OzVMX Forum

Clubroom => Tech Talk => Topic started by: firko on March 12, 2011, 10:44:56 pm

Title: MX 360 jetting.
Post by: firko on March 12, 2011, 10:44:56 pm

Can someone please give me a good starting point for jetting a 36mm Mikuni on a 360 reed valve Yamaha?

Title: Re: MX 360 jetting.
Post by: Iain Cameron on March 12, 2011, 11:12:42 pm

Hi firko what Ive got is needle 6f15, cut away 3.0 ,pilot #50 ,air 2.0 ,starter #80 , float 23.4 ,main 280 , that should put you in the ball park

Title: Re: MX 360 jetting.
Post by: firko on March 12, 2011, 11:28:37 pm

Thanks Iain, much appreciated. ;D

Title: Re: MX 360 jetting.
Post by: Freakshow on March 15, 2011, 12:04:44 pm

my mains are up on that start at 300,   i think im on 310-320 on my 34mm but i like rich, not sure what the 36mm is on but i think 340-350mm rings a bell.

ID be starting up there MArk, it'll fire up fine and you can always came back  ;)

Title: Re: MX 360 jetting.
Post by: firko on March 15, 2011, 03:10:56 pm

Quote

Hi firko what Ive got is needle 6f15, cut away 3.0 ,pilot #50 ,air 2.0 , starter #80 .float 23.4 ,main 280 , that should put you in the ball park

I've managed to dig up all of the needed parts to set up the carby but I'm a bit confused by starter #80 . Is there another name for it or am I just dumb?...(don't answer that ;D)

Freaky, I've got a 34mm that's been raced on a mates MX360 back in the 90s. It's got a 320 main, #50 pilot (cant remember the rest). I'm no carby scientist but I'd assume you'd run bigger jetting on a 34mm/360 combo than on a 36/360 set up. I'm actually going to use that carby on my reed DT2 motor.

Title: Re: MX 360 jetting.
Post by: Freakshow on March 15, 2011, 03:25:17 pm

Firko you only ned to fork about with the ones you can see when you open up the Bowl, all the others you worry about if it doesnt rev where and when you want it to.

I'd be starting at #340 and work from there.  ONE quick throttle chop and you can see how far your out before you even sit on it.
Make sure you have your air filter oiled up the same way as you would when you riding it.  Folks try to jet on No or dry filters only to find when they oil up a filter to race they bike runs like a bucket of pus and way too rich to even get on the pipe.

Title: Re: MX 360 jetting.
Post by: bazza on March 15, 2011, 03:27:50 pm

Not sure what #80 starter is-does not compute to my Mikuni Bible
Rest of settings make sence
Klub Kevlar Tuning Dept

Title: Re: MX 360 jetting.
Post by: firko on March 15, 2011, 03:54:03 pm

Quote

Not sure what #80 starter is-does not compute to my Mikuni Bible

Same here Mikey....I've looked up my Mikuni book and the Sudco website and 'starter' isn't mentioned.

Freaky, You may quite possibly be right, especially seeing that the bike's a pure dirt tracker that'll be on the main for most of its time on the track. This is the main reason I'm going to HBBB, to jet my three bikes (and have some fun of course). After 40 years I'm still learning the black art of jetting so I asked for jetting specs for the 360 because I've never actually set up a Mikuni reed valve Yamaha engine from scratch. I've got a full range of mainjets and a few needles and slides so with master tuner Frank Stanborough holding my hand, I reckon we'll get it pretty close.

Title: Re: MX 360 jetting.
Post by: Freakshow on March 15, 2011, 04:17:30 pm

Fwiw - I have a 38mm on a YZ/RT and it runs a #400  so im guesing youll be playing around the #340 mark so just take the jets around it. 
Being a reed valve its going to let you run really Fat anyway. 

Also try to take some Avgas or that new 100 bowser Pump gas and mix out at 32:1 regardless of what brand name is on the bottle.  ( that poxy caltex at broadford sell's shit fuel IMHO)

With the RT on full niose you cant go wrong.

Title: Re: MX 360 jetting.
Post by: Lozza on March 15, 2011, 05:10:10 pm

Just rig an EGT gauge and take the guess work out of the equation.

Title: Re: MX 360 jetting.
Post by: Freakshow on March 15, 2011, 05:30:38 pm

FIRko, just take the jets there will be no guess work.

Title: Re: MX 360 jetting.
Post by: firko on March 15, 2011, 06:12:52 pm

Thanks for the welcome advice but I have done this before fellas :). I'm not exactly a jetting virgin, I've been building vintage bikes for 22 years and those who know my bikes know that they aren't exactly slowpokes ;). I gaurantee that by weekends end all three will be going as best as they can with their different setups. My next plan is to get the Cheney's 360 engine up to Lozza....this weekend suit you at all Loz?

Title: Re: MX 360 jetting.
Post by: Iain Cameron on March 15, 2011, 06:28:51 pm

Hi firko the figures I gave you where from cycleserv mx 250/360/500 service manual ,been looking for the starter my self ??? sorry for giving you a bum steer

Title: Re: MX 360 jetting.
Post by: firko on March 15, 2011, 06:47:08 pm

Yep it's got me buggered, my mate in the US has never heard of a starter either.
Iain, are those specs for a 36mm carby on a 360 or for the standard 34mm ?

Title: Re: MX 360 jetting.
Post by: bazza on March 15, 2011, 07:08:35 pm

the plunger  the choke lever pushes down is called a "STARTER"plunger in some diagrammes (but not numberd)
Mark make sure  Uncle frank is sober...lol

Title: Re: MX 360 jetting.
Post by: firko on March 15, 2011, 07:15:53 pm

Starter=choke.....That makes sense, Japlish translation.

Title: Re: MX 360 jetting.
Post by: Iain Cameron on March 15, 2011, 08:09:06 pm

just checked its a 34 dumb  :-\