yz125mm700
New member
i have been riding with my buddy out west, he has a 2005 summit 800ho 152x16x2.3 track. i have a 2000 mm700 144x15x2 we both have other misc mods done to them, nothing drastic just cans, and what not. but on to my question, he runs circles around me in the deep snow and climbing. 
i know he has way more track and its newer but i need to do somthing to keep up. i hate to say it but after riding that rev in the powder and then back on mine, i was almost ready to buy a summit that day. so how much would a MPI tunnel help deep snow performance? Would a 16 inch wide track fit in That tunnel?
i know he has way more track and its newer but i need to do somthing to keep up. i hate to say it but after riding that rev in the powder and then back on mine, i was almost ready to buy a summit that day. so how much would a MPI tunnel help deep snow performance? Would a 16 inch wide track fit in That tunnel?
yes the 16" track will fit in the tunnel it will fit in the stock tunnel with some mods.Part of the problem with the mmax's are the approach angle.Mpi makes a kit to change that.Most of the silencer lose 2hp on the 700 single pipers do the exhaust mod to your stock can it's worth 2hp.Get a hold of srxsrule he had his rocking with a lot of homade upgrades.I would go witha 151"track and relocate your skid.
yz125mm700
New member
here is the performace mods that have been done. carbon fiber reeds, reed spacers, boost bootle (i think thats what its called, goes across all three carb boots) layer of headgasket removed, dyno port can, 2 - 2.5" slp flowrites in the dash. i was wondering about a new tunnel becuse it would roll the chain case, and move the driveshaft 4" back and 1" down. also the kick up in the back. how would i go about moving the skid back? and how far would i have to move it to go to a 151"
If you are really serious about changing tunnels, I'd contact the guys at Fab-Craft. I ride with their parents on a regular bases and both of them have that tunnel and to me fits the mountain type tunnel the best.
However the tunnel alone is not going to cure your problem.
I have been racken' my brain now on this subject for the past several months, reading all the post here and have posted several times (this same topic myself) asking for cures to the trenching problem and poor performance of the mountain viper and mountain max. And even though I have improved the problems on my mt. viper to where I feel it is liviable, I have not cured all the problems, but have come to the conclusion that I have what I have and I like it for other totally different reasons. But my investigations have lead me to these conclusions and if anyone differs, I am still open for any and all suggestions.
Trenching (to me) means that the sled has the inability to balance or level itself out and maintane a level surface on top of the snow. This can be caused by either to much approach angle in the track and suspension or to-much transfer of weight to the rear of the sled. A cavatation effect of snow beneath the track and finally no snow remaining under the sled to support it's movement over the snow.
Another reason for trenching and poor performance is the inability of the sled to remove the snow accumulated in the tunnel fast enough to replace it with new snow and move forward, virtually digging it self along rather than pulling in new snow.
Here is a quote from Fab-Craft's Mike Cassidy," Sleds that wheelie when climbing, look cool, but they are actually wasting power and trenching, which slows your ground speed. The cure is more track to tunnel clearence, less approach angle and a controlled weight transfer."
Now if a guy is serious and can afford too, here is my way of thinking to cure the problems of the yamaha in the powder.
Trenching.......you have to lessen the approach angle, to do this you will have to roll the chain case down and back, this will also allow for more clearance between the track and front of tunnel. A number to shoot for is 21/4 -21/2 inches of clearance. (Presently the MM and Mt. Viper with a 2" track has 1 to 11/2" of clearence.) Now we can get the snow out of the way, out of the tunnel and grab on to new snow.
Secondly, a bigger foot print will definitly help with the transfering of weight, more foot print, more weight carrying capacity, but how much is needed? That is determined by what you want to do with the sled.
For me a 162" track is only good for someone who wants to go straight up.
Myself, I am more of a boondocker, tree rider, and have decided that a 151" track is enough for my riding style and am even been concidering going with a 11/2" track versus a 2" for more track to tunnel clearence, plus with other changes I have made should balance my sled out.
Thirdly, controlled weight transfer. A completetly new after market suspension, designed for powder riding or a simpler move is to modify the yami suspension by removing the transfer rods so you can have more control of the transfer on that suspension and more adjustability.
So, all in all, if you want to compare apples to oranges, a MM with a 141 to a Summitt with a 162, first you have to equal the equation.
Yes you can do simple things to stay close to him, (transfer straps,longer track,increase HP) but unless you spend the money to totally redesign your yami, you can never stay even or ahead of him and just changing the tunnel won't get you in the ball park. I am sorry to say apples are not oranges.
Now if you want to ride on more equal ground with what you have, take him to the trees.
In my mt. vipers present state, I will ride with anybody in the trees.
