28mm mikuni

Is a 28mm mikuni carb to big for this head?
JRPW Attack Series Level 10 cylinder head package. 32mm intake valve, 28mm exhaust. Fully machined in house. Ported and polished, includes our Signature 3 angle valve job. Assembled with dual valve springs, HD retainers and keepers, it ready to bolt on, add rocker arms and go.
 
You gotta turn a lot of rpms for this carb to not be too big and unless you are seriously racing that thing hard I'm gonna say yeah it's a bit big. You will lose a lot of low end throttle response.
 
You gotta turn a lot of rpms for this carb to not be too big and unless you are seriously racing that thing hard I'm gonna say yeah it's a bit big. You will lose a lot of low end throttle response.
I've got a .310 cam capable of 9000 rpm, I turned 7461 sat night. I did notice coming out of 2 and 4 it bogged down but picked up at end of straight, also engine cut off on me when I floored it for green flag. Would a 22mm chikuni work better?
 
First of all is this a racing kart or a minibike/yard kart application?
Race kart.
What cc engine is it on?
Predator 212cc non hemi with this head.
JRPW Attack Series Level 10 cylinder head package. 32mm intake valve, 28mm exhaust. Fully machined in house. Ported and polished, includes our Signature 3 angle valve job. Assembled with dual valve springs, HD retainers and keepers, its ready to bolt on, add rocker arms and go. Don't know spring #
 
Bottom of head
 

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I've got a .310 cam capable of 9000 rpm, I turned 7461 sat night. I did notice coming out of 2 and 4 it bogged down but picked up at end of straight, also engine cut off on me when I floored it for green flag. Would a 22mm chikuni work better?
Ok
Obviously, some things can be done to improve performance.

If bogging off corner, and below target rpm, change gearing. With the numbers, and bogging off corner, my reccomendation would be to drop a tooth or two on driver, if possible.

If you think you are 9000 rpm capable with your setup, why are you at 7500?
Now, matched components can bring usable rpm down, with over rev still available to those numbers.

As previously stated, smaller carb can help off corner performance, and still have over rev, with less on top.

Where are you getting beat?
I'm betting off the corner.
Tune to help your deficiencies. For engine, and kart.
The rest will take care of itself.
 
Ok
Obviously, some things can be done to improve performance.

If bogging off corner, and below target rpm, change gearing. With the numbers, and bogging off corner, my reccomendation would be to drop a tooth or two on driver, if possible.

If you think you are 9000 rpm capable with your setup, why are you at 7500?
Now, matched components can bring usable rpm down, with over rev still available to those numbers.

As previously stated, smaller carb can help off corner performance, and still have over rev, with less on top.

Where are you getting beat?
I'm betting off the corner.
Tune to help your deficiencies. For engine, and kart.
The rest will take care of itself.
To piggyback off 95 Shaw you can also tune the carb. Move the needle and change jets. Definitely change gear and get the rpm up. Bogging off the corner I’d say you’re a bit rich. A 22mm might suit you a little better.

are You running a billet rod and flat piston? What flywheel? What coil? A lot of things in play here
 
My only experience with the 28 Mikuni is on an open animal I have. We run on small or smallish tracks around here and my animal is sluggish coming out of the corners. Runs like crazy after it gets wound up but the corners here are not fast. So theres that. On my Chinese open motors I run 390 alky carbs and they are great on these tracks, but they aren't 28mm.
 
My only experience with the 28 Mikuni is on an open animal I have. We run on small or smallish tracks around here and my animal is sluggish coming out of the corners. Runs like crazy after it gets wound up but the corners here are not fast. So theres that. On my Chinese open motors I run 390 alky carbs and they are great on these tracks, but they aren't 28mm.
My next suggestion was a 390 alky. Lol
 
Is a 28mm mikuni carb to big for this head?
JRPW Attack Series Level 10 cylinder head package. 32mm intake valve, 28mm exhaust. Fully machined in house. Ported and polished, includes our Signature 3 angle valve job. Assembled with dual valve springs, HD retainers and keepers, it ready to bolt on, add rocker arms and go.
A 28mm carb on that head should work just fine if it is jetted properly, you just want to keep the carb mm no larger than the intake valve.
 
A 28mm carb on that head should work just fine if it is jetted properly, you just want to keep the carb mm no larger than the intake valve.
I think that's my issue.
Ok
Obviously, some things can be done to improve performance.

If bogging off corner, and below target rpm, change gearing. With the numbers, and bogging off corner, my reccomendation would be to drop a tooth or two on driver, if possible.

If you think you are 9000 rpm capable with your setup, why are you at 7500?
Now, matched components can bring usable rpm down, with over rev still available to those numbers.

As previously stated, smaller carb can help off corner performance, and still have over rev, with less on top.

Where are you getting beat?
I'm betting off the corner.
Tune to help your deficiencies. For engine, and kart.
The rest will take care of itself.
Bogging off the corner as in its starving for fuel, I can go to a 12/65 and get more from the motor
 
To piggyback off 95 Shaw you can also tune the carb. Move the needle and change jets. Definitely change gear and get the rpm up. Bogging off the corner I’d say you’re a bit rich. A 22mm might suit you a little better.

are You running a billet rod and flat piston? What flywheel? What coil? A lot of things in play here
Arc ultra light billet flywheel, weston piston with an arc billet rod and side plate, a high output coil from jrpwracing.net and I'm sorry it's a vm22 26mm that I just ordered so here is to that. I just took off a stock appearing .690 bore carb and she ran like a champ.
 
Usually I'm the guy saying everyone's trying to run too big of carb, but I can't see where a 28mm carb is going to be too big for that cylinder head. I don't know what Jimmy's done to the runner, but the IN valve size is fine for that carb. Would a 22 throttle better? Sure, but it won't make the power, especially on top where your cam and the rest of your build wants you to run (9000.)

Just gear the thing where it should be and I think you'll like it a lot better.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Usually I'm the guy saying everyone's trying to run too big of carb, but I can't see where a 28mm carb is going to be too big for that cylinder head. I don't know what Jimmy's done to the runner, but the IN valve size is fine for that carb. Would a 22 throttle better? Sure, but it won't make the power, especially on top where your cam and the rest of your build wants you to run (9000.)

Just gear the thing where it should be and I think you'll like it a lot better.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
I think it's getting to much fuel and choking itself out, still need to tweak the carb a little, I wish I had a dedicated on hand mechanic or someone close buy who could help with hands on. I mean I can mess around with it some more. South Carolina.
 
I think it's getting to much fuel and choking itself out, still need to tweak the carb a little, I wish I had a dedicated on hand mechanic or someone close buy who could help with hands on. I mean I can mess around with it some more. South Carolina.
Move the clip on the needle to lean it out a bit. You can also adjust the air fuel screw. YouTube has several videos on adjusting slide carbs.
 
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