So basically my issue is my switchback back is painfully slow.

I am only able to get 68 mph out of it. Has a respectable amount of bottom end but nothing up on top.

It has been stretched to a 144" with 2" paddles.

Gearing is a 21t top and a 40t bottom.

Primary clutch has 10-64g weights (currently sitting at 2,200ft) but I started out with 10-62g. Both sets of weights are brand new. With the 10-62 weights I was hitting 8200 rpm and with the 10-64's I managed 7900 rpms in poor conditions (low snow)
I have a venom products lime green primary spring 150/340 which is new. Secondary clutch has a new venom products spring red/black 140/240 (stock rate). Helix is the stock 42 straight.

120psi on both cylinders.
Exhaust valve/bellows are clean and in good condition. Reeds and intake boot were replaced 750ish kms/two seasons ago. Oil filter and fuel filter have also been changed 750ish km/two seasons ago.

Every single idler wheel bearing in the skid has been changed maybe 500 kms ago or last season. Track was aligned and tensioned this season.

I am basically at my wits end. The only things I have left to try is a 56/42/36 helix out of an rmk that I have currently installed in my secondary but have not had the chance to test it and I have some 20/41 gears from an rmk I can swap in.

According to the polaris gearing chart, on a stock track, I should be good for 93mph. I know the longer paddle track will take away top speed but take so much away that it falls on its face above 50 mph?

I have a 2007 arctic cat 600 crossfire 136"/1.25" as well for the other half and I raced my buddy last year across a lake. He was on my crossfire and I on my switchback (with the 10-62g weights at 2,200ft). He absolutely embarrassed me. It was awful.

 

The video is with the 10-62g weights and the stock 42 straight helix.

https://youtu.be/F2cFCZ6ZHgE

my best guess is that it is a clutching issue.  I would see if your belt is running to the top of the primary while riding and not on a stand.  Take a black marker and make a line from the bushing to the top of the sheave.  Run it and see where the line is erased and what is still there left.  You should be running right to the top.  Your gearing should be fine and the extension with track IMO wouldn't take 30mph out of the sled by any means.  I have a 1.35 on mine and if i went down to a 1" track i'd only gain 5-6 mph based on my gearing.  21/40 is 1.9 gearing so not out to lunch with what you're trying to accomplish.  

Look at the primary first.  If it were me, i'd send it right back to stock to where it was running properly for gearing and clutching and then see if it goes to where it should be.  Expect a loss of MPH with the 2" and extension even when stock, but it gives you a starting point.  

When did this loss of power start happening.   AS well, when was the last time that the injectors were flow tested

Edited December 9, 20204 yr by McLovin

My injectors have never been tested. This is my third season with this sled and I don't put a lot of miles on. (Hopefully I will put in a lot more this year). 

It has always been like this but last year is when I really noticed because I actually rode with someone and was on a lake where I could really stretch it out. Season before I was just on little bush paths so I wasn't aware of my shit top end.

My primary looks like this with either of the 10-62 or the 10-64 weights. I have also changed my spring back to a wore stock rmk spring and same results.

The picture with both clutches in it is from yesterday with the 10-64 weights and the 150/340 spring. The stock rates are 120/340.

The other is with 10-62g weights and the 140/330 stock rmk 700 spring.

Edited December 9, 20204 yr by Tomas.

I don't have the tools to pull off the spider. But when I have the cover off, the rollers appear to be in good shape, weights are new with no slop, buttons seem decent and the sheave seems to move without restriction.

your getting the proper rpm so the spring is fine.  You aren't getting to the top of the sheave if that is your mark.  what is your belt to sheave clearance?  IIRC typically should be about .02 as it should grab the belt right at engagement RPM and not slam into engagement.  If it's greater the clutch will shift out but the belt doesn't make contact so by the time the weights are fully out, the belt is still trying to work it's way up but now can't fully shift out.  Also check to see if the belt is 1/8" above the secondary sheave at idle.  Another thing to check is the condition of your belt and that deflection is proper.  I don't have a manual for your sled but its should be around 1.25".  

10 minutes ago, McLovin said:

your getting the proper rpm so the spring is fine.  You aren't getting to the top of the sheave if that is your mark.  what is your belt to sheave clearance?  IIRC typically should be about .02 as it should grab the belt right at engagement RPM and not slam into engagement.  If it's greater the clutch will shift out but the belt doesn't make contact so by the time the weights are fully out, the belt is still trying to work it's way up but now can't fully shift out.  Also check to see if the belt is 1/8" above the secondary sheave at idle.  Another thing to check is the condition of your belt and that deflection is proper.  I don't have a manual for your sled but its should be around 1.25".  

The belt is a brand new polaris 115 with just testing in a field by my house.

The belt sits just above the secondary. 

Does not slam into engagement. 

Edited December 9, 20204 yr by Tomas.

and your belt to sheave clearance?

ideally you should bring this sled to stock gearing, springs and see where you top out at and then do process of elimination.  Kind of like adjusting all your springs and tensions in your suspension all at once to get a better ride.  You need to do one thing at a time and test to see if it works or not.  

