YZ 360 tuning

[Rossvickicampbell]

Guys - those that know me understand my bike maintenance is basic at best.  However I have a slight issue with my 360 I would not mind having a go at.

TUNING the carb!!!!!

For a couple of meets now my 360 has been absolutely brilliant when coming on the pipe and pulls like the proverbial tractor - however at low throttle openings, coming out of corners it tends to be a bit lazy, dirty and slow to go - to run clean.

From what I have been reading so far am I correct in looking at the pilot circuit?  The bike does not idle, air screw changes don't help so am thinking maybe I need a larger air jet or smaller pilot jet to run a little leaner?

Shan't waffle - am expecting the usual slanging - but that goes with the territory  and will appreicate those interested enough to comment positively 

cheers

PS - carb is a VM 34 round slide.  If I remember rightly currently running a 35 pilot jet and a 2.0 air jet?

[suzuki59]

Rosco I will resist the opportunity to bag your riding ability and offer some constructive advice.
It sounds like pilot jet to me but I have found over the years the best way to resolve carb issues is to start with a brand new carb.
A man of your wealth could afford the $150 I guarantee that this will make a huge difference and make your tuning effort easier.

[Rossvickicampbell]

Craigy - as I wrote my topic I wondered how long it would take you to reply - and guess what - you didn't fail to impress me.

Thanks mate - was actually thinking of going along that line also - but as I think I am so close to being spot on was a little reluctant.  I also see I can't get a bigger air jet than a 2.0 anyway so looks like maybe  a#32.5 pilot jet?

Where does everybody buy their carbs from?

[Iain Cameron]

Rosco have you checked that its not blocked with a bit of dirt , give it a clean first and reset float before shelling out for a new carb . Hatricks in the back of VMX for a new one though . Iain

[Rossvickicampbell]

thanks iain - have just gone through that exact exercise - made the mistake of leaving it site for a loooong period of time with fuel in it - so gave it an extremely good clean as a result of what was left after that time. 

[Slakewell]

I love the fact that most blokes VMX bike run like shit because they feel that a 40 year old part that wears quickly should still be ok. How your bike is jetted and runs cleanly affects so many little small things not just engine performance.

For real advice It's a 360 with a reed valve buy a new 36mm carb and pay someone to set it up correctly its not just jets its slide cut away etc. You will wonder why you didn't do it years ago.

[80-85 husky]

Drop the needle 1 clip and see what happens as you are in the pilot needle range when getting back on the gas. with the bike snapping into the band, you may be rich in the needle range and getting an extra hit as it cleans out.

try the clip 1 up and 1 down from where it is and see if that makes any difference.

repack your muffler, will give a little more onto the band oomph if its all burnt out

[Davey Crocket]

What Slakewell said....buy a new 36mm, run the std YZ360B jets as per the Yamaha parts book and you will be surprised how much better it goes....BTW, your problem sounds like a blocked pilot jet.

[Rossvickicampbell]

Slakey shouldn't assume already that it is a 40 year old part that has worn out    Even a new carby wil still need setting up eh!  This carby isn't that old - year or 2 at best.

John - thanks - have already done that - played with the clip and that is why I think I am getting close.

YZB - muffler - repack - you mean the little straight through pickle hanging on the end that never had packing in it 

Interesting the idea of throwing a 36mm on though.

[Slakewell]

If the carb is new try filing a 1mm off the back of the slide ( wet and dry after filing) and see if that crisp up stuff.
I ran a 36mm on my 250 A most of the time. I would be thinking even 38mm given its a reed valve.

[80-85 husky]

Reeds ok? nothing under them?? if you cant get an idle and the airscrew is not changing anything there must be an airleak?

[OverTheHill]

Hi, not doubting your ability [although i doubt my own sometimes--the stupid things i do] get someone experienced at sorting unusual problems to ride it under the same conditions that you mentioned--just in-case it's not a carb problem. In saying that--over time the slide needle & the jet it slides in get's worn & although dropping the needle might get you by, it usually cocks it up somewhere else so in the end a new needle & [emulsion tube] jet is best bet. These parts are pretty much the only moving parts that wear that will effect the running [broadly speaking]. Idle mixture probably needs two turns out. People think [screw] & screw this mixture screw home then wonder why it floods up coming on after a closed throttle into a corner. Had damaged reeds causing havoc before now--chip of the corner of a steel reed etc. Anyway--just some ideas. Cheers.

[Iain Cameron]

Rosco its obviously broken so I'll take it off your hands as a favour . Iain

[Rossvickicampbell]

OTH - lack of ability is causing plenty of doubt but lots of good thoughts to try - shall mull them over - oh except yours Iain 

thanks guys - luv trying to sort  things out and the help is appreciated

[Lozza]

How much throttle does it need before it will run? If it needs an 1/8th turn you would just be supplying more air I think your correct with lack of air/too much fuel on the pilot circuit. The air corrector (in the bellmouth at the bottom) really only feeds air to the needle jet and helps stop the mixture getting ever richer as rpm increases.
Genuine mikuni pilot jets go in a step of 5 but there would be a OEM jet that is in between(RGV's have 27.5 pilots) so maybe s look at 150-250cc road bike jets on CMSNL?
Next would be to check your ignition with a timing light while the engine is running.