CB360 Mikuni 32 VM tuning

crazypj said:
As I said pages ago, I'm using XS650 emulsion tubes in VM32's
The jets are different, you use large round head instead of hex head (the thread is also slightly different pitch)
I lost confidence in SUDCO years ago when they started selling 'proprietary' jetted VM32's that just plain didn't work until re-jetted
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PJ- How much tweaking would have to be done when trying to fit 366-Y0 into a VM32?
You say that you need to use round Mains and a shorter needle. How much?
Also, what about the fit of the NJ itself into the NJ journal?
Thanks for you help and info about Mike's parts list.
 
crazypj said:
On XS, the slide is about 1/3 open all the time, it doesn't bottom out, carb body is machined to keep it open
On VM, when slide closes, the needle pretty much fills the needle jet.
I don't remember which needle I used though, original was too long and bottomed on the main jet
I think the emulsion tubes sit slightly high, the flange is slightly thicker.(probably 0.010"~0.015")
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Correct. On BS series CV carbs the slide does not close down all the way because it's not the throttle, it's a jet adjuster.

Y-0 is 3.10 compared to say a P-4 which is 2.67 or say an O-2 which is 2.610mm. That must be making the lower midrange much richer than it was before. So it would go some way to overcome the Bleed nozzle lean effect at low throttle settings. Odd that it isn't way to rich in upper midrange with a needle jet that large.

I wonder if you used a BS type needle. They tend to be thicker at the root. GT750 4DN18 is 2.98mm at the root, and XS650 4N8 needle is 3.0mm, compared to 159 needles which are typically 2.5-2.52mm at the root.
 
teazer said:
175 has a thinner (less deep) top flange than a 159 series and 176 are slightly thicker and stick up by around .5mm into the flow. Either will probably work as a 159 replacement. It looks like the 176 has been replaced by #270 series. 175 appear to go to Q-0 and 176 appear to stop at P-8 which is marginally smaller.

See what you can get
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Teazer- Ok, so I'm gonna order a set of 176 styles. The chart I found list the 175s are for 28mm and the 176s are for 30-35mm. With you saying that a 159 P-5 would compare to a 176 O-8 or P-0 and I seem to be having lean out on off idle(without choke circuits on) when running 159 P-4s, safe to say I should grab a set of 176(210) P-0 OR??? I haven't had time to play with the bike and have been a bit disheartened. But pulling up my boots straps. So, #176(or 210, if that is what they are called now) P-0 I really don't want to get into adapting XS CM jets. EVERYONE, MUCHO MUCHO GRASSY ARSE for all your time and input.
 
Correct about 175/176 fitment - go with 176.

Other way round on flow. 176/270 flows less gas out of the same sized hole as a 159 series because it's flowing air as well as gas. Go for the largest 176 you can get and let's hope and pray that it's big enough to get the job done. The difference is that a 159 flows less at the bottom and more at the top - relatively speaking. Or put the other way, a 159 that works at the top will be too lean at the bottom end on a 4 stroke.

What we're trying to do is to richen up the bottom end without the top end getting too rich.

In this post we're talking RPM and not throttle openingwhen we talk top end and bottom end. Did you see the pics that PJ posted from that old Suzuki carb manual?
 
teazer said:
Correct about 175/176 fitment - go with 176.

Other way round on flow. 176/270 flows less gas out of the same sized hole as a 159 series because it's flowing air as well as gas. Go for the largest 176 you can get and let's hope and pray that it's big enough to get the job done. The difference is that a 159 flows less at the bottom and more at the top - relatively speaking. Or put the other way, a 159 that works at the top will be too lean at the bottom end on a 4 stroke.

What we're trying to do is to richen up the bottom end without the top end getting too rich.

In this post we're talking RPM and not throttle openingwhen we talk top end and bottom end. Did you see the pics that PJ posted from that old Suzuki carb manual?
Click to expand...
The chart I pull up has 176 running from N-0 thru Q-8. Being a P-4 is 2.670, I'm gonna grab a set of say Q-1(2.705) or Q-2(2.710). Unless you really think I should go up to Q-8(2.740) or Q-8( 2.745)?

Side note, I played with my carbs today. I took a look at me float levels. If, as it states in the VM manual, measurement is from the bottom of the float to the bowl casting seat, then mine were way low. 22-24mm. So, my pilot may have not have been deep enough into the fuel level. Getting more into it tomorrow. But the rain is coming tonight, so I won't be able to test ride it. After adjusting the float levels and replacing the #25 Pilot with a #30 it seemed to idle much better and I was actually able to get her to throttle up. Gonna have to double check my brand new P Cock for flow rate as well.
Anyway, I figure I would get a set of
 
NOPE. Played with bike a bit today. Idles great. But wont rev up. When I put the Starter/Choke Circuits on I can then rev her like a mean B EYE TEE SEE H. Sudco only has a 176 P-8 as the largest. So, what to do. Sudco Rep suggests I go with a 159 P-5, being the largest 176 they have is a P-8 and 176 flow equal to four sizes smaller than the 159s. Wish I could get a 176 Q-0 or 1.
 
Try those 176 P-8s and if necessary go up one size on pilots to cover any "gap" from idle to needle. Sometimes it's necessary to have teh idle richer than perfect so it's OK when you roll the throttle on.
 
teazer said:
Try those 176 P-8s and if necessary go up one size on pilots to cover any "gap" from idle to needle. Sometimes it's necessary to have teh idle richer than perfect so it's OK when you roll the throttle on.
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Thought you'd say that. Wouldn't I achieve that with the 159 P-5? I can always control mid-top with Mains if it get too rich. If the 176 flow like 4 sizes smaller than the 159s then a 176 P-8 would essentially be that 4 sizes from my 159 P-4 I already have, no?
 
