Strange RPM Problem

So I had a weird issue come up on my last ride that I haven't seen discussed here before. Started out the day fine. Conditions were 12-18" of fresh, wet snow with snow continuing to fall and about 30 degrees. I had changed my helix angle by 2 degrees on the finish rate the night before the trip. Team Tied clutch so not much disassembly to do this. Sled felt sluggish and I thought it was the steeper helix combined with the heavy snow loading it up too hard. Stopped at lunch to inspect and realized the belt was about to come apart. New belt improved the situation substantially. Right before this I tried to climb a short, steep wall from a dead stop and the sled just would not rev up to go up it. About 4000 rpm and would bog out. A few other times that morning it would bog trying to take off like it had a TSS problem, but TSS has been unhooked for some time.

Fast forward a couple hours to the late afternoon when we were getting low on fuel. Got into the bottom of a ravine with no way out the bottom. Sled starts acting up again, but beyond what it had done earlier that day. It decides it doesn't want to rev past 3000rpm. It would rev to that point and just want to die. Once in a while it would get up to 3500 (engagement on my sled when it starts to move), but still die. I thought maybe it was clutch/load related so I rolled the sled up on its side far enough to get the track out of the snow and I could get it to rev up and spin the track that way. Eventually I got it feathered through the 3-3500 problem spot and it took off and ran like it was supposed to all the way up and out of the chute.

Now here is where it gets really weird. Any time you stopped and let the sled come down to an idle you couldn't get going again. If I stood at the front of the boards and two guys lifted the rear of the sled to get the track spinning with the engine running 4500 they could drop the sled and I'd take off no problem. Would run like normal and pull RPM like it should as long as you didn't stop. Furthermore, we figured out the sled would not even start if the nose was pointed down hill. If it was pointed uphill a little bit it would start first pull and idle just fine, but still wouldn't take off under its own power. I have a clear trail tank and could see where the fuel was when this was all happening. If fuel was at the back of the tank it could start. If it was all in the front it would not. When I got back to the truck I had maybe 2-2.5" of fuel in the bottom of the tank. This is the first time I've run it this low in quite some time.

This has me thinking that maybe I have a fuel delivery problem with the smart valves in the tank. Anyone experience these type of symptoms that were fixed by changing them out? One other thing that was different recently was I had some race fuel mixed in the tank from some low-elevation running I did on the last trip. Up until recently it had only ever seen 91. Maybe that brand/formula of fuel reacted with the seals in the valves? I pulled the whole works out of the tank this morning and the hoses seems to be pretty hard. The valves were holding fuel in the lines and not leaking until I turned the assembly on it's side. One of the rear ones then released and let air in, and then all the fuel ran out the front valve. Seemed odd, but I don't know how these things are supposed to work exactly. I didn't touch the valves when any of this happened. just holding them by the lines and pump.

Other pertinent info on the sled:
-BDX hood, intake, headlight delete (old style)
-900 BMP 197hp full motor kit with PCV
-Oil injection delete
-Cat Tether
-Diamond S Ti quiet can
-2018 Primary clutch, MDS weights, Tied secondary, 2015 style Ti jackshaft (400 miles on this setup)
-TKI Belt Drive geared 2.52
-162 3" PC track
-This year it has had a new voltage regulator, stator, PCV, and reeds. First dealer that mis-diagnosed the stator problem said they had all the ignition harness connections apart, blew them out, and greased them.
-2300? miles on the engine, wire harness, and fuel system.
-Sled started as a 2014 pro-lite so it's had all of the engine mods since it was new.

Allseasons said:

Is it possible your clutch was sticking? It’d be like putting a car in 4th gear and starting off from the set of lights, it’ll bog and stall

Click to expand...

It felt similar to that or when you slam on the brakes and come to a stop with the belt stuck down in the secondary. Just like taking off in too high of a gear, but not even attempting to move or slip/burn the belt. Which is odd.

