Midrange Stumble around 5500 RPM

[RoostinRyan]

I have a 2013 Pro RMK 800 with a SLP Stage 5 setup, reflashed ECU instead of control box.
Sled is pulling 8300 rpms. It idles perfect and tachs great. But when I get off the throttle and get right back on the throttle it stumbles violently. Falls on its face, then seems to clean out and pull 8300. The stumble/backfire/hesitation happens around 5500 or so. Sometimes when it happens while holding the throttle the engine light comes on. As soon as I let off the throttle engine light disappears. It's not throwing any codes.
-TPS voltage tested okay; although I haven't ruled this out.
-Reeds are great
-plugs look great
-Voltage regulator was replaced
-Compression is about 110
-Tested fuel pump with a battery to make sure it's pumping good
-Fuel filter is clear
-Clutches look good

It seems to act like it's loading up when releasing the throttle but it could possibly be lean too? I had to replace the voltage regulator because it had a hole burned in it. Is it possible the ECU took some damage when regulator went bad? Also I bought the sled from a guy in Boise. Is it possible the mapping is too rich now that at higher elevation?
Also, the issue doesn't seem to happen until the engine has 'warmed up'. Last time I rode it, it ran great all day until the last hour of the day then started happening again. Really need some direction on this one! Anyone dealt with this?

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Out of curiosity what is the usable range of compression on these sleds? In new to them as I've only had it for 2 months but 110 psi seems low. My 01 700 was at 140 psi and my friends 12 with mtntk performance kit is close to 150 psi so maybe look into that.

 

[Zone28M7]

Out of curiosity what is the usable range of compression on these sleds? In new to them as I've only had it for 2 months but 110 psi seems low. My 01 700 was at 140 psi and my friends 12 with mtntk performance kit is close to 150 psi so maybe look into that.

110 is about spec for a these sleds stock.

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[RoostinRyan]

Sweet that's good info to know!

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[The Bob]

Out of curiosity what is the usable range of compression on these sleds? In new to them as I've only had it for 2 months but 110 psi seems low. My 01 700 was at 140 psi and my friends 12 with mtntk performance kit is close to 150 psi so maybe look into that.

120+ is good. 110 your going to want to start thinking about pistons.

 

[Zone28M7]

120+ is good. 110 your going to want to start thinking about pistons.

This compression depends on elevation. Does it not? Because in Colorado 120 on a stock pro would be a bit high.

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[The Bob]

This compression depends on elevation. Does it not? Because in Colorado 120 on a stock pro would be a bit high.

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I was going off the other sleds he listed looked like sea-level tests. I saw sea-level mentioned a couple other times in the thread. Could of been just others settings.

Also his profile says Yakima, WA. Which has a elevation of 1000'. So answer is at 1000' ft 110 is not ideal, chances are it isn't going up!

 

[Caper]

I had a burn down on SLP full porting, head, pipe etc and ECU flash.
I knew better, but for some stupid reason I listened to them and didn't run a Power Commander.
Rebuilt and installed the PCV and ran deadly!

 

[freekweet mods]

This sounds like the same problem I am having with my '13 pro,if I and come off the throttle and then pin it I get an exhaust sound like B-E-R-O-G-H-U-A-W-A-T-T-----dun dun dun dun dun and then me on the flipper bwop bwop bwop- pin it and braaaaap alls good until the next time I am not FFB.I have noticed if I throttle up slowly and nurse thru the half throttle position problem is not as pronounced and sometimes even non existent .My thought was exhaust valves - pulled valves and cleaned them, they really didn't look to bad-pulled solenoid and it had that gooey spudge that comes from premix after all the gas evaporates- cleaned it out with carb cleaner.Now I can not tell you if this fixed the problem or not because I plugged the out port on the solenoid and took it out for a test ride.At 6000' I could not get it to mimic what it has been doing while riding at 8000 to 10000'.I hope this cures it.

 

[RoostinRyan]

This sounds like the same problem I am having with my '13 pro,if I and come off the throttle and then pin it I get an exhaust sound like B-E-R-O-G-H-U-A-W-A-T-T-----dun dun dun dun dun and then me on the flipper bwop bwop bwop- pin it and braaaaap alls good until the next time I am not FFB.I have noticed if I throttle up slowly and nurse thru the half throttle position problem is not as pronounced and sometimes even non existent .My thought was exhaust valves - pulled valves and cleaned them, they really didn't look to bad-pulled solenoid and it had that gooey spudge that comes from premix after all the gas evaporates- cleaned it out with carb cleaner.Now I can not tell you if this fixed the problem or not because I plugged the out port on the solenoid and took it out for a test ride.At 6000' I could not get it to mimic what it has been doing while riding at 8000 to 10000'.I hope this cures it.

This is the best description I've ever read haha awesome!

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[freekweet mods]

Took the sled out today to see if plugging the port on exhaust valve solenoid cured my problem -was at about 8000'. Hit a short hard pull and threw a det code-pulled the spark plugs and color looked good,so I pulled the plug out of the port on the solenoid and rode back to the trailer w/o a hiccup.Any thoughts on old school type valves vs new type controlled by spam.