Tillotson 212 - Mikuni 22 mm or 24 mm Carb?

Looking for some advice/recommendations on Mikuni carbs on the following. Building a Tillotson 212 engine to use on a Trailmaster mini bike. Engine has governor removed, CS grind .265 lift cam, billet flywheel w/8 degrees advance, ARC rod, 26# valve springs, 27mm intake and 24mm exhaust valves, .010 head gasket and stock Tillotson carb running an upgraded jet and air filter. I want to move to a Mikuni carb. Trying to decide between the 22 mm and 24 mm carbs. I've done quite a bit of research. Not a lot of information out there on the Mikuni 24 mm carbs that I’ve found. I see lots of information on Mikuni 22 mm carbs improving overall performance on clone 212 engines. Anybody have any results with the Mikuni 24 mm carbs on a clone 212 engine? My concern is that the Mikuni 24 mm may be too much carb for my build. Thanks in advance for any and all information.


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22mm should be ideal for your heavy bike and engine build. I run this type of clone/mikuni on my bikes and works good with the high idle choke setup too. once you get it dialed in, the choke will work good.
just like ond said earlier. start with a 130 jet maybe lower?and a 17.5 pilot

couple other things you also could do to help the mike perform better. install a larger rear sprocket and if you can fit the bike with a torque converter(with higher stall springs) and the rear driven with a 7inch pulley or if it's a clutch only setup you will have to rear gear the jackshaft and also run a higher stall spring in the clutch. all this will allow the bike to rev up quicker and move the bike faster. without those to thing done it may take you some distance to make the bike move out quickly...…...
Thanks for the replies and information. I really appreciate it. A little background on this project. Bought the Trailmaster MB200-2 and it came with a torque converter, jackshaft (10 tooth chain gear), 38 tooth rear sprocket and 196cc clone engine. I did a lot of research and spoke to several sellers before buying. Actual performance of the mini bike and estimate from research were very different! Top speed stock with throttle stop screw removed was 22 MPH on GPS and you couldn't even start on a slight grade. Bike weighs 165 lbs. and the heaviest rider, me, weighs 175 lbs. Not much fun for us to ride. Went with the Tillotson 212 which is supposed to be 10 hp. That upgrade produced 30 MPH on GPS. Added a Stage 1 (carb jet, header & air cleaner) that produced 34 MPH on GPS. Removed the governor for testing purpose, that produced the same 34 MPH on GPS. But, you got there a lot faster. Actually starting to be fun to ride! Testing with a tachometer while riding, actual top RPM running was 4,200 RPMs. On a stand, rear wheel off the ground, engine would rev easily to 6,200 RPMs. So, I concluded that I have a gearing issue to get where I want to go. My goal is to get this mini bike to top out at approximately 45 MPHs with decent pulling power. Riding range will be between 25 to 35 MPH. As a note, with Tillotson engine, Stage 1 kit and 38 tooth rear sprocket, this setup pulled fine under our current riding conditions. We have access to a couple of miles of groomed trails (20-25 feet wide) with long straightaways and open flat fields.

I currently have 10" of snow on the ground. Before the real snow sets in, I expect to have a couple of days of testing with my new build. Haven't been able to test the built engine yet. Also, have both a 50 tooth and 60 tooth rear sprockets. My initial plan is to start with the 50 tooth rear sprocket and go from there.

The reason that I like the Mikuni carbs is the anticipated overall performance gain throughout the operating range with them over stock jetted carb and smoother throttle response, feel and setup.

Sorry to be so longwinded. Just want to give as much detail as possible to assist others that are contemplating a Trailmaster MB200-2 mini bike purchase or doing a similar engine build.

So, am I heading in the right direction or asking for too much from this build? Thanks again for any and all comments and information.
Look into getting a Mikuni VM22-133, way better than the chikuni 22 and I have had both. With your build I don't see a 24mm doing anything for you and the vm22-133 may be easier to setup, tune and start then a vm24. Most use a pilot in the 15-20 range and main 125-140. 20-135 for me.
I just ordered one. I bought the TCT carb to compare against the stock. I am not a fan of the Mikunis and prefer the stock look. I am also going to try to keep the stock muffler if it fits the frame. If not I am thinking a header with hot dog muffler.
I just ordered one. I bought the TCT carb to compare against the stock. I am not a fan of the Mikunis and prefer the stock look. I am also going to try to keep the stock muffler if it fits the frame. If not I am thinking a header with hot dog muffler.
I'm not a big fan of the Mikuni look either, especially the vent lines that hang below them. My build is all about function and performance. One thing that I really like about the Mikuni carb is the throttle setup and feel after I rode a mini bike with a Mikuni carb. Based on comments/posts from this thread and talking to a guy that has been doing a similar build to mine with a Tillotson 212, I ordered a Mikuni VM22-133 earlier this week. Should be here in a week or so. The guy claimed that the Mikuni really woke up his Tillotson.

