Here is the problem. I have an '02 MXZ 800, and I am having major clutching problems. This is what I have tried in the past:

1) Stock-ok, but not good enough

2) Goodwin kit-Awesome hole shot, if you could get it to hook and no topend.
kit consist of gp4 ramps(like doo 228), 200/270 primary(?), 21.6 grams pin weight, a 52/48rer helix, and a goodwin blue spring, 185/290.

3) Engine mods- New pistons, 2mm base shim, extra intake ports, and RK-Tek head. Tried Goodwin kit and it would not work with these mods. Changed everything under the moon to try to get some topend out of the sled. 95 mph is it.
I have had 280 ramps, 301 ramps and 287(which are working the best). I have changed the primary spring to a 200/350 and I am running around 17 grams of pin. I have had numurous helixes, 47/44, 52/48, 52/44, 50/47 and now have give me any more topend. The clutches run cool under normal riding but get HOT doing WOT runs.

4) Now I have changed eveything. I have lowered my cylinders. I now have a 1.2mm shim instead of the 2mm shim. New domes, porting work, and now planning on a set of CS trail pipes and can.

I need a good start for clutching. I would like to see this sled run atleast 105mph and still have as much of the bottom end as I can.

Any Ideas?????

Thanks for your input,
Brian

With what you were using are your rpms getting sucked down on top? say the tach reading 77-7800 rpm? Whats your gearing? I assume everything in the drivetrain is spinning free, track etc...you said you had a 2mm base in there, thats pretty huge, out of curiosity what was your compression, and what did you doo to bring it back up, was it the Rk head designed to work with the gasket or a tall piston dome.. at any rate what compression did it work out at?

The pistons do have a taller dome in which Kelsey remachined to fit his domes in his head. Cranking compression was 150psi with the 2mm shim as well as with the 1.2mm shim. New domes were made for the change in deck hieght. Compression ratio is 13 to 1 with the 2mm and 12.5 to 1 with the 1.2mm shim
I have run 27/43 gearing, 26/44, 27/44 27/42, 26/42. The 26/44 works the best. I run the rpms at 8200 on the tach (8000 true).
And no, the rpms stay pretty much at 8200 at WOT.


Brian

mxzwfo, i have stated this in a previous post, and it will work equally as good with your set up on the 800 , as i have the same mods as you do. 24/43 gears, which is 1.79 final ratio, 54/48 helix , you can get it for the rer, "new" beige set for a start at b-6. 297 ramps are awesome, a doo red/230/410 spring. with those ramps, spring, and your mods bring the pin weight up to 20g or so to start with. why do people complain about the 700 beating the 800, i just told you how to make the 800 work awesome!!!

i have a good 500 foot set up for you if you would like it :D .

Running with the 301, then change out to the 287, what is the difference of how the sled runs between the two?
...What events are different right up to top end?
Im suspecting from looking at the 301, the engine might lay down a little?

If you have done engine mods and will continue to do so adding pipes/can, are you going to wait till you are all done these mods before you tackle clutching?

Do you know the rpms that the pipes/can will run at? Stock is 7850, what is the new rpm you will have to run at?

Yes Joe, the 301's lay down in the mid-range and the 287's pull hard from start till I hit 8200. The only problem is with any of the set ups, is I still end up at about 95mph. It is pretty sad to have 600's, 700's and other 800's walk past you on the top end :angry: .
I know I have changed a lot since last winter. I will be planning a clutching session as soon as the first snow fly's. :) I am just trying to get some ideas to ponder before it gets here.
I feel sure that lowering the cylinders down will help as well as the other things that I have done.I also think that the edition of the the twin trail cankshops will help to. I am the type of person that jets to the day and I watch everything closely, so I am not worried about the twin pipes.

Thanks eveybody!

Brian

clutchman,correct me if I am wrong,but I dont think the rer secondarys have holes to set the spring up at differant tensions? ??? I don't have an rer sled but I was present when mxzwfo and idooski done some clutching.

Dooman, They do have the holes but, trying to find a spring that doesn't bind under full shiftout is the problem.

Brian

Mxzwfo,how much do you weigh?We built an almost identicle sled this past winter and had the same problem.The sleds owner was about 150-160tops and we could only pull(consistantly)19 grams with a 200-320 primary spring,and more importantly we found a straight 50 rer helix would pull just as strong but top end better than any of the compound helixs,52-47,53-48 etc(we tried a bunch)Also were your pistons welded up on the skirts(at the exhaust port bottoms)we tried this without much sucess,you had to lean it down so much just to get the power back to stock it was more than a little unnerving,and in the end the skidoo pistons made more power(theyd pull more weight at least).Again if you are over 160 i think i would put a 200-320 spring and start at 18.2 to 19 gram pins.

