Mikuni selection advice

[Sirxloin]

Hey guys,
I am looking for some advice from the pros.
I have a brand new Predator 212 motor that I put the OldMiniBikes Warehouse Ultimate Hemi performance kit in. It came with Valves, springs, rod, piston, cam, flywheel.. ECT.

I am using the stock car jetted up a size. I am thinking about a new carb and need some help on which diameter to use. I know bigger is not always better.

Also I have a question on intakes It looks like the curved would be better on a bike, but is the longer runner better/worse for performance

The bike is an El Tiger with a Comet TAV2 and a 75 rear sprocket.

Thanks!!

 

[osu1978]

I run the Mikuni VM22-133 and it should be plenty carb for your build. Would not go any bigger. Throttle modulation is great on the Mikuni.

Are you talking about intake manifold or the actual intake filter?

 

[Sirxloin]

Im talking about the manifold.

 

[delray]

22mm mikuni/clone carb will be you best choice. for your jetting? your cam,valve size ,porting,etc…. and other things too that can affect your jetting. most builds like yours will be in the 120-130 jetting. for your intake, keep it short and straight if possible.

 

[ole4]

^^ what Delray said was good advice.

 

[massacre]

Usually long runners are designed to promote low end torque, and short runners are designed to promote high end horsepower. On a single cylinder minibike engine, it might not be as significant is it would be on other bigger engine applications tho

 

[ole4]

Usually long runners are designed to promote low end torque, and short runners are designed to promote high end horsepower. On a single cylinder minibike engine, it might not be as significant is it would be on other bigger engine applications tho

This is true but the lengths and benefits/drawbacks are rarely understood. For our little motors depending on cam timing a typical length (by Sr) is 11 inches for. 7000 rpm peak. At 3500 rpm the turning will cause intake reversion and the air fuel will blowback out the carb as a cloud of fuel and air and then be sucked in again picking up more fuel and causing a over rich condition. So it is for a narrow range that it picks up power but causes issues at other speeds. For drag racing where revs stay above the untuned range it’s worth the increase in the engines VE. But for a fun to drive mini not so much.

 

[DaddyJohn]

Simple curved intake manifolds (maybe "angled" is a better descriptor) for Mikuni don't seem to add much length over a straight one.

I think maybe you're looking for an "inverted intake"? They're available to buy, but I don't have any info on how well they work.

I'll admit, getting the carb/filter out of harm's way is pretty appealing. That said, it looks like you can't use the stock fuel tank with this set-up.

 

[ole4]

The blue one is off ebay and the slightly longer one from GPS. The rubber spigot would be taken off to use the chikuni which is the carb in the picture. Here is a link to the blue style.
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=163306489135
You have to make sure that the carb sticking straight out is ok for your frame and that your leg does not hit it. On a lot of mine I make a curved manifold but there are some of those on ebay made for clones.

 

[Strigoi]

Simple curved intake manifolds (maybe "angled" is a better descriptor) for Mikuni don't seem to add much length over a straight one.

I think maybe you're looking for an "inverted intake"? They're available to buy, but I don't have any info on how well they work.

I'll admit, getting the carb/filter out of harm's way is pretty appealing. That said, it looks like you can't use the stock fuel tank with this set-up.

I've been curious to try one of those. It would work with the tank I have, but I would have to run a fuel pump (which I have on a shelf) for it to get fuel. I really like how they look and how the carb is up and out of the way. Just not a fan of how much the intake cost. I'm sure a buddy of mine that can fab stuff could make one for much cheaper.

It's one of those "maybe" things that I'll end up randomly buying out of curiosity. In the limited searching I've done it looks like there aren't many people running them. I haven't really seen anything posted about them on here, other forums or youtube.

 

[DaddyJohn]

I've been curious to try one of those. It would work with the tank I have, but I would have to run a fuel pump (which I have on a shelf) for it to get fuel. I really like how they look and how the carb is up and out of the way. Just not a fan of how much the intake cost. I'm sure a buddy of mine that can fab stuff could make one for much cheaper.

It's one of those "maybe" things that I'll end up randomly buying out of curiosity. In the limited searching I've done it looks like there aren't many people running them. I haven't really seen anything posted about them on here, other forums or youtube.

I’m pretty much right there with you on all points. I might try fabbing one myself someday, but have about a million other things to get to first!

 

[Bow]

I've been curious to try one of those. It would work with the tank I have, but I would have to run a fuel pump (which I have on a shelf) for it to get fuel. I really like how they look and how the carb is up and out of the way. Just not a fan of how much the intake cost. I'm sure a buddy of mine that can fab stuff could make one for much cheaper.

It's one of those "maybe" things that I'll end up randomly buying out of curiosity. In the limited searching I've done it looks like there aren't many people running them. I haven't really seen anything posted about them on here, other forums or youtube.

I run one of those "Inverted" intakes on my Cyclekart. I've had no issues in the 2 years of running it on my 212 Hemi with a Mikuni VM-22... HOWEVER... they DO NOT clear the fan shroud as advertised... I had to make a 3/8" thick aluminum spacer to fit between the head and the intake to space the intake/carb out enough to clear the shroud