Gumpit, what mini bike and engine are you working on? I'll be interested in hearing your comments and feedback on the TCT carb. I got one with my Tillotson 212 but, never used it. Bore seemed to be a little smaller than the stock Tillotson carb, not sure about that?

I too tried to keep my stock exhaust with my build initially. According to the supplier that I bought the Tillotson from, it was supposed to be a lot less restrictive than a stock muffler. When I put a header and RLV muffler on the Tilly engine, it really woke it up.
According to the literature on the Tillotson engine, the TCT is an added option. As an FYI a year of more ago, when the TCT first came out, a member here tried it on his modified Predator. He was not impressed, and noted the smaller venturi.

Also, i am using a Mikuni VM22 on a modified flat head four horsepower Tecumseh. I have also used one on a very modified Briggs. They are easy to tune, but they must be tuned. A lot of guys don't have the will, or the desire to get involved with that. For that reason, you see a few people talking down about them. I love them. Once you get the jetting down, it's a simple matter of setting the needle for fuel flow during transition. Also, I have no lines hanging down. There is one drain line for the bowl over flow that comes into play when I lean the bike on the kick stand with the engine running. (I use a fuel pump) Level, it is adjusted correctly. I am sure you will be happy with the new VM22. For what it's worth, they look much more cool than that Chinese thing surrounded by plastic.

I am with Dave on the cheap Chikuni. I have used them on a lot of mini's from flathead to drag motors and with almost the same jetting, 15 or 17.5 pilot and 125 to 130 main jet. Their oval slide gives a more granular opening of the throttle than the round slide VM24. I have had issues with them on a kart that bounces around my backyard but on the minis they work great. There was one member who contacted me about jets and when we compared carbs his had different style jets so there are apparently a number of different china manufacturers of them and you could wind up with one with different internals, outside they looked identical. If you get carb from Isky he also carries the jets.



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i'm with ole4 and dave on this. if you have mechanical ablitities they are easy to tune. dave quote= A lot of guys don't have the will, or the desire to get involved with that. For that reason, you see a few people talking down about them. I agree 100 percent on that and not to bark down anyone that may of said they are no good. if you are having a problem trying to get one running correct because you don't have the ability ? well just post a thread on it and I or someone will try to help you get it right. if I am correct the last time I check this web site was about helping each other out on a problem like this.
there really isn't no stock clone carb that can out run this mikuni carb.
are we posting pictures of are carb's ...……...well me too:)
I think I had a bad Chikuni. Tried about every air/fuel screw, pilot and main jet combo and it never ran that well. VM22-133 was so much easier.
Great looking mini bikes/engines in the pictures in this thread. I appreciate all the replies and information.

I don't have any experience with Mikuni carbs. I'm not concerned about being able to tune the Mikuni carb. Figure if I need help, I'm confident that I'll be able to get good advice from members on this forum. The primary reason that I wasn't crazy about the look of the Mikuni carbs is the ones that I've seen locally were setup with vent tubes wrapped around them and goofy cheap looking air cleaners on them. If I can make the Mikuni carb look like the above pics, I'm good.
***UPDATE*** Put the mini bike back together w/o the Mikuni for now. I've changed the shocks (that changed the swing arm angle which required shortening the chain), changed the rear sprocket (50 tooth). Wanted to test the engine as a know quantity and then add the Mikuni carb. Test rode the mini bike for a short time yesterday. Better than it was, but not where I want it yet! I am also dealing with a TAV issue. Supplier of the Tillotson engine sent me a new TAV driver setup due to the shorter Tillotson PTO shaft. They also included a longer sized drive belt. Based on 6" driven pulley and driven bolt to driver bolt centerline, belt should be approximately 1/2" smaller then the one the engine supplier sent me that I'm currently using. I have a smaller belt, so I'll be testing that in the future.

Question: Feels like the rear wheel is binding a little. Let off on the gas and don't get much roll. Chain tension is correct. Sprockets in line. Tire pressure ok. Checked the brake caliper. I'm used to working with motorcycles where you put them in neutral and can easily spin the rear wheel a revolution or two. Bike seems to roll ok. With Trailmaster/Baja Warrior, how much should the rear wheel free spin with the chain, disc brake and TAV belt installed? With the mini bike wheels off the ground. Front wheel will spin several revolutions. Using the same spinning force, the rear tire will free spin approximately 1/3 to 1/2 turn. Is that correct? Looking for some advice. Thanks in advance for comments and feedback.