Excessive water coming from exhaust. Bogs in water not on land

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troytoy05

New Member
96 GTX
Recent work:
Rebuilt carbs
New fuel lines and selector
Cleaned Rave Valves
New battery, starter and solenoid
120psi each cylinder

Problem: I am getting a lot of water coming from the exhaust port. It runs fine and revs up nicely on land, but once in water or hooked up to the hose, it bogs down and shuts off. No water is getting in to the engine, just have a lot coming out of exhaust port on back of ski.

Waterbox valve baffle was loose, so I repaired that. I blew through the two ports on the valve and it blew straight through, seems like it shouldnt be like that since the purpose is to regulate water not let it flow freely.

Please help, this is driving me nuts!!!
 
I hate to be the bearer of bad news, the problem is 120psi compression, it's low, time for a rebuild. What you are experiencing is classic symptoms for low compression. How many hours on your ski?

Lou
 
NOOOOOO Take it back!! I had the jugs off, one had a cracked outer wall allowing water to come out so I got a used one. Walls and pistons looked great on both. Do you think new Piston rings would fix it? And is there any other possible solution? Cheapest route possible would be ideal. No idea on hours
 
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Isn't 120 on the low side for a 787?

There usually isn't much harm in running it till it gives up if you go the full rebuild route, however I see a new engine in your future. And while "just a top end" may get you going again, you do have a 17 year old crank/seal/RV/bearings...
 
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You should be able to read the hours on the multi-gauge, just toggle through with the mode button.

Lou
 
If you used new cylinders with the old rings that would definetly contribute to low compression.
Cheapest route would be to hone the cylinders and put a set of rings in there. It will still be a $150 by the time your done with rings and gaskets.

Sent using Tapatalk
 
The multi gauge screen is fried. The compression didn't change from one cylinder to the next. Would new rings raise my compression 20-30 psi though? I can do the work myself, I did all the other stuff, so that will save some $$. How hard is it to re-sleeve? And with
New sleeves, do I need new pistons too or just new rings?
 
Everything the guys above, said is correct.


Did you check the size of the used cyl's and your pistons before you put it together? Remember... an "Over size" is only 0.25mm. (about 0.010") So... STD pistons will go into an "Bored" cyl... and it will feel ok.

If your engine was running OK before... you would have been better off, just welding the crack on the outer cyl wall.


Putting in new sleeves, isn't anything a NORMAL home mechanic can do. You have to cut out the old sleeve... prep the cyl... heat the cyl... put the new sleeve in... and then machine the sleeve to the proper size. With that said... I've done it at home... but I have more equipment than the regular home mechanic.












 
Haha I love the muffins in the background!
It ran well after I put it together, but the front rave valve came loose so I tightened it back down and after that is when it started bogging. Not sure if its related or coincidence.

Only replaced one cylinder and didn't check size. It was from a trusted friend and said it was OEM bore. How can I determine wether or not new rings will solve the issue? Or who do y'all recommend I send the jugs to to have bored?
 
I assume 80mm is ideal. Is there wiggle room for +/- any bit. I have an electric dial caliper at work I'll bring home Monday and check it with.

Are we sure I can't just tune the carburetor better? More fuel etc.
 
troytoy05 said:
Are we sure I can't just tune the carburetor better? More fuel etc.
Click to expand...

At 120 psi you will never get that 787 to run properly, even at 135 psi it is tough. That being said, I do find it odd that you only changed one cylinder but both have the exact same compression.
I dont know how good your compression tester is, but try and find another one to compare it to. If your lucky your tester is out to lunch and you have 150psi in both cylinders. If that is the case then its a whole new troubleshooting story.
 
troytoy05 said:
Should I add oil to the piston to see how much it jumps? Will that give any more insight?
Click to expand...

ARGH !!!! NO !!!!!

All that will do is give you a false reading.


Here's what to do.... (if there is extra oil)

1) start the engine for 10 seconds or so
2) Let it cool
3) Remove both plugs (ground the wires)
4) Put the tool in one hole
5) Hold the throttle open
6) Crank for peak pressure. (normally 4~5 revolutions)
7) check second cyl.



As the guys above said... at 120 PSI... that engine just isn't going to run.

Here's the deal... there are a lot of other engiens out there, that can run at 120. But... that is their design pressure. When the spec is 150... then the only way the static pressure can be that low, is if the cyl pressure it leaking down past the rings. (or there is a hole somewhere) When that pressure leaks down... two things happen:

1) During start up, and low RPM's... that pressure is getting into the lower half. In turn... that keeps the lower half from properly filling (so it will act lean) and... that means the bypass pressure is lower also. (so the cyl's don't fill properly)


2) During running/high RPM's... hot combustion gasses are getting past and A) Polluting the fresh air/fuel mix AND B) burning the thin oil layer off the cyl walls. So... in the case of "B"... not only does the engine go lean... it will run hot, and then melt the piston crown, and score the skirts because of a lack of oil.


So... reflect on that... and think about, how fixing it now, can save a meltdown because you want to be a little lazy. A patch job is OK on a lawnmower engine... but not on a high output engine. Think about it... you have an engine, the size of a large shoe box, making the same HP as a typical small car. (not trying to be harsh... just want to brutally honest)
 
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Well, if we are gonna be brutally honest then you should be doing the botton end as well. A fresh top end will work the hell outta that 15+ year old crank.

I don't know the history of your ski, if its ever been rebuilt at one time but that old crank and bearings is a ticking time bomb with a fresh top end on it. It might last 3 years or 3 minutes. Its your call and $$$$.



Sent using Tapatalk
 
Save yourself the ultimate in time and money. Get a rebuilt engine. I'm not trying to be mean but if you didn't check ring gap, cylinder bore, and other vital measurements with that new jug, then you need to leave it alone and swap it out. If you've now learned something and ready to tackle it again, GET THE SERVICE MANUAL. Read it, cover to cover, three times. (At least the engine section) then consider PROPER replacement parts and a realistic timeframe. You'll find a rebuilt motor with a warranty is the more economical route. Remember- the crankshaft seals and bearings are crucial to proper running and engine health. As of right now they are compromised, so whatever you are about to put into it $$$ wise- could be a waste.
 
Dr Honda said:
*trimmed*
... but I have more equipment than the regular home mechanic.



Click to expand...

Ya see Doc, thats where your wrong. I too have an oven! :lol:

I just can't get my wife to let me use it for press fitting parts.

Nice tools, I wish I had a CNC at home :(

Subscribed.
 
Well... the wife was about to kill me on that one. It was a 90 degree day, so the house was closed, with the AC on. Well... after about 10 minutes, the black paint started to smolder, and the house stunk for the rest of the day. (lol)

The only reason I was safe... she wanted to boat to run. I bought it as a project, with a blown engine. 2 weeks later... it was running, and I was forgiven.
 
Bought a new guage today. Still at exactly 120psi on both cylinders. I did the oil thing just in case as I've heard it helps some come to conclusions, but after adding a cap of oil to the cylinder, it read 142psi on both.

I noticed that when the ski is started, exhaust comes out of the rave valves where they mount. Is that ok or does it need addressed? Also the mag rave rubber boot had come off the valve so I put that back on before I did any tests.

And I'll do the rebuild if I have to, but testing new rings would be a lot easier on my wallet. Ski only runs a few times a year, it's secondary to my 97XP.
 
I would fix the exhaust leak. Buy the rave rebuild kits or contact Minnetonka. I do find it strange both cylinders are reading equally low compression
 
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