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 23hp gator tail mikuni jetting help 
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Post 23hp gator tail mikuni jetting help
As stated I have a 23 hp gator tail with a mikuni carb, mild cam, exhaust, and the heads have been cleaned a little. Nothing big. The motor was running rich as hell with a #30 pilot jet and a #330 main jet. With some coaching from from folks on here I think I have the idle and top end acting right. I now have a #20 pilot jet and a #200 main jet installed. My problem now is mid range. The carb has a 159q-2 needle jet in it now. No matter where I put the clip on the needle, the engine bogs when I stab the throttle. If I ease into it it will pick up and run on out to WOT but when I left off it throws a puff of black smoke and backfires. I’m assuming the needle jet may be too large? An help is appreciated

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'98 1648 Xpress
'08 23 hp Gator-Tail


Sat Aug 29, 2020 8:35 pm
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Post Re: 23hp gator tail mikuni jetting help
It’ll be very tough if not impossible to get rid of the bog when you smash the throttle. You really need a pumper carb like the TM33 to be able to do that. Just get used to rolling on the throttle. Once you get past about 1/8th you can get on it with out the bog.

I personally wouldn’t start messing with needle jets quite yet. I’d start out finding someone with a wideband O2 sensor and making sure your jets are right. You may still be off a bit.

Other items I would check while troubleshooting are valve lash and do a leakdown test to see if you’re leaking past your valve seats.


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Sun Aug 30, 2020 12:04 pm
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Post Re: 23hp gator tail mikuni jetting help
Update.

I went and ran the boat today. I ended back up with the jets that were in the carb when I bought the motor. 30 pilot jet and a 330 main jet. I think I must have had a piece of trash in the carb that was causing it to run rich and I finally got it cleaned out. That being said the motor is running great but I still can’t get the boat up on plane without working my ass off. I had my wife and four year old with me and they sat toward the front along with my k2 cooler which I strapped to the bow to help keep it down. Once I finally got it planed off I was only able to get 20mph @ 4000rpms out of it. I was doing much better with a stock kit motor I had before. Could it be the prop being too large??


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'98 1648 Xpress
'08 23 hp Gator-Tail


Sun Aug 30, 2020 6:50 pm
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Joined: Tue Jun 05, 2018 3:25 pm
Posts: 69
Post Re: 23hp gator tail mikuni jetting help
What are you using to determine the correct jetting? A 130 jump in jet size is huge. You should be seeing darastic changes between the two.

Different boats are picky about load distribution. Sometime you can have too much weight forward and the motor has to work it’s ass off to get on plane. May need to shift some weight back to get the nose on top of the water. My GD rig, I have to trim up pretty substantially and slowly lower back into the water as I’m accelerating to hop up quickly.

To me the prop cup looks good. Maybe someone can give you the measurements off a new one to see if you are missing blade width or diameter. Any idea what pitch that prop is? Knowing the pitch, gear ratio, you can use a prop slip calculator to see what you should be running speed wise. To me 20mph at 4K seems a little low. If so, it’s likely due to prop wear and not engine issues.


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Mon Aug 31, 2020 4:27 pm
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Post Re: 23hp gator tail mikuni jetting help

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'98 1648 Xpress
'08 23 hp Gator-Tail


Mon Aug 31, 2020 7:09 pm
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Joined: Sun Jul 12, 2020 6:50 pm
Posts: 20
Post Re: 23hp gator tail mikuni jetting help
I’ve been doing a lot of research. My next check is valve lash and push rods. I didn’t even think about that but a bent pushrod could be causing the loss of power too. Thoughts?

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'98 1648 Xpress
'08 23 hp Gator-Tail


Tue Sep 01, 2020 7:47 pm
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