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Discussion Starter · #1 ·
I've been futzing with my 380f since I got it. I start it in the garage and it runs great. I get it on the ice and it bogs and craps out for a good 20 min before running better. Well this past weekend I was up on Nippissing and they were doing Speed Runs. I stopped and talked to a few of the guys and asked why they were warming up their new sleds?? Boy did I get strange look. They told me when the weather is so cold, -45 that day, you have to let the two strokes warm up for a good 20 to 30 minutes!!! Holy crap! I never figured that out!!! Well the rest of the weekend I let the 380f warm up a good 25 min and it ran great!!! Hit the track they plowed the day after the event and got it up to 110 kph!!!! I'm never touching those Carbs again!!!! Except to clean of course.
 

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I don't know about 25-30 mins but I let my sled warm up for a good 15 mins, and use a sled jack to spin the track and get it loosened up before I ride. Then once I do get on it I go easy for about 5 mins
 

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X2, 20+ minutes sounds like a bit much, you will start to foul plugs if you let it idle too long. Warm it up till the heat exchangers are warm on liguid cooled and probably 10-15 on a fanner.
 

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20-30 minutes is a bit excessive. If it runs bad still after 10 minutes of warm up and you have to choke it more your pilot jets might need to be cleaned out or install bigger ones don't forget to use some sea foam or some type of 2 stroke approved fuel de-ice in fuel to keep the carbs from icing up ect... I warm my liquid up for about 10 minutes and on a bumper stand slowly for to let the belt warm up ect..
 

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Fan cooled motors get warm pretty quick. Probably 10 minutes is more than enough. Liquid cooled sleds take longer simple because you have to heat up the liquid to running temp as well. I know it sounds strange to warm up the coolant, but you really do want it at operating temp.

Another reason Racers tend to warm up their sleds a lot is because they may be using race pistons. If I recall this correctly, the forged Wiseco pistons heat up quicker than the cylinders so a typical warm up procedure is to let it warm up for about 5-10 minutes and then shut it off for 10 minutes, then start it again for another 10 minutes. The idea is to get them all warmed up about the same rate.

Plus, if you're going from cold to wide open throttle, that has to be hard on the motor. If you let your 380fan warm up 5 minutes and then take it easy for the first mile or so, you should be fine.
 

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Like others have said I warm it up until the heat exchanger is warm. Not hot. Failing to warm your sled up can cause a cold sieze. That where the piston expands faster than the cylinder. Combustion temps are around 1200° to 1400° coming out of the cylinders so warming up the engine is crucial.
 

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One other thing about the racers letting it warm up is hot expansion chamber is a hp maker a cold one is not

Sent from my HTC One S
 

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A liquid cooled sled needs to be cleaned out on a warm up stand. They will puddle fuel and start to bog down and drop idle rpm. That why you want to get it of the "choke" as soon as it will stay running. Dumping a lot of fuel into a cold pipe will foul plugs. When clearing the engine out slowly raise the rpm until the clutch grabs and roll over the track for a little while then let it all coast to a stop and do it again. Like others have said to if you jump on a cold sled and hammer it you will swell up the Pistons and cold seize the motor. It's called a 4 point seize and when you see it that makes perfect sense. The piston on either side of the wrist pin will grow the fastest and grab the cylinder wall. The engine loading up during warm up varies by temp as well. A carb sled jetted for -20 is going to be pig rich trying to ride on a 45 degree day.
 

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Discussion Starter · #9 ·
I've tried running it after only a 10 to 15 min warm up now and it still bogs on me. I start it with the choke on and when the sound changes I turn off the choke and let it idle for another 10 min or so and it runs great. I've upgraded the pilots to 42.5 from the stock 40 and it still does the same thing. I haven't noticed any plug fouling as I pull them after every trip and look to make sure i'm not running lean. On another note though what is the purpose of the Air Box? Does that serve to warm up the incoming air in any way?
 

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Nope. Sleds don't have air filters. It's there to give the engine outside air and to keep belt dust and debris out of the engine. Also reduces noise.
 

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I've tried running it after only a 10 to 15 min warm up now and it still bogs on me. I start it with the choke on and when the sound changes I turn off the choke and let it idle for another 10 min or so and it runs great. I've upgraded the pilots to 42.5 from the stock 40 and it still does the same thing. I haven't noticed any plug fouling as I pull them after every trip and look to make sure i'm not running lean. On another note though what is the purpose of the Air Box? Does that serve to warm up the incoming air in any way?
Your carbs are dirty. You might have gotten the jets clean but the passages are still gunked up. I have a 99 formula with a 500 fan that I inherited after sitting for 5 years. After cleaning the carbs the first time it would idle but horribly and I ended up leaning the air screws to 1.5 turns just to get it to stay running. It wouldn't come off idle without choke. Anytime it needs choke to come off idle the idle circuit is plugged somewhere in the carb body. Strip the carbs down, give them a 1/2 hour bath in chem-dip followed by a hot water rinse and then blow them out with compressed air. There are ports in the main carb throat on the engine side of the slide that are part of the idle circuit. If they are gunked up it will do exactly what you described. That engine should be able to come up of idle after starting it with no choke and lightly feathering/increasing the throttle.
 

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Discussion Starter · #12 ·
I have cleaned these carbs so many times now I can do it blindfolded. The last time was two weeks ago. I stripped them completely and soaked them over night in a can of carb cleaner and then blew them out with air. Sleds always done this from day one.
 

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Fan cooled motors get warm pretty quick. Probably 10 minutes is more than enough. If you let your 380fan warm up 5 minutes and then take it easy for the first mile or so, you should be fine.
I do the same on my 550 F - 10 minutes warm up and then going easy for the 1st km.

Take your glove off and put it over the fan exhaust air port and you'll feel when the motor is warm enough to go.
 
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