Cool reference page. Holler if anyone sees incorrect info on it.
http://kawtriple.com/mraxl/carb/mikunineedle.html
 
you can try to get the 159s to work my juggling air jets and main jet. The difference between B and P nozzles is droplet size and how well it burns plus the fuel slope is different. Try say a 1mm air jet and that should richen up WOT at high revs versus a 2.0 air jet.

Air jets change the way that the main jet delivers fuel over the rev range. So at WOT at low revs, air jet makes small differences, but at high revs the extra air makes a bigger difference.

Lean off idle is either pilot too lean or cutaway too large or needle/jet combo too small.

You could also look for a needle with smaller root diameter and the same or larger tip diameter. That will change the way it operates over the throttle range.
 
Quick update. After consulting with an old time vintage racer, he gave(sold) me a different Jet Needle. If I remember correctly it's a 6F5. I went there for a 176 Q-0 or if need be a 159 P-5 but he had difficulty finding the 176 he had in his hand when we talked on the phone the day before. He's got a race coming up at Willow Springs in a month and has 10 bikes(engine builds on 4) to prep for his crew, so he's a bit busy. But he pulled out the 6F5 needle and an old Mikuni book chart. The needle I had was a 6DP17, on the leaner side. I headed home after pickin his brain and drooling over his Triumph Bonnie racer with a frame that is one of three ever made in a canceled bike built with Benelli and Montgomery Wards back in the day.
Anyway, I got home and put in the other needles and new plugs. And she has woke up boys!!!! I'm on the last bottom clip slot for the needle, so may move to a P-5 NJ. I took her for a run and she is screaming. I think I'm a bit rich on the pilots with the #30s, so back to the #25s. She's pretty strong off the line but could be a tiny bit better on low RPMs.
Wooohooooo. I'm excited.
FYI, Gary Swan, my old racer connect didn't agree with the 159s are for 2 strokes theory. He says he barely ever uses Bleed style NJs.
So, right now this is what I am set up with.
Needle Jet 159 P-4
Needle 6F5
Main 180
Pilot #30
Slide 2.5

May change just a bit.
 
I hear that all the time and he's right that if it runs, so what (up to a point).

In reality a 159 series is very hard to get right across the whole rev/throttle range and leaves a lot of unburned fuel in the exhaust. For most racers the bottom end is not relevant, and as long as it doesn't completely bog, racers often don't care about a smooth power curve with perfect carburation. Ask him what the unburned HC and CO numbers were like across the throttle and RPM range on the dyno. For a street bike it's more important to get the midrange and bottom end right because that's where you spend 99% of the time. On a race bike, not so much. We leave the line at 9000 or more and never see less than 6000 on the tacho on a 11,000 rpm bike but I like to have crisp clean pick up out of corners.

Bottom line: If it works for you, that's great.
 
Yep, I don't remember how long ago I posted the mods were for street and not race.
159 tubes deliver fuel 'faster' when throttle is yanked open but suck (pun intended) if your trying to ride at a fixed throttle
They actually are an advantage when you 'over carb' an engine as the lower velocity airflow allows them to work pretty much as they would on a twostroke.
As Teazer points out, race bikes are just about always at top half or more of rev range
 
I agree with you guys. I went there with the intent of buying a set of 176 Q-0s. Not sure what happened,
but he handed me what turned out to be 176 Os(not Q). I didn't look at them until I almost got home. I mark it up to low lighting in his backyard garage, his eyes, as well as me trusting him and not looking at the numbers. He was more insistent on the 6F5 needles could be more effective and I wouldn't have to start all over with matching up the 176 NJs with Pilot and mains., for now.
I'm still interested in the 176s and as you explained, the finer vaporizing of the fuel for more efficiency, visavis, better mpg and cleaner exhaust system.
But for now I got her screaming down the road. Time to collect some bugs in the teeth.

Thank you guys for every moment you sat down and typed out your valued input!!! ;D
I wish there was an inexpensive bike dyno near me......
 
Yep EGA on dyno would save a lot of time and give a much better idea of where the issues are
I haven't had access to one for a few years now, which kinda sucks ;)
 
It's not as if we are on the dyno every year let alone every week, but with a new (to us) bike, it's a good investment.
 
Hey all. Been a bit. Thank you again for all your help on the carbs.
I wanted to pass on this photo and info that I figured out for all CJ360T owners looking to
get rid of that ugly and overly massive stock silencer that Honda must've pulled from the Goldwing
piles.
I found this 2009 CRF 450F silencer to quite literally bolt right on. It curves perfectly down and around the swing arm and frame to meet right up with the stock collector. All I needed to do was remove the graphite sleeve gasket and then slide it on. As you can see, I made a support bar off the frame shock mount. All those that have not cut off their passenger foot peg frame loops, you can make your support bars off there instead.
I'll shorten mine up about 2-3" by cutting back on the stock collector outlet and possibly shortening the CRF connector pipe as well. Can't shorten too far due to the kick start. I
AND IT SOUNDS AWESOME. Quiet on bottom but has a great slightly muffled scream Low-Mid to top end. I'll try and post some video later. It gives very little back pressure and the little 360 engine seems to love it.
Go the little girl screaming up to 85-90 mph under redline quiet easily while there.. Stock sprockets and wheels.

This is a great simple fix for all CJ360 owners.

IMAG1642-1-1.jpg
 
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