How can I adapt these Fake Mikuni VM30's to my CB360 manifold?

[ejb]

Howdy,

I just bought a couple VM30's from here: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&vxp=mtr&item=230745564338
Hell of a deal. Although, I've heard that there are quite a few knock-offs, so maybe that's what I got.

Anyway, I quickly discovered that the flange holes on the carbs don't align with the holes on the engine. And the stock carb adapter boots can't fit the flange in any way.

You can see from the pictures that the carb holes are about 48mm center-to-center and the stock carb boot is about 62mm center-to-center.
Does anyone know if there are adapters out there? Or maybe you have a cleaver idea about how to make one. Unfortunately, I don't have much in the way of machining tools (yet!) so I can't whip an adapter up myself.

Also, if anyone knows if these are knock-off Mikuni's please let me know.

Once, I get them adapted I'll start the tuning process. The main jet is 100. Pilot is 20. I'll be running short-ish pipes with mufflers. And either stacks or uni's. Will those jets get me in the ballpark?

Thanks

 

[cleoncleon]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

You'll want something similar to these:
http://www.britcycle.com/Products/651/651_30.htm

Basically some sort of Flange to Spigot Adapter.
But yes they are 'Knock's.' VM30's don't have a flange mount.
I think all VM's bigger than 24mm can only be spigot, from Mikuni.

 

[ejb]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

You'll want something similar to these:
http://www.britcycle.com/Products/651/651_30.htm

Basically some sort of Flange to Spigot Adapter.
But yes they are 'Knock's.' VM30's don't have a flange mount.
I think all VM's bigger than 24mm can only be spigot, from Mikuni.

Damn, I was afraid that they were knock-offs. Seems like they're going to be trouble from the get go... I can't find any adapters for the carb bolt hole lengths. Looks like I'll have to get something fabbed. Is there any harm in getting an aluminum flange-to-flange adapter so long as there are gaskets or o-rings in each side to give a good seal? That would eliminate the stock boot entirely.

 

[Sonreir]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Definitely not VM30s. They might not even be VMs? That looks like a butterfly valve in the first pic and VMs are slide carbs. I'd try to get your money back on those, man.

 

[ejb]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Definitely not VM30s. They might not even be VMs? That looks like a butterfly valve in the first pic and VMs are slide carbs. I'd try to get your money back on those, man.

That's the choke valve on the other end. Check out the pics on the ebay listing. Do legit VMs not have that? Thinking I will return these... d'oh.

 

[Sonreir]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Not on the VM30s they don't. I can't vouch for other sizes and styles though. Also, I think those are 26mm anyway, not 30mm? At least they look to be stamped with a 26 in the eBay photos.

 

[ejb]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Not on the VM30s they don't. I can't vouch for other sizes and styles though. Also, I think those are 26mm anyway, not 30mm? At least they look to be stamped with a 26 in the eBay photos.

They are indeed stamped with a "26" but I just measured the inside diameter on the engine side and it's 30mm.

 

[ejb]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

I'm going to see if I can get something fabbed up to make these work. I'm thinking that a flange-to-spigot adapter like the one cleon linked to would work. I could get it made out of aluminum instead of rubber and it would look just like the engine side of the stock carbs and fit into the stock boot. The other option would be to ditch the stock boot all-together and make a flange-to-flange adapter with an o-ring/gasket groove on each end.
Like I said, I don't have much in the way of fabbing skills or tools but maybe someone else would like to get their hands dirty with this project? If these carbs end up working well it could be a cheap alternative to, well... real VMs. Any takers?

I think I'm opening a huge can of worms here but... regarding the length of the intake tract (from the engine side of the carb to the engine ports)... for starters I'll try to match the length of the stock setup but I've heard that a longer intake tract can improve performance. Can anyone comment on this?

Thanks for the help.

 

[teazer]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Those carbs appear to be copies of a Keihin carb with Mikuni on the outside to avoid copyright problems from either company. They are 26mm with oval bores.

The bad news is that they are not VM Mikunis. The good news is that they are probably a nice size for a street motor. Be careful with jets. You will have to work out what jets they are and where to get them. They may be kehin style jets or Mikuni - you will need to check the jets to be sure.

 

[ejb]

Re: How can I adapt these Mikuni VM30's to my CB360 manifold?

Thanks teazer. How do you know that they're 26mm Keihins? Are you going off the 26 that's stamped on them or do you know which Keihin they're ripping off?

