HELP! Minibike Predator 224 Revs high wanting to take off on start and dies when trottle...??

[Mrshopter]

Have you tried turning down the idle even more?

I've tried even turning it out to the point where it was gonna fall out to see what would change. But still not much change

 

[Denny]

Is the spring between the barrel slide and the cap missing? Does the slide go all the way down freely with the idle screw all the way out? Is the mixture screw adjusted properly? Is the throttle cable adjustment too far out of the barrel cap keeping the throttle open? Now we are going to need some pictures. Good close up clear pictures.

 

[Mrshopter]

Is the spring between the barrel slide and the cap missing? Does the slide go all the way down freely with the idle screw all the way out? Is the mixture screw adjusted properly? Is the throttle cable adjustment too far out of the barrel cap keeping the throttle open? Now we are going to need some pictures. Good close up clear pictures.

The spring is there. The slide moves up and all the way down freely. Slide Doesn't get hung up. I've adjusted the mixture screw to 1 / 5 turns put from all the way in adjusted from there when the bike was warm. The trottle cable was properly set in I even took it out to see if it was but same problem occurred. I'll get some pictures out right now I'm not at the bike..
Also the bike stalls off choke

 

[Mrshopter]

Is the spring between the barrel slide and the cap missing? Does the slide go all the way down freely with the idle screw all the way out? Is the mixture screw adjusted properly? Is the throttle cable adjustment too far out of the barrel cap keeping the throttle open? Now we are going to need some pictures. Good close up clear pictures.

What places specifically should I take pictures? I don't want to post wrong pictures that have no involvement in what may be going on.

 

[Denny]

Remove air cleaner picture down the throttle bore at rest and full throttle. Remove barrel and pictures down the bore and of the slide. And overall of the carb installed at rest.

 

[Denny]

Also have you checked the float levels? Just because it is new don’t mean it’s right.

 

[Mrshopter]

Also have you checked the float levels? Just because it is new don’t mean it’s right.

I'll have the pictures to you soon, Also I did check the float levels they where parallel level. But I couldn't find the right measurements online for float height for the VM22 clone mikuni.

 

[Mrshopter]

Remove air cleaner picture down the throttle bore at rest and full throttle. Remove barrel and pictures down the bore and of the slide. And overall of the carb installed at rest.

 

[Denny]

The only thing I can see is the float may be 1/16”-1/8” to high. Where is the spring that goes between the barrel and the cap? Where is the cap?

 

[Mrshopter]

The only thing I can see is the float may be 1/16”-1/8” to high. Where is the spring that goes between the barrel and the cap? Where is the cap?

Ok, also the cap and the spring I didn't take a picture of but I do have both

 

[Mrshopter]

I raised the float to a perfect Parallel still having the same problem.
The engine stalls when I turn off the choke. But lowering the choke slows down the back tire spinning. Just that at a certain point of putting the choke off it starts to stall out.

 

[Karttekk]

Check the troubleshooting section of this guide, maybe there's something in it that could help.

http://www.mikuni.com/pdf/vmmanual.pdf

 

[Karttekk]

Mikuni Carburetor Tuning

There is a large amount of horsepower to be found in a properly tuned carburetor. Unfortunately, there isn't a universal setup that will work with every engine combination. Jetting that works great with one engine may not work so well with another. Armed with an assortment of jets and a free...

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[karl]

I don't think it was asked, what size main jet are you running?

Probably too lean , and running a vm22 on choke will cause the RPM's to go up.
When you take it choke off it leans out and shuts off .

Or it still has a vacuum leak.

Note- when ya buy the cheapest things on amazon/ ebay, you get what you pay for. Ive had good luck
with vm22's purchased from NR racing, or any reputable karting site.

 

[Rat]

VM22 has an air/fuel enrichment screw which is responsible for buffering the idle and up to about 1/8 open throttle... you need to start there.

You want to turn the air/fuel screw all the way in till it bottoms out (soft seat DO NOT CRANK ON IT) and then set the default 2 full turns out BEFORE you start the engine again.
You want the idle screw set to 2-2.5 full turns from lightly bottomed out as well (it will be a way high idle but it's part of the process)

Let it idle or run however good or bad that may be... you absolutely cannot tune the carburetor on a cold engine and expect it to run worth a damn at normal operating temps.

