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Discussion Starter #1 (Edited)
Purchased a 1986 JS440 Last week. The seller started the ski on the trailer for only a few seconds. I drug it home. Compression is in the 120's and evrything looks intact. Took it to the lake. Starts fine, Revs up fine but only for a few seconds. Then dies under throttle. I can restart it each time but, it will only run if I have it full throttle. (It sputters and barely runs when doing this) If I let it set 10 minutes it will do the same thing.

I don't have a manual yet, but it looks as though the Ski is unmolested by it's previous owner. Hoses are good and appears to be in good shape.....

Here is what I have found so far. The Tank Relief Valve doesn't hold pressure and allows suction and pressure through in both directions. Could this be my problem. I'm under the impression that this valve is what pressurizes the tank and pushes fuel through the system. If I'm wrong please tell me.

BTW, I am unable to find a replacement before the weekend and have thought about using a windshield washer valve to substitute til the new one gets here. Is there any other temp fixes or ideas.

If there is something I'm missing, please advise.

I live in Wichita KS. Motorcycle Enthusiast, 2 kids. I have a Polaris SL780 for the kids to ride. The JS is for me to play.

Vesparider is in reference to my 2004 Moto Guzzi V11 Rossa Sport. Vespa=WASP. Guzzi was purchased by Piaggio that also owns Vespa..
The italians get it, some don't.

Thanks,
Richard Zimmerman
 

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Check your inner and outer exhaust boots.

Also confirm your jet settings are correct, highs and lows

Also check your carb diaphrams.
 

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Discussion Starter #3
Check your inner and outer exhaust boots.

Also confirm your jet settings are correct, highs and lows

Also check your carb diaphrams.
Thank You. Any online resources for the jet settings? manual won't be here til next week.

Richard Z.
 

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Just checked my manual for you. 86 440 low speed= 1 turn out. High speed= 5/8 turn out. The carb should be a Mikuni BN38. The low speed screw is located low on the left side of the carb, and the high speed high on the right.
 

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Discussion Starter #5 (Edited)
Just checked my manual for you. 86 440 low speed= 1 turn out. High speed= 5/8 turn out. The carb should be a Mikuni BN38. The low speed screw is located low on the left side of the carb, and the high speed high on the right.
Spent the day on the Lake today... The carb screws were a bit off and the Fuel Pressure relief Valve must have been an issue... I temp swap a GM Evaporative valve and the ski would maintain power. The screw adjustment made the ski really come to life.... Now, I really hurt. Every muscle on my body is sore and I can't remove the grin on my face....

Richard Z.
 

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Glad to hear I could be of assistance. I know what you mean by the grin. Got out last week for the first time this season. Can't wait till the next chance to go splashing.
 

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Discussion Starter #7
Glad to hear I could be of assistance. I know what you mean by the grin. Got out last week for the first time this season. Can't wait till the next chance to go splashing.
I did have another issue just before we left the lake. I'm working on it now.. The ski ran out of gas on the kid and now it will not restart. The tank is full and there is SPARK (ask me how I know). Just no fuel to carburetor. I'm not familiar with the hose routing with the reserve/on switch. I guessing I have some sort of issue with the switch or a leaking hose. The carb just won't prime... My manual will be here tomorrow, that should help me greatly.

Going back to lake tomorrow after work and will be working on it.

Richard Z.
 

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I have had many 2 stroke boats, motorcycles and pwc's. I have never run my engines dry because you're running the engine without oil. Some people seem to get away with it, the only time I ran out of gas, the engine seized.
 

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I have never had a problem with running a 2-stroke out of gas. I do it every time I ride my dirtbike. At the end of each ride I turn off the fuel petcock and let the motor run the fuel out of the carb. If you run it out of oil then you have a serious repair bill!

Vespa did you try priming the carb by putting fuel into the throttle body. That will fire the engine for sure, and possibly be enough to draw the fuel through the lines and to the carb. Remember that is a long was to pull fuel on a diaphram fuel pump with the lines full of air.
 

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Discussion Starter #10
I have had many 2 stroke boats, motorcycles and pwc's. I have never run my engines dry because you're running the engine without oil. Some people seem to get away with it, the only time I ran out of gas, the engine seized.
The boy was out on it when it happened. The engine cranks fine and priming the carb gets it to start but wont stay running. I was on the lake at the time and it was attached to the bouy, so I didn't get to work on it while being washed away with boat wakes (in the NO Wake area). Been busy at work and will get out today to work on it.

Thanks for the tips...

Richard Z.
 

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Discussion Starter #11
Got some time today to see what the problem was. Duh. Carb mounting bolts had backed off. Found some narrow nuts and doubled them up on the studs. That should hold them.... Went through the entire engine area and double checked bolts screws etc for tightness. Rode all day.... Damn I'm tired...

Richard Z.
 
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