Walbro PZ vs. Mikuni vs. Tillotson...

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Brettm57

Member
Myself and two others have built limited modified Animals to race on our local sprint/road course. We started out with the stock PZ22 with the alcohol jet kit and they run great that way. But - racers being racers - we want to go faster. We've tried 24mm and 28mm Mikunis in both round slide and flat slide versions, but we can't cure the problem of (apparently) sloshing fuel through the corners, so they sputter and cough through the turns - especially through left-right-left combinations. I've got the Mikunis jetted so they run fine straight ahead - turns cause the problem. We've put Tillotsons on them and they run good with those too. I know most will say "So just run the Tillotsons then". I'm not one to throw in the towel easily, and I want to make a Mikuni work. I don't understand why the PZ works, but the Mikuni doesn't. Internally, they're almost identical. I know there's people out there running Mikunis, so what am I missing?
 
Start by seeing actual running fuel levels.

Put a clear line on the overflow, drain on your pz. Hold the line upright, and open drain valve.
Start engine, and mark running fuel level on carb side.

Do the same for the mikuni.

Does the mikuni have an overflow drain?
 
I will be trying a PZ 26 on alcohol on a Limited Modified set-up so I will be watching this thread. Motorcycles turn in all directions and over much rougher terrain then karts with no adverse effects so it will be interesting to see what your solution will be. Are all of your carbs running alcohol ?
 
There's no reason that you can't make your Mikunis work well, even on rough surfaces and high G corners.
We build them fairly regularly for oval racers and have never had this complaint.
Not sure what's going on without knowing your entire build and set-up, but don't give up on the Mik28 - that's a fantastic carb for what you are doing.


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95 shaw said:
Start by seeing actual running fuel levels.

Put a clear line on the overflow, drain on your pz. Hold the line upright, and open drain valve.
Start engine, and mark running fuel level on carb side.

Do the same for the mikuni.

Does the mikuni have an overflow drain?
Click to expand...
Float level may be too high , causing a rich condition .
 
I found this diagram of the pump-around system used on shifter karts. It's an expensive alternative, but I've seen enough shifter karts run to know it works. Being that this setup cures the problem makes me think the problems I'm having are due to fuel starving in the corners. With this setup the fuel bowl can't possibly go dry as long as the fuel pump keeps up.
 

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Assuming it going dry .
That is a special pump with a return side built in ?
The inlet needle seat are they the same diameter between the pz and mikuni ?
Lack of fuel seems it would show on a long straight run vs a turn .
There were a few conversations about pump around setups in 2cycle or the uas forum.
 
Ha ha yea , obviously . So does the pump have a retun side ?
Answer- yes it has a return pump .
 
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