John, I weigh about 220 in full gear. The pistons are aftermarket Art ProX twin ring. They are not for this application but with a little machine work on the dome they work fine. And no the skirts have not been welded and I don't think the Exhaust wave port is an issue in these engines. I DO think the carbs are a big issue and idooski is working on a fix.


Thanks, Brian

those twin pipes only need to be 8100-8200 rpm to get the most out of them we have found they pull best there . ive done a lot of different ramps and the 298 230-380 with 18 pins with the 414 860700 belt , 52-46 @21 lbs net me a constant 115mph @155lbs driver the belt alone is a 5 mph improvement

Originally posted by Dynamo^Joe@Jun 14 2003, 10:43 AM


Do you know the rpms that the pipes/can will run at?* Stock is 7850, what is the new rpm you will have to run at?
Joe, the Crankshop trail twins are made to run around 8200 rpm's. My engine now, even before the pipes pulls good at 8200. So that is the number that I am shooting for.

Brian

:D Brian, when you get ready to test your sled, I will be the "sacrificial lamb" for your clutching session.

Are you sure your exhaust valves are staying open on the long runs?

Originally posted by tb2@Jun 15 2003, 09:00 PM
Are you sure your exhaust valves are staying open on the long runs?
As best I can tell, yes they are. But, that don't mean they don't close back slightely. What would be the best way to check and see if they are staying open? I thought about taking the springs out completely and making a long run. I have backed the tension screw off a lot. The only thing gained or should I say lost was low end performance along with the midrange.


Thanks,
Brian

I would think if the valves wern`t opening the reves would fall off, the bottom line is that if your pullin x amount of rpm AND THE CLUTCHES ARE SHIFTED ALL THE WAY OUT you got your mph, right? thats basic, no problem...in theory...

I have the RPM's but I am not getting the clutches to shift out all of the way. The BEST that I have had it is 1/2" shy of the top of the primary pulley.



Brian

95 mph
287 *working best*
200/350
17 grams

Comments:
301's lay down in the midrange because make engine pull harder in top end.
287 pull hard until 8200.
Clutches - Cool normal riding, HOT @ W.O.T. run.
No top end
47/44, 52/48, 52/44, 50/47


This is what i'm focusing on...
95mph - top end down;
...Wondering if primary has enough push to open secondary.
...Wondering if secondary sheaves have enough clamp on the belt to pull top speeds.

287 pulls hard until 8200;
...My experiences with 800's, knows 800 is 7850 engine.
...Knows that tachs read 175rpm high on average.
...Remembers all the feedback I get drivers telling me they run best at 8100 "Tach RPM"

Clutches - Cool normal riding, ................:
...Has enough clamp to grab belt keep sheaves cool
...Sometimes too light of flyweight can keep clutch temps down.

Clutches - .................., HOT @ W.O.T. run:
...Usually caused by lack of sheave force clamping on belt.
i]from not enough spring force
ii]too large of helix angle at finish
....simultaneous occurrence of both details.

Details i'm keeping on the backburner:
17 grams
...During the procurement we played a lot with the flyweight and right now with a 125lbs engine we use 18 grams. Now I know that the angles on my stuff is not remotely close to what you mention in the finish angles, but warm near the start. Our 800 pull that 18g just breaking 8100 "barely" Other guys with higher compression run more weight.

301 lay down in the midrange.
...Not enough info here. Would like better explanation of what happens when watching tach when you feel this "lay down"

xx/44, xx/48, xx/44, xx/47 "these finish angles"


The hunch I have right now with the present clutch setup, I get the feeling that there is not enough flyweight and not low enough helix angle.
I wish I could elaborate on the helix's I made and how substantial of angle changes before our 800 actually felt good to drive.
So just my testing and the experiences I gained, this is the hunch Im going with right now. This is just dealing with your details you have, and what direction I personally would take to "Compensate" and make a change so we can measure a new and hopefully better outcome.

...and tell you the truth, you can go waaaaaaaaaay more on the final # on that primary spring. heh heh

I personally have not experienced the valves closing or fluterring on long runs but I have heard of it being a top end problem on the 800s.I would remove the springs or find a way to secure the valves in the open position. Just about any clutching combo and stock gearing should yield better top end results than what you have. Time to go back to the basics I guess. Check belt length and width, clutch alignment and center to center distance, spring and component conditon in both clutches, motor mounts and bump stop. If your sure those components are in spec its time to look at the motor..