A forum for owners of Yamaha TTR250 trail and enduro bikes!

barra8 · Guru

What jets do you have installed?

brindabella · Senior Member

standard 2011 bike, yamaha #50 pilot, yamaha #147 main, needle clip 1 step leaner, 2 to 3 turns out on fuel mixture screw (I think), runs well at 700M altitude, but who knows, maybe it could be jetted better.

by "leaner" on the needle, I mean the clip moved 1 groove up, ie further AWAY from the pointy end compared to standard - to the 3rd groove from pointy end (which is the middle groove).

I can't compare with your jets because I don't know who made your jets.
If your jets (eg pilot) are not yamaha ones, the numbering will almost certainly be incompatible.

I wonder whether your #52.5 pilot (a Mikuni size?) is actually leaner or richer than a standard yamaha #50.

For main jets at least, equivalent mikuni jets have slighty larger numbers, so perhaps a sigma jet kit uses mikuni numbering and so anyway, a #150 main is much closer to standard than would appear?

needle clip position has most effect when varying speed at about 1/3 throttle and should not really have any noticeable affect at "wide open throttle".

regarding the effect of altitude etc, in order of importance:

1. high altitude (and so lower air pressure) - bike will run rich, so need to go leaner (switch to smaller jet number)
2. high temperature - also need to go a bit leaner
3. high humidity - also need go leaner (but humidity has only minimal impact)

so if you are up at 900M in the Australian tropics, then you need to go a bit leaner than a bike ridden near the coast in England, which makes it all the more surprising to see your larger jet sizes.

there is an equation for combining all that to get a figure for "oxygen density" from which required jet flow can be calculated, but since the jets just have funny numbers which do not equate to flow, you just have to use trial an error anyway.

and as Brian suggested, maybe the TTR is not particularly sensitive to main jet selection.

-- Edited by brindabella on Friday 25th of January 2013 10:56:56 PM

barra8 · Guru

Not sure why you did'nt buy an aftermarket twin air filter to lean it out but that's your choice i guess.

I can tell you that the Sigma #150 is MUCH larger than standard as i have tried using the standard #147 jet on the standard setting....N2. (N3. if needed when assembled ) from the bottom. Also making it richer by lowering the needle clip postition to the richest settings ie. clip at sharp end of the needle & it ran HOT at the header pipe in both settings. Also the hole looks much larger. The #52.5 SIGMA pilot jet is also MUCH larger as i cannot run it (very well) on the normal #50 (or #48 for older models) . It also looks MUCH larger.

For example: If i dropped my #150 jet to the standard setting ei. Second clip position from the bottom it is TOO RICH with the standard airbox.

Also for example: If i use the richest setting possible (bottom clip postiton) on the standard main jet #147 it is still TOO LEAN.

My low to mid range is perfect with the #52.5 pilot jet & goes 10x compared to the standard #50 (or #48 on older models)

It is also to be noted that they gave me a #140 + #145 main jet with the SIGMA kit (that i gave to a mate for his xt225 serow)

So you understand........I'm not trying to re-jet mine as i have it perfect. I uploaded my settings above This thread is merely to find out what jets OTHER people have installed,what mods,elevation, tempreture ect. & how it runs so you have answered these.

The thing i find is there is no HARD & FAST rule with jets & why i'm interested in what works best in different environments ect.

.................................

Thanks for letting me know your jet sizes & all relavent info.

To let you in on a secret it's mainly because i can't believe Brian is running a #147 with #52 pilot??? Maybe he is'nt but if he does have a #147 it is WEIRD??? I guess it could be put down to the porting (if so). It would be great to see how much difference the porting work made. I think HEAPS but it's not verified.

Also just to extend my knowledge on settings that actually WORK for different bikes/temp/atmosheric pressure ect. not just the normal yadadayada that a bike shop will tell you.

This subject can get confusing when talking about the needle & why i edited it to include ''clip postition''

To help with this i have uploaded a pic.....

Thanks Brindabella for letting me know your jet sizes ect.

Something funny= When i first wrote this i had it the wrong way around with the rich/lean. I then relized & edited it & smoothed things out as you see it.. Then i decided to post the pic above......Guess what? You Guessed it.....I mixed up the rich/lean on the needle..hahahaha. biggrin I'm not in a real good thinking mood today i guess smile All info is good now though wink

...........................

Jarrah.

-- Edited by barra8 on Friday 25th of January 2013 01:43:01 PM

barra8 · Guru

Okay this is what i have found that confuses the living hell out of me.....
I am using the totally standard "blue" model carb settings and jets with a Motad silencer and it seems absolutely fine.

Brian

Not sure how this can be so as mine is a 74mm bore but with head work & there aint no way it would run ''fine'' on the standard Blue bike jets ?
Either Brian's 325 runs way too lean or something is not right here hmmm...

Now thinking he has a standard air filter & the needle clip position at the bottom setting to enrichen it but even that seems lean to me ??????

..................
Jarrah.

-- Edited by barra8 on Friday 25th of January 2013 04:10:37 PM

barra8 · Guru

This is very confusing confuse confuse confuse The exhaust must be a little restrictive to make this possible as it does'nt seem right confuse confuse Either that or the climate plays a BIG part in this.

Thanks though Brian for confirming this. It now makes me wonder how a bike can change so much from climate ect. but i guess it's part of the mistery of carbs.

Well.... we now have three bikes all different settings aww aww aww We are getting to the bottom of this slowly.

.............................

Jarrah.

-- Edited by barra8 on Friday 25th of January 2013 04:56:39 PM

TTRfan · Super Guru

147 main jet, Twin Air filter, needle in standard position and the 325 is still running a bit rich.

My mates WR450F gets better mpg than my 325 wink

Brian