The Great 951 Rpm Caper (Missing Rpm)

[JeremyD615]

I dunno about those water regulators.... they are a mystery to me. As you did, I took mine apart and played with everything... tried to understand how it works. I didn't see a problem and when I put it back on the ski, o gains were noticed. Then... before leaving for a ride, I swapped Water Pressure Regulators from a different ski. The ski was much better in the top range of RPM and it was noticeable. I never figured that one out. LOL

I had a similar issue to this... I went through and replaced everything inside of one regulator that just never did act right. I swapped it for a spare that I had lying around and that one was fine... They’re finicky for sure.

 

[etemplet]

So near as I can figure, the WCV doesn't shut down water flow all the way but restricts flow at high power output measured by water flow from the cooling system. If this is true there are a number of issues that can prevent the WCV from working as designed.

 

[etemplet]

I did some research and came across this thread. Now I am confused with the operation of the WCV but that ain't bad thing.

787 Water Regulator Performance

 

[JeremyD615]

So near as I can figure, the WCV doesn't shut down water flow all the way but restricts flow at high power output measured by water flow from the cooling system. If this is true there are a number of issues that can prevent the WCV from working as designed.

You’re right, it doesn’t shut off flow completely, but there is a definite reduction in the flow rate... I haven’t metered the water flow at various throttle settings, but I have ridden my 787 ski with clear tubing from the regulator so I could monitor the flow. It’s a noticeable reduction at WOT...

 

[etemplet]

In the article I linked, if everyone can access it, the guy measured flow and there was some discussion. Differences of opinion still remain in that discussion. I'd like to gather info on exactly what happens when we move the red adjuster on the WCV. IF, with no spring the valve fails "open" and gives full flow to the mid-pipe then backing the adjuster "out" should bias the valve to remaining open. Turning the adjuster "in" should bias the valve to closing. So much for going around the world to get around the corner. If that is correct that is.

 

[etemplet]

One thing did get my attention was that the internal piece of the valve should NOT move. One should NOT able to remove it. I had one that I could move like that so naturally I reinstalled it that way. LOL

Remove the bellows and pull up on the center post. If the entire center portion of the valve pulls out post and all, then there is your problem. You may have to tug a little hard, but it isn't supposed to come out at all, EVER. At this point, you need to either CAREFULLY glue the center section back into the body, or buy a new regulator. I have glued to many to count at this point and for the most part have had them return to full function afterwards.

 

[mikidymac]

That’s correct the inner plastic sleeve should fit tight in the outer housing and shouldn’t pull out easy or leak water.
That being said there are two rings with a groove in the middle that’s perfect for an o-ring and will prevent the valve from leaking.
Mine was loose but ran perfectly so I added an o-ring in the groove.

I haven’t had a chance to try it yet to see if there’s an issue.

To the OP, I checked my 2091 XP and the adjuster is flush with the cap.

 

[CreekerMike]

That’s correct the inner plastic sleeve should fit tight in the outer housing and shouldn’t pull out easy or leak water.
That being said there are two rings with a groove in the middle that’s perfect for an o-ring and will prevent the valve from leaking.
Mine was loose but ran perfectly so I added an o-ring in the groove.

I haven’t had a chance to try it yet to see if there’s an issue.

To the OP, I checked my 2091 XP and the adjuster is flush with the cap.

Thanks miki, ill try screwing mine down flush with the cap and running WOT, hopefully ill get a run in after work today. Ill post an update then.

 

[etemplet]

This is good stuff !!

 

[CreekerMike]

I got out on the river but unfortunately it was too choppy to get any good numbers at WOT. Now that im home i decided to pull the fuel filters. This one was filled with crap! I bet this was robbing me of some fuel...

 

[etemplet]

Flush that system out best you can. Robbing fuel and destroying the engine.

 

[CreekerMike]

Flush that system out best you can. Robbing fuel and destroying the engine.

I cleaned out that filter and housing with some braklean, blew out the other filter with about 100psi of air. Im going to test the ski this friday and see if there was any improvement. I dont think all that crap was from my fuel though... i use a vp racing jug to mix all my fuel and theres almost zero debris/ dust that enter my tank. But i could be wrong. Or maybe my premix deterorated something that gasoline alone hadnt knocked loose before. Either way we will see this friday!!!

 

[mikidymac]

What "other filter" are you referring to?

Alos with theat much crap in the strainer there is a good chance your little filters in the carbs have stuff in them also.

 

[CreekerMike]

What "other filter" are you referring to?

Alos with theat much crap in the strainer there is a good chance your little filters in the carbs have stuff in them also.

In the front compartment of the ski there was an inline filter spliced into the feed line.

 

[JeremyD615]

In the front compartment of the ski there was an inline filter spliced into the feed line.

Get rid of that inline filter! It’s restricting your fuel flow, and that may be your whole problem. Get rid of it and see what she does...

 

[Ckrawiec]

In the front compartment of the ski there was an inline filter spliced into the feed line.

Could be something, could be nothing...SO, I'm throwing it out there for discussion/consideration.....in your original POST, you indicated that you re-assembled the engine, etc.....there is a thing called a SQUISH gap built into these ski engines (i recently have read about it in my '96 shop manual).

The manual states, "if the squish gap is increased, a loss in power will occur". I'd never heard of such a thing (learn something new every day)....but if we are talking about losing/finding power.....who knows????

