Low Frequency Backfire, Loss of Power

EotS1

EotS1

Member
Joined
Oct 19, 2014
Messages
67
Location
Petoskey, MI
The last ride of my 01 SXR600 Redhead Triple ended badly. We rode about 150 miles Friday and Saturday, and in the last two miles before I got home things went South.

First, I noticed what sounded like a ringing sound in the motor. Shortly after, I was experiencing power loss and backfiring. I did get some of the normal "bang" backfiring, but also heard several of what I can only describe as low-frequency backfires. It's like they're almost below the frequency of human hearing, you feel / sense them as a thump.

I had noticed the sled doing that perhaps three times throughout the Winter. Other than that, it performed flawlessly.

Anyway, back to the last ride: I limped home at about 10 mph just to try and salvage what I could. When I'd try to give it any gas beyond that, it would backfire and bog.

Today, I went to step one: Just wanted to check the compression. I was sure that I would find one cylinder shot... But nope. They measured (starting with the clutch side) 107, 107, 110.

I did notice that the boot had come loose from the airbox to the clutch-side carb. I'm pretty sure that couldn't cause such issues.

Any thoughts on what's next?
 
Oh, by the way - I went through the carbs at the start of the season. The pilots were plugged up, but the rest of it looked pretty good.

All was clean and functioning nicely after I went through them.

It was my first year owning the sled.
 
Sounds like an ignition problem. Like something with the timing is off or the crank is out of phase. Compression seems a bit low. How many miles are on it? Possible rub through on the wiring harness.
 
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Is this the same motor that was run with a sizeable chunk missing out of primary clutch? Shade tree way of checking phase of crank is to pull plugs and using a screw driver or similar rod/dowel. Bring each cylinder to absolute top dead center. When each cylinder is all the way up use a Sharpie and mark primary. Should end up with 3 marks 120 degrees apart. Not that I think that's it per say but easy enough to rule it out. Next I would pull the carbs and get a real good look at the reeds. Wore out, collapsed, chipped or straight up broken reeds will do some weird things.
 
Yep, that's the one devilin.

I just recently came up with a new primary for it and haven't swapped it out yet. I don't know how many miles it's driven on that clutch, but the crankshaft bearings have crossed my mind...especially that slight ringing sound I heard. Could have been a bearing...

I'll do your check next.

I'm considering a full rebuild this off-season, even if it's not a major issue. I really like this sled setup with the 600 triple and the M10 and all.

If I go thru the engine, I'll know where I am for years to come.
 
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