Clutching/gearing in depth. Guru's chime in.

C

crimsonride

New member
Joined
Sep 29, 2005
Messages
183
Okay, So I've got two issues here. Gearing, and clutching. I need some guru's to chime in for me.

The sled in question is an exciter 570, lightened to close to 400 lbs, piped, (currently clutched but I don't know what weights and spring), and spinning a 144 with seven tooth drivers.

To begin with, it's going to already be geared down to some degree as a result from the seven tooth drivers I'm using. I know, seven tooth drivers rob power, yada, yada...

Top speed is not a concern, low end power is and a top speed of say 60 is all I need. I do want the sled to be able to reach that top speed fairly easily, in other words, I'd rather run out of gear and rpm before I run out of power.

Give me your oppinions on gearing and clutching. Does gearing have any effect on the opperation of the clutches, ie. do I need to change weights and springs to compensate for lower gearing? My primary sping is broken so i'll be replacing it anyway.

Chime in and let me know what you would run for a clutch and gear setup.

Pics of my project to come soon.
 
well to help you out would need the rpm the engine is to run at with pipes or whatever mods you have and what gears are in the chaincase right now.

yes, gearing affects the clutch's, the easiest way to explain it is the steeper (higher numeric ratio)the gear the easier it is for the clutchs to move the sled, the less it loads the motor.
 
alright, that's what I figured.
Right now the gearing's stock except the change over from nine tooth to seven tooth drivers. I'll have to do some math to find what that's done to my gear ratio. I've heard that for each tooth off a driver you lose about 15 mph, if that's the case I've lost 20 mph off 96 and I should be right where I need to be.
I'll do some research to find what rpm I should be at.
 
For the most part all Exciter pipes made the best HP right at 7500rpm. Only Decker or PSI twins had a higher rpm @ 7750~8000. Also most had no over-rev HP at all, if you shift at 7700rpm you could be down 8~25hp from 7500rpm. A Exciter mod back in the late 80's was to cut 20mm from the stock Y-pipe. It would give up hp on the bottom but add a few peak hp but really helped over-rev hp.

Make sure you have 1990 (and newer) Exciter jets (main, needle, nozzle jets) in the carbs before runing any perf pipe. The round slide Mic's on 1987~1989's had the wrong carb spec that would cause lean burn downs, even jetted pig rich.
 
If it's within your budget find a good set of used YXR clutchs off a Exciter II. Then your clutching is overdriven because you can run a wide belt and updated clutching (from YPZ 1-1/4 thin belt). If it's not within your budget. Buy a 1-3/8 wide belt for the Exciter II. Then find someone with a YPZ grunt tool. Split the YPZ and shim the spider out to fit the wide belt (I use .020 clearance). Then take your driven off, remove the helix. Take the helix and cut 1/8th off the back side seating surface (by the c-clip). Shim your driven so the 1-3/8 belt rides 1/16 or so up and put it back together. Now you have "poor mans" overdriven clutchs, and they work just as good.
 
very good info. I was having a hard time trying to find the rpm specs and getting all kinds of differing info.

I'll look into those carb parts. That's very helpfull information, I'm willing to bet I'm going to need to be switching parts.

So, explain to me what an overdriven clutch is. I'm sure I could shim and cut the clutch, I'll look into what sets are going for off exciter II's, they can't be that expensive.
 
I've had a little experience with Exciters over the years and still have two that are my backup sleds for when we have company or if the wife decides she wants to ride.

First off, I am by no means an expert on Exciters and do not want to get in a pissing match with anyone. But the information posted by toydoc about the Exciter carbs, I believe, is possibly incorrect. Now if I'm wrong, then someone please correct me, but I'll tell you what I had learned from my experiences.

The 1987 - 90 Exciters used the Mukuni Power Jet carbs, and in 1991 Yamaha went to non powerjet carbs. After the switch in 1991 to non-powerjet carbs Yamaha suffered an extreme amount of problems with lean burn downs on the 570 engines. Yamaha was going nuts trying to figure out what the problem was, along with PSI Performance in Utah.

Anyway, through extensive dyno testing PSI was able to figure out that the rod taper on the late model Mukuni Carbs was incorrect and created a lean spot in the upper RPM's no matter what you did with jetting. They then started manufacturing there own rods which stopped all the above problems and I believe to this day you can still get rods from them and they cost about 40 or 50 dollars for a sets of rods.

