Yamaha TRX850 Enthusiasts Forum

The plastic spacer that sits over the needle before it’s dropped into the diaphram is stepped so that the needle enters the jet straight.
At its thickest part does anyone know how thick this spacer is as I’m making my own as I only have flat ones which are after market- am trying to put carbs back to standard to rule out issues- getting there slowly

Many thanks

ac@39 wrote:The plastic spacer that sits over the needle before it’s dropped into the diaphram is stepped so that the needle enters the jet straight.
At its thickest part does anyone know how thick this spacer is as I’m making my own as I only have flat ones which are after market- am trying to put carbs back to standard to rule out issues- getting there slowly

Many thanks

You'd be surprised how few people know that the spacer is stepped to align the needle, I have a couple of old junk carbs. I'll check them tonight and measure the spacer and if there is a pair you can have them, if that helps.
R

Rod.s wrote:

ac@39 wrote:The plastic spacer that sits over the needle before it’s dropped into the diaphram is stepped so that the needle enters the jet straight.
At its thickest part does anyone know how thick this spacer is as I’m making my own as I only have flat ones which are after market- am trying to put carbs back to standard to rule out issues- getting there slowly

Many thanks

You'd be surprised how few people know that the spacer is stepped to align the needle, I have a couple of old junk carbs. I'll check them tonight and measure the spacer and if there is a pair you can have them, if that helps.
R

That’s a generous offer but just the measurements would be great as already have the material to make new ones up

I filed the round aftermarket plastic ones fitted to a set of carbies on 1 of Marko’s Trx’s when I serviced it recently.
Located beautifully I filed a flat edge on the metal washer too.

i did think about doing that but i had a yzf750 few years back and seemed to recall the spacers were thicker than those i currently have - which if i file the step onto them wont leave much left -

All measured using a micrometer (except internal Dia)
A- Dia, 9.0mm
B- Internal Dia, 2.98-3.0mm (or Dia of needle)- slight interference fit to stop the spacer turning when installing needle assembly.
C- Hight, 2.55mm
D- Step down total hight, 1.60mm
E- Distance from step-down to opposite edge 7.0mm

i read on here somewhere that the spacer is not meant to have a cut away section in it....someone had done this mod to get the needle to sit central in the tube but then people were saying the needle is supposed to be off centre lightly touching the side of the tube to prevent globules of fuel running down the needle ..Im confused as which is correct .

The reason for the needle dragging on the jet is to stop the fuel running down the needle and "drip" into the airstream causing misfire symptoms

Rod.s wrote:All measured using a micrometer (except internal Dia)
A- Dia, 9.0mm
B- Internal Dia, 2.98-3.0mm (or Dia of needle)- slight interference fit to stop the spacer turning when installing needle assembly.
C- Hight, 2.55mm
D- Step down total hight, 1.60mm
E- Distance from step-down to opposite edge 7.0mm

Top man!! thank you

devonnick wrote:i read on here somewhere that the spacer is not meant to have a cut away section in it....someone had done this mod to get the needle to sit central in the tube but then people were saying the needle is supposed to be off centre lightly touching the side of the tube to prevent globules of fuel running down the needle ..Im confused as which is correct .

not sure if the theory is correct but i was under the impression the stepped spacer comes with the carbs as standard so im going with that - if you go to allens performance they would sell you a spacer with the step i believe

devonnick wrote:i read on here somewhere that the spacer is not meant to have a cut away section in it....someone had done this mod to get the needle to sit central in the tube but then people were saying the needle is supposed to be off centre lightly touching the side of the tube to prevent globules of fuel running down the needle ..Im confused as which is correct .

Where did you read this?

Someone put something up about this relating it to SU carburettors and cars.
My thought straight away was a multi cylinder vehicle using a bank of cylinders on 1 manifold to draw on I carburettor with larger jetting may be the reasoning behind a theory like this but struggled to see how as I can only see it promoting wear. I thought the actual emulsion tube design would dictate more on a problem like this. This is the reason why TDMR’s are much more efficient and you find better gains of up to 10Nm than FCR’s in the midrange. Much better atomisation of the fuel.

Re: Carby kits common fault to be aware of..
Postby dandywarhol » Mon Apr 16, 2018 7:00 pm

cobbadiggabuddyblooo wrote:
Trx has I intake working on 1 carburettor and a multicylinder car motor would have multi cylinders impacting on 1 or 2 manifolds. Maybe why the difference????


The reason for the needle dragging on the jet is to stop the fuel running down the needle and "drip" into the airstream causing misfire symptoms

This is what i read...if it is not related to trx carbs then maybe the mod is a good idea .

So what would cause the fuel to run back down the needle???
Lack of intake vacuum to continually draw the fuel up.
Possibly from a Lower compression motor like in a car motor which was common back in the carburettor era with multi cylinders flowing through a common manifold??
Or is from inconsistent Venturi vacuum compensating for altitude and temperature changes????
First intake option sounds more like a jetting issue so maybe Venturi option 2???