Once heated up you want to listen close to the engine response while turning the screw out 1 full turn at a time... the idle should climb higher (count the turns) you should give 30-45 seconds between rotations for the engine to respond to the adjustment. You are specifically listening for the rpm to no longer respond to the air screw adjustment. Now take the turns out +2 and that will give you a ball park of the appropriate pilot size change (ie 4 turns total jump 2 maybe 3 sizes bigger pilot)

I can tell you by the described symptoms your pilot is in fact too lean currently.

You ALWAYS want to tune the pilot jet first of any other adjustment because a rich pilot can cause your mid and upper throttle ranges to be pig rich, while the main jet is only going to change the mid to WOT range fuel delivery.
An engine won't idle right if the pilot size is wrong and if its far enough off (lean or rich) you can fiddle with the idle screw and air screw for the next 20 years and still never get it right.

The needle clip setting only buffers the middle 1/3 range and should be the absolute last thing fiddled with

Ideally you want to dial it in so your engine runs at an optimum with 2-4 turns out on the idle screw,1.5 to 2.5 out on the air screw, needle varies too much to say but the clip groves are read top to bottom 1-5 or (or 4 or 6 depending on the needle) and the default is #3 on a 5 position needle for a 4 or 6 position needle it's going to be the higher of the middle 2 positions.

The thing about jets is there is no "magic bullet" jet size that works across the board because altitude, seasonal humidity, and seasonal ambient temperatures all play largely into fuel delivery needs. Someone riding at 2000ft or more would need less fuel through the carb than someone riding under 800ft because there's less atmospheric pressure and a little less oxygen ppm than at lower altitudes

 

[karl]

VM22 has an air/fuel enrichment screw which is responsible for buffering the idle and up to about 1/8 open throttle...

To further help others, you are talking about the brass screw underneath the carb, infront on the bowl?
Never had to mess with that, maybe im just lucky.

 

[Rat]

To further help others, you are talking about the brass screw underneath the carb, infront on the bowl?
Never had to mess with that, maybe im just lucky.

Extremely lucky but then again putting a Motorcycle carb on an equipment engine isn't exactly what one might call standard practice.

It also litteraly just occurred to me while typing this specific reply that a VM22 is way too small of a carb for an engine over 198cc ISH. There is a formula to calculate the needed carb size for pretty much any engine.

√(D)×2=X
[D=actual CC displacement not the advertised]
The PWK 24 is slightly too small for my 208.

√(224)×2=29.93 meaning a VM30 should be used on that 224 NOT A VM22

 

[karl]

It also litteraly just occurred to me while typing this specific reply that a VM22 is way too small of a carb for an engine over 198cc ISH.

It all depends, there is a reason the stock 224 does not ship with a huge carb.

But for my hopped up 224 it ran very strong with a big bore gx390 carb.

 

[Rat]

It all depends, there is a reason the stock 224 does not ship with a huge carb.

But for my hopped up 224 it ran very strong with a big bore gx390 carb.

That very well may be, but a larger equipment engine carb is NOT AT ALL the same thing as swapping for a custom intake and a motorcycle carb.
When you swap to a motorcycle carb, the rules change entirely simply by design even though the rules of flow volume and velocity remain a constant without porting the head.

A motorcycle carb (in the OP's case a VM22) flows more freely than any lawn equipment carb ever will and delivers fuel a lot more efficiently as well. Where there's more air flow there must be more fuel, except when you use too small of a carb you end up having to jet leaner than normal to counter act the intake signal being to strong for the carb which inadvertently will cause a given jet size to behave like one much larger. The same rules apply in reverse when a carb is too big, the intake signal will effectively be too weak and larger than normal jets would be required to get the correct fuel to air metering. Out of range too far either direction will be trash for overall performance as a whole.

I'm not interested in an online pissing match, but I've got a lot of years playing with carburetors and carbureted engines of all types and sizes. (except diesel although I fully understand the way they function)

I'm also not quick to back down in a debate when hands on experience has shown me many things including things I'd never have expected... unless you happen have indisputable concrete proof to offer that's not hearsay

 

[Rat]

To further help others, you are talking about the brass screw underneath the carb, infront on the bowl?
Never had to mess with that, maybe im just lucky.

That would be correct.
The particular screw of mention is between the body and Bellmouth, and can be left or right handed, though all adjustments are kept on the same side of any one specific carb body.

EDIT FOR CLARITY: Left or right handed is carb body orientation, not a thread reference