Sluggish 787

[soccerdad]

Just rebuilt the carbs (real mikuni parts). The ski idles well and seems snappy on the trailer and hose. Compression 140-145. On the water max revs are 6400 and max speed is 49 gps. It just feels sluggish, kind of labored and not crisp. Carbs are set to spec at one out on the LS and HS all in on both. Brand new plugs. After about 45 minutes they look like this. The light one is the PTO side. Popoff was 28 for both. Note that the ski was not revving right before I went through the carbs so I am not sure if the problem is somewhere else. The waterbox valve looks OK and I don't see any leaks. Any ideas always appreciated.

 

[POPPS]

Check your rav valves,,,they may be sticking or stuck,,,that could cause your issue on an 800.

 

[1of500]

Did you verify consistent spark. I would try trimming 1/4 off the plug wires and reinstall the boot

 

[soccerdad]

I will try both. The raves are easy to move, but I will pull and clean them anyway. The ski feels like they are not working. It pulls up on plane well. It seems pretty normal out of the hole, but when cruising at 30-40 mph and you give it full gas, it just rolls up to 6400 rpm. It does not bog, but is just a flat acceleration. It doesn't have that "hit" that a 787 typically has.

 

[Ckrawiec]

I will try both. The raves are easy to move, but I will pull and clean them anyway. The ski feels like they are not working. It pulls up on plane well. It seems pretty normal out of the hole, but when cruising at 30-40 mph and you give it full gas, it just rolls up to 6400 rpm. It does not bog, but is just a flat acceleration. It doesn't have that "hit" that a 787 typically has.

Impeller and wear ring? Age?, check gap between imp & wear ring.

My '96 behaves similarly.....won't snap to it from a cruising speed but will "eventually" catch up to itself....it doesn't really bother me that much but I know it can be better.....it's still the fastest ski in my fleet though once she gets to full speed.

 

[soccerdad]

Impeller and wear ring? Age?, check gap between imp & wear ring.

My '96 behaves similarly.....won't snap to it from a cruising speed but will "eventually" catch up to itself....it doesn't really bother me that much but I know it can be better.....it's still the fastest ski in my fleet though once she gets to full speed.

Good thought but it does not cavitate at all. The wear ring clearance is good. It is the crispness of acceleration and lack of top RPM. It feels like carbs, but I have been in them twice. I may have missed something, but not real likely. I am pulling the head and raves tonight to put my eyes on that stuff. Then checking all connections and plug wires (cutting them). Anyone know if the rectifier could be doing this? I have not checked that. I have a bunch of spare electrical stuff, but I hate throwing parts at it.

 

[Ckrawiec]

Good thought but it does not cavitate at all. The wear ring clearance is good. It is the crispness of acceleration and lack of top RPM. It feels like carbs, but I have been in them twice. I may have missed something, but not real likely. I am pulling the head and raves tonight to put my eyes on that stuff. Then checking all connections and plug wires (cutting them). Anyone know if the rectifier could be doing this? I have not checked that. I have a bunch of spare electrical stuff, but I hate throwing parts at it.

If the rectifier is not operating properly, then you would be depleting the battery power from the ski....which IN THEORY could cause degredation of the spark.....so anything is possible.

You didn't mention anything related to the dreaded 12V Low message, so it's probably not an issue.....a simple check of the charging system is to put a meter on the running ski at the battery and see what your voltage is.....should be in the vicinity of 14V, pretty steady reading.

My best guess is the carbs....they are so freakin' finicky.....I've twiddled mine many more times than twice to get to where I'm at right now.....another 1/4 turn could make all the difference IDK.....it's really a trial and error thing with older machines and carbs.....you just gotta keep making tiny adjustments until you hit that sweet spot. Good luck.

 

[soccerdad]

Check your rav valves,,,they may be sticking or stuck,,,that could cause your issue on an 800.

Winner Winner-I hope....
I found one rave cap was stripped out and although the cap was lifting (I have holes in my caps to watch them work) the valve did not move. So the lower port timing probably was enough to kill the revs. I can't put it on the water for a while, but I expect that is the problem. It was only one rave though. The other was fine. I am still going to look at other stuff. Does this sound like it would be enough to kill 400 RPM and 5 MPH?

 

[GGuillot]

Winner Winner-I hope....
I found one rave cap was stripped out and although the cap was lifting (I have holes in my caps to watch them work) the valve did not move. So the lower port timing probably was enough to kill the revs. I can't put it on the water for a while, but I expect that is the problem. It was only one rave though. The other was fine. I am still going to look at other stuff. Does this sound like it would be enough to kill 400 RPM and 5 MPH?

