How To: Carburettor Tuning

[Calum]

@irongamer727 The bowl is adjusted by the float valve. Why would taking the main jet out affect the float valve.

[gbone85]

Very helpful thanks a lot

[pajo1230]

Hi fellas wondering if anyone knows the main jet size for aftermarket exhaust on DT 125 RE 2004 stock is 210 i have 240 on my mind.

[Calum]

@pajo1230 240 is the default jetting for early DTR's

Carb tuning is region specific. You have to take into count atmosphere.

Most pipes recommend default settings so you should be okay.

It all depends on your state of tune.

[pajo1230]

Im on a normal atmosphere like 100m or smth, the point is that the exhaust will be made from a guy who i know from Akrapovič it will be handbuilt and made for preformance, makes me think that i will need a bigger main jet then.

[Calum]

@pajo1230 You in the UK? Thats what I mean. If it's cold and the fuel is shit then yeah up the fuel. If you've modified the intake then bump the fuel. Check the spark plug colour as an indication to how th e fueling is doing.

[pajo1230]

Im from Slovenia i tank 95 gal mix it with Motul 510 2t so you think there will be no need for main jet to get changed?

About the intake im thinking of removing the duct tape on the airbox (it covers half of it) so it can take more air.

[Calum]

@pajo1230 If you're going to increase the air intake, you will want to rejet to suit. But it's not something I can simply tell you. You have to jet it to your surroundings and environment. You may have high quality fuel, in which case uping the jet may not be necessary.

[pajo1230]

I mean "increase air intake" was the duct tape on airbox like hole under the seat ment to be there or was that added after because i didnt do that and it seems logicly to increase air intake with full exhaust but i wont like drill holes in the airbox or something like that just remove the duct tape.

Because i see alot of people having 230-240 jet on the bike with aftermarekt exhaust that makes me want to change the main jet.

[Calum]

@pajo1230 Yeah, want and need are two different things. Jet accordingly would be my advice. If it's lean, up the settings, if it's rich, lean it off.

[pajo1230]

Right, ty for the advice.

[terry.tz]

@Calum a guy I watch on youtube put a video up yesterday and I also been doing my jetting as you know so I thought I would come have a look what was put for re-jetting on here think you could add about plug chopping as there more reliable and simplify the procedure

[Calum]

@terry-tz Plug chopping is really only an indication of roughly where abouts the fuel is under load.

If you really want to do it properly, you buy a wideband and monitor the AFR getting it spot on with the fueling.

[terry.tz]

that's just not gonna happen though unless your a professional 2 stroke tuner or a racing team with money to waste

[declan]

@terry-tz I got a carb that’s running rich on idle and I can’t get a pilot small enough higher revs the bikes good any ideas?

[terry.tz]

I'm no expert @declan just tinkering so I wouldn't like to say but don't see why you cant get a smaller pilot jet

[declan]

@terry-tz they only go so small I’m on a 32 lowest is 30 I care from a 36 I believe but it’s still way too much I roasted an head gasket because I had the af screw too far out to combat the problem (I knew the risks)

[NINJA]

I found this vid on YT, which may be very helpful to those looking to tune their Mikuni carbs;

https://www.youtube.com/watch?fbclid=IwAR2OspBdvJfZnFdVVttSrgyHoz3NxRYGmBDbIYmRem0HCbkKVO3nJ91yl1I&v=67Nb3DI-B3s&feature=youtu.be