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Discussion Starter #1
I have a 1979 Motoski Mirage 300. I use it for ice fishing and, as I live on Lake Erie in Ohio, so I don't use it much. We currently have ice! I took the sled for a test ride, and it ran great. I pulled the plugs, because I didn't remember how long they had been in there and it has always run rich. The plugs were wet and black, so I changed them out and turned the air screw out an eighth of a turn. I rode it out on the lake for about tree and a half miles in a single file group. Just before we stopped, it started to bog down until I was almost at full throttle to keep up. We rode out slow, so I was at around a quarter throttle the whole trip. I figured that the low speed had caused the plugs to foul, so I pulled them. The PTO side looked wet fouled, but the MAG side was dry fouled (first time for that). I assume it was from the additional air. I rode in by myself, so I kept the throttle at or above half. It was fine on the way in, and the plugs looked better, but still had carbon deposits on the electrodes (wet on the PTO, and dry on the MAG). The insulators were tan to brown. I guess, more air wasn't the answer, so what is? The compression is 125 PTO and 124 MAG. Other than that eighth turn on the air screw, everything else is set to specs on the carb. The only thing that I know I can change is a smaller main jet, but from what I understand, that is only used above three quarter throttle. It does smoke alot at idle. Can you get smaller pilot jets for these Mikuni carbs? Or could it be that my float height is off? I would appreciate some advice. Thanks
 

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Discussion Starter #7
I removed the carb, took off the bowl, turned it upside down, and blew through the fuel line. I could hear a little air passing the valve. I had rebuilt it with an aftermarket kit. I can already see a ring on the needle. The original looks better. I’m cleaning it up, and putting the original back in.
 

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Hole in fuel pump diaphragm will suck gas through impulse line and richen up mixture.
Common in old Mikuni fuel pumps, just had to rebuild the pumps in my Manta.
 

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Discussion Starter #9
That did it! It runs better than ever. The plugs look great. Unbelievably quiet,too! Thanks for the suggestions.
 

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Discussion Starter #13
Yeah, it’s awesome! I’ve been struggling with this for years. I picked the sled up about eight years ago. I probably rebuild the carb right after I resurrect it. I don’t think that aftermarket seat and needle ever was right, by the way it’s running now.
 

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Wow so sorry I didn't know I was so contagious!
Unfortunately that is how most of us Old Guys learned all this stuff, the hard expensive way!
 

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I have a 1979 Motoski Mirage 300. I use it for ice fishing and, as I live on Lake Erie in Ohio, so I don't use it much. We currently have ice! I took the sled for a test ride, and it ran great. I pulled the plugs, because I didn't remember how long they had been in there and it has always run rich. The plugs were wet and black, so I changed them out and turned the air screw out an eighth of a turn. I rode it out on the lake for about tree and a half miles in a single file group. Just before we stopped, it started to bog down until I was almost at full throttle to keep up. We rode out slow, so I was at around a quarter throttle the whole trip. I figured that the low speed had caused the plugs to foul, so I pulled them. The PTO side looked wet fouled, but the MAG side was dry fouled (first time for that). I assume it was from the additional air. I rode in by myself, so I kept the throttle at or above half. It was fine on the way in, and the plugs looked better, but still had carbon deposits on the electrodes (wet on the PTO, and dry on the MAG). The insulators were tan to brown. I guess, more air wasn't the answer, so what is? The compression is 125 PTO and 124 MAG. Other than that eighth turn on the air screw, everything else is set to specs on the carb. The only thing that I know I can change is a smaller main jet, but from what I understand, that is only used above three quarter throttle. It does smoke alot at idle. Can you get smaller pilot jets for these Mikuni carbs? Or could it be that my float height is off? I would appreciate some advice. Thanks

Try isopropanol dry gas first
 

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Discussion Starter #17
I’m curious, are you saying that moisture in the tank can cause the plugs to foul?
 
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