose.

45000Km on the clock. Just replaced the plugs 2weeks ago. Plug leads, I'll check it out, but everything seems ok. I struggled to get the right plug out. It is not in a very accessible place to get your hands in. Bit of a mission to get it out!

Could be the old fuel tap position problem: leave it in the pri position and fuel flows freely through the vacuum tap into the engine. When you first fire her up, it bangs as it burns! Do you leave the tap on Pri or On? Always leave it on ON.

emulsion tubes i would suspect at that mileage
Could be valve clearances closed up.

I'll check out the petrol tap position tonight. As for emulsion tubes and valves...lets hope not. I'll be pulling out my hair if I cant go riding while she stands there in pieces.

The fuel tap is is in the on position. So its not that. How do I know/test if is the plug leads? It looks good and I wiggled it a little, but seems good.

Any tips for next time I service my rex. I dont want to take the engine out neither take the radiator off. I struggle to get my hand in to change plug number 2 (right hand one). Any tips to make this easier?

remove the 4 bolts that the rad hangs on then push the rad away from the motor. Taking the fairing off makes it easier.

does it start easily? if not, then valve clearances are the most likely suspect.

could you have pulled the plug cap off the lead slightly? are the caps seated fully on the plugs?

JW-TRX wrote:The fuel tap is is in the on position. So its not that. How do I know/test if is the plug leads? It looks good and I wiggled it a little, but seems good.

Any tips for next time I service my rex. I dont want to take the engine out neither take the radiator off. I struggle to get my hand in to change plug number 2 (right hand one). Any tips to make this easier?

Check the manual found on this site, SHOULD be able to check ohm on the cables and coils.....

It starts very easy. First time. (except if the battery is flat...replaced that recently). The caps are sealed. Will check the impedances of the coils with my multimeter.

Thanks for the tip youngy.

I've got more that one manual for my bike. FYI...One is the haynes manual and a nother one... Will check out what you've got...But only saw the parts manual, this I got from your site...thanks again for that....was looking for that every where.

There is a strong smell of petrol in that exhaust. This makes me think the mixture in that carb is to rich and/or the plug isn't burning all the petrol. Will check those impedances this weekend.

Yamaha´s own service manual is here!

JW-TRX wrote:It starts very easy. First time. (except if the battery is flat...replaced that recently). The caps are sealed. Will check the impedances of the coils with my multimeter.

Thanks for the tip youngy.

I've got more that one manual for my bike. FYI...One is the haynes manual and a nother one... Will check out what you've got...But only saw the parts manual, this I got from your site...thanks again for that....was looking for that every where.

There is a strong smell of petrol in that exhaust. This makes me think the mixture in that carb is to rich and/or the plug isn't burning all the petrol. Will check those impedances this weekend.

starts easy first time, stinks of petrol = emulsion tubes imo

What will happen if I don't give the emulsion tubes attention? Will it mess up the rest of my engine with time? (I'm no mechanic. Don't even know what emulsion tubes are. Just know its got something to do with carbs.)

Killerwhale, can any you be so kind to point me to the manual.

JW-TRX wrote:What will happen if I don't give the emulsion tubes attention? Will it mess up the rest of my engine with time? (I'm no mechanic. Don't even know what emulsion tubes are. Just know its got something to do with carbs.)

Killerwhale, can any you be so kind to point me to the manual.

Mai oui...http://trx850.motomaniac.net/forum/view ... f=47&t=595

Jw, do a search as there is shed loads of info on the emulsion tube problem. They are easy to change. they are the tubes that the needles run in, they get ovalised and allow too much fuel in.

Dave E