Need to Check Rotary Valve Clearance if Installing NEW Valve and Cover?

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79MKII

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Hello All,

I'm helping my daughter with a used '95 GTX that she recently purchased (657X engine). It is very hard starting after it's warmed up. The ski has a primer kit installed, which to me, signaled that it might have had this issue for a while. Back when I was riding, the primer kit was a work-around for excessive rotary valve / cover clearance.

If I determine that the RV / cover is the issue, I would consider purchasing a new valve and cover. My question is, will I still need to check the clearance if I install a brand new cover and valve together? This is assuming that the case isn't worn, of course.

Thanks!
 
Does it require more fuel to get it restarted or is it flooded and hard to restart?

Hard starting can also be caused by leaky needle/seat or a host of other fuel related issues that cause fuel to dribble into the carbs once shut down and flood it out. This usually requires you to hold the throttle WFO while turning the motor over and it will eventually fire back up.
 
Does it require more fuel to get it restarted or is it flooded and hard to restart?

Hard starting can also be caused by leaky needle/seat or a host of other fuel related issues that cause fuel to dribble into the carbs once shut down and flood it out. This usually requires you to hold the throttle WFO while turning the motor over and it will eventually fire back up.

The plugs are bone dry even when it won't start. Definitely not too much fuel. I have a clear fuel filter going into the carbs and the fuel supply doesn't appear to be an issue. When warm, seems to start best when slightly pumping throttle about 1/8 max. Priming didn't seem to help either. I've been through most of the troubleshooting and I'm afraid it's the RV. I had the same issue years ago on my 580 and had the cover machined. I was just wondering if a new valve and cover are replaced as a set, would the clearance still need to be checked? Seems like that might be easier than having the cover machined.
 
Yes even with new parts the clearance should be checked. Use the solder method, its more accurate.
 
Yes even with new parts the clearance should be checked. Use the solder method, its more accurate.
In theory, the new parts should be in spec, right? I would want to check to be sure, but in general, replacing the parts is an alternative to having the cover machined?
 
I have purchased a reman cover with new valve before and clearance was worse than the cover I was trying to replace. Purchased a used cover and clearance was near perfect, no more hard starts. What is the clearance now?
 
I have purchased a reman cover with new valve before and clearance was worse than the cover I was trying to replace. Purchased a used cover and clearance was near perfect, no more hard starts. What is the clearance now?

Oh man, that's not what I wanted to hear. I was hoping to avoid all of the measuring / calculating / machining / measuring by getting new parts. Guess that isn't going to be the case.

I haven't measured the gap yet...still working on other possible issues but I'm afraid I'm heading there soon....
 
Had the ski out last night to try out some work I've done on it. It started up quickly cold and ran great. Wouldn't start after the first stop....even after only a minute or two. I noticed that holding the throttle wide open is definitely the best way to get it started again. It's looking more and more like a RV clearance issue. :(

The pipe came apart at the tuned pipe / exhaust cone clamp and it was almost dark so I didn't get to mess with it after that. By the way, the exhaust it has looks to be from a GTS. The GTX doesn't have the cone, at least according to the parts manual. Hopefully it has the GTX engine.....I'll have to look into that as well.

sea doo exhaust diagram.jpg
 
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Have you rebuilt the carbs? What kits did you use and what all did you replace?
 
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I did a complete disassembly and clean of the carbs. The pop off pressure was within spec and everything looked good. All of the jets were the correct sizes and I set the high and low speed screws to the standard setting. I also tested the diaphragms by making sure that the carbs held pressure...I forget the exact details on that test but it was good. I put the carbs back together and added an inline fuel filter as I haven't changed out the old gray lines yet. There is a lot of fuel coming out of the return line so fuel supply seems good. I also checked the small water separator near the tank and it was clean.

I installed new spark plugs with the .020" gap even though the old plugs were a nice tan color. I also had a couple of water leaks that I fixed...one was on the pipe on one of casting plugs that go bad, and the other was a broken plastic fitting on a water outlet line from the pipe.

I want to check the compression when I have a chance and if that's OK I guess it's probably time to check the RV clearance. Am I missing anything?
 
