Vmax 500 RPM's Fall Off

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urdone

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So I bought a 1997 Vmax 500 last year that was owned by a guy that used to ride it in the mountains. As far as I can tell and based on some old receipts I found he had some clutching mods done to run the higher elevations and accompany the 136"x1 3/4" track he put under it.

So I've brought this sled out east and I seem to have an issue with rpm's falling off now. It will rev up to about 7700rpm and then once you get up to speed the track speed drops a bit to around 70-80km/h and rpm's start to fall off down to about 6200-6500rpm. I don't believe it's an engine issue as it runs just fine, no bog or anything. I'm clutch illiterate though so not sure if it's a primary or secondary issue, weight issue, spring issue or what although I feel in the end my issue is going to be in the primary.

So to start with does anyone know what a 1997 vmax 500 would have in it for spring colour and weights in the primary? And any tips on how to diagnose which part of the clutch would be the best place to start making changes?

Thanks
 
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I think for me if it was running at high elevation and now its at a lot lower elevation I would check the jetting first thing. The air is more dense at lower elevation so it needs more fuel. Find a jetting chart for it and see what you have compared to what it should have for your elevation and the coldest temp you will be riding in.
 
Jetting is fine. Plugs look good. It was only running around 4-5000' if the guy was riding where I think he was based on the receipts I got with it. Also my experience says it would be low on power across the board not just fall off on power once it gets up to speed-it would never get there in the first place.
 
You can get stock specs from the tech section. There is a link toward the top right side of the forum. It will have all the stock clutching specs. You might have to lighten up the clutching a bit to bring the rpms up. I don't know where the rpms should be with that engine. Do you know where the rpms were for the previous owner? Just out of curiosity what elevation are you at? Did the previous owner change gearing that you know of? Might be better off lowering the gear ratio a little if it is stock. That's a pretty good size track to spin.
 
drew24 said:
You can get stock specs from the tech section. There is a link toward the top right side of the forum. It will have all the stock clutching specs. You might have to lighten up the clutching a bit to bring the rpms up. I don't know where the rpms should be with that engine. Do you know where the rpms were for the previous owner? Just out of curiosity what elevation are you at? Did the previous owner change gearing that you know of? Might be better off lowering the gear ratio a little if it is stock. That's a pretty good size track to spin.
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Thanks I'll check that out.
Currently riding at about 1200'. Previously when I rode it around 2900' it had the same issue but not quite as bad.
Gearing may have been lowered already due to the track size. Haven't opened the chaincase to count gear teeth to confirm yet though but considering the money the guy spent )back in the late 90's when it was new) and knowing the shop that did the work I'm sure he did. To be honest top speed of only 80-90 km/h I'm fine with, I just want it to hold the rpm. The little I do know about clutching I too feel it may need a little less weight and/or maybe a different spring. Was thinking of setting it up as stock and going from there so I have a baseline seeing as I don't know at this point what is in there.
 
Well it DEFINITELY does not have the stock springs in it according to the stock specs.

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Supposed to be w-p-w in the primary and red in the secondary.
I noticed my belt is sitting a bit low in the secondary (flush with the top of the sheaves). Is there an adjustment to raise it a bit? I know the Cat I used to own had shims and the Doo's you just turned the ring.
 
If track speed and rpms drop together then something is robbing power or it simply is not making the same power. If the clutches backshift on you are full shift out your rpms will actually climb. I think you want to be at 7800 rpm for that sled.
 
There are 3 bolts on the back of the secondary. If they have a washer on them you take a washer out to raise the belt in the secondary. I still would check the jetting just to confirm since they don't get on the main jet for a good bit. I have the manual for the 94-96 vmax and it showed 2 jet sizes different between 1200' and 5000'. Not saying that's the problem but its easy to check(especially on the twins) and could make it lose power once it gets on the mains.
 
