Yamaha TRX850 Enthusiasts Forum

Hello!

I hope everyone is well. Firstly, just a big thank you for your help with the relay issue - that problem was solved, met with another where the bike wouldn't charge, and solved with a new stator... And yet, the issues persist

The latest being... I started the bike up today, no problem. Fires straight away, and idles lovely. Took it for a 20 minute test ride with the new stator installed and fresh oil. Toward the end of the journey the bike started to run poorly at low speeds. I took it easy en route home, and in the driveway let it idle. It idled really intermittently. Sitting at 1000rpm and spluttering about to as low as a few hundred. Some audible pops could be heard underneath the tank, and placing my hands on the tank, you could feel them too. After about 40 seconds of idling, it just cut out.

Anyone have any idea? Possible vacuum problem? Would that be the case if it runs perfectly before it gets warm?

Ta in advance!

Unlucky Kyle

The obvious culprits are vacuum leaks.
The intake rubbers between the carbs and the head perish over time and develop cracks.
The cover of the air-cut valve, particularly the one on the RHS carb, cracks apart.
The two vacuum hoses running from the head to the fuel tap and the fuel pump.
Have you had the carbs off?

Hi Dicky!

Great to hear from you again.

Oh right that's interesting to know. I haven't had the carbs off yet, but I'll have a look. And check the air cut valved too.

I've checked the 2 hoses you mentioned and they seem okay and the clips nice and tight.

I took a video of it running, a friend said it could even be spark plug/lead/cap/coil related?

https://youtu.be/z2335kplnMs

Here's the clip ^^

Many years ago when I was active in car rallies, it was well known that 90% of carburetion problems are caused by the ignition system, and vice versa!

Change the plugs, it never hurts.
You can replace the caps and HT leads while you're at it, they do degrade over time.
The coils may also be dodgy, you can check the winding resistance with an ohm meter but if they are breaking down under load then that may not show up.
If you can get a few feet of solid copper core 8mm HT lead it just screws into the coil and plug cap.
Not many places in Oz sell it these days, the auto shops only want to sell you a complete set of pre-made leads. Scumbags.
I found an auto electrics place run by a grumpy old bastard. He had half a roll and was glad to sell me some.
If you want to get fancy you can replace the entire coil/lead/cap with some fancy coil-over plug caps. I think CBR600RR from '05 to '18 are the ones to get.