Personally, I'd blow the money on all new parts on the carbs and brand new needle and seats. Not knowing the age of the parts alone is enough for me and they surely don't last forever. I'd venture a guess that 90% or higher of guys here would have bought all new rebuild parts and N&S and start there. I just think jumping right into the RVC is a little deep. Many hard start issues on these skis fall back on the carbs not being right and having needle and seats that leak, I know you passed the pop off test. You say it starts better when you hold the throttle wide open, giving it more air...it's gotta be getting the gas from somewhere. These are just my thoughts and opinions, I'm not trying to get you upset or pissed. Just throwing stuff out there.
 
Sure, no problem at all. I appreciate the feedback! I think a rebuild on the carbs is probably a reasonable next step, even though everything checked out OK. I could then be almost 100% sure that it's not the carbs if the problem were to continue.

If the needles and seats are leaking, it would be too rich at warm start-up, right? The primer doesn't help, so that would make sense. The guy I bought it from didn't mention that it had a primer. He started it up on the trailer for a minute and I took his word that it would be OK on the water. Guess I got burned there....should always water test!

Here's another bit of information to consider. After I get the ski back home, say 15-20 minutes after pulling it out of the water, it will start instantly without the primer. Could that be useful information?
 
I had a thought about the carbs and wanted to see what you guys thought. If the ski starts right up cold, runs perfectly throughout the throttle range but won't restart even 30 seconds after a ride.....does that leave enough time for a carb issue to cause a hard start? It doesn't seem like enough fuel could leak from the needle and seat in 30 seconds to cause a problem. Is my logic flawed?

On the other hand, it doesn't want to idle for a minute or so after a warm restart.....doesn't that seem more like a carb issue than a RV? IIRC, my old sea-doo with the RV problem ran great once it started...it was just hard to restart.
 
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Pull the carbs, pop the needle out. Use an eye loop, look at the tip, if you see a distinct line where the seat would rest it's time to replace them. Like I said, many of us will do just enough to hear it run, then proceed with the "regular" fuel system and oil injection system overhaul. Then rebuild the jet pump, bearings seals and new wear ring and then what ever else looks questionable. I'd hate to make you rebuild the carbs and still have the issue with the RV cover, but I just see the RV as the last possible resort, personally. Please don't buy aftermarket carb parts, genuine Mikuni parts only.
 
It's been a while, but it's almost spring here in NE Ohio, so I plan to pull the carbs again real soon. I bought all new Mikuni carb kits with the needles and seats. I'm hoping that takes care of the issue. I'll update when I have more information.

On a related note.....I'd love to get rid of this primer and go back to the factory choke set up. It sure seems that it would be easiest to buy a used set of carbs and transfer all the parts (rather than ordering every part separately). Are there specific years / models / carbs that share the same choke parts? Does it have to be a set of '95 GTX carbs only? I'm hoping all 657 engines with dual carbs would work?
 
So disappointed. I just tried the SeaDoo after a complete rebuild of the carbs and fuel system. It starts much better but bogs randomly and almost stalls....even at full throttle. Happens when you hit a hard wave for sure, but can happen when just going slowly as well. I'm officially stumped. The only thought I have is maybe something with the vent system? There is a check valve and a pressure relief valve that seem to be working OK but I'm going to look into it a little more. :(
 
Just to ask.

When you had the carbs off did you do a quick feeler guage check of the rotary valve cover clearance?
 
I wish I had an absolute answer for you.

On the the carb rebuild just make sure that the needle and seat size as well as the pop off spring tension are the same as stock.

When chasing down a running problem it is best to be patient and only change one element at a time. You said you rebuilt the carbs and the fuel system at the same time and now it runs worse, so now you have multiple question areas to work on.... live and learn.

As for the running problem before the carb rebuilds. The RV plate clearance is critical in making the machine run "properly" even though an out of spec cover will still let the machine run good enough if you are not very critical on performance.

As an example, the 91 model year Doos had rv plates on many machines that had too much clearance straight from the factory. At that time I worked as a SeaDoo/SkiDoo mechanic and did all the PDI's on the SeaDoos. 100% of the SP's failed the test run. I would run them for a few minutes, shut them off to check for anything out of place and none of them could start again until they cooled off. The problem was only about .005" clearance outside of the factory spec of the RV plate.

