Another RPM Question

eyefish123 · Feb 4, 2018

Have been reading different posts and am seeing where people are losing RPM when they get to full throttle. Found the same thing with mine yesterday. Finally got on a surface smooth enough I could really roll on the throttle. Was almost pinned and had 8300 RPM and then took flipper the rest of the way to the bars and went to 8100 RPM. Just did TPS and all clutching is good. Anybody have any solutions for this issue yet? 2017 Axys 163x3

skippy · Feb 4, 2018

Did you have this problem before or after TPS adjustment? There has been a lot of talk on here lately about broken exhaust valve cables and what not, but if your seeing 8300 rpm I would think they are working properly.

eyefish123 · Feb 4, 2018

Have not been getting full RPM since last year. Did new motor mounts, balanced clutch, aligned clutches, clean power valves, change clutch weights and now TPS. Had to do a trail ride yesterday so was finally able to roll throttle on to see problem.

adamg · Feb 5, 2018

eyefish123 said:
Have been reading different posts and am seeing where people are losing RPM when they get to full throttle. Found the same thing with mine yesterday. Finally got on a surface smooth enough I could really roll on the throttle. Was almost pinned and had 8300 RPM and then took flipper the rest of the way to the bars and went to 8100 RPM. Just did TPS and all clutching is good. Anybody have any solutions for this issue yet? 2017 Axys 163x3

If you get in there and look through your throttle bodies, I bet you they are going past 90 degrees and starting to close. It causes decreased airflow while the ECU thinks it needs to feed 100% throttle worth of fuel. My 16 163x3 Axys was doing this, and Polaris replaced the throttle bodies and TPS on warranty.

If you leave it as is, you'll get more power by not going to full WOT.

Another option is to build something that limits the throttle body movement. For instance a sheet metal spring clip piece that adds spacing in the throttle limit block.

eyefish123 · Feb 5, 2018

That's what I am afraid of is that the plates are going past 90 degrees. What really sucks is that I had it all apart and the air box off last week when I adjusted the TPS and I didn't check it then.

skippy · Feb 5, 2018

adamg said:
If you get in there and look through your throttle bodies, I bet you they are going past 90 degrees and starting to close. It causes decreased airflow while the ECU thinks it needs to feed 100% throttle worth of fuel.

Any idea of what causes the throttle bodies to change past 90*? I'm guessing his sled pulled RPM full throttle when it was new,right?

eyefish123 · Feb 6, 2018

Pulled enough RPM that I had to add weight in clutch when new. Now I can't take enough weight out to get to 8300 RPM.

rx1tonofun · Feb 6, 2018

The sleds are going into a soft over rev. It acts like a limp mode and won't rev past 8150 at wide open. Clutching is the biggest factor most of us are dealing with. I've got a SLP stage 3 on mine and clutching has been a nightmare. I tried a Gates CF belt this past weekend and it helps a lot. The stock belt gets glazed too easily and slips when you're at lower elevation and causing the soft over rev as you go higher and it kind of goes away.

Check out the TRS N/A clutching thread, there's some great info there.

adamg · Feb 10, 2018

eyefish123 said:
Pulled enough RPM that I had to add weight in clutch when new. Now I can't take enough weight out to get to 8300 RPM.

Ah, maybe your problem is not what I wrote. I know in my case, even brand new the sled wouldn't pull factory clutching at factory elevation, and even dropping 2gr on clutch weights it still wouldn't pull them. And now, 1400 miles later, tried a dozen things, no improvement.

sledhappy · Feb 25, 2018

I also battled this. Changed clutching replaced motor mounts etc. adjuster TPS tried another ECU. After all that we replaced the egt sensor. Since it can start to go bad not fully to throw a code but will pull timing. And now after 2 years it’s pulling 8450 no problem. If you have a spare or a buddy will let you switch it out for a few runs they are about $180 so not a cheaper part to just try.

Good luck on you venture to overcome low RPM

eyefish123 · Feb 25, 2018

Have a friend with a 2018. If part # is the same I am sure he will let me try his. Thanks for the idea.

Sheetmetalfab · Feb 25, 2018

eyefish123 said:
Have a friend with a 2018. If part # is the same I am sure he will let me try his. Thanks for the idea.

They are different.

eyefish123 · Feb 25, 2018

Does anybody know what the resistance is supposed to be on the EGT sensor so I could check it that way?

Sage Crusher · Feb 26, 2018

I can tell you this- I had cutting out issues and was trouble shooting my 16 Axys.
Pulled my EGT probe out of my well running 14 pro and installed and it in my Axys, running it still for 2 years now...

No it didn't cure the problem ..That ended up being a TPS issue-----But the EGT probe worked, and is still working. I have the 16 Axys probe in my 14 pro and no running issues have come up ../ never changed them back around - never needed to...... FWIW

eyefish123 · Feb 26, 2018

My son's 15 Pro is parked in the garage next to mine (thawing out). I am going to switch with his tomorrow since it is the same part # and see what happens. Thanks

rydningen · Feb 27, 2018

skippy said:
Any idea of what causes the throttle bodies to change past 90*? I'm guessing his sled pulled RPM full throttle when it was new,right?

Took a look at a 2016 sks 800 I have on the bench now, and I noticed that the throttle stop on the throttlebody now is a part of the cast aluminium and not a steel part as earlier models. This sled only has 20hrs on it and you could clearly see where the steel had contacted the aluminium, may it just be that wear on this spot causes the throttleplates to open too much?

Also, wont the TPS read to high max values causing issues with the ECU making fueling changes if it opens to wide?

Added pictures of the throttle at zero and max on the axys engine and another of the earlier design, a 2014 pro throttlebody.

I have a 2016 pro myself, revs well over 8300 at 90% throttle but as soon as I press it to the bar it falls back to 7900-8000. Leaning more and more against it being an issue with the throttlebody..

adamg · Mar 1, 2018

rydningen said:
Also, wont the TPS read to high max values causing issues with the ECU making fueling changes if it opens to wide?

I don't think the mapping takes into account this overtravel scenario on the throttle bodies. The mapping and TPS calibration assumed that 100% throttle position is max airflow; more throttle always means more air, which leads it to always add more fuel. So if you actually hit max airflow at 80% throttle, from 80 to 100% you are removing air while adding fuel. So it ends up way rich on the mixture. And there's no way to calibrate that out with the TPS.

Really all you can do is physically limit the throttle bodies from overtravelling with a home-made stopper. Or replace throttle bodies.

mountaincat 800 · Mar 2, 2018

Why couldn't you just loosen the throttle cable? That's what I would try.

eyefish123 · Mar 4, 2018

Looks like it was the EGT sensor. Took one out of my 2015 Pro (same part #) and got my RPM back. Sled has lots of pull like it did when it was new. Now have to deal with dealer about warranty replacement since I have 4 year warranty. Not sure how they will handle this since I found the problem. Thanks everybody for your help.

Another RPM Question

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