96 787 Very rough midrange.

[jjsinaz]

Was out this morning and did not seem any better, actually seemed like it got a little worse the more I rode it. It runs great on the upper end so I did have a good time blasting around on it. I have not done a plug chop yet because I'm still breaking in the new engine and did not want to hold it wide open for an extended period (Now have 7.2 hrs on the new engine) Pulled plugs anyway to see how they look at the PTO cylinder looks lean to me. I even have the HS screw turned out 1/2 turn too. I'll post pics of plugs.

I don't know Suke, those new carbs are sounding better. How much is a brand new set anyway?

 

[suke]

Was out this morning and did not seem any better, actually seemed like it got a little worse the more I rode it. It runs great on the upper end so I did have a good time blasting around on it. I have not done a plug chop yet because I'm still breaking in the new engine and did not want to hold it wide open for an extended period (Now have 7.2 hrs on the new engine) Pulled plugs anyway to see how they look at the PTO cylinder looks lean to me. I even have the HS screw turned out 1/2 turn too. I'll post pics of plugs.

I don't know Suke, those new carbs are sounding better. How much is a brand new set anyway?

I think before any discount they're $400ish shipped. Normally you can catch sales and get free shipping and if you're part of the Facebook group you can get 10% off if put that in the notes.

 

[R-u-n2it]

Since you have the TSB there was another 1 before that and there were valves that the stem would break and the valve would drop in cylinder, they were identified by the number cast in the valve, can't remember but may have been 303, but they were not slotted. My XP is like a toggle switch mid range, no stumble or anything, try to cruise and get to a point where it's like you pressed the NOX button, it's the valves raising. Maybe 1 of your valve spring is weaker. run the red caps flush with the top of cap, it's better to open early than late, less finicky. And whoever said they bent the mylar strip up, those come with a curve so when installed they positively close, without any flame arrestors and at idle look down the throat, if you see any fuel dripping out the center you have a dribbler from a leaky check valve, it will be worse when flying into a bouy corner and let off at high RPM, you have hige manifold vacuum so high fuel pressure and it can load up and stumble on exit, you scratch your head since you think jetting has changed somehow. I've heard where some have had to stack 2 to stop the dribble. (Know why Snoop Dog would be a terrible weather man? Always a chance of drizzle.) The new style valve holders without the bleed/by pass allows all the pressure to enter the bellows chamber and get a crisp valve opening. Many cut windows in the caps to verify in sync valve opening.

 

[Mekanix]

A di shouldn't exhibit these symptoms... I mean its not like they suffer from the same carb issues.
I wonder if there is something else I'm missing then...
I'll see for sure after new carbs.

 

[Trailrider]

A di shouldn't exhibit these symptoms... I mean its not like they suffer from the same carb issues.
I wonder if there is something else I'm missing then...
I'll see for sure after new carbs.

I agree a DI shouldn't have these same symptoms if the problem is fuel delivery.
I came across this thread because the problem has been described better than I was able to. I have another thread open with my poorly worded description.
I have cleaned my raves and it has made no difference. Adjusting the rave caps flush makes it much worse and at a lower rpm's, turned in all the way in the rpm range effected by the problem is smaller.

 

[R-u-n2it]

I agree a DI shouldn't have these same symptoms if the problem is fuel delivery.
I came across this thread because the problem has been described better than I was able to. I have another thread open with my poorly worded description.
I have cleaned my raves and it has made no difference. Adjusting the rave caps flush makes it much worse and at a lower rpm's, turned in all the way in the rpm range effected by the problem is smaller.

Wow, this is telling us something but it's not clicking yet.... lower RPMs is expected, lower spring pressure needs less exhaust pressure to lift but the problem is following along with RPM.... Hey, you should try running without springs so the valves lift way early and see how it reacts, not saying this is a fix but might help understand what's happening, got to narrow down the possibilities. You can help narrowing it down by trying larger pilot jets to see how it reacts. A fuel problem can be jetting, pop-off, fuel pumps, leaky pulse line to carbs fuel pumps, too much/not enough restriction in fuel return line, fuel supply line restricted/leaking, filter by hood hinge can leak air in, have to eliminate all posibilites till BINGO, you find it. Now get to work {;o).

 

[Trailrider]

Thanks, all of the suggestions are of value. Given mine is fuel injected the typical carb jetting requirements do not apply.

I am stuck on a couple of things, first the ski will run properly all day if we take off gently and keep the rpm below 5k. The first time we give it full throttle the problem will come on and stay that way until it cools down overnight. This is what lead me to believe a sticking rave. The ski will also work well above 5400 rpm to full throttle and also at idle. Anything in between is rough running with low power.

I have fuel pressure testing equipment to check it, but have lacked the motivation to do so given it is getting lots of fuel to run at above 5400 rpm where it needs the fuel volume. New to skis for me and finding they are more sensitive/complicated than the rotax sleds with similar technology.