Personally, I like the powerjet carbs, and I've done alot of jetting by trial and error and have had a great deal of luck with them, and never had a lean burn down using them. Where we ride the elevation is between 6000-8000 feet, on my 87 I have a PSI pipe along with the early model Powerjet Carbs, and my jetting is 290's on the mains, and 150's on both sides in the powerjets. It has really good power and my piston wash and plugs look great. On my 91, I also run the powerjet carbs but a little leaner on the mains (270's) because it runs the stock pipe, and once again I have had no problems.

As I said, if someone can provide me with any other information that shows this old fool is wrong, then let me have it with both barrels!

As a added note, my 1991 Exciter I have geared with a 17T top gear with 35T bottom, great low end power and very quick to about 60 MPH. I'm looking to re-gear my 1987, have already dropped the top gear from a 17T to a 16T and I'm looking to find a 33T or 35 T for it. In case you didn't know Yamaha also changed the gears in 1991 and they are not interchangeable with earlier years. So if anybody has the above gears I'm looking for, get in touch with me along with a price.

Thanks!
 
Last edited:
awesome. I have two sets of carbs. I know right now I'm using the newer set which I believe are 91's and I think the other set are from 88. I'll go swap them over if I need too. I'm sure I do most of my riding in the 9000 to 10000 foot elevation area (Utah), and I have a PSI pipe, so your jetting information is very helpfull. Are those the only two jets I need to worry about changing? I'm just aboout done with the track swap so I'll count my teeth and run the sled around to see what it shifts like.

What's a good engagement RPM for the clutch on these?
 
First off, I will give you the following factory specifications for the carbs and gears:

Factory gearing was: Top Gear 17T Bottom 31T

Factory Power Jet Carbs:

Mains 320 - Powerjet, Clutch Side 160, Powerjet, Mag Side 200

These specifications were okay at or near sea level and factory always liked to jet them a little on the rich side. But if you went up in elevation like where you or I ride, you were flat out pig rich. The early problems people had when rejetting the carbs was they would just change the mains hoping to lean down the mixture but wouldn't touch the powerjets at all and would find they were still rich and after doing this several times became fustrated. As I stated earlier, they are not the easiest carbs to tune, but when you find that sweet spot by rejetting both the powerjets and mains together, it makes all the difference in the world how your sled will perform.

If you are sure your riding all the time at the elevation you suggested above in your post you could jet your carbs even leaner than I have mine set at because of the increased elevation. I would not be afraid personally to start out with 270's or 280's in the mains and install 140's in the powerjets, run and take several readings on your plugs and see how they look. If they still show a little rich drop the mains one size and then drop the powerjets down to about 137.5's and try it again. But I'm betting if you start with 270 mains and 140's in the PJ's you will be very close to getting what you want.

As to your question about engagement RPM, I run Comet clutches on both of my machines and they are set identical, I run a Comet silver spring and my engagement on both of them is right at 3800 PRM, which suits me just fine.

It seems you and I are alike, I'm not a top speed freak at all. Because frankly, the area where I ride just doesn't allow it because of the terrain, but boy I do love the awesome acceleration from 0-60 MPH with the gear changes I did to my 1991, hence the reason I want to change the 87 around to be like the 91.

Please let me know how things work out for you and if I can help you with anything, let me know!

Good Luck!
 
Thanks for the help. I almost have the track and suspension installed, I'm working on lightening this thing up all I can, It's going to be pretty light. Soon as we get some snow here I can start working on jetting.
 
Oregon Exciter said:
I've had a little experience with Exciters over the years and still have two that are my backup sleds for when we have company or if the wife decides she wants to ride.

First off, I am by no means an expert on Exciters and do not want to get in a pissing match with anyone. But the information posted by toydoc about the Exciter carbs, I believe, is possibly incorrect. Now if I'm wrong, then someone please correct me, but I'll tell you what I had learned from my experiences.

The 1987 - 90 Exciters used the Mukuni Power Jet carbs, and in 1991 Yamaha went to non powerjet carbs. After the switch in 1991 to non-powerjet carbs Yamaha suffered an extreme amount of problems with lean burn downs on the 570 engines. Yamaha was going nuts trying to figure out what the problem was, along with PSI Performance in Utah.
Click to expand...

No one has wrong information. The Exciter had lots of updates and changes, sometimes mid year or YEARS later from yamaha. So what one you have, what year you bought it and what updates yamaha has for it can make it seem like wrong info. The 1987 Exciter came with butterfly carbs that had issues. Only 88 and 89 came with Power jet carbs. 1987's yamaha would switch out the butterfly carbs to PJ carbs as a update. By late 1989 yamaha had another update to PLUG off the power jet circuit in ALL PJ 1987,88 and 89 Exctier carbs as part of the DEALER prep. Remember way back in 1990 (or later) you could buy a NEW 1988 Exciter so MANY Exciters left the dealer with the PJ pluged off from yamaha. The only reason yamaha even tried the power jet was to get them to live, and that didn't work.