Edited December 9, 20204 yr by McLovin

For belt to sheave clearance, if I am measuring correctly I think it is around 0.02-0.03

everything points to it being okay.  but the mark on your sheave tells me that it's not getting the height you need.  Was this sled a 144 when you bought it or did you convert.

I also don't have the factory gears or spring. 

belt looks fine.  I see a mark on your clutch that i'm assuming is a marker for how high your belt goes as shift correct? or is that from something else

i'm not going to say that track and extension isn't pulling the sled down.  That's a lot of paddle to pull, but the fact you're losing 20mph is quite a bit. i still think there's something in your clutching that's not right.   If you wait, there's a lot of really smart people coming in that can help you out as well. 

Edited December 9, 20204 yr by McLovin

6 minutes ago, McLovin said:

i'm not going to say that track and extension isn't pulling the sled down.  That's a lot of paddle to pull, but the fact you're losing 20mph is quite a bit. i still think there's something in your clutching that's not right.   If you wait, there's a lot of really smart people coming in that can help you out as well. 

Yes. Those marker marks are showing belt height. I just put a stock rate slp spring on order. Should have it by Monday.

The sled was already converted to a 144 when I bought it. All the guy used for the conversation is slp rail extensions and dropped one tooth on the top Gear.

as i thought, which is common.  What i would do is just have that clutched pulled and gone over.  Never hurts if it's not been done before because whenever you get some else's toys, you never know what you get.  I would try the RMK gearing and helix.  Not really for that sled, but it gives you an idea of where you're at.  who knows, it may even work. 

at your top speed are you still pulling the 8100rpm or is it dropping off? make absolutely sure the tiny pulse hole in the cylinder for your ev are clean.Very common for one to get plugged and that valve stop working..The 800 is supposed to pull 8150-8250 so I would start there.Of course check rollers in Primary clutch . You could gain a little by gearing down but you are runnin 1.91 gearing now which should be ok for a 144x2 track.. which track is it? I have had people put full lug tracks on and loose top end big time because the resistance the track created in the tunnel.

3 hours ago, Phat Bastard said:

at your top speed are you still pulling the 8100rpm or is it dropping off? make absolutely sure the tiny pulse hole in the cylinder for your ev are clean.Very common for one to get plugged and that valve stop working..The 800 is supposed to pull 8150-8250 so I would start there.Of course check rollers in Primary clutch . You could gain a little by gearing down but you are runnin 1.91 gearing now which should be ok for a 144x2 track.. which track is it? I have had people put full lug tracks on and loose top end big time because the resistance the track created in the tunnel.

 

The track just says cross country on it.

Those little holes in the valves are clean. And the video I posted was when I had a ultimax XS belt on. Right after that video was taken, I switched to the brand new polaris belt (115) and I hit 8200 rpm. It doesn't drop rpms.  Seems to hold constant.

Also, it is the 700 not the 800. But you are correct, it should be at 8200

Edited December 11, 20204 yr by Tomas.

After looking through all of these posts, and seeing that your primary clutch clearly didn't fully engage to wipe off that line you put on it, perhaps the outer sheave is sticking on the shaft.  I've seen that before.  Take the face off the clutch (6 10mm bolts) which will let the spring be removed, and then you should be able to slide the outer sheave back and forth freely.  IF that is not happening by hand, the bushing, or 'bearing' as it may be called is sticking.  

Just be careful when you remove and replace the outer cover so as not to scuff up the bushing/bearing on the cover itself.

Edited December 11, 20204 yr by Mag6240

your rpms are bang on.  any higher and you'll lose power band.  

 

Phat Bastard is talking about the two holes that are in the cylinder by the EV valve.   You need a small wire to push through to get the junk out.  Also, the EVs have holes in them as well that should be cleaned.  you have to break the whole valve down to get to them.  They are very small and are overlooked.  I use brake cleaner and compressed air on the valves and just compress air on the cylinder holes

Edited December 11, 20204 yr by McLovin

So I pulled my valves out and I see the two holes (one on each cylinder). I used a nail and I was able to put it in the hole at least an inch before it hit a stop like the casting. They were empty.

Primary sheave move free with the cover off. The sheaves touch together no hang ups

 

Edited December 12, 20204 yr by Tomas.

Just took an air compressor to the holes in the cylinder and the was no obstruction. I used my mouth and double checked the exhaust valves where the hose goes on and they are free of obstruction as well.

Sounds strange.

Edited December 13, 20204 yr by Mag6240

Some hopes and dreams for this weekend's testing.

So I probably shouldn't have been out testing as we definitely don't have the conditions for it. But I did it anyways lol.

So with the black/pink 120/340 spring which is factory rates added an extra 5 mph, bringing the max up to 73 mph.

My rpms are maxing out at 7850 with the 64g weights. 

So I think my next step is to put the 62g weights back in to see if that brings my rpms back up to the 8200 mark.

I also think that the sheaves moved closer together as well. I don't know if that is because if the spring or not.

Also the 120/340 spring is shorter than the 150/340 spring. I don't know if that is because the spring rate is different or not.