Yamaha TRX850 Enthusiasts Forum

Hello, a few month ago I bought a complete TRX engine to be used in my XTZ750 frame.

It turned out I've got hold of a white framed, black engined TRX originally made for the Japanees domestic market ('94 I think with a frame serial numer 6XX).

Anyway, the carburettors does not look like the ones I've seen on ebay/repair manual. They look modified, see pictures below. It would be great if someone could take a guess/explain what modifications has been done on them aswell as what the modification does.


This is an original TRX carburettor found on ebay for reference.


The nozzles are approximatly 0.1-0.5mm in diameter, directed in the gas flow direction. Most likely home made. Are these acceleration pumps.. on a CV-carburettor?


Metallic screws (looks very home made)


View from the inside of cover and mating part (slider).

The metallic screws stops the sliders (throttles) just right (at max open). Perhaps previous owner first did some experimentations and this is an attempt to roll back to normal? Does non modified covers/sliders have a plastic pin/stop in this area?

Please comment!

Maybe it was a home made 33 horsepower "not quite passed my test" tweak.....................

WTF? no idea why anyone would do that (other than to meet 33bhp?)

A 1994 TRX !! maybe 1995, mine is an early white frame, black engine import model, just going to look at the carbs now though to see..............................

Dave E

Nope definately not the same as mine, bodgem and run. Surely the 33bhp law wasnt in then??

Dave E

That's terrible, who would do such a thing??????

Besides, if it was for restriction purposes, would it not be easier (less damaging!) to restrict the cable movement?

Thanks for the relplies!

To bad it sounds like this is some very odd and probably meaningless mod.

Anyway, I'm going to disassemble and do some testing of the nozzles function.

Let me know if there is any interest in more pictures.

@ slow codger:
Yeah, you are right, it is a 1995 TRX model and not a 1994.

Update:
I sent the picture of the acc. pump to Topham asking them what it is, if it is OEM, installed aftermarket kit or homemade.

Hello,
yes as far as I know the Japanese versions of the TRX850 were fitted with BDST38 carbs useing an acceleration pump.
The nozzles you have marked on the intake side are the pump nozzles and the hose connects the nozzles to each other ( only 1 pump is used for both carbs ! ).
We do not have any technical data on these carbs only parts lists for the European models - see attachment.
Best regards - S. Topham

@slow codger
You are sure you don't have these nozzles on your japan imported TRX?

To the best of my knowledge all Japanese market ones had pumper carbs and I'm pretty sure both carbs had a pump plunger

Will have another look tomorrow, been very busy and at the moment have a lot of wires hanging through the ceiling (spotlights dont you know).

Dave E