I don't mean to sound harsh, but after beating myself up for the past few years on the same topic, I have come to the realization that I enjoy for Mt. Viper for the way I ride it, and an apple is not an orange, so don't be comparing them like they are the same. If you want to kick his a%$, buy a Mt. Apex with a turbo, and blow his doors off.
Better to ride a Yami home, than a poo and walk.
However the tunnel alone is not going to cure your problem.
I have been racken' my brain now on this subject for the past several months, reading all the post here and have posted several times (this same topic myself) asking for cures to the trenching problem and poor performance of the mountain viper and mountain max. And even though I have improved the problems on my mt. viper to where I feel it is liviable, I have not cured all the problems, but have come to the conclusion that I have what I have and I like it for other totally different reasons. But my investigations have lead me to these conclusions and if anyone differs, I am still open for any and all suggestions.
Trenching (to me) means that the sled has the inability to balance or level itself out and maintane a level surface on top of the snow. This can be caused by either to much approach angle in the track and suspension or to-much transfer of weight to the rear of the sled. A cavatation effect of snow beneath the track and finally no snow remaining under the sled to support it's movement over the snow.
Another reason for trenching and poor performance is the inability of the sled to remove the snow accumulated in the tunnel fast enough to replace it with new snow and move forward, virtually digging it self along rather than pulling in new snow.
Here is a quote from Fab-Craft's Mike Cassidy," Sleds that wheelie when climbing, look cool, but they are actually wasting power and trenching, which slows your ground speed. The cure is more track to tunnel clearence, less approach angle and a controlled weight transfer."
Now if a guy is serious and can afford too, here is my way of thinking to cure the problems of the yamaha in the powder.
Trenching.......you have to lessen the approach angle, to do this you will have to roll the chain case down and back, this will also allow for more clearance between the track and front of tunnel. A number to shoot for is 21/4 -21/2 inches of clearance. (Presently the MM and Mt. Viper with a 2" track has 1 to 11/2" of clearence.) Now we can get the snow out of the way, out of the tunnel and grab on to new snow.
Secondly, a bigger foot print will definitly help with the transfering of weight, more foot print, more weight carrying capacity, but how much is needed? That is determined by what you want to do with the sled.
For me a 162" track is only good for someone who wants to go straight up.
Myself, I am more of a boondocker, tree rider, and have decided that a 151" track is enough for my riding style and am even been concidering going with a 11/2" track versus a 2" for more track to tunnel clearence, plus with other changes I have made should balance my sled out.
Thirdly, controlled weight transfer. A completetly new after market suspension, designed for powder riding or a simpler move is to modify the yami suspension by removing the transfer rods so you can have more control of the transfer on that suspension and more adjustability.
So, all in all, if you want to compare apples to oranges, a MM with a 141 to a Summitt with a 162, first you have to equal the equation.
Yes you can do simple things to stay close to him, (transfer straps,longer track,increase HP) but unless you spend the money to totally redesign your yami, you can never stay even or ahead of him and just changing the tunnel won't get you in the ball park. I am sorry to say apples are not oranges.
Now if you want to ride on more equal ground with what you have, take him to the trees.
In my mt. vipers present state, I will ride with anybody in the trees.
I don't mean to sound harsh, but after beating myself up for the past few years on the same topic, I have come to the realization that I enjoy for Mt. Viper for the way I ride it, and an apple is not an orange, so don't be comparing them like they are the same. If you want to kick his a%$, buy a Mt. Apex with a turbo, and blow his doors off.
Better to ride a Yami home, than a poo and walk.
sled
I'm not shure mpi would teel you how long of rail extensions you need if you relocate your skid they have a whole kit for doing it.I would go to the new style yamaha ski's you wouldn't believe the difference in the add flotaion.
I'm not shure mpi would teel you how long of rail extensions you need if you relocate your skid they have a whole kit for doing it.I would go to the new style yamaha ski's you wouldn't believe the difference in the add flotaion.
yz125mm700
New member
snomoguy that all makes good sence, i hear what you are saying. mine is livable i can ride with everyone and make it to 90% of the places they do. its just they float and climb better, 
but just as you say it not comparing the same things, and yeah i dont what to drop thousands and thousands of dollars into it. one other idea i have entertained. i can get a 144x16x2.5 track for very little money, do you think that would help my flotation? what would i have to do to make that work? smaller drivers?
but just as you say it not comparing the same things, and yeah i dont what to drop thousands and thousands of dollars into it. one other idea i have entertained. i can get a 144x16x2.5 track for very little money, do you think that would help my flotation? what would i have to do to make that work? smaller drivers?