Oregon Exciter said:
Anyway, through extensive dyno testing PSI was able to figure out that the rod taper on the late model Mukuni Carbs was incorrect and created a lean spot in the upper RPM's no matter what you did with jetting. They then started manufacturing there own rods which stopped all the above problems and I believe to this day you can still get rods from them and they cost about 40 or 50 dollars for a sets of rods.

Personally, I like the powerjet carbs, and I've done alot of jetting by trial and error and have had a great deal of luck with them, and never had a lean burn down using them. Where we ride the elevation is between 6000-8000 feet, on my 87 I have a PSI pipe along with the early model Powerjet Carbs, and my jetting is 290's on the mains, and 150's on both sides in the powerjets. It has really good power and my piston wash and plugs look great. On my 91, I also run the powerjet carbs but a little leaner on the mains (270's) because it runs the stock pipe, and once again I have had no problems.

As I said, if someone can provide me with any other information that shows this old fool is wrong, then let me have it with both barrels!

As a added note, my 1991 Exciter I have geared with a 17T top gear with 35T bottom, great low end power and very quick to about 60 MPH. I'm looking to re-gear my 1987, have already dropped the top gear from a 17T to a 16T and I'm looking to find a 33T or 35 T for it. In case you didn't know Yamaha also changed the gears in 1991 and they are not interchangeable with earlier years. So if anybody has the above gears I'm looking for, get in touch with me along with a price.

Thanks!
Click to expand...

That is correct PSI did find the problem with the 1988~89 needle jet. The stock 1990 yamaha Exciter had the correct (PSI copy) needle with no power jet. But that wan't the only issue. PSI twins and Deckers STILL had burn downs after carb updates. After 7500rpm the 570 had harmonics issues so PSI also found adding weight to the Exciter flywheel cleared up that issue. Later Yamaha also added weight to the stock Exciter flywheel.

IMO, the reliability of the Exciter was and still is it's best with Exciter II 1991 and up. No carb, harmonics or cooling issues. Lots of very good updates are all done stock on the Exciter II's.
 
Last edited:
Okay, so this thing's dialed in tight except for the clutching. I'll have to get a pic up because this thing is bad a$$! The clutching on it is totally messed, the guy I origionally got this engine and clutch from had tinkered a ton with it so it's got a arctic cat clutch with who knows what weights and springs in it.

Can anyone sugest a weight and spring combination that will give me shift around 7500 rmp and a high engagement around 3800-4000?
 
I'd start with 49g weights and a Cat Yel/Grn spring and see what rpm you have. At 9000' you may have to drop some grams, but i'd start low and work your way up to the rpm you want.
 
That's the exact combo I was going to go pick up today. I guess you and I are on the right page. I'll try it out and report how it runs.
Thanks for the info.
 
Hey TOYDOC and Oregon Exciter, can you sugest a gearing setup to try for this sled. I've installed the yellow/green spring and I have engagement right at 4000 with 48.5 g weights. I've ran it with the track suspended in the air and at full shift I'm only getting maybe 40mph out of the track (That's and estimate by looking at the track as it spins, could be off). I'm going to go pull the cover off the chaincase and look at what my gearing setup is to tell you where it currently is. I have a 29 and 17 tooth gear laying around that I could use if I needed to.
I think those seven tooth drivers are gearing me down a lot more than I thought they would.
 
Okay, So I did a little more math. The sled had a 31t bottom and 17 top so I swaped in the 29 for the bottom to bring it up a little. The calculator shows that I should have a top speed of 68 with the setup that I had. There's no way I was reaching that. The calculator now says I should have a top speed of 74. I'm going to go test it out right now and mess with some weights and springs.
 
One more thing. I took it out and it went very well. One thing I had done was clean off the sides of the helix that had some gummed up grease on it that I think was keeping it from completely shifting. It definitely picked up quite a bit. I'm not sure how much since I didn't have my GPS to tell me my speed.
RPM's hung out around 8000, that's bad for an exciter, I need to bring them down to around 7500. I have a set of 52g and 58g weights I'm going to try. I guess I'll see where that puts me on the rpms. I may even go to a gold spring for a little higher engagement.
Let me hear your oppinions.
 
You must log in or register to reply here.


Back
Top