Just this week I had to have .017" taken off the RV plate of my 94 XP 657x because of 24 years of wear. The XP was ok starting, terrible low end, rough idle but ran awesome past 3/8 throttle. I thought carbs were the culprit so I took them down, found one lever out of adjustment giving me very low pop off on one carb, but good overall. I slapped everything back together and the machine ran worse on the low end after getting the carbs "set up". So I bit the bullet, paid the money to have the RV cover face, flange and groove machined and the machine runs almost as good as the day I set it up out of the crate 24 years ago.

Get a clearance measurement on that RV cover. If it is out of spec, has lots of grooves worn in it (like an old vinyl record), has a knife edge thin lip on the outside edge where the disk did not wear the cover down then that needs to be corrected. It is part of the intake/carburation of that machine and will cause running problems that can not be corrected without replacement of the part or resurfacing by a macine shop.
 
I had to have my '91 RV cover machined way back in the 90's. I first tried a primer kit for the hard starting but it didn't help a whole lot. When I realized that this GTX had a primer in place of the choke, I got worried that the RV/cover clearance might have been a problem. Do you agree that if a new RV and cover are purchased that the new cover might need machined to achieve proper clearance?

Also, it really seems like the starting issue is fixed, although I only tried it a couple of times. It's the random bogging that is a problem now. That type of issue wouldn't be caused by the RV, would it?
 
I've also been meaning to ask....the SeaDoo factory service manual states pop off pressure on dual carb models to be 16-21 psi. The new mikuni springs put both right at 19 psi. SeaDoo reference shows that the pop off should be 19-35. That's a big difference. Is the manual correct for sure?
popoff pressure, manual.jpgseadoo source carb info.jpg
 
Throw away the in line filter. I chased carb problems on my SPI the instant I installed the in line filter. It ran great for an hour then issues. I took the carb apart 3 times, tested the fuel flow, pressurized the system, pulled the fuel tank a second time tested the vent system.... you name it. The ski ran great for 1/2 hour, then wouldn't run except idle. I threw that filter away and haven't had a problem since. You already have 3 filters in the system. Try it
 
As for the rotary valve clearance. I am working on a 717 SPX. I machined my own cover and put the clearance at .014". Pain the butt it was. :) For $25 I was going to opt for a used part, then I figured a used part may have the same problem. The problem doing the surface is you have to machine 3 surfaces and the bottom of the O-ring groove is a pain. :) I told my cousin... I spent 3 hours saving $25. :D:D I did not want to check my rotary valve clearance either. Seemed like too much of a pain. It was... ha ha.
 
The seadoo source list has some mistakes so I would go by the manual and the mikuni spec sheet.

I ran into the exact same situation in reference to the seadoo source and the shop manual with the 657x motor spec. The difference being mine is a 94 xp 657x, and the 94 shop manual doesn't list different pop off pressures based on the number of carbs, it simply gave the xp a lower pop off while all other models, including the twin carbed 657 GTX, a higher pop off.

Not trying to hyjack the thread.

I just had the RV cover on my 94 xp machined. It had a "crown" to it where there was a significant amount of extra wear on the areas where the intake holes are, the sides, and less down the center from top to bottom. I can only figure that this uneven wear pattern was caused as the valve itself was pushed outward by the piston coming down and having the case pressure push the disk into the cover in the port area. The only "reference" point we had was a razor thin lip on the outter edge of the cover face where the disk did not wear the cover. I told the machine shop expert to start his reference at the tip if that razor edge and measure until the plate surface was even finished. I had him then mill the flange the same distance plus .002" so the face would be a hair further towards the valve. I did this because the edge of the factory rv cover face has a slight chamfer edge that had been part of the surface that was worn down, so where we started measuring on the initial face refinishing was not truely the factory finished surface the disk rubs against. My logic was "if it is a hair under factory clearance" when we put it on the machine I can always pull it of and wet sand off a thousandth or two on the cover face to "fine tune" the clearance. As it is my "WAG" and a top notch machine shop expert got the clearance dead on .012" where the spec is .010 to .014.

The point being is that a worn RV cover might not be worn consistant and doing the solder method at multiple points and averaging the numbers won't always work.
 
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