.650 stock carb, gx390 carb, mikuni?

[taotao110d]

Hey everyone, I am looking for some info, opinions, suggestions on carburetors for my Predator 212 hemi. It is on my old kart that pretends its a race kart. Right now it just has airfilter/adapter, header, jet/e-tube basic external bolt ons. It soon will be getting an arc billet rod/flywheel, gov delete, valve springs etc and most likely a CS grind .265 lift cam. And lately have been thinking about carburetor options for when the extra compression and lift come into play.

I could keep using my stock pred 212 carb and re-jet (both cheap and easy)

I could get a .615-.650 bored clone carburetor (still pretty darn cheap and easy, and a little more airflow that I want)

I could use a stock gx390 carburetor I have laying around (which I imagine will flow more air that a 196-212 stock carb. But I don't know what is needed to run a 390 carb on a 196-212 clone)

I could get a Mikuni carburetor as I like the mikuni slide carbs on dirtbikes/atvs. But it seems to be the most expensive option for my yard kart.

Would a .650 bored stock carb be what I want for my 212 hemi with CS grind cam?

Would a gx390 stock carb work well for me?

I'm sure I can make the mikuni run great with my setup, but is it overkill for my setup?

Discuss and enlighten me on these carbs please

 

[Davis]

The 650 bore would work good but a mikuni 22 would be ideal.

 

[San Diego]

The 650 bore would work good but a mikuni 22 would be ideal.

+1. That cam will benefit from either carb.

A lot of people have problems using the GX390 carb on gas, works best on alcohol or other fuels.

 

[fhpe77]

taotao110d, I'm in the same boat. The engine is going together nicely, flywheel, rod, cam, etc. The bottom end is back together. Getting the head milled this weekend..hopefully. I have the same question. Which carb? A clone/honda carb would certainly be easy but I'm thinking going for a Japan spec Mikuni VM22-133. My reasoning is that the stock style carburetor was designed for stationary equipment with two speeds, low and full. For a vehicle like a minibike it's what's in between that counts. A motorcycle style carburetor makes sense if you are looking for smooth response.

 

[TheDullCarbide]

The 390 carb will be too expensive to adapt to gas compared to the other options. The Mikuni offers simple and flexible tuning in basically all throttle ranges. The 650 SA carb will be a cheaper option and have more of a "sleeper" look I guess, but you loose some ability to tune the midrange mixture. If you're just running tracks where the throttle is ON/OFF, the 650 SA will be fine. Other than that, I say Mikuni.

 

[taotao110d]

Is there a specific bored/blueprinted carb you would recommend? It would be nice to find a bored Keihin instead of a cheap chinese copy if possible.

Do you think it would be beneficial to go larger than .650 bore stock carb? I think I saw a .675 but I think it said alky only, but not sure.

 

[TheDullCarbide]

What rpms do you want to run? Do you need any low-end?

I personally would trust a Ru*ing carb looked over by NR. They can polish a turd pretty well. Now the genuine vs clone VM22 is a whole different story. NR doesn't detail their clone VM22, they just sell them, so you're relying on that shitty Chinese quality control.

 

[taotao110d]

I plan on running up to about 7k rpm with a .265 lift CS grind cam. And I would love some lowend. I am not looking for the highest peak hp number.. I am looking for a nice fat power band. Preferably with more power than I am making now from 3-7k rpm.

 

[TheDullCarbide]

I plan on running up to about 7k rpm with a .265 lift CS grind cam. And I would love some lowend. I am not looking for the highest peak hp number.. I am looking for a nice fat power band. Preferably with more power than I am making now from 3-7k rpm.

You want the 650 carb. You loose low-end the bigger you go.

 

[DeadPixel]

My vote is the 22mm Mikuni knock off. It might still need tuned but its more designed for what your going to be using it for. The 22 will make more power than the .650 and have better throttle response.

 

[DeadPixel]

The only thing better about the .650 is its super easy and quick to tune and its a lot cheaper.

 

[Moto Walt]

If you know how to make a 390 carb work, do it. No issues with my or any of my peoples 390 carbs on gasoline. Need any tips pm me.

 

[taotao110d]

I think I'm going to go with a .650 bored blueprinted stock carb. If I ever feel the need to swap out the .265 lift cs cam for something bigger, I will likely step up to the 22 mikuni.
Thanks a lot everyone!

 

[TheDullCarbide]

Don't go with the cheap Mikuni. If you're going to get one, make it a real one. The knockoffs have a bad reputation for crib deaths. +1 on a 650 SA carb, Chinese or Jap.

 

[taotao110d]

I also have a few, good keihin pz20 dirtbike/atv/pitbike carbs laying around, but don't know if it would be an upgrade over even the stock carb. Or a downgrade...

 

[taotao110d]

Anyone know if a pz20 carb would be even a small upgrade over a bone stock clone/predator 212 carb?

I feel like stock and .650 bored are smaller than 20mm (my metric conversion sucks lol)

Anyone know where to get an intake manifold/adapter to bolt my pz20 I have layhing around to my predator 212? Or would not be worth it (pz20 carb is free and just taking up space)

 

[osu1978]

Get the real mikuni. Easier to tune then the chikuni and way better throttle feel compared to the .650.

 

[DeadPixel]

You might be able to use a 22mm mikuni intake. I think the mikuni has a 48mm bolt pattern and the 20pz has a 47 at least that's what google says lol. I would oblong your bolt holes on the carb and try it.

 

[taotao110d]

The pz20 carb is a 2 bolt flange. It looks very similar to the mikuni 22. Also a slide carb.

I'm just starting the mikuni is overkill (both $ and size) for my build. The 212 will be built around the .265 lift CS grind cam. If I ever decide to step up to a larger cam, I will swap to a mikuni.

But I have a few pz20 round slide carbs laying around, and seeing how similar it is to the mikuni everyone uses (just a tad smaller diameter, yet I think bigger than stock and .650 bored stock carbs) I figure it might be better than all honda gx/clone carbs, and possibly better sized for my build with the CS grind cam in mind.

But I'm not sure how to bolt it to my head. Unless I could use the clone/mikuni adapter intake manifold.

The keihin pz20 round slide carb just seems like a 20mm mikuni, which might be better suited for my build than the 22mm mikuni

 

[DeadPixel]

There only about $15 and I have a mikuni intake. I will order one tonight and see if it fits easy on my intake. I also want to see if it works better than stock. I am building my motor for torque.