I've attached some more pics for reference. I think the jets are the Keihin type. They look almost identical to my stock carb jets.
First pic has jet sizes / any numbers I found on parts... hopefully I can make sense of this and find a source for these jets if I end up needed them.

 

[teazer]

I can't swear to what model they are copied from or modified from - there are too many OEM styles. I suspect taht they were made to fit a particular Honda copy and were then modified by th emanufacturers to avoid patent laws and as a result they may well be hard to get jets for.

I'd start by calling the number in their advert to see what, if anything, they have available.

or try to match them to these http://www.pjmotorsports.com/keihin-jets.html or here http://www.sudco.com/keihinjets.html

 

[ejb]

They're mikuni. The main is a N100.604 and the pilot is a VM28/486. See http://www.pjmotorsports.com/mikuni-jets.html

Also these carbs seem to be called the "PZ30" among the Chinese cloned carburetor world. I miraculously found an intake manifold for the bike that the were possibly intended for here: http://www.highrpmracer.com/intake-manifolds-intake-manifold-07-for-chinese-200cc-atvs-and-dirt-bikes-p-9627.html and here http://www.motopartsmax.com/index.php/main_page/product_info/products_id/753. The latter has better measurements

Hooray for the chinese motorsports blackmarket. Will report back if I order anything.

 

[crazypj]

They are modified Kei-Hin with Mikuni logo
Kei-Hin jets have a different thread pitch to Mikuni jets, when you know what you have jetting is pretty simple
second link isn't coming up for me?
I made adapters to convert to spigot, no way I could make them that cheap though
3" dia 6061 machined down takes a bunch of time

 

[ejb]

They are modified Kei-Hin with Mikuni logo
Kei-Hin jets have a different thread pitch to Mikuni jets, when you know what you have jetting is pretty simple
second link isn't coming up for me?
I made adapters to convert to spigot, no way I could make them that cheap though
3" dia 6061 machined down takes a bunch of time

I tried a Kei-hin 100 main in them and the thread pitch was definitely off. Found someone on another forum vouching for the two Mikuni jets I mentioned above. They're a dead-on visual match and the measurements match.

Here's another chinese parts site with an even cheaper price on that same manifold: http://ezatvparts.com/store/index.php?dispatch=products.view&product_id=1136

As for making a spigot adapter, could you get away with threading a pipe with a 30mm ID into an aluminum plate that would be the flange. Then it would be a matter of drilling the 2 bolt and center holes in the plate, tapping the center hole, and maybe lathing the groove into the pipe that would lock the carbs into the boots. IDK if that would actually be any easier and less time consuming / expensive.

 

[crazypj]

As for making a spigot adapter, could you get away with threading a pipe with a 30mm ID into an aluminum plate that would be the flange. Then it would be a matter of drilling the 2 bolt and center holes in the plate, tapping the center hole, and maybe lathing the groove into the pipe that would lock the carbs into the boots. IDK if that would actually be any easier and less time consuming / expensive.

I doubt it would be easier, it would use a lot less material though
I just designed a two piece clamp on with 'O' ring. (in my head ;D )
I'll do a sketch before I forget

 

[teazer]

Even better if they take Mikuni large hex main jets. That would make things much simpler.

I have seen poeple slot the mounting holes to allow them to fit on something like a CB200, but you need two flanges. If one of those chinese manifolds works, go for it. It will have to be mounted at teh right angle though.

 

[ejb]

It will have to be mounted at teh right angle though.

Yeah... I'm a little worried about that. The manifolds/adapters I'm eyeing appear to have an odd angle to them.

 

[ejb]

Any luck with that sketch / idea, PJ?

I'm thinking that I'll buy ~30mm ID aluminum and some aluminum plates and get a manifold welded up. Unfortunately, an aluminum pipe with a 30mm inside diameter is a hard thing to locate. It's in between NPS 1 and 1.25. Anyone know where I can find some?

 

[crazypj]

I have a sketch, haven't tried making anything though.
Similar to the way the exhaust pipe clamp fits on pipe, only all alloy, tighter tolerance and an 'O' ring to prevent leaks

 

[teazer]

Grab a slab of aluminum and turn part of it down to fit in the stock rubber mount and make a flange out of the rest to bolt the carb to.

Sort of like these.

Think of the carb side as if it were a flat plate (for the carb) with a tube sticking out to go into the stock mount.

just like these posted by some PJ guy ;-)