Yes, exact issue I had on the 97' GTX, RAVE blade fell out of the threads and it dropped several hundred RPM and at least 5 mph on top. The solution is another RAVE housing, not just a threaded cap. The excessive housing wear causes excessive vibration which strips the threads. How do I know this? I bought some of those nice anodized aluminum caps and the same thing happen again...not only stripped the threads in the cap but trashed the RAVE blade threads also.

 

[mikidymac]

Yes, exact issue I had on the 97' GTX, RAVE blade fell out of the threads and it dropped several hundred RPM and at least 5 mph on top. The solution is another RAVE housing, not just a threaded cap. The excessive housing wear causes excessive vibration which strips the threads. How do I know this? I bought some of those nice anodized aluminum caps and the same thing happen again...not only stripped the threads in the cap but trashed the RAVE blade threads also.

That's crazy it stripped the aluminum caps, wow.

I have seen the plastic cap threads melted from either old hard o-rings or worn housings though.

 

[soccerdad]

I’ve melted them from that oring issue as well. Thanks for the heads up on the housing. I will check that for sure.

 

[Ckrawiec]

This forum is a monster....the WEALTH of information and personal experiences shared is PRICELESS. If you've been around even for a short while.....damn near everything is discussed, analyzed, tested & figured out...you should be able to find info or a solution for almost any old ski related issue.

Thanks for EVERYTHING.

I highly doubt my ski would still be running today without the things I've learned on this forum, what to watch out for, time-savers, etc.....

 

[slatere17]

Winner Winner-I hope....
I found one rave cap was stripped out and although the cap was lifting (I have holes in my caps to watch them work) the valve did not move. So the lower port timing probably was enough to kill the revs. I can't put it on the water for a while, but I expect that is the problem. It was only one rave though. The other was fine. I am still going to look at other stuff. Does this sound like it would be enough to kill 400 RPM and 5 MPH?

Just another bit of experience to reinforce the RAVE theory, my 97 GTX was running a little sluggish at the end of last year just like you described. Turned out to be an issue with one of the RAVE valves. The valve had broken where the shaft meets the blade and the blade of the valve was floating around free in the slot. The valve came out in numerous pieces, with the main blade only about 70% of its original length (not melted but worn down by contacting the piston and rings presumably), and the spring and diaphragm were completely destroyed.

Even with all this damage, the ski was still running but probably lost about 500rpm and 5-10mph. Amazingly there was no visible damage to the piston or rings, and compression still checked out. Replaced the entire valve along with the housing as it had worn into an oval shape, and regained that performance.

 

[Lothsahn]

Just another bit of experience to reinforce the RAVE theory, my 97 GTX was running a little sluggish at the end of last year just like you described. Turned out to be an issue with one of the RAVE valves. The valve had broken where the shaft meets the blade and the blade of the valve was floating around free in the slot. The valve came out in numerous pieces, with the main blade only about 70% of its original length (not melted but worn down by contacting the piston and rings presumably), and the spring and diaphragm were completely destroyed.

Even with all this damage, the ski was still running but probably lost about 500rpm and 5-10mph. Amazingly there was no visible damage to the piston or rings, and compression still checked out. Replaced the entire valve along with the housing as it had worn into an oval shape, and regained that performance.

Wow. Just wow.

 

[Jtamaro]

This forum is a monster....the WEALTH of information and personal experiences shared is PRICELESS. If you've been around even for a short while.....damn near everything is discussed, analyzed, tested & figured out...you should be able to find info or a solution for almost any old ski related issue.

Thanks for EVERYTHING.

I highly doubt my ski would still be running today without the things I've learned on this forum, what to watch out for, time-savers, etc.....

I here you mate, so very true. Big thanks to everyone

 

[soccerdad]

Yes, exact issue I had on the 97' GTX, RAVE blade fell out of the threads and it dropped several hundred RPM and at least 5 mph on top. The solution is another RAVE housing, not just a threaded cap. The excessive housing wear causes excessive vibration which strips the threads. How do I know this? I bought some of those nice anodized aluminum caps and the same thing happen again...not only stripped the threads in the cap but trashed the RAVE blade threads also.

So I put on another cap and the revs came up. Now the ski is running at normal speed! But I didn’t change the housing and after an hour long ride the cap is stripped again. You you told me so and I should have listened . So with a couple housings and caps and I will be good to go. Thanks.