Comet 108 tuning

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gabbett1

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Joined
Feb 25, 2015
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Location
Valparaiso, IN
I have a 97 700 SX with the Comet 108 clutch and I'm not finding any information on tuning for it. I have the head gasket mod, AAEN triple pipes and I'm struggling to figure out my clutching (not stock. Secondary is NOT Yamaha). I think I have the secondary very close, but I just can't seem to get this figured out.

The sled will engage around 3800 rpm. It seems to stutter off the jump but it runs well in the low to mid range. WOT from a dig will hit around 8800 rpm but immediately starts to fall off before holding 8000 rpm. If I'm already moving it will pull about 8500 rpm and hold.

I have google searched for "comet 108exp tuning chart" and have found nothing.
 
Contact Comet, they use Polaris Weight's, they will send you a chart & give you their recommendation. Then go from there....🐒
 
I tried a comet 108 on a Vmax 540 many years ago. Never had any luck tuning it, and it killed that sled. Rebuilt the the 102 I had on it previously and the sled started ripping again. Never was fond of the 108 after that.
 
It's been a long time coming, but I think I just about have it figured out. The first time I post, I wasn't sure what my secondary was. Now I know I have a Comet 108 exp primary and an Arctic Cat Bearcat secondary. This sled used to be my brothers racing sled and they put that clutching on along with all the mods you used to be able to do to this sled.

At the moment I have the Polaris blue spring in the primary. Yellow spring on tightest hole for secondary and 47.6 g weights. They read as A-1's but they are about a gram lighter than what A-1's should be. I'm pulling and holding about 8600-8700 rpm. I've noticed though that I might be just a tad rich, so before I change anything else on the clutching, I'd like to get my main jet figured out.

Anyone have advice on what my EGT should read? I'm currently seeing low 1200's.
 
EGT readouts are more relative to the distance the probes are from the piston and the desired temp established when compared to the jetting you establish by tuning to piston wash and reading plugs.
1200 is not unreasonable. On a tuned sled I would not start leaning it out without good fuel and reading plugs as there is little extra power available if it is a couple jet sizes to rich.
I would concentrate on refreshing the clutches and dialing in the rpm.
I found a ported piped 700 Red Head liked about a 4000 - 4500 rpm engagement...usually 4500 and shift rpm 8800 - 9200 max rpm with Aaen pipes.
 
sideshowBob said:
EGT readouts are more relative to the distance the probes are from the piston and the desired temp established when compared to the jetting you establish by tuning to piston wash and reading plugs.
1200 is not unreasonable. On a tuned sled I would not start leaning it out without good fuel and reading plugs as there is little extra power available if it is a couple jet sizes to rich.
I would concentrate on refreshing the clutches and dialing in the rpm.
I found a ported piped 700 Red Head liked about a 4000 - 4500 rpm engagement...usually 4500 and shift rpm 8800 - 9200 max rpm with Aaen pipes.
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Yes, my engagement is right about there. I just have to dial in the high end. I just wasn't sure if the richness of the motor left enough power off the table to keep my RPM's down just a bit. I do understand the concept that EGT temps are dependent on distance from the piston. I was really careful on the placement of my probes to be as exact to recommendation as possible. As far as reading plugs. That's not a skill I've learned. Every time I look at plugs, they all look the same. Brown.
 
Unless you are racing its always better to have the sled a little rich then you are not changing pistons😬 Also a couple hundred rpm low on shift out not a big deal either and with triple pipes its always better to under rev a little then to over rev for power output. For trail riding it sounds like you have the sled pretty close.
JM.02c
 
General rule of thumb in clutching...if your top rpm falls on a long pull. Run a lighter clutch ramp. Or a stiffer rate of primary spring.

With the Aaen pipes you will need a 300lb-320lb finish rate primary spring and likely in the neighborhood of 45-46 gram ramps.

Just for your reference. The polaris Blue spring is a 120-300lb.

The EPI red primary spring 145-300lb or the EPI silver 165-300lb are a nice choice for the mod 700 triple pipe. Good Luck.
 