I got to looking more closely the other night and I do in fact have a broken primary spring. It's broken right at the bottom next to the spider. I looked at it out on the hill when I changed my belt and it looked fine then. It must have finally shifted enough and the very bottom coil is now pooched out. I broke a spring like this right at the bottom on my 2014 clutch one time. It had little effect on engagement though and I was just loosing 200rpm on the top end. Engagement with that setup was 38-4000. The lower 3500 engagement of the 2018 clutch setup coupled with losing 1 coil must have been dropping the engagement right down to the 3000 range. Not enough power being generated to move the sled at that RPM and killing it?

I still believe I have a fuel problem though as the broken spring doesn't explain starting/not starting with orientation of the sled. Maybe the stalling at takeoff was a combination of the bad spring and starving for fuel. Anyway I ordered a new smart valve setup for in the tank for less than $100 and I'll get another spring coming. Hopefully that fixes the glitch.

Thought I had this issue solved at the end of last year. Changed primary spring and fuel pickup tube/smart valves and all seemed well. Tried a spring with a little higher engagement around 3800 and the engine liked that better. May in Cooke on spring snow with the weights loaded up was pulling right where it should be. Couple weeks ago riding up to about 8000' elevation sled felt like it was running pretty well and target RPM. Trip before that as well.

Fast forward to last weekend in Cooke... Pulled a couple grams from the clutch weights for the higher elevation. Would hit 8500 RPM on the trail no problem. Felt ok around 9000' Got into some deep heavy snow up around 10,000' mark and was struggling with RPM again. Would hit 8100 after takeoff then pull all the way down to 7600 at times on an incline like it didn't want to backshift. The longer I held it to the bar the worse it got. Then it started wanting to bog and not takeoff from a stop at times. Seemed like another broken primary spring. I started watching it close and if I brought the RPM up slow it would engage about 3800 then immediately drag the motor down to 3300 and bog. If I hovered 2500-3000 then stabbed it would bog after engagement. If I stabbed the throttle from idle it would pull through and go.

Toward the end of the day I hit a rock that broke a top ball joint. Tied it together and limped into Cooke. Cat dealer there had one so they ran it in the shop and fixed it quick for me. They ran it back out fine. I started the sled when I went to leave and it drove forward 3'-5' and died. Would not re-start. My old style Cat tether is on it's way out and I noticed it had a 5 sec delay killing my sled earlier in the day. So I thought maybe that's it and it has water or something in it. Rocked the sled side to side...no change. Rocked sled up on its side, pulled the rope and it fired. Let the sled back down on it's skis and it died. Rocked it up again and no fire after about 15 pulls. Held it there a while and tried again and got it going. Started driving forward with sled on it's edge and hopped on with it moving. Rode to edge of town, stopped, put scratchers down, and ran fine 9 miles back to the truck.

Got it home and can't see a break in the primary spring with the clutch assembled on the sled. Weights and rollers seem free. Checked compression a month ago after I had a plug boot pop off and get eaten by the secondary clutch (first trip of the season). 135-140psi depending on how many times pulling the rope. Same reading both cylinders. Don't have a leak down tester or I would have checked that. Couple mild scuffs on the front side of pistons. Back cylinder walls look perfect. Inside of exhaust was a little white, but I chalked that up to residual race fuel. I'm probably around 2600 miles total on the engine now. Have a new tether on order. Got to thinking today about the not starting thing and how similar it seemed to what happened last year. Getting down on fuel, weird RPM issues, not starting facing downhill (was slightly nose down sitting outside the dealer). Fuel level was down to probably lowest it's been so far this year so still thinking it's a fuel delivery problem.

Going to disassemble both clutches tonight and see if anything is out of place. If they check out I'm thinking I need to test fuel pressure. Anyone know the spec for that? Will I get the same pressure hotwiring the pump to 12V motorcycle battery as I would with the sled running?

