F7 blew up. Looking for advice - HCS Snowmobile Forums


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Old 02-16-2017, 10:00 PM   #1 (permalink)
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Default F7 blew up. Looking for advice

05 F7 carb model. Has 4000km on it. I put 300-400km on it since modifications (since I bought it). Has D&D y pipe, single pipe, BMP exhaust valve spacers, and 2.5* timing key.

I always run premium fuel. Gas station was out of premium, I was at 1/4 tank, so I just filled up with 87 octane. I'm thinking this was bad fuel.

After about 20km on the trail, sled felt sluggish for a minute, then died under WOT. PTO side got hot.. melted exhaust side a bit and wrecked the jug. mag side shows good wash, but has fine pitting starting close to the center of the piston.

Where can I find good prices on a new or used jug, and CAT pistons?
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Old 02-16-2017, 10:10 PM   #2 (permalink)
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Originally Posted by Mavrick14 View Post
05 F7 carb model. Has 4000km on it. I put 300-400km on it since modifications (since I bought it). Has D&D y pipe, single pipe, BMP exhaust valve spacers, and 2.5* timing key.

I always run premium fuel. Gas station was out of premium, I was at 1/4 tank, so I just filled up with 87 octane. I'm thinking this was bad fuel.

After about 20km on the trail, sled felt sluggish for a minute, then died under WOT. PTO side got hot.. melted exhaust side a bit and wrecked the jug. mag side shows good wash, but has fine pitting starting close to the center of the piston.

Where can I find good prices on a new or used jug, and CAT pistons?
Can it be re-nic'd?

CVTech has reconditioned cylinders.
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Old 02-16-2017, 10:35 PM   #3 (permalink)
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You definitely need to run Premium Fuel with that timing key.
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Old 02-16-2017, 11:12 PM   #4 (permalink)
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WFO using low octane(ethanol?) with modified timing, you didn't have a grenade I take it?

Sorry, only advice I can offer is do not do it again...
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Old 02-16-2017, 11:36 PM   #5 (permalink)
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Everything I read told me that the carb models were way retarded on ignition timing. I didn't think that a little over a half tank of regular fuel, mixed with 91octane would cause this issue so quickly. Live and learn, I suppose.
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Old 02-16-2017, 11:49 PM   #6 (permalink)
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Most likely it was the pipe that needed more/better fuel, than the key. We use to trail ride with a lot of timing on the carbed models. (3.5-4 degrees) but I ran good fuel and was aware of the hotspots midrange. Yours was likely starting to let go midrange, then you held it WOT, and well, you know. Millennium Technologies, and power seal usa are two more shops that should also have cylinders ready to exchange.
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Old 02-17-2017, 10:07 AM   #7 (permalink)
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Modded and running WOT on 87 gas... Cant see where this can go wrong
Lesson learned.
Fill up with a few gallons and get to the next gas station while taking it easy (WOT isn't listed in taking it easy) and you probably would have been fine.

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Old 02-17-2017, 12:25 PM   #8 (permalink)
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Mavrick,pm me I have re-niked cyl's and pist's. I'm in Mich. Hdal
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Old Yesterday, 12:47 AM   #9 (permalink)
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Replated cylinders are junk, it don't matter how clean or new the ID of the plating is, look and measure the entire thing, find a good used cylinder and stay away from junk plated cylinders. Stick with cat pistons if you can, or a good name brand, wossner etc, good OEM gaskets.
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Old Yesterday, 01:09 PM   #10 (permalink)
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Put a Koso EGT gauge, its a good tool
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