96 Vmax Mtn Max. From a dead stop it pulls great, very strong, no hint of bogging. However, when you let off of a hard throttle at the top of a hill or in a corner, then give it throttle again, it takes FOREVER to get back to a good RPM and start accelerating again. In very deep powder it gets so bad I am sometimes afraid the engine is going to die, though it never has. It is piped and has no power valves so I understand that the low RPM power is going to be poor, still I think the real problem here is the secondary shifting back too slow. Since it does so well from the line, I find it hard to believe it could be a carb problem.

I replaced the secondary spring with a new stock spring and cranked up the preload from the specified 70 degrees to the full 120. I don't really think it helped, or at least very little. The manual specifies engagement at 3700+-300 and peak of 8000+-300, and it does engage at 4000 and tops at out 8300 on the tach.

(As a side note, I would like to raise the engagement to about 4500 but keep the same peak rpm. If somebody knows where to find a selection of yamaha primary springs, let me know that too.)

The helix that's on there should be the stock 39 degree straight cut. I haven't verified that but let's just say it is. The drive gear has already been changed down from 21 tooth (stock) to 19 (specified by yamaha for high altitude). Based on this information, can anybody give me an idea where to start? I'm thinking multi-angle helix, but I've never experimented with such a thing. I also haven't found too many sources for Yamaha clutching. Maybe I'm on the wrong track?

Suggestions?

James

the v max stock is clutched for sealevel and at Hood your probably 4-6K' ? may have to take a rivet out of the weight? new drive spring would be a good start before you do anything also. That's all assuming your secondary is in good shape, belt etc all OK. I wouldn't swap the cam but would verify it is a 39. I'll try and post a gauge you can measure it with.

here it is, just print it on regular printer paper

Yeah I haven't checked the primary rivets yet although it seems like 8300 RPM max is high enough for my taste and the life of my crankshaft. Maybe I'm just being paranoid. I should at least check it and try the factory recommendations for my alt if it's not already there.

Yamaha's service manual for this model specifies different drive gears for different altitudes (less teeth for more altitude), with the same secondary spring and preload for all altitudes. Looked crazy to me, but it's so. After my first test ride I got a brand new spring and cranked up the preload all the way but no real big change. I already have it geared for over 5000 feet, which is a pretty average altitude for me as you guessed, although the trails sometimes dip under 3500. Anyway I want acceleration, not top speed, so that gearing works for me in theory.

I cleaned the secondary and the slider shoes look good. I did notice that the belt deflection was too tight so I fixed that, haven't ridden since. Seemed like a minimal change, I doubt that's the problem.

This thing does have altitude compensation, and the plugs look fantastic, so again I highly doubt carb adjustment problems.

And thanks for the guage. That is awesome. I'm at work now but I'll check that cam today.

James

My apologies to anyone trying to learn from this thread. Another test ride was very revealing. The lesson here has been don't assume. First, I was wrong, the sled does not pull good from the line, it burns the belt from 4000 to 5000 rpm, then it takes off good. Basically, as it was suggested, the primary clutch was set for a much lower altitude. I had to order new weights because I just couldn't get the old rivets out, and they had already been grinded on. $75 there that I really didn't want to spend, and of course the parts are not in stock, ETA sometime next week, and it is snowing right now. We're expecting 2 feet this weekend. Sunday and monday are going to be sweet days, but I'll just have to ride nonmotorized snowcraft I suppose. The short track EXT isn't going to cut it in that much fresh.

Second, I began to suspect that the carbs were running lean. The exhaust smoke was pure white and smelled different than any sled I've ever been around. This is my first Yamaha and it ran so strong that at first I thought it must be jetted correctly. The plugs seemed a bit hot, enough to worry me, but nothing over the top. I didn't do readings at all throttle ranges, just checked plugs every so often. Remembering that this is an "electronically controlled carb" sled (altitude and temp compensation), it should only have one possible main jet size, which I have verified through multiple sources as 162.5 in mikuni small round. It also has the SLP pipes on it. I talked to Jim at SLP and he said it should be at least at 167.5 for this sled with those pipes. Well I finally opened the carbs and found to my horror, 157.5 main jets. I think the previous owner tried to follow the jet chart from SLP not knowing that that chart can't be applied to the ACCS carbed sled. Good thing I put less than 50 easy miles on it and it didn't burn up before I found out. Also, the directions from SLP do specify that the airbox baffle be removed, and mine is still in place, so that reduced airflow may have saved me. Now with the bigger jets I'm trying to decide if I should keep the airbox baffle in or take it out.