Ski-B said:
General rule of thumb in clutching...if your top rpm falls on a long pull. Run a lighter clutch ramp. Or a stiffer rate of primary spring.

With the Aaen pipes you will need a 300lb-320lb finish rate primary spring and likely in the neighborhood of 45-46 gram ramps.

Just for your reference. The polaris Blue spring is a 120-300lb.

The EPI red primary spring 145-300lb or the EPI silver 165-300lb are a nice choice for the mod 700 triple pipe. Good Luck.
Click to expand...
I think you are right about the finish rate of the primary spring being my issue. I bought the Aaen clutch tuning book and found the exact issue I'm seeing talked about in that section. There's only 2 springs I've found though that fit the bill. One has a finish rate of 310 and the other 340. My question would be, is 10 more lbs on finish rate enough to stop the 400-500 rpm drop? Will the 340 finish rate be too high?
 
It starts to get a little more complicated if you are fussy and fine tuning for the 9000 rpm peak. The 10 lbs spring will not be the ticket.

If you feel the sled is responsive on the back shift and good off... on throttle response? I would move on to the secondary clutch and run a dual helix angle. If you can increase the finish angle of your helix it will help hold rpm on top. Example if you are running a 45-43 helix try a 45-40 or 45 39. I believe the redhead triple has a straight 45 degree helix in it stock. It starts to get expensive trying different helixs but you have to experiment to achieve your target rpm.

To ditch the falling rpm on top. You have to slow the clutch upshift down on the top end. The clutch is over shifting or to much push in the primary.

For the average guy running a lighter weight to achieve the top rpm is easier...but with a lighter ramp you will run into the situation of over rev on acceleration to achieve top rpm goal. If you are fussy and want the ideal shift curve... you will have to go with a steeper angle on the initial angle to ditch over rev. Example. 45-43 to a 49-43 or 50-43.

Two different wats to achieve the shift rpm a person is looking for. Good Luck.
 
Ski-B said:
It starts to get a little more complicated if you are fussy and fine tuning for the 9000 rpm peak. The 10 lbs spring will not be the ticket.

If you feel the sled is responsive on the back shift and good off... on throttle response? I would move on to the secondary clutch and run a dual helix angle. If you can increase the finish angle of your helix it will help hold rpm on top. Example if you are running a 45-43 helix try a 45-40 or 45 39. I believe the redhead triple has a straight 45 degree helix in it stock. It starts to get expensive trying different helixs but you have to experiment to achieve your target rpm.

To ditch the falling rpm on top. You have to slow the clutch upshift down on the top end. The clutch is over shifting or to much push in the primary.

For the average guy running a lighter weight to achieve the top rpm is easier...but with a lighter ramp you will run into the situation of over rev on acceleration to achieve top rpm goal. If you are fussy and want the ideal shift curve... you will have to go with a steeper angle on the initial angle to ditch over rev. Example. 45-43 to a 49-43 or 50-43.

Two different wats to achieve the shift rpm a person is looking for. Good Luck.
Click to expand...
I've messed with the secondary quite a bit to no avail. If you think the extra 10 lbs isn't enough, do you think the extra 40 is too much?

Also, I'm not sure if you're aware, but I don't have anything stock in the clutching. Primary nor secondary. I think the number I saw on the helix was a 49? I might be off, but whatever it was it was identical to the helix on my buddies 700 SRX. Neither had a dual angle helix.
 
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No i don't think the 10 lbs or the 40 lbs will do the job.

Honestly i would run a lighter weight. Or better yet try a 49-39 helix. That straight 49 degree straight is way to much helix for a 9000 + rpm engine.

If you have a buddy with a straight 39 deg? See if you could borrow his and try it on you sled. It won't do much for hard acceleration but should give you an indication if the 39 works on the top end.
 
I just did some research on a ZRT-600 with aftermarket pipes. Might be similar clutch set up as your sled. Other than the Bearcat secondary is way larger than the a standard 10 5/8"-11" cat secondary.

