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Author Topic: vm28 vs vm30 on cl360  (Read 1081 times)

Offline hillset

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vm28 vs vm30 on cl360
« on: Jan 15, 2018, 13:29:56 »
Hi Everyone- I have a 74 cl360 (stock engine) that is currently using mikuni vm32 carbs (PO put them on).  When I first bought the bike I had it tuned on a dyno and it ran ok, but the PO had open ended exhausts and I recently put reverse cone mufflers on, which changed the carb dynamics.  Since I put the mufflers on, I've never been able to dial in the jetting on the vm32s properly.  The best I've been able to do is get the bike to idle ok and run pretty well in the right temp / humidity, but its always finicky and never idles/runs smoothly. 

In the back of my mind I always knew I'd need to downsize the carbs (everything I've read says vm32's are way too big for a stock 360 engine), and I'm in the process of planning how I'd like to do this.  After reading alot on DTT and other forums, I've basically come up with two options that I'd like some advice on if anyone can help.

1 - vm28 roundslides - https://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetors-mikuni-28mm-001-022.html 

Upsides
-Easier to tune
-Better size for a ~28-30 bhp cb360 per the mikuni manual (see image) 

Downsides
-For me the main downside is that it there aren't alot of comments on base jet settings on the forums (there are way more comments on vm30s), and I'd basically have to source all of the parts myself (ie intake boots, air filter, throttle) vs ordering a "complete kit".  This isn't necessarily a huge problem if I can make sure I get the correct parts before ordering.  I was also planning on ordering several sizes of jets so I could try to

The vm28s from DCC come with the following
Main 200
Pilot 60
Needle jet 169 N8
Needle ???
Air jet 30
Valve 2.5

Per this post: http://www.dotheton.com/forum/index.php?topic=62687.0 , raptormeat is running the following settings for a vm28 on a cb360 (at almost 7000ft elevation):
Main 180 (but suggested going to 200 if you aren't at his elevation)
Pilot 30
Needle jet 175 P2
Needle 5DP7 2nd notch down
Valve 2.5
1.6mm adjustable air jets

Based on these, I was thinking of starting with something like a 200 main and 25 pilot.  Once I get those dialed in I can start working on the needle jet and needle.

2 - vm30 roundslides - https://www.dimecitycycles.com/the-coveted-mikuni-vm30-carburetor-complete-kit-for-honda-cb-cl-350-360s.html

Upsides
-Way more comments on the forums about other users' jet settings, so hopefully I have more information to dial in the jetting if I'm struggling.
-Complete kit, so I know I won't have to confirm the intake size, boot size, etc. 
-Also comes with several sizes of main and pilot jets.

Downsides
-Slightly oversized for a cb360 (but from what I read they can still be jetted to work properly)
-Maybe not enough of a downsize from the current vm32's (if I'm struggling to get vm32's to work properly, is dropping to vm30's really going to make that big of a difference??)

I'm also planning on ordering several sizes of main and pilot jets to get myself close to dialed in when I order the carbs.  I was wondering if anyone has feedback on the following jet sizes to get close to dialed in?

Pilot Jets - 25, 22.5, 20 (I already have 50, 45, 40, 35, 30 from previous attempts with my vm32's)
Main Jets - 220, 200, 190, 180, 170, 160

So basically, I have a few main questions for anyone that can help:

1.  Would you recommend getting:
vm28
+ 25, 22.5, 20 pilot jets
+ 220, 200, 190, 180, 170, 160 mains

or getting the vm30 kit? 

Would you recommend getting any other sized jets to start with?

2.  Will this K&N filter fit the vm28 (RU-2690) - https://www.knfilters.com/search/product.aspx?prod=ru-2690

3.  Will this "Mikuni specific carb boot" fit the vm28 and fit the intake port of the cb360 - https://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-intake-parts-honda-cb-350-mikuni-rubber-carb-boot-002-053.html

-Also, will that boot need to be modified to fit the cb360 bolts since it is designed for a cb350.

4.  Is there a suggested 2 into 1 throttle for the vm28 (or is there a better one for the vm30 since I've read some negative reviews).  Would it be possible to re-use the throttle I'm currently using for the vm32's and just attach that to the vm28's or vm30's?

5.  Does anyone have a good basic starting point for getting the vm28's running?  Of note, I am currently at sea level in an area that is typically very humid.

Thanks to everyone for reading this long post, and for any feedback you can help with.  I really appreciate it.

Offline irk miller

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Re: vm28 vs vm30 on cl360
« Reply #1 on: Jan 15, 2018, 18:22:45 »
Mine is bored to 378 and I'm running VM28's with Uni filters.  I would go with the 28, not the 30.  The boots Common Motor sells works with the VM28 carbs, which I think are stock boots.  Plus, you'll get better torque from the 28.  Also, Needle jet 169 N8 is a primary style needle jet for 2 strokes.  The needle jet Raptormeat is running is what you should have.