Mikidymac...your thoughts on this? I have absolutely NO EXPERIENCE with this topic.

 

[JeremyD615]

Could be something, could be nothing...SO, I'm throwing it out there for discussion/consideration.....in your original POST, you indicated that you re-assembled the engine, etc.....there is a thing called a SQUISH gap built into these ski engines (i recently have read about it in my '96 shop manual).

The manual states, "if the squish gap is increased, a loss in power will occur". I'd never heard of such a thing (learn something new every day)....but if we are talking about losing/finding power.....who knows????

Mikidymac...your thoughts on this? I have absolutely NO EXPERIENCE with this topic.

I don’t think this is a squish problem, I think there’s a good chance it’s just that extra fuel filter in the line.

I always want to think of squish as being like changing head gasket thickness in an automotive engine, but that’s not really the case in a two stroke. The motors really need to be set up with the correct measurement to control the flame in the combustion chamber correctly, and obviously to avoid having the piston contact the head. The measurement isn’t really something variable that you can play around with the way you can gain compression or PTV clearance by changing gasket thickness in a four stroke... I could be wrong, but I think it’s highly unlikely that this is where the problem lies here...

 

[Ckrawiec]

I don’t think this is a squish problem, I think there’s a good chance it’s just that extra fuel filter in the line.

I always want to think of squish as being like changing head gasket thickness in an automotive engine, but that’s not really the case in a two stroke. The motors really need to be set up with the correct measurement to control the flame in the combustion chamber correctly, and obviously to avoid having the piston contact the head. The measurement isn’t really something variable that you can play around with the way you can gain compression or PTV clearance by changing gasket thickness in a four stroke... I could be wrong, but I think it’s highly unlikely that this is where the problem lies here...

Yeah, I don't disagree with that assessment...but I found it noteworthy to point out that it warranted a specific section in the engine re-assembly section SO there MUST be some degree of variability to take into consideration (the manual gives clearance specs to measure for). Like I said...I have absolutely no experience with this topic...but the OP has stated that he "lost some rpm's" - couple hundred, so I thought - Huh....squish? maybe? IDK!!! still learning

BUT, yes...get rid of the added fuel filter, etc.....

 

[mikidymac]

Not sure this is as big of a problem on the 951 but yes, squish should always be checked.

Here is a note from Harry at Group K...
"Base Gasket Thickness - "Jon's Story" - One of our early test boats was an XP that was to be raced in region one offshore. We shipped the kit to the owner, who had it assembled at a local shop. After the break-in, the test rider reported a little better top end, along with average bottom end power. We were concerned because all our other test riders had reported big increases in bottom end as well as peak rpm. After a few unsuccessful attempts to resolve the problem with carb tuning, he came to our shop with the machine. After a quick test ride, we found this XP to have mediocre acceleration and a 6900 rpm peak (that's 150 rpm short of the norm). Back at the shop we checked out every possible problem. Besides the indicated compression being just a little low, the only other inconsistency was that the squish clearance seemed to be about .010" (.25mm) too thick. At the time, we didn't think this was the problem...but it was the only thing we saw that we could "fix". We removed the .024" (6 hole) base gasket and replaced it with a .016" (4 hole) base gasket. The next morning we gave the boat a short break-in...then gassed it. The difference was unbelievable. The boat pulled viciously up to 7040 rpm...just like all our other test boats. No one was more shocked than us, that .008" of base gasket thickness could turn a weakling into rocket. After this experience, we specified for our assembly instructions that a .038" - .042" squish clearance must be maintained on all Group K modified top ends. Since then, we have not experienced this problem again. (Note : This XP won the 90 minute 1200 pro overall at the Havasu Global Offshore Finals)"

 

[JeremyD615]

That’s an interesting read! I still think the OP would be well served by trying the ski without the additional filter first since it’s such a quick and easy fix, but it sounds like an improper squish is quite possible if Group K got those results... I would have thought the increase in squish would have a pronounced enough effect on the whole rev range that it would be obvious right away that something was “off.”

 

[mikidymac]

That’s an interesting read! I still think the OP would be well served by trying the ski without the additional filter first since it’s such a quick and easy fix, but it sounds like an improper squish is quite possible if Group K got those results... I would have thought the increase in squish would have a pronounced enough effect on the whole rev range that it would be obvious right away that something was “off.”

Totally agree, get that additional filter out of there.

 

[CreekerMike]

I havent changed base gaskets since I originally built the engine, im still on the same base gasket wich allowed me to turn 6950-7000rpm. I really wish I could get out on the water today and report my findings but unfortunately its gonna have to wait until tommorow afternoon. I will be getting rid of that inline fuel filter as you all have suggested.

 

[CreekerMike]

Alright a little update! I got out in the pautuxent today to go to the battle creek raft up annnnnd!!!! Im still at 6600-6700rpm at WOT. Not ruling out the possibility of a fuel issue yet though. Ill have to take a look at the carbs internal filters. Boy what a headache this is.

 

[POPPS]

it. Would appear that your only "altered"changed variable, would be your water regulator. ..why did you change the head gasket in the 1st place.?

 

[CreekerMike]

it. Would appear that your only "altered"changed variable, would be your water regulator. ..why did you change the head gasket in the 1st place.?

If you go check out my last thread you can get the detailed view but heres the summary, I had smoke coming from a pisser port and it turned out it was exhaust fumes entering the cooling system through a blown head gasket. So one headgasket later here we are.