YZ 465G Jetting Question

[Twistagrip]

I have a quick question for anyone who has experienced this problem. I will describe the existing setup and then my problem.

1980 Yamaha 465g
bored +040 w/wiseco
boysen power reeds
reed spacer
DG pipe and silencer
Uni air filter
2001 or 2002? Mikuni VM-38 carb
No porting or other mods.
6000+ ft. altitude
Fuel - 50/50 mix sunoco 110 and 91premium w/yamalube2R 32:1
Main jet:380
Needle Jet:P8
Jet needle:6F16 clip at 2nd notch from top
Slide:2.5 cut to about 3.1
Pilot: 50 w/air screw 2 turns out

The performance is as follows:
Starting and idle is good, throttle response is crisp and excellent. The bike pulls like a tractor to about 3/8 throttle where it starts to sputter and won't clean up. At throttle positions 1/2 to full...well lets' just say it is a rocket ship. The bike runs clean and perfect at every throttle positon but @1/4 to 1/2 throttle. I have tried changing to a leaner clip position. The bike runs better overall except it does not seem to affect the "blubber" at 3/8. I am thinking that I either need to cut the slide further or find a different needle with a fatter initial taper but I don't know which way to go!

Any help would be greatly appreciated!

 

[cladoo]

Sounds like you already know what to do. If you can find a needle athat is leaner at the top that could work but, finding a 3.5 slide or cutting yours should help. I had the same problem on my '83 CR480 when I moved here to higher elevations (4000ft to 6000ft) and I change the needle and the slide.

 

[Twistagrip]

Thanks for the reply Cladoo, I don't have a chart and have no idea what needle to try. The slide I can do but before I cut it i would like to try the needle first. what number should I use?

 

[ACS]

The factory workshop manuals for the YZ's used to have a list of different needles in them from leaner to richer. Hard to find nowdays but try asking a older friendly dealer to dig up their library for the original workshop manual. If you get stuck I might be able to get the list. Whether the needles are available from Yamaha no idea but Sudco or others might have them.

 

[Twistagrip]

Thanks! I'll stop by the dealer here and see if they have the literature. This baby is so close to having the perfect powerband and jetting of anything I have ridden. I sure hope I can get it cleaned up.

 

[cladoo]

I found a site that had some needle charts on it. 650motorcycles.com .
You need to find a needle that is fatter (leaner) at the top of the needle D! to D3. Remember to keep the same size further down the needle (D4 toD6)to keep the jetting there the same. You could order a Sudco Manual, I've seen them on their site for $10 plus shipping, that would probably help. Do you need an owners manual? I have one PM me back if you are interested.

 

[Twistagrip]

Thanks!