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yes youwould have to go with smaller driver to make a 2.5" work if you do a search there is guys on here that put 16" wide tracks on.
Sure it will help greatly just due to the larger foot print, but remember, the major problem with yamaha mountain sleds (even guys with the new Apex mountains are saying yamaha should of increased this distance) is the track to front cooler clearance; more track will bring more snow thru the same opening. And going with longer lugs is going to decrease that distance even more. You can only force so much water thru a 1" pipe.
One option of consideration is porting the track to alliviate some of the snow that is carried thru the opening, but I'm not convienced as yet that the tracks are holding up under increased HP. So we are back to increasing that distance by redesigning the sled and rolling the chain case back and down for more clearance and a lower attack angle.
Sure anything done will benefit to some degree, but I was just letting you know the inheirant problems we as yamaha mountain sled riders face, so you can decide what options and money you want to spend, for it to do what you are asking of it.
One option of consideration is porting the track to alliviate some of the snow that is carried thru the opening, but I'm not convienced as yet that the tracks are holding up under increased HP. So we are back to increasing that distance by redesigning the sled and rolling the chain case back and down for more clearance and a lower attack angle.
Sure anything done will benefit to some degree, but I was just letting you know the inheirant problems we as yamaha mountain sled riders face, so you can decide what options and money you want to spend, for it to do what you are asking of it.
MPI's tunnel is pretty much an Ekholm (which has since gone out of business, although I here Larry is still doing work on a smaller scale). It's hard to beat the $ for the MPI considering it includes the chaincase mods for the d+r and heat exchanger. I would hop on Snowest and ask around in the Yamaha forum for some 1st hand experience.
Smaller than 8t drivers sounds like a bad idea to me. Seems like you would be making that front radius very tight for the track plus moving the rail tips closer to the track = rail-stab-city (not to mention possibly hurting the attack angle). I would go 16 wide or 151 if the tunnel and d+r is out.
You still have room to grow on that engine too. Pipes will uncork that thing (my single, best mod yet), especially with the reeds, flowrites, boost bottle, and gasket mod. The MPI transfer kit helped my trenching a ton but my skid is still gonzo as soon as I find a deal. Lightweight parts are starting to show up cheap in the classifieds if you are patient. This chassis is starting to get old for the serious climbers and many are parting. This chassis is a tank in stock form and there are lots of places to loose some significant weight. The other thing that comes to mind are those stock skis. They just suck for anything off-trail. I have Simmons(1st generation), my buddy had Powder Pros, and I have heard good things about the new Yamaha skis.
Smaller than 8t drivers sounds like a bad idea to me. Seems like you would be making that front radius very tight for the track plus moving the rail tips closer to the track = rail-stab-city (not to mention possibly hurting the attack angle). I would go 16 wide or 151 if the tunnel and d+r is out.
You still have room to grow on that engine too. Pipes will uncork that thing (my single, best mod yet), especially with the reeds, flowrites, boost bottle, and gasket mod. The MPI transfer kit helped my trenching a ton but my skid is still gonzo as soon as I find a deal. Lightweight parts are starting to show up cheap in the classifieds if you are patient. This chassis is starting to get old for the serious climbers and many are parting. This chassis is a tank in stock form and there are lots of places to loose some significant weight. The other thing that comes to mind are those stock skis. They just suck for anything off-trail. I have Simmons(1st generation), my buddy had Powder Pros, and I have heard good things about the new Yamaha skis.
yz125mm700
New member
thanks for all the great advise. i think mabye i'll just ride it this year and think about my options when the season is almost done.
yz125mm700
Didn't aim to bust your bubble, keep working and thinking, that is what this is all about. Just wanted to point out what we are facing, so you don't make the mistakes the rest of us have made, and money spent in waste.
Guys like you and the other guys on this site have made great strides to improving the way our sleds handle.
You may be the one that finds that perfect set-up or solution.
Hang in there.
Good Luck 
Didn't aim to bust your bubble, keep working and thinking, that is what this is all about. Just wanted to point out what we are facing, so you don't make the mistakes the rest of us have made, and money spent in waste.
Guys like you and the other guys on this site have made great strides to improving the way our sleds handle.
You may be the one that finds that perfect set-up or solution.
Hang in there.
Good Luck
yz125mm700
New member
Thats the Reason i asked was to get your opinion and insight, i dont want to throw a bunch of money at somthing if it isnt going fix my problem. i think i may go with a bigger track (mabye 151x16) and a set of those transfer straps. see what that does for me. oh, what would i search for to find details on what has to be modified to fit a 16" track? if heard about grinding some bolts thats about it.
