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Discussion Starter · #1 ·
I have a 2000 Formula Deluxe 600. At start up, I pull start it (no battery). The engine will either backfire instead of start, or once running will have a miss. It isn't steady or predictable. Once it has been running for a while, or even after I have ridden it, it will still have a miss, even when at cruising speeds.

I also find that when I give it gas, it wants to bog down, so I have to feather the throttle to get it going.

While in for other work, the dealer did a compression test. 140psi drive end, 155psi other end. Are these related?

Would swapping plugs solve the miss/backfire?
 

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That's way to much variation in compression. You're running lean on the PTO side. Think you'll find you've got a bad seal or cracked boot on that side. Sounds like you're gonna need to do a top end. Surprised the dealer didn't say anything.

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Discussion Starter · #3 ·
That's way to much variation in compression. You're running lean on the PTO side. Think you'll find you've got a bad seal or cracked boot on that side. Sounds like you're gonna need to do a top end. Surprised the dealer didn't say anything.

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They did tell me that it likely needs rings. What are the seals or boot you are talking about?

When I park it for the summer, I will rebuild the engine; at least the top end.
 

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Seal would be be the crank seal, boot would be the rubber boot between the carb and engine. If either is leaking, you won't make it till spring before it blows. While the sled is running, spray carb cleaner on the carb boot and behind the clutch. If the engine speed varies, you've got a leak.

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Discussion Starter · #5 ·
Seal would be be the crank seal, boot would be the rubber boot between the carb and engine. If either is leaking, you won't make it till spring before it blows. While the sled is running, spray carb cleaner on the carb boot and behind the clutch. If the engine speed varies, you've got a leak.

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Sprayed those areas. No noticeable change in engine rpm. I am guessing I will make it till spring, and beyond.

Part of me is thinking it might be old plugs. I plan to swap them out at the end of the season anyways.
 

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A carb clean up would be your first plan of attack.
Remove, disassemble, spray carb cleaner through all the passages and jets. Compressed air helps too if you have it. With carbs off its also a good time to check your Reed cages and petals.
 

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Sled nut
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Put new plugs in it . Your old ones currently soaked if you pull them ?

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Start with the plugs they're like $12. A misfire on any motor is a bad thing. You can't just ride it and forget it. And if it's a lean condition that's just a time bomb waiting to blow. If it were me I wouldn't ride it until it's running right.
 

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Post a few pics of the old plugs. They are like a map of how your engine is running. Somebody may be able to see an issue.
 

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You can go the the full version at the bottom of the page and it has more posting options when your typing a reply. At least that's how I do it.
 

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Discussion Starter · #13 ·
So, I swapped the plugs.

No miss or backfiring. The plugs were worn. They were not carboned up or any other issues besides the gap. I wish all of the problems were such an easy fix.
 
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