Yamaha TRX850 Enthusiasts Forum

Don´t forget the rubbers on our bikes are 38mm, i´ve actually been running 41mm carbs with 38mm rubbers for some time

billy bollocks !!!!! your right ,,just tried some spare rubbers on my new 41s , they fit but as you say they are smaller .. so whats the answer ?? do we trim the rubber back from the inside ? or is there a new rubber to be had

steve speed wrote:billy bollocks !!!!! your right ,,just tried some spare rubbers on my new 41s , they fit but as you say they are smaller .. so whats the answer ?? do we trim the rubber back from the inside ? or is there a new rubber to be had

The tuner who did my extra head actually noticed it and he used his tuned dremel to take my spare rubbers up to 41mm.
Can´t believe i didn´t think of this myself......bugger!

lets hope you get some more bhp !! i wonder if it will make a difference

steve speed wrote:lets hope you get some more bhp !! i wonder if it will make a difference

Well, if it does not it´s anyway CORRECT...but i can imagine 41mm of air going into 38mm must mean some kind of restriction....

the difference between 41mm bore and 38mm bore is nearly 200 square mm so you would think it would do,, quantime will be along soon to put us right !! lets hope this is the first time its been spoted and it gives us 10 bhp more

steve speed wrote:the difference between 41mm bore and 38mm bore is nearly 200 square mm so you would think it would do,, quantime will be along soon to put us right !! lets hope this is the first time its been spoted and it gives us 10 bhp more

10?????? YOU GREEDY BASTARD!!!

it,s more wishful thinking and don't you call me greedy bastard yes greedy no

Sorry lads, old news The trickiest part is to get the rubbers correct in shape, they do change form when the inlet and carbs are mounted (at least mine did...). First time I used a small sharp knife, second time a Dremel. I doubt it makes a lot of difference, who knows, the mixture may even benefit from the extra turbulence...

I start to imagine some pulsating snorkels, so thin they are to become
So at certain revs you're gona getting kind of a pump effect.
Beside the extra turbulence.
If that's not going to bring some extra 10 BHP?
You can do it if you really want...lalala..la..la

You might be better off trying to reduce the diameter down from 41 to 38mm gradually if there's enough length in the carb rubber to match the inlet tract and keep the gas speed up. A sudden increase in area, either up or down, is A Bad Thing. Failing that, I'd suppose it'd be a case of opening up the carb rubbers and matching the inlet tract to them.

Kayla wrote:You might be better off trying to reduce the diameter down from 41 to 38mm gradually if there's enough length in the carb rubber to match the inlet tract and keep the gas speed up. A sudden increase in area, either up or down, is A Bad Thing. Failing that, I'd suppose it'd be a case of opening up the carb rubbers and matching the inlet tract to them.

Yup, my inlets are taken up to match all way thru....with piranha teeth in them

Pulsating snorkels ... ooooh Vicar!


Seriously though, I was watching mine last week, and at tickover there's an appreciable bit of movement in the carb rubbers, carbs pulsing up and down etc... Might have something to do with not having an airbox on top to hold them down .

G

my std 38s pulse in and out now so i think this is quite normal,,,,just to put the record straight were only talking about the centre bit of the rubber inlet,which is also the thickest bit of the rubber,, its the bit the alloy stub buts up to and only requires 1.5mm of rubber to be removed

the plot thickens ,,ive just had a look at some more spigots that trixynut gave me, they are for the 41s but they are a bit shorter in length and they are 41mm at the carb and 38mm at the end that goes into the rubber so there must be loads of different ones i am going to stick with the long ones that trixynut had on his bike and just blend them in ,,, (i might get 104bhp with a following wind !!! )