I brought the topic back up to the top for you.
yz125mm700
New member
perfect just what i needed, thanks
My decision to mod came after I made my last payment. It felt good not to have a payment and I really didn't want to take on another just to stay current. I've found that by picking away here and there, I can keep up with my buds on newer iron for far less. Plus I get to tinker (who doesn't like that?) and make the improvements that I want/need to at my pace. You get to see what makes a difference and what doesn't. Mods also have a cool factor about them too.............who likes to look at a stock sled?
Next for me is a sweet Ekholm tunnel that I picked up for cheep and a rear skid upgrade.
Next for me is a sweet Ekholm tunnel that I picked up for cheep and a rear skid upgrade.
A K MtnViper
New member
I ride with a 2007 Skidoo 800r with a 16 X 151x 2? , A 2007 Dragon 15 x 155? x 2 1/4". In the trees we are all good. 500' drag its me with the doo Catching up fast.. Hill climb?, toss coin, but ski doo is right there or 10' above the rest. Deep powder, if I had a 156' we would be equal. Note: they are stock, I'm not. Long track. pipes and skis make a huge dif. I'm thinking of going to a 156 MPI light weight skid, drop[ 30# and get the highmark back. Horse power is not the issue, weight and track are.
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are you still wondering about setup?
I am in Shakopee MN. I have 2 MM one 99 and one 2002. I put 156" tracks on both, Bender pipes, Cut head, MPI transfer enhancement kit. I rode my 99 with the stock 136" track and the suspension in the stock place in the tunnel talk about a trenching Mfer. I had pipes and spacers and reeds then that was in 2000-2001. In 2002 I bought my son a brand new MM. I rode with some polaris guys with 151 and 156's. when we got home I called hartman inc and bought 156" extensions and gearing and called tracksUSA and got 156" tracks. Relocating my 99 skid to the same place as the 2002 skid made an unbelieveable difference. In 2003 or 2004 I bought the MPI transfer enhancement kit. My son and I put them on and we had about a foot or so of fresh powder here in shakopee. The sled almost fell over it was so different to ride without the transfer rods in there. We went out to Cooke and they ride like totally different sleds from before they jump right up on the snow and climb really good also.
My sled has a ported motor case and cylinders and you can feel the difference in HP from my sons. I ride with Polaris guys on brand new dragons and skidoo guy on brand new revs. I can go anywhere they go and I am not a TRACK WH*RE. We ride in the trees alot. The weak link in my set up right now is ME. I don't get enough time in the seat to get better but my sled really flys.
If I was rich I would buy all lightweight parts and then I would smoke all those guys. I didn't like the way the rev rode but I was told you need to ride it for 3 days to get used to it.
I have 156" extensions from hartman. I finally broke my original suspension so I bought an RX-1 151" and got the extensions to go to a 156". Once again My sled rode different this year than last. It rode like my sons sled with the 2002 141" extended to 156". Also I just bought a peak head with 20cc domes.
If you want to come and see my setup maybe take a test ride PM or call me
John 952-403-9786
I am in Shakopee MN. I have 2 MM one 99 and one 2002. I put 156" tracks on both, Bender pipes, Cut head, MPI transfer enhancement kit. I rode my 99 with the stock 136" track and the suspension in the stock place in the tunnel talk about a trenching Mfer. I had pipes and spacers and reeds then that was in 2000-2001. In 2002 I bought my son a brand new MM. I rode with some polaris guys with 151 and 156's. when we got home I called hartman inc and bought 156" extensions and gearing and called tracksUSA and got 156" tracks. Relocating my 99 skid to the same place as the 2002 skid made an unbelieveable difference. In 2003 or 2004 I bought the MPI transfer enhancement kit. My son and I put them on and we had about a foot or so of fresh powder here in shakopee. The sled almost fell over it was so different to ride without the transfer rods in there. We went out to Cooke and they ride like totally different sleds from before they jump right up on the snow and climb really good also.
My sled has a ported motor case and cylinders and you can feel the difference in HP from my sons. I ride with Polaris guys on brand new dragons and skidoo guy on brand new revs. I can go anywhere they go and I am not a TRACK WH*RE. We ride in the trees alot. The weak link in my set up right now is ME. I don't get enough time in the seat to get better but my sled really flys.
If I was rich I would buy all lightweight parts and then I would smoke all those guys. I didn't like the way the rev rode but I was told you need to ride it for 3 days to get used to it.
I have 156" extensions from hartman. I finally broke my original suspension so I bought an RX-1 151" and got the extensions to go to a 156". Once again My sled rode different this year than last. It rode like my sons sled with the 2002 141" extended to 156". Also I just bought a peak head with 20cc domes.
If you want to come and see my setup maybe take a test ride PM or call me
John 952-403-9786