Zrt 600 with pipes yellow cat spring. 170-330 lb. 45-50 grams of weight. 55-40 helix with yellow cat spring. 9000-9300 rpm

Just thinking that Large Bearcat secondary might be throwing off your Centre to Centre distance or need a longer belt? Not sure.
 
Ski-B said:
No i don't think the 10 lbs or the 40 lbs will do the job.

Honestly i would run a lighter weight. Or better yet try a 49-39 helix. That straight 49 degree straight is way to much helix for a 9000 + rpm engine.

If you have a buddy with a straight 39 deg? See if you could borrow his and try it on you sled. It won't do much for hard acceleration but should give you an indication if the 39 works on the top end.
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I've tried lighter weights. All it does is the exact same thing but in a higher RPM range. I did tighten the secondary spring and it stopped the over rev but I would only see 86-8700 RPM. I thought I was on to something so I went with a very small weight adjustment and all of a sudden I went from holding 8600 RPM to over reving to 9500 and dropping to 9000. It acted like it wasn't opening the secondary since I wasn't getting over 80 mph. When I say small weight adjustment, I mean small. I only went down .4 grams per weight.

Unfortunately I do not have anyone that has any spare helix. Not many tuners in my group of friends.

I do find it interesting in your ZRT 600 example that the spring finish rate is 330 and on a 600. My weights currently are 47.6 g and a 49 helix. That's very very close to mine other than my finish rate is 300. I do not think the belt is the issue. I spent a lot of time and money sorting out the belt and there isn't any other belt out there that fits as well as this one. Besides, if my memory serves me right, I think I remember the original builder of this clutching setup confirming the belt I'm using. Unfortunately, he will no longer answer his phone, otherwise I'd be asking him these questions. He is the one that told me to try the 300 finish rate spring, but I wonder if I'm making a little more power than he thought I would have been.

Appreciate all the help btw.
 
Just going through some old notes of mine.

I had a friend running Aaen triple pipes on a redhead triple. His setup was one layer of head gskt .010" thick. Piston cut mod. Reed spacer. Open air box. stock carbs. He ran #150 main jets. #47.5 pilot jets. 2 turns out on fuel screws. second needle clip. (needle dropped one clip)

When it was on the pipes it ran really hard... unfortunately it was fussy as hell to keep on the pipes and more often than not was off the pipes. Seemed like really cold days it ran it's best. Once outside air temps come up it was off. Maybe he was a little rich @ 150 MJ and 1700ft?
 
Ski-B said:
Just going through some old notes of mine.

I had a friend running Aaen triple pipes on a redhead triple. His setup was one layer of head gskt .010" thick. Piston cut mod. Reed spacer. Open air box. stock carbs. He ran #150 main jets. #47.5 pilot jets. 2 turns out on fuel screws. second needle clip. (needle dropped one clip)

When it was on the pipes it ran really hard... unfortunately it was fussy as hell to keep on the pipes and more often than not was off the pipes. Seemed like really cold days it ran it's best. Once outside air temps come up it was off. Maybe he was a little rich @ 150 MJ and 1700ft?
Click to expand...
I'm at about 700 ft and I'm pretty sure my main jets are at 151.5's (or round about). I'm pretty sure I'm rich. I can't say I've had any issues with the sled since having the pipes on. I've ridden it for the last several years with them on the trails. Just hadn't been able to get the wide open throttle figured out.

Edit: After reading what you post again. It sounds like he went too thin on his head gasket. It was recommended to me to only peel off one layer. I've had no issues with some decent power increase.
 
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Just for kicks, I thought I'd look up the primary spring rate on a stock SRX but can't find the details anywhere. The stock spring is the 90501-570A0-00 but cannot find rates listed for it.
 
we had a dusting of snow today so I made my clutching adjustments and did a little testing. Felt really good. Seemed like it was holding, but I didn't have a long enough stretch to really test it out.
 
Some info for you on the spring. Original number 90501-551L9-00. Blue-silver-blue.
Preload 35 kg =77lbs.
Full shift out 101kg =202lbs.
Spring rate 2.00kg =112lbs.
Length long.
 
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