Mikuni VM20 replacement

[Jeffbo1]

Hello, I am new to the forum and am hoping someone can help me with a recommendation for a carburetor to use on my Ace 100 engine...I am building up an Ace 100b+ and I am not sure what dimension or size of carb to use....It appears that original Mikuni VM20 carbs are not to be found in useable condition but there are many clones out there...I just don't know if the mounting flange on these new carbs will match up with my stock manifold.....any suggestions would be much appreciated.....Jeff

[Bruce Young]

Why look for a replacement, why not rebuild what you have with the all new the most extensive carb. kit introduced to date by Hodaka-parts inc, in Missouri. Owner, Terry Larson has been working a year to get this kit into production, testing and now it here, see their site for info on the new product to rebuild your carb., its here and ready to go. Call them for detail, --1--314--313--5635, Bruce Young
"

[Al Harpster]

If you are working with a stock Ace 100 cylinder and stock intake manifold then the only carb that will fit is the VM20.

If you HAVE a VM20, work with that. Some parts are available as mentioned.

If you don't have a VM20 you might find a used one to repair or recondition.

Failing those two options things get pricey.

I would GUESS the least pricey would be to find an Ace two bolt reed manifold assembly. This will allow you to install a modern VM22. The VM22 can be had from various internet sellers for about $70. My personal experience says it's stock jetting is OK for starters. You'll also need a clamp on foam aircleaner, $20.

The reed manifold is going to be tall dollars, if you can find one.

Everybody is going to tell you that you will have to machine boost ports in your cylinder to use the reed valve. You don't.

But to get the performance advantage for the money you'd put into the carb and reed manifold you'll want the boost ports.

One other little bit crazy option would be to buy an intake manifold for an EARLY Super Rat & see if you can modify it to fit a Two bolt Ace cylinder. That manifold would take a VM22. You'd need the plastic heat block too.

This last idea might do the trick. I'd try it, but I own a Mini Mill that I'd rely on for the modification attempt.

Good luck!

[mac]

Just an idea of something that could be made that would enable the use of a modern carb,maybe like a vm22 on the Ace.

This is an adapter that I bought years ago to enable the same thing to be done to my Bultaco. I think it could work,but might not allow room for the stock air cleaner.

[Al Harpster]

I think what's pictured could work for the Ace.

You'd be swapping out a flange mount to a spigot mount.

That's okay. Seems like most modern Mikuni offerings are flange mount anyway.

Yes, the Ace airfilter has to go. But that's just the way it is if you don't have a VM20.

I like this idea.

One might be able to do something like this with standard aluminum flat stock and standard hand tools.

[mac]

There might be a flaw in my idea Al,I haven,t been able to find a spigot mount vm22,only flange mount so I,m not sure if they are available that small.
You could get an OKO in 19 or 22 size from mid Atlantic trials,but those may not be ahrma legal if that’s where you planned on riding.

[viclioce]

If you’re not going to be a stickler for an original Mikuni VM20, someone is selling VM20 duplicates (clones), with a flange mount, on eBay.

Here’s a link to my last search! Victor

https://m.ebay.com/sch/i.html?_sacat=10 ... ikuni+VM20

[Al Harpster]

I believe the "bolt spacing" on this modern VM 20 carb is on the order of 50 millimeters.

If memory serves, bolt spacing on Ace manifold is about 40 millimeters.

And "bolt diameter" on this modern carb may be 8 millimeters. Stock manifold is 6.

Long, long ago Strictly Hodaka had custom manifolds to mount one of these modern VM 20 carbs to an Ace cylinder.
But price was $200 plus as I recall.

[viclioce]

It would seem you could use a drill press to make the gap 40mm. And I think you could taper that down on the flange to 6mm by using a smaller drill bit than 8mm. Seems like that would be pretty easy to remove 5mm off each side. But thats just me, thinking out loud. What do you think Al??? Victor

[mac]

In the photos on line there doesn’t, look like enough room to even get 5mm off each side,but hard to tell without having one in hand. So far,if you have a repairable stock carb,the best option is to get a rebuild kit from Hodaka Parts.
Here his a pic of the new 22mm with the 50mm spacing.

[matt glascock]

Kelly gives an excellent demonstration on carb rebuilding, lapping operations, etc. in one of his Super Rat preservation videos on his Socal channel. Check it out - it's really well done. Unless the internal corrosion is so severe that the internal passageways are destroyed, virtually any carburetor should be considered a candidate for rehabilitation. Especially one as rarefied as a stock VM20.

[mac]

10-4 Matt,excellent video from SoCal and the now offered rebuild kit makes it much more easier to keep the stock 20mm.

[Bruce Young]

Just a quick note on those early carbs, some where made of pot metal and some where almn, the pot metal one eroded very badly inside and out and should be turned into fish weights, the almn ones can be rebuilt with good results, see the Hodaka Club resonator that Ed Chestnut did way back when. Bruce

[Bullfrog]

I don't think I've ever characterized "pot metal" carbs as being fish weight material simply because they were "pot metal". I DID make that sort of claim for the Model 94 "A-type" carb . . . but ONLY for that particular carb.
Ed

[Bruce Young]

Ed, I am sorry, I misspoke, I had read the info you put in the resonator and when I talked to people at Hodaka days, several of the old guys seemed to think that model of carb., and refereed to it as the pot metal model, it seems to be, corrosion seems to be more prevalent, so I miss-spoke of it as the pot metal model. Thanks for the correction, I will change my way of addressing this carb.,in the future , and its issues. Bruce

[Jeffbo1]

Why look for a replacement, why not rebuild what you have with the all new the most extensive carb. kit introduced to date by Hodaka-parts inc, in Missouri. Owner, Terry Larson has been working a year to get this kit into production, testing and now it here, see their site for info on the new product to rebuild your carb., its here and ready to go. Call them for detail, --1--314--313--5635, Bruce Young
"

Thanks for the info but I don't have a carb as yet....I know Terry and he tells me he will have complete rebuilt VM20 Carbs available soon....be assured Im on his list for one.....thanks again!

[scmark]

I have a question regarding the Hodaka Parts, Inc. VM22 kit for the ACE engines. Has anyone specifically measured a VM22 for the mounting hole center to center dimensions? How close is it to the center to center distance for the 94 Wombat VM24 mounting hole dimension? The reason I ask is an ACE I bought last year has a reed kit on it with a 94 Wombat VM24 carb. If it can be worked out I would like to go to the VM22 rather that the VM24.