Update:

Went through my clutches last week. My "low mile" 2018 roller primary clutch appeared to be in bad shape. The white/gold Dalton spring has been binding up badly and scraping the cup in the cover pretty hard. setting the spring on its end on the bench its top is distorted about 1/4" over from the bottom. Definitely wouldn't provide very even pressure in the shape it's in. Checked play in the cover bushing...can almost lift the clutch off of the top of the bench by binding it sideways on the center bushing surface. Movable sheave has as much play rocking it side to side and back/forth against the buttons on the spider as my original 2014 stock clutch that had 1900 miles on it. Spider buttons were starting to put wear marks in the towers of the movable sheave. Over half of the spots on the cover that mate up to the towers have the little edges cracked on them that others have shown in the Ascender section. I think two were that way when I got it. Pretty sure this thing was binding up once it got hot and was dragging the RPM down. This clutch was used when I got it and I'm betting it had more miles on it than what was thought. Either that or my Ti jackshaft is flexing enough that it's pulling the secondary out of parallel, thus side loading the primary. I don't have belt wear issues though. Completely replaced clutch and installed a new white/red spring I had on the shelf (ran this spring rate before going to the stiffer initial rate white/gold). Running same MDS weights I just put bushings in not long ago.

Tore the Tied secondary apart. Still clean inside. Individual rollers and helix bushing seem to have some play to them. Put the whole assembly back together without the spring and couldn't get the sheaves to rock or bind and it seemed to slide smoothly. Zero rubber on the sheaves in the bottom to evidence that the belt was getting to the bottom and slipping. I've run it up to 80+mph with 2.52 gearing. Put it back together as-is.

Plumbed in a fuel pressure regulator with a gauge up by my steering post so I could monitor the fuel pressure. Have the pressure screw backed off as far as I can without it leaking fuel so it's not providing a restriction. At 55-60 degree temp in my garage it will hit 44psi every time starting the sled. Shut it off, it drops to 25psi, then over the course of an hour bleeds down to 10psi. Repeated multiple times with 1/2 tank, siphoned down to 1/4 tank, and then elevated the rear of the sled with 1/4 tank so the rear bumper was at my chest level. Same results every time.

Replaced my old Cat style tether that that had broken rubber over the plunger with new Cat magnetic one. Just in case that was acting up.

Ride Report:

Just got back from 3 days of riding in Island Park. Crossed over the 2500 mile mark. Every morning when starting the sled cold the fuel pressure would pop up to 49psi and hold there as we took off. Cold premix fuel makes sense it would develop a little more pressure. By a few miles into the ride the pressure would drop off to 41-42psi. Anything longer than 2-3 seconds at WOT and it would fall all the way down to 39psi and hold. This seems like a pretty substantial drop to me. Could the heat exchanger under the fuel tank be warming the fuel enough to see that kind of drop? When shutting the sled off the pressure would maintain the same pattern as above in the shop for the first two days. On the third day I caught it dropping all the way down to 0 a few times. It never gave me a starting issue when it did that and the pressure came right back as soon as I pulled on the rope. Still suspicious to see it drop though. No bogs taking off on days 1 and 2, but a couple on day 3. Not sure if the lower rate spring was just getting broken in at this point and not always holding the Rs up on takeoff. Probably should have tried to pull a plug after a WOT run and see if it was starting to run lean...

Hero snow conditions. Could cut in 12-18" then hit a solid base with exceptional traction. Start/stop almost anywhere, climb anything, and make sure you come down on an edge or you were going for a ride. I shoot for 81-8200 and I could pull 8150 at lower load, but drag down to 78-8000 with the track all the way in the snow under load first day. Pulled a little tip weight for second day and was at 8200 under hard load, but would hit 8500 and have to let off on sustained WOT low load climb. Much better response in the trees though than first day. If I tied into a slope from a stop and immediately cut into it with a hard carve it would take a bit for it to climb to peak RPM. Fresh secondary spring may help or a little less weight in the middle of the primary weight.

New tether is awesome.

Next Step:

Get another primary spring with stiffer initial rate. Get delrin washers under it. Look into a ZRP cover since they claim to have more spring clearance in the cup. Get a new secondary spring. Continue to monitor fuel pressure. Anyone know for sure what the spec is supposed to be for that?

Also, I forgot to mention that I noticed some open holes in my gauge cluster last week where the button cover fell out. Filled that whole area in with silicone in case I was getting water in there and shorting something out. First day I had starting issues last year was the same day I lost that cover in deep, wet snow.