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Carburetor help

8bsimpson5

8bsimpson5

Member
I've got a vm24 on my small block open motor at full throttle it falls on it's face. I have a 155 jet in it. But at 3/4 throttle it screams just when you go wide open it acts like you turned the kill switch to off let off a little and comes back alive. What have I done wrong
 

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Jets too small .
When you let up to 3/4 throttle you reduce the air flow riching the mixture .
Pull up on the choke / enrichment valve at full throttle if it helps then its lean
No doubt .
Fuel flow could be a possibility through the inlet and needle valve .
Another option is the metering needle full open its the narrowest at 3/4 throttle it may be much thicker , thus limiting the fuel . Which would be leaner .
So drop the needle as far as possible . Test . Then pull the choke valve up , one or the other should do it .
 
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Yeah before race day. Then went out for practice and was cutting out so i thought it was lean so moved the Needle on slide all the way down and it made it worse in heat. So moved it back to the top for feature
 
MO Predator Racer said:
Why would it be idle jet he is at full throttle when the issue occurs?
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As I read the article, he's transitioning from three-quarter throttle to fall throttle. There's a short time waiting for the fuel from the high-speed dump. It's probably already a little lean on the low-speed, and the sudden need for extra fuel causes the blog, or hesitation, until the fuel from the high-speed needle gets there. I've experienced the same thing several times.
 
alvin l nunley said:
As I read the article, he's transitioning from three-quarter throttle to fall throttle. There's a short time waiting for the fuel from the high-speed dump. It's probably already a little lean on the low-speed, and the sudden need for extra fuel causes the blog, or hesitation, until the fuel from the high-speed needle gets there. I've experienced the same thing several times.
Click to expand...
Wouldnt you just be on the main jet then?
 
alvin l nunley said:
As I read the article, he's transitioning from three-quarter throttle to fall throttle. There's a short time waiting for the fuel from the high-speed dump. It's probably already a little lean on the low-speed, and the sudden need for extra fuel causes the blog, or hesitation, until the fuel from the high-speed needle gets there. I've experienced the same thing several times.
Click to expand...

Al,

You may want to dig into the VM24 Mikuni a bit. This is not a "weed-eater" carb like on the KT100, or even anything like a Tillotson carb that was used on Italian engines back in the 70's and 80's.

It's a slide carb, typically used on motorcycles, ATVs, etc. It has a float bowl, a pilot jet, main jet, slide and needle - and functions very differently from what I believe you may be using as a "reference point".

PM
 
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