 

[R-u-n2it]

Damn DI.... so no pop-off, no jetting, I have a big goose egg of knowledge on those, in fact I've messed with carbs so much I'm more like retarded when it comes to injected 2 strokes. DUH!!!! So fuel still recirculates with the DI, right? My OEM service manual stops at 1996 so no help there. A bud has a shop that I help out sometimes, I'll run this by him and see if he has any ideas. Lee

 

[R-u-n2it]

So how do you get past 5400 to know it runs well at high RPM, feather the throttle?

 

[Trailrider]

So how do you get past 5400 to know it runs well at high RPM, feather the throttle?

Yes tend to feather the throttle, but simply punching it to full throttle will also do it after a bit of stumbling and at 5400 it takes off. Keeping the rpms between 5400 & 6700 it runs well. Holding the throttle steady while slowly bringing the rpm down it will fall on its face when it gets below 5200-5400.

Might need to have the TPS checked but that is a pure desperate guess.

 

[R-u-n2it]

Holding the throttle steady while slowly bringing the rpm down it will fall on its face when it gets below 5200-5400.

This sure doesn't sound like it could be related to the RAVEs but the TPS fits, if you have an analog (not digital) volt/ohm meter hook it up (with engine running I would guess) and watch what the meter does when you use the throttle, if it jumps around at the RPM problem range you have narrowed it down to the TPS likely (maybe module but TPS I bet)

 

[Wmhorlock]

I've been working on both my GTXs with performance enhancement issues since May. I bought them last year a 96 and a 97. Built the engine on the 97 from parts off ebay.... replaced everything. 96 had no fire issues and MPEM problems.

Rebuild carbs on both skis then did it again and apart for checks, more cleaning.... reset pop off to different settings, etc. I was almost ready to rejet the 96. Here is what I'd do. If you are sure you have mikuni needle and seats and diaphragm and all the good parts in the carbs..... I know you know about the 3 holes in the barrel.

Install slotted rave valves (I machined my own slots in my raves) and buy "new" upgraded valve bodies. A little information on the problems I was experiencing.....After all the work I did to both skis, the 97 still had acceleration issues, a flat "smoke a cigarette and get back to you" attitude from 2500 to 5 or 6K, then came on like a raped ape. I raced my wife often on the 96. I'd jump out to lengths and stay there till she hooked up and drove by me. Her's is faster top end but I just built the engine. The 96 was the smoothest with regard to transition RPM. Had I not had the 97 I would have figured the 96 was pretty darn good. On the speed difference 2-3mph on the GPS I refuse the resort to cheating to make my ski faster.

That said... after the rave valve work she told me her ski didn't come on as hard at 6K. We lined up for a race.... she pulled way from my ski from the start and walked off into the distance. I couldn't get a sniff. I have not rode her ski but judging by what happened, her flat spot ain't flat no mo. LOL Someone on the forum posted about a technical service bulletin to do what I did for customers complaining about a flat spot or hesitation on the 97 models. Give that some due diligence. Good Luck.

I'm having the same problems with the rave valve, they are actually dented some addy the end that touches the cylinder. I have a couple of machine shops on my UPS route, i'm going to have them machine new ones. My question is, what material should i have then made from or does it matter? It does the weight need to be the same? Any info is greatly appreciated.

 

[etemplet]

You are going to machine Completely NEW Rave Valves?? I'd be careful with the material choice. They are Aluminum but which grade I don't know. That is a lot of work from my perspective. I wouldn't do it and I can. LOL You can buy used ones in good shape pretty cheap and that's what I'd do. I'd suspect the operational section before I'd suspect the valve stem. My stems are a little worn but not too bad. I smoothed out the worn area so it wouldn't hang up.

From working on the rave valves I'd suspect the housing bore and diaphragm unless there was physical damage to the stem as you are having. It would take a significant amouint of physical damage to decrease performance.
Post some pictures of yours

 

[jjsinaz]

I don't think the actual valves are made of aluminum. If they are then it's mighty heavy aluminum. The housings are definitely aluminum

 

[R-u-n2it]

They ARE aluminum, use a magnet and see for yourself. Stainless would be too heavy and if you think they are titanium..... pinch yourself and wake up. Or go to a machine shop and when you get the $ quote you will wake up or have a heart attack.

 

[jjsinaz]

Wow, you're right. I have an old set and I took a closer look at them. I never would have guessed they'd be made of aluminum. That explains why they wear out the way they do. Also makes me wonder, after seeing some of the pics where they broke and the broken piece was never found, if they melted.

Are they plated with some other metal?

 

[R-u-n2it]

I believe they are hard anodized. You all know you have to run synthetic 2 stroke oil right? If you don't you get carbon buildup that sticks the blade instead of the synthetic "black goo", messy but no sticky. And you need .020 min clearance between blade end and piston after a rebore.