They don't drop together really. The rpm's drop off and hold around 62-6500. I think the track speed drops off as I was riding in deeper snow off trail so as it loaded up due to the deeper snow it would slow down (if this makes sense). I'd grab more of the flipper and would slowly get a bit more r's and a bit more track speed but it would be really slow and never get right back up to rpm. Almost like it wouldn't backshift. On the trail it would take off hard, root along fine up to about 70-80km/h fairly quick but as soon as I hit that speed the rpm's would drop by a 1000 or better. Speed would hold fairly consistent though and if I let off and slowed down a bit and hammered on it again the same situation repeats.
 
drew24 said:
There are 3 bolts on the back of the secondary. If they have a washer on them you take a washer out to raise the belt in the secondary. I still would check the jetting just to confirm since they don't get on the main jet for a good bit. I have the manual for the 94-96 vmax and it showed 2 jet sizes different between 1200' and 5000'. Not saying that's the problem but its easy to check(especially on the twins) and could make it lose power once it gets on the mains.
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Makes sense. Sled specs say 151.3 Main. Are they usually stamped on the bottom or do you have to pull them out to check what they are? Been awhile since I had to swap jets around in any carb (2005 lol). Been spoiled riding Doo lately with DPM or EFI. As much as the TRA sucks I doo miss clickers!!

Didn't see any washers on the secondary bolts and the belt only has about 200km on it (looks new still). I wonder why it's sitting so low? Before the last ride it was sitting right where it should be.
 
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You don't have to pull the jets out to check. Magnifying glass is nice though. I am not sure on the hp's on the 500 but its possible it is running out of power before full shift out because of the bigger track and/or jet size. Might be fine for deep powder but might need to adjust for hardpack trail riding. Sounds like it probably will need some adjustments but might as well check jetting first to make sure you are at full power.
 
drew24 said:
You don't have to pull the jets out to check. Magnifying glass is nice though. I am not sure on the hp's on the 500 but its possible it is running out of power before full shift out because of the bigger track and/or jet size. Might be fine for deep powder but might need to adjust for hardpack trail riding. Sounds like it probably will need some adjustments but might as well check jetting first to make sure you are at full power.
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I'll check them out. Compression is down a bit-both holes at 110psi but seems to run and start fine.
If jets are good I might move on to the clutching-back to stockish and if that don't work then a lighter rider (my wife) might get a sled to ride and I'll just go get the Sidewinder MTX I've been eyeing up lol.
 
urdone said:
I'll check them out. Compression is down a bit-both holes at 110psi but seems to run and start fine.
If jets are good I might move on to the clutching-back to stockish and if that don't work then a lighter rider (my wife) might get a sled to ride and I'll just go get the Sidewinder MTX I've been eyeing up lol.
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Ha. Now that's a good plan. lol
 
Sorry. I mixed it up, to raise the belt on the secondary you need to add the washers to the bolts on the back.
 
The springs seems to be custom because of only one dot on the primary and I don't think I've ever seen a white secondary spring either. Try to get it stock like first. Really, shouldn't be that much different than the clutching of a venture 500 of the same era. I've even played with heelclickers on my Venture 500 liquid, seems to work well and the sled does 130 km/h. I'm no jetting expert but did you try chocke when getting up to speed? Seems like the mains aren't flowing? Also check your reeds.

However, if it feels like it's not backshifting, it probably isn't doing a very good job. I'd start with the clutches.
 
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drew24 said:
Sorry. I mixed it up, to raise the belt on the secondary you need to add the washers to the bolts on the back.
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On second look with a flashlight it does have two washers. I think you were right the first time though.
 
norwegian said:
The springs seems to be custom because of only one dot on the primary and I don't think I've ever seen a white secondary spring either. Try to get it stock like first. Really, shouldn't be that much different than the clutching of a venture 500 of the same era. I've even played with heelclickers on my Venture 500 liquid, seems to work well and the sled does 130 km/h. I'm no jetting expert but did you try chocke when getting up to speed? Seems like the mains aren't flowing? Also check your reeds.

However, if it feels like it's not backshifting, it probably isn't doing a very good job. I'd start with the clutches.
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I'm sure it is a custom spring setup. It was done back in 98 by a sled shop in the Rockies. Pretty sure there weren't kits available back then.

I'm going to check the carbs tomorrow for the main size but like I said plugs look fine. Pretty sure it's on the mains as it gets up and at it pretty hard for a 20 year old 500.

After that going to go back to stock springs and weights and see what happens. It might turn it into a big turd off the line but we will see.
 
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