Best 2 stroke carb? Looking for a push/pull type throttle

[FinnishFish]

This isn't for any particular application, but I'd like to build a dirt flat tracker style bike with something like a banshee motor in it. Ive got an old 2 stroke now, its got a Mikuni VM22, I know its a good carb, but this one likes to get stuck wide open lately. I'd love a push/pull type throttle, so that really can't even be an issue.

I started looking at later model carbs, such as the Mikuni TM style flat slide, and Mikuni did have a push/pull throttle on some of them, but I don't think that was for the 2 stroke variants. I've heard decent things about the TM, and the 2 stroke models are about as simple as the old VM, the one complaint is when compared to a Keihin FCR (obviously on 4 stroke applications) they are not as easy to get parts for. Others I have seen are pretty exotic like off an RZ500 or NSR250.

But I also got to thinking... What about the Keihin FCR? I think you can get them down to 32mm. Probably disable the accelerator pump if applicable. They can probably be jetted for anything under the sun too. I think they would be a bit big for a lot of applications, but high comp/big bores could get away with it. Anything that would stop me from using one? Any other carb that's relatively easy to come by that I missed?

[85RZwade]

OEM RZ350 carbs have a push-pull system, and are basically a VM design. They're not hard to find, either.

[m in sc]

true, and they work well. pain in the ass to tune but good when are dialed in.

if your vm22 is hanging up, either the carb is slap worn out , the cable is fucked or something else.

[FinnishFish]

Oh I see that. I think I looked at them, but didn't notice they were any different. Decent option.

Any thoughts on the FCR though?

if your vm22 is hanging up, either the carb is slap worn out , the cable is fucked or something else.

Well it is 50 years old. Its a bit odd, doesn't get ridden much, just happened out of the blue. I need to blue the slide and see where it is rubbing, may just be able to replace or adjust the aligning peg. Not really worried about that bike though, I was just looking at 2 stroke carbs and wondering why so few were push/pull.

[m in sc]

yeah you should be able to sort it. a good portion of my bikes are that old, and i'm running even smaller carbs on a few, they always need some dressing of the body. (polish the inside where the slide goes)

ive never seen an fcr on a 2 stroke but anything can be made to work I would guess. heck my 2023 honda xr150 is carbureted and it doesn't even have a push pull carb on it (which surprised me, I thought they were mandated at one point?).

another option is an aftermarket 'nibbi' brand carburetor. not push pull but the quality is actually excellent, even though they are dirt, dirt, like suspiciously dirt cheap.  Yes, i have one and  was shocked how good a 40 dollar carb was.

[racerclam]

Question? If you are building a flat tracker why do you want such small 22mm carbs? Anyway a VM round slide is a great choice , when modified wit a  UFO a round slide will out flow a flat slide up to 15/16 throttle. And if its bored out most of the slide eddy will be eliminatd for even better flow, also the air bleed bosses can be stream lined at the opening in the rear. In the end you have a awesome sleeper carb. And I can fabricate venturi divider in either round or flat slide carbs , that make for a much more linear power delivery. You can give me a call if you like and we can talk. Check out my web site 

Richstaylordporting.com

702-858-9177

[FinnishFish]

yeah you should be able to sort it. a good portion of my bikes are that old, and i'm running even smaller carbs on a few, they always need some dressing of the body. (polish the inside where the slide goes)

ive never seen an fcr on a 2 stroke but anything can be made to work I would guess. heck my 2023 honda xr150 is carbureted and it doesn't even have a push pull carb on it (which surprised me, I thought they were mandated at one point?).

another option is an aftermarket 'nibbi' brand carburetor. not push pull but the quality is actually excellent, even though they are dirt, dirt, like suspiciously dirt cheap.  Yes, i have one and  was shocked how good a 40 dollar carb was.

Yeah, I hit it with a scotch brite pad once, its going to need to be cleaned up better than that. I'll save my 40 bucks though unless I screw it up somehow lol.

Ok, idk if I will go the fcr route, I really like them though, just nice to confirm they should work. Ive never seen one used on a 2 stroke either. And yeah, that is really odd, I thought it was mandated too, thats not even a model that was grandfathered into the current year.

Question? If you are building a flat tracker why do you want such small 22mm carbs? Anyway a VM round slide is a great choice , when modified wit a  UFO a round slide will out flow a flat slide up to 15/16 throttle. And if its bored out most of the slide eddy will be eliminatd for even better flow, also the air bleed bosses can be stream lined at the opening in the rear. In the end you have a awesome sleeper carb. And I can fabricate venturi divider in either round or flat slide carbs , that make for a much more linear power delivery. You can give me a call if you like and we can talk. Check out my web site 

Richstaylordporting.com

702-858-9177

Oh I'm not building one with a 22mm carb. That is what is on my TS185. At the smallest itd be what comes stock on a banshee. The smallest fcr Id use is a 32mm, but that'd probably be down to availability/appropriate size. I'm definitely not looking for tons of power, I'm sure it will have plenty on tap. If I were to get rz350 carbs I might look into modding them to get them dialed in better, but the fcr is probably flexible enough as it is. I'm actually looking into putting some round slides on my car, I might actually call you up about that instead lol.

[racerclam]

What care are you thinking of putting round slides on? Back in the 1970s I thought about putting eight 44mm on a small block chevy. Never did it though , I just stuck with a tunnel ram and two 600cfm hollys. The Mikuni's would work better than four webers since each carb could be calibrated for each cylinder rather than done in pairs by changing air bleeds to meet each cylinders needs . Plus a manifold with a plenum works better anyway , with a broader power band.

Rich

[FinnishFish]

It is an 87 Honda Accord, 2.0l. Ive got the carbs and can just as easily mount these as I could make a manifold for DCOEs. I believe they are Mikuni VM29s, push/pull round slides. I have it written down in a notebook, so I am not 100% sure, just going off this jetsrus page https://jetsrus.com/carburetor/carb_mikuni_VM29_carb_exploded_view_parts.html Kind of funny, its a very similar carb to what I was just asking about, just made for a 4 cylinder 4 stroke.

[LMS]

What care are you thinking of putting round slides on? Back in the 1970s I thought about putting eight 44mm on a small block chevy. Never did it though , I just stuck with a tunnel ram and two 600cfm hollys. The Mikuni's would work better than four webers since each carb could be calibrated for each cylinder rather than done in pairs by changing air bleeds to meet each cylinders needs . Plus a manifold with a plenum works better anyway , with a broader power band.

Rich

Reminds me of when I had a modified Datsun 510 with dual side drafts. Thought that was the ticket! Looked amazing, sounded amazing. I then had to get it smogged, found a stock manifold and carb. Put that on to pass visual, f-ing car ran so much better and faster. Sold that other crap.

[FinnishFish]

Heh, I am pretty pleased with my stock carb. Some non adjustable Keihin feedback carb that I devacuumed and converted to a manual secondary. Keeps me in the STS autocross class with your average modified NA Miata and runs right along with them. Only thing keeping me from slapping the bike carbs on, along with the suspension upgrades needed to handle the speed, is it will bump me up to SMF, which also includes new Civic Type Rs. The carbs will easily bump it up to around 180hp with a lot of low end and the top end being limited to how much rpm it can take without causing piston slap. Either way, its not something you would even expect to be quick.