Offline hillset

  • Posts: 64
Re: vm28 vs vm30 on cl360
« Reply #2 on: Jan 15, 2018, 18:42:03 »
Irk, as always thank you so much for the advice.

Do you think the jets I was planning on ordering should get me in the ballpark (my 360 is stock, not bored)?

Any reason to go with uni filters over k&n?  I've read a few threads on here about the uni vs k&n debate but it seems to me the only real difference is uni's need to be oiled regularly vs k&n's don't, but I could be totally off on that.

Also, any thoughts on speedmotoco's vm28 kit? https://www.speedmotoco.com/vm28-mikuni-complete-carb-kit-carburetor-CB350-CB3-p/vm28.wot.htm 

I've been looking at it, but I've heard speedmotoco jets the carbs very rich.

Offline irk miller

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Re: vm28 vs vm30 on cl360
« Reply #3 on: Jan 15, 2018, 19:05:31 »
My understanding with any of the kits, you'll still need to re-jet unless you're lucky with the stock jetting. Like I mentioned in the comment, the needle jet at least needs to be swapped out.  CrazyPJ probably has the best numbers, but I think the numbers you're getting from the Raptormeat thread , plus your own list, should get you sorted.  Cxman (Murrays Carbs) builds certain model kits that Speedmotoco sells, iirc, so he may be a guy to know what their standard jetting is on other kits.  I did like you and started out with VM32 and came back to 28 on my 378. 

Offline hillset

  • Posts: 64
Re: vm28 vs vm30 on cl360
« Reply #4 on: Jan 15, 2018, 19:21:49 »
That sounds good irk.  I was planning on re-jetting even if I got a kit since I've heard they can be off, I just thought it would be convenient to have the boots and 2-in-1 throttle all together in a kit and know they fit when I order. 

Any advice for getting in touch with cxman?  Is he active on DTT or should I just send a message through murrayscarbs.com?

Also, what is the difference between the 159 and 175 needles?  It looks like DCC has P-2 needles for sale (https://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetors-mikuni-vm30-p-2-needle-jet-003-209.html),

but they are 159 series (their website says the 159 series works with vm30s). 

From jetsrus, it looks like the 159 series is 48.5mm and the 175 series is 39mm long, is one specific for the vm28 and the other specific for the vm30?

Offline irk miller

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Re: vm28 vs vm30 on cl360
« Reply #5 on: Jan 15, 2018, 19:27:45 »
Cxman is pretty active here.  You could pm him too.  I would imagine he could do a kit for you too.  I get what Jets R Us lists for the carbs.  I'm not totally keen on the differences.  Also of note, I think you'll want a 2.5 cutaway on the slide.  At least that was what is recommended for mine. 

Offline hillset

  • Posts: 64
Re: vm28 vs vm30 on cl360
« Reply #6 on: Jan 15, 2018, 19:29:53 »
That sounds great, I'll send cxman a pm on here and if I don't hear back from him I'll just send an email through his website.  Thanks for all of the help Irk, i really appreciate it.

Offline crazypj

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Re: vm28 vs vm30 on cl360
« Reply #7 on: May 12, 2018, 16:33:53 »
According to Mikuni chart you posted, 22mm to 26mm would be more than enough for 189cc / 18HP per cyl.That's actually my experience as well, 26mm are more difficult to fit but work well.
Use Needles and emulsion tubes for  aircooled Yamaha RD350 or RD400
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CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline cxman

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Re: vm28 vs vm30 on cl360
« Reply #8 on: May 13, 2018, 10:56:55 »
i run baby 28s (small form factor) mikunis on mine and on my sl350 hauls ass using uni foam 2 stage filters


1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

Offline teazer

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Re: vm28 vs vm30 on cl360
« Reply #9 on: May 13, 2018, 11:46:21 »
Just to add another data point to the thread, SL350 used to have 24mm Keihin carbs which are slightly smaller. I would think that 26 or 28 would be fine. We run a pair of VM26s on a Cb160 (240cc) race bike and they work well and a pair of 26mm Keihins on a 180cc CB160 racer and both run cleanly.

#159 needle jet fits larger body 34mm carbs and is for 2 strokes.
#175 is stock in an RD400 and fits smaller body 26/28mm carbs and is a Bleed (4 stroke) style. That's what you will probably end up using. Different years of RD400 use P-2 or O-8 size.  Either should be OK to start. I suspect that an RD400 needle (5J6) might be rich at 3/4 throttle, but worth a try. RD350 needles (5I4) are slightly leaner towards the top end and might be better.