So I've got the carbs where I hope they should be and the primary clutch will be there sometime during the week. I'll post my results and then we'll see if I really have a helix/secondary problem or not. It's looking like my first impression was totally wrong.

And let me give huge credit to SLP for answering questions about a product that they haven't sold for 10 years. I am very impressed with SLP.

James

Got the primary clutch finally set up for the high side of my altitude range. The (hopefully) proper main jets are installed. Will ride test no later than Monday. I'm going to leave the airbox baffle in at least for now. I don't know, I'm scared to blow up my engine, but if low-end power stays poor I may have no choice but to try it removed. I'll report my results...probably next Saturday. We still have a ton of snow so I'm hoping to get at least 3 more good days this season if I can afford the gas.

My BRP tech buddy has also reccomended dropping yet another tooth from the drive gear in addition to what I've already done, but if I do that it's going to be over the summer. I'll probably end up doing it since what I really want is climbing power/acceleration and not top speed...and according to the service manual I can still use the same chain if I drop one more tooth.

I'm very optimistic about my test ride but I guess we'll see...

Well I rode at 4000 to no higher than 4500 feet and my primary clutch is now set up for 4500-7000 feet, so it should have revved high. Well, not yet. The engagement was even lower, like 3500 RPM, and the peak dropped to 8000 max (although the lakes are melted and the trails are real bumpy so I didn't really get a chance to open it up for very long). It still burns the belt until about 4500 RPM when trying to start off. I have definitely dropped total arm weight from how it was before, but the previous rivets were installed backward (with more weight to the outside, which definitely is backward from the chart) from how they are supposed to be (by the previous owner) so that clearly had an effect.

Has a ton of power once it gets going, as before. Also it didn't have as much trouble revving back up after letting off throttle (my original problem). It felt better and more responsive all around, but there's no more powder to really test it in.

At any rate, I've ordered a new primary spring from the dealer. Not in stock of course, I'll report how long it takes them to get it. I should have noticed that when I changed the weight arms it was way too easy to push the primary sheaves together. I can compress this clutch with one hand, whereas my EXT clutch takes the total force of my body to compress. Doing my metric conversions, these two primary springs shouldn't be that different.

Better news, I found the part number for OEM Yamaha clutch engagement shims on totallyamaha.com. 90201-483P9-00, it says you can use up to three at a time but they don't give a thickness measurement. Also not in stock at Action Motor Sports even though it's the same shim for every yamaha sled clutch. What do they do when they need to do work on people's machines? Make them wait a week? Yeah, probably.

It was hot this week. We have a ton of snow but it's starting to melt fast. I'm hoping to get in a test ride once I get that spring installed, but it has to arrive first. I guess we'll see. I don't want to still be fussing with this clutch next winter, so I'll take it for a run if at all possible. It could still snow here...

All fixed! The primary spring was the completely wrong spring. Sort of a pattern with this sled, having the wrong parts installed. I think I see what the previous owner was trying to do with the tuning but it ended up bad and I'm glad I got it right again. Don't know if the spring was worn or not but it was too long and a smaller wire diameter than what's supposed to be there. It's funny how the RPM range before and after changing weights and spring is similar yet the performance is dramatically different. It's engaging at 4000 and topping out at 7900 in my limited test run. But now it GOES when it hits 4000 RPM rather than burning the belt, and it doesn't have that weird slow backshifting that I originally described. Yay. I might crank the RPMs up a touch with one shim but as far as responsiveness and just feeling the way I want it to - and curing my original problem - I'm pumped.

Hillpounder thanks for the tip. It seems SO obvious now. Really, I mean it this time, I'm never going to even test-ride a newly purchased used sled again without tearing open the carbs and both clutches. All three sleds I've owned, all local sales, arrived with clutching and jetting totally wrong. All three dangerously lean. The EXT was clutched to overrev like crazy, the widetrack underrevved, and this Yamaha had what seemed to be the proper RPM range but you could tell something was obviously wrong in the clutching. I'm glad it was a simple fix in the end. Not exactly a discussion for the high-performance tuner but maybe a reminder to not overlook the basics.

