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Discussion Starter #1
I have a 78 and a 79 Jag, both w/ 340 F/A motors with matching eng. #'s. I thought my 79 had plenty of power & ran great, until I bought the 78. WOW! The 78 will spin the cleated track on powder or hard pack, snap the throttle on a low speed turn and it will do a a 360 with no problem on hard pack. If I move my weight to the rear of the sled it will actually pull the skis off the ground for several feet befor they come back down to the ground. I can literally come off the hill at angle to my driveway at about 15 mph crack the throttle wide open and bring it around in a 360 and keep going the way I was before the spin, without a problem. It easily does 180's without even a grunt on hard pack! The 79 will barely get sideways doing the same thing off the hill onto my driveway. The 79 will not spin the track from a dead stop--ever! It just launches. I can also hear a difference in how they run. The 79 is stock and previous owner said the motor was rebuilt last year just before I bought it, claims to have had less than 200 mi. on it. The 78 I have no idea--the previous owner of that one claimed it was stock also. The only difference between the 2 sleds is the suspension. Both have factory exhaust and clutches/belts
I guess I want to know 2 things--
1)Is it possible to have a bad seal or something that will cause slight power loss but the motor will still run good?

2)If the 78 was rebuilt and bored-will there be a stamping on the top of the piston that can be verified by removing the heads? If not, how do you know if the eng. is modified from stock?

As I stated before, you can definately hear a difference in the way they sound when idling or revving them up a little. Both are very responsive w/ no flat spots or bogging. There is definately a power issue here I beleive.
Anybody have some knowledge to share with me on the possible diff. in power between these 2 sleds?
The sleds are shown in my avatar. The 76 Jag w/ the chrome tank you see is advertised on this site and E-Bay until Thursday for sale also.There is a bid on it, so I will have to let it go for highest bid.
 

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maybe go over your clutches, those hex's always seem to wear out on me.
 

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Discussion Starter #3
I have wondered about the condition of the clutch as well. I have never had one off/apart. Does the entire clutch need to be removed to take it apart and inspect it-- or can the fron cover be removed with the clutch still on the sled? What exactly is too much wear on the clutch pads--or how thick/thin should they be before needing replaced?
 

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The difference could be in the clutching. Either the 79 is worn or sticking or the 78 may have a better set up. The best way to go over the clutch is to take it off. You'll need a clutch puller specific for the hex clutch. I know you can get them through Dennis Kirk, Hi Performance Engineering, Shade Tree Powersports and other aftermarket places. You might want to check the carbs also. The 78 may be leaned out one step on the jet needle or a smaller main jet. From the factory the carbs are always set on the rich side.
 

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There is a fiber bushing in the "Hex" clutches that will wear and allow the movable part of the clutch turn a little on the shaft and bind. It usually involves changing the bushings ans the weight pins as well. Better to replace the clutch with a Comet 102 or a newer cat clutch.
 

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check the compression of each, if they are the same motor then it might be that the one is low, also check the clutches and maybe the gearing in the chaincase, i know some snowmobiles did come with optional gears you could get.
 

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Discussion Starter #7
I'll check compression,like I stated you can actually hear a differnce in how the two sound when running at idle or revving them. It's not a profound difference but it is noticeable. They both run/idle excellent it's just the unbelievable power difference. It's like riding a 340 then jumping on a 500. I'm thinking it is a combination of the clutching/worn components and someone possibly rebuilt the motor and punched .020 over or something. I'll post the compression #'s when I get a chance to look into it.
I'm currently trying to figure out what's wrong w/ my new 78 Jag I got yesterday (see other post for got 2 more sleds!!)
 

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Discussion Starter #10
I was going to check the gears but like I stated previously there is a very distinct sound difference between the 2 sleds. The engines sound totally different the way they idle and rev. they bothe have stock carbs and exhaust also. I'll figure it out someday when I pull the cyl. heads apart probably will find one was bored out!
 

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check the carbs, I don't think that just boring it would make it that much different
 

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A rebuilt drive clutch can make world of difference. I do not have my master cat service book near my PC, but have noticed they changed the ramps from year to year as I redid my 79 jag clutch last season. I believe they actually had the same ramps as a 76 eltigre?
The weights are measured in grams, and are color coded by cat to easily identify them. If you do not have the correct weights in the clutch it will drive poorly (read that lack of performance)

One last thought about the 79 being a little doggy compared to the 78 is if you take a look at the rear skids the 78 has the old el tigre steel style setup with ALOT less travel compared to the much plusher 79 and up aluminum skid.
It could be you are just gonna experience a different ride out of the hole becuase the 79 has got to work harder to compress the extra travel in the suspension before it can make the track hook up.

The old sleds with almost no travel in the rear suspension like my 72 tnt 440 f/c will hole shot faster then the newer 500 fan cooled machines with three times the extra amount of suspension hung in them

Think about it, the ride would suck but if you were able to take out practically all the movement out of the rear suspension the track has no choice but to grab or spin. This would happen immediately as there is hardly any force required to overcome the spring suspension on your rear skid frame.
That is one reason why drag racers use ladder bars to keep a car's rear suspension from 'wrapping up' prior to take off.
 

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yea bud the clutching can make a world of difference in sound...IMO....jeez dude your getting more vintag sleds than i have, gonna have to buy a couple more soon, im up to 6 how about u?
 

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Discussion Starter #14
I'll have to get a clutch puller and inspect both clutches.

I'm up to 6. Actually 5, I sold the 76 Jag. It's still here, the new owner hasn't come to pick it up yet. I bought the 79 Trail Cat but it's still in Boulder Junction,WI. The guy is going to bring it to me when he goes to Chicago (unless it snows real good before that--then I'm going to go get it) So for now I just have the 78 Jag- 2 79 Jag's- 80 Pantera- 79 Trail Cat. I'm eyeballing an early 70's Cheetah or Panther down the road. It's got a dual plug motor in it but I don't know if it's a 340 or 440. I don't want the sled-I want the motor for the 79 Jag I picked up a couple of weeks ago. The 340 F/A that was in it is major toast! It would cost more to fix than it would to get a used motor/sled
 

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I have a 75 el tigre with the quad plug motor, i cant wait until I put the CDI into and get it running, it should sound sweet, the next couple sleds im getting are a 72 panther with a 303 wankel, and an 81 ski doo blizzard 9500, and im also thinking about a 73 raider, sooooo, i need snow to work so i can get them.....Snow depends on a lot of stuff right now, they're not calling for snow down here for a while, we just went out a did a full days worth of cutting jobs last thursday, go figure, cutting grass on the 22nd of December
 
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