Yamaha TRX850 Enthusiasts Forum

The standard TRX Mikuni carbs are known to have a wear problem leading to carburetion problems, typically hunting or surging while at constant throttle between 2 to 4 thousand RPM.
The needlejet - the jet inside which the needle sits (also known as the emulsion tube) and the jetneedle - the needle inside the jet (needle) wear oval shaped due to the way the carb sits in the TRX.
There are after market carb kits available from Factory Pro, DynoJet, Keyster and maybe others.
Details of how to disassemble the carbs are in this thread... http://www.trx850.com/phpBB_forum/viewt ... =36&t=1386
Pics of the worn tube and needle can be found here... http://www.trx850.com/phpBB_forum/viewt ... 611#p20611
More details in this thread... http://www.trx850.com/phpBB_forum/viewt ... =37&t=8890

replace mine yet again today. 3rd time. I have 94000km on the bike and the needle jets last 20,000km to 25,000km before I fine it running too rich

What does a correct assembled jet needle assembly look like. I bought a rebuild kit for my carburetors, but it is not similar to the old ones. The old ones had the locking ring, a white POM spacer (thickness 3 mm), and a washer. If I am not mistaken the new ones has the locking ring, a washer, and a rubber ring.

SEARCH is your forum friend.

http://www.trx850.com/phpBB_forum/viewt ... sion+tubes

You should be able to use the nylon spacer from the original needle on the replacement.

You can fix the wear Problem on the emulsion tubes by inserting a Dynojet Aluminium needle. Before inserting it, polish the needle for the best result and like that it should work without Problems and running to rich after 20k km.

But these needle are very hard to get.
You can ask micronsystems.
The new Dynojet Stage 1 Kit has Aluminium needles too But I cant gurantee that it is in your Country as well

The std needles in theory should not wear. It’s only due to mismanagement of maintainence that will create the problem.

So here is the politics behind it all.
How many buy a kit because it’s a cheap option giving all you need to possibly just to fix a blocked pilot and just replace things that are not warranted and then create a problem??
All they may have really needed was a gasket for the bowl!!!!
How many don’t realise to seat the needle correctly when just cleaning carbies and create a problem??

Word goes out on the grapevine there is s problem and it’s easy to place fear into the mind to sway opinion but it’s harder to question the fear and change their mind once again...

Here is an example of worn emulsion tubes.
You can see that the hole has been worn to an oval shape.