After yesterday's test ride I'm still not happy with the way it pulls from a stop. I have the engagement up to 4100RPM but it still doesn't move at that point with me on it. If I get off it goes fine on engagement. This is in very wet, crappy snow (80 degrees out), so it might pull better on real groom, and the engine will have more power in cold air. But since this is supposed to be the mountain max, I want more pulling power. You really have to juice it, like at least half throttle, and then it goes like crazy. Not like any other sled I've ridden. My buddy blames the pipes for killing low-end power, Jim at SLP begs to differ. But Jim did say that although the pipes were designed for that engine, they were not designed for my model - I take that as code for "not mountain" performance applications. I've heard similar poor engagement stories from other 94-96 Vmax owners, so it could be the sled design I guess. The belt still looks really good. Only about 100 miles on it though. I want to keep the pipes and try attacking the problem with gearing.

Anyway, I ordered the 17 tooth sprocket and 70 link chain (this is going past the top of the altitude chart), which is the lowest gearing I can get without changing track drivers, which are 9 tooth. According to SW's calculator, this will drop my theoretical top speed by 9MPH to 76, which is fine with me. This sled is not for lake racing. Probably won't be able to post results until late fall...

Update: I just read the "Torque vs Horsepower" article in the tech section and I think it confirms my friend's suspicion about a major cause of the clutching problem being pipe-itis. This quote stands out to me: "As the speed then decreases, so does the torque, and with less torque feedback there is no backshift into a lower ratio to compensate. This results in an engine and a clutch that live in disharmony, constantly chasing each other around, trying to agree on a place to coexist." My main complaint was really poor backshifting. What the article seems to be saying is that when you have an engine that's lost it's low-end torque by piping, it doesn't "pull" enough at the lower end (against the torque coming from the drivetrain) to make the secondary backshift.

Quote: "The wider the torque backup, the easier the engine is to clutch. Having maximum torque down lower on the powerband also gives great acceleration out of corners and off the line. " Reverse all that for a narrow power-band and it sounds real familiar.

So "not enough torque" begs the question "compared to what?" Well, compared to how the sled was tuned before it was piped. So are twin pipes on a mountain sled a lost cause? I think so, but I'm going to give them my best shot.

Quote: "The heavier the machine is, the wider a torque band you need to make it work right."
Yeah and any machine with my butt on it is a heavy machine.

Okay - you can control how much "weight" the clutch "feels" through gearing. So I think my gearing strategy is the right one any way you look at it. Less torque from the drivetrain, through gearing, to match the decreased torque in the engine. But will it be enough? I have already seen good results from clutching the primary lighter for higher RPMs across the board, delivering torque earlier in the power band. I know from last year that it still pulls hard at 8300 (from what I read that tells me I haven't reached the point where power starts to fall), so I may try going even higher like the 4500-8500 range.

I can't think of anything else at this point in terms of stock tuning. I changed out the secondary slider buttons last night. They were kinda worn. I really won't know how successful all this was until I'm in 2 feet of powder.

Just a quick update, I took the Vmax up to about 9500 feet last week and it climbed awesome. The high-end power honestly amazed me. The peak RPM never dropped below 7800, and that was only on the longest, steepest stretch at about 8500 feet. It ran at 8000 RPM the rest of the time, even at my personal highmark. Considering I clutched it to 4500-7000 feet according to the Yamaha clutching chart, that truly impressed me. It tells me that I must be getting a really nice boost in peak horsepower from the SLP pipes, so I can see why people like them. It pulled really hard. My buddies went to about 10,000 feet, but I was too scared to keep climbing. My sled definitely is more capable than I am. It had all the power I could handle (at peak rpms) and the 136x1.5" sent me right up the mountain. It was an exciting and technically challenging day and I honestly doubted that my sled would be up to the task, but it did as well or better than I could have hoped.

Anyway I think the primary and secondary are right where I want them. I set it 20 degrees looser than stock on the secondary spring and it seemed to shift and backshift better than ever, but I don't know if that's really the reason. And it still doesn't backshift any kind of hurry.

My 17 tooth drive sprocket and 70 link chain should be in tomorrow. I think that's going to give me some of the power at engagement that I'm still missing. Should help on those extra-steeps too. But, seriously this time, I won't know until next winter because I won't be riding until then.