Yeah, I hope to have it running by this weekend. If all goes well, it should be nearly 100% bolt on. I'm ok with the coke not being up top also.

 

That choke cable design was asking for problems from the very beginning. Water gets into the cable the dashboard, and runs downhill directly into the carb. Here's a photo of my stock YFM ...



Sorry for the crappy pic. It's hard to get an auto-focus pocket camera to get a good shot, but the inner sealing surfaces of the Enrichment Circuit Plunger (choke) are terribly pitted, allowing lots of gas to get by the o-rings and make the bike run very rich.

 

The carb design is just fine, but mine had been neglected to the point of failure. If yours has good sealing surfaces and isn't all pitted, new soft parts and a good cleaning should be all you need.

 

Finding some of the OEM parts were less than fun. It was cheaper for me to replace the entire Carb. then buy all new OEM parts to "rebuilt" it. Also mine, I assume is in a similar shape to what Stretch's was.

 

So I installed the VM20-273 Carb. yesterday on my 1988 Yamaha Moto 4 YFM 225u. I had to modify the top throttle cable retainer on the top of the new carb. I removed the adjustable brass screw from the top of the carb. and drilled out the treads to match the stock hole in the stock throttle cable holder on the top of the carb. This is located under the blade nipple in the picture below. I reused the entire stock throttle cable and factory mount and e-clip. After I drilled the hole larger everything snapped in like stock. If you have a streched out throttle cable you'll have to buy a new one since my newish one I barely had enough adjustment at the thumb to remove the slack in the cable. I am positive if you had an old cable you wouldn't be able to remove all the slack in the cable.


I also removed the factory coke assemlby completely since the new carb has it on the side.



I needed new hardware to bolt the carb to the stock flange. I had some M6 x 1mm x 40mm ARP hardware laying around so I used that. Bolted on great. 35mm long bolts might be a little short. The M6 hardware fit great. I centered the flanges and bolted it together.



I forgot to write down the jetting, but it is slightly rich at idle with the factory carb settings. I'll update this when I find the paperwork. The jets are off-the-shelf mikuni jets.

Cold start was fine in 30F weather. The YFM225 moto 4 has a lot more low end power, and much better throttle response. It doesn't have great high RPM pull though. I think this matches the 225cc engine a lot better, and turns my IPT mud lites A LOT BETTER.


I hope that helps everyone. I was going to get pictures, but was in a hurry to eat dinner before the wife beat me. lol

 

Great work!

 

-md- enforcer, i ordered the same carb you did for a moto4 225.
Do you know what jets you ended up using? Thanks in advance.

 

After ordering the same carb as -md- enforcer, i installed it yesterday.

The carb bolts right up fine, but the o-ring on the carb which will connect to the boot to the engine, that boot is larger than the oring so it won't seal as well as it should. At work my dad was able to make a bracket that was put between the boot and the carb, which allowed the o-ring to seal properly.

The throttle cable also needs to have as much slack removed from it as you can, as this new carb will give you more slack than the stock moto4 carb.

The carb is great and performs just as -md- enforcer said. Leaving the stock jets in the carb, the moto4 225 might be slightly rich, but it should be fine for normal use. Overall the vm20 carb that -md- enforcer and I used is a great choice for the moto4 225.

 

I have just found this forum and am having a similar issue. I have recently bought a Yamaha 85 Moto4 YFM200NS. It didn't have a carb on it when I bought it, as well as some other parts. I bought a chinese knock off Mikuni to put on it from ebay, it was a VM22 26mm. I am a diesel mechanic and don't know a lot about ATV's, so please bear with me.

I had to do the bolt hole mod, to make it bolt up. The choke is a lever on the side on the carb, like others had said. It starts easily most of the time, and runs. I have driven it short distances with no issues. Today I rode to my father in laws place, a few blocks away, and when I got there it stalled when I put it in neutral and let it idle. Would not restart. I am thinking the coil gets hot and opens, losing spark. After I loaded it in the truck and brought it back home, it fired right up. But it will idle good for 30 seconds to a minute, then stall. It's getting fuel to the carb, I have a clear hose on it and a full tank of fresh fuel. Carb is new. Putting the choke on increases the idle by quite a bit, but doesn't choke it out the way I would expect, even on a warm engine. Opening the choke it will idle down and sound fine, but will slowly lose RPM and stall, even if I bump up the base idle. Then it's really hard to get started again unless I let it sit for a few minutes. Am I dealing with a fuel issue? Guys in the previous posts mentioned VM20 and VM24, and mainly VM26 carbs. Did I get one that can't feed my engine? Can I rejet the thing and get it to work? I'm not sure where the adjustment screws are, other than the idle speed adjustment, I did change that a few times. Is there only an idle mixture adjustment? And where would I find that?

Thanks for any help anyone can offer.

 

First off, make sure the valves are in spec. Even a perfectly tuned carb won't run right if the valves are all wonky.

If the valves are just slightly too tight, the engine will start okay, but as the valve stems get hot and elongate, the clearance becomes less and less until the valves don't close properly and start dumping compression. Once the engine cools and the valves shrink a thousandth or two, they'll seal back up. Honda XR's and similar 4-strokes are notorious for this... if you have a hot-start problem, adjust the valves.

Valve clearance for my '86 225 is:

Intake: .002 - .004 inches
Exhaust: .004 - .006 inches

Your '85 200 may be similar.

Let us know how it turns out.