I have a 96 Speedster that just came out of 2 years of storage. I posted another thread about all of the oil that was in my cylinders. I took care of that and got them started finally last weekend. I took them out for a spirited run and everything was fine until I backed off to 4K for about 30 seconds, then full throttle again. The right engine started to spit and sputter and would only go to about 5k. I got the boat on shore and replaced the spark plugs and they fired right up and ran great. I revved them up a few times and they both had good throttle response. So I took it out on the lake again today and immediately had the same problem. Do you think I need to clean the carburetor and where should I begin?
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Need an Expert Opinion on Loss of Power
- Thread starter Carhopper
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Waterluvr
New Member
This might help you grasp the bigger picture in getting your boat to run and perform properly and how and where to start looking for problems. http://www.seadooforum.com/showthre...er-5900rpm-max&p=426231&viewfull=1#post426231
Waterluvr
New Member
You asked for an expert opinion, no one here can really give that to you. The only ones that fit that mold are the engineers that designed these things at the factory.
Go and read that post one more time please. What's the very first thing on that list? Nothing else matters if the motor has reached a point beyond it's mechanical limitations and that's very commonplace with these.
Waterluvr
New Member
I read your other thread regarding oil loss from the reservoir tank to the crankcase. Chances are pretty good if your inner crank seals are leaking atmosphere and allowing oil to drain into the crankcase while sitting static then your outer seals are leaking air or will be soon.
Your carbs can't be tuned and won't function properly once the outer crank seals start to leak air into the crankcase, the ratio of fuel and air mix will lean way out and your motor's will self destruct starting with the pistons and cylinders.
The idea is to catch these things before compression drops to the point where your piston's start seizing from the heat making it's way past the top of the piston and rings and transferring molten aluminum to the cylinder walls and into the bearings. It's time to rebuild those engines, save your cases before something lets loose and destroy's them.
Waterluvr
New Member
Your engine(s) (not sure if your working on just one or two) are well past their useful service life with leaking crank seals and compression numbers that low. At 120 psi the heat from blow by at the rings is going to cook the oil film from your pistons and they will melt and smear if they haven't already.
I was serious when I ended post #6 with the recommendation you rebuild your engines before something let's loose and destroys the value of the cases and whatever else is left that can be saved, again after reading your other thread and learning you had leaking crank seals that was enough.
Your piston's will come apart in pieces and take out the crank and everything else of value in there if you keep running like that. In the real world these engines have a service life of about six years / 300 hours of use if they are well maintained and the fuel systems are kept clean and tuned to keep the motors off the deaths edge of lean running conditions.
Your's made it 18 years if they haven't been rebuilt yet, they had a good run.
Please don't think I'm questioning your explanation because I don't know squat about these things, but the shop manual says to rebuild if they drop below 90psi. I'll check my left engine shortly to see if it is also 120psi. I picked this up for 2,000 in pretty good physical shape and was hoping for a couple of seasons before I sell it. Before this happened, it ran both engines at 7,000 RPM and 47mph. That's only 3mph short of the rated speed and I weigh 220lbs.
Edit: Sorry I misspoke, I read the 90psi minimum here on the forum http://www.seadooforum.com/showthread.php?23679-Compression-Test-96-Sportster-How-to
Edit: Sorry I misspoke, I read the 90psi minimum here on the forum http://www.seadooforum.com/showthread.php?23679-Compression-Test-96-Sportster-How-to
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Waterluvr
New Member
A fresh 717 engine properly built and tuned will make 150-155 psi and 85 HP with an 82mm bore, at or near 127 psi and lower you will see the onset of excessive heat and seizure signs such as piston scoring and oil coking on the piston skirts, they don't last long from that point on and you can expect compression to drop off sharply with continued use.
Expect to have a pretty loud and destructive failure well before your motors continue running to a low point of 90 psi. and you already know the crank seals are bad.
Your piston skirts will come apart from oil film loss and extreme heat before you'll likely ever see 90 psi. on a compression test, and your crank seals are leaking coupled with low cylinder compression, that's plenty of information to draw the conclusion it's past time to rebuild them while there's something left to save.
Your carbs could probably be rebuilt and tuned on the boat after installation to compensate for outer crank seal leaks and make it run pretty well at this point with 120 psi of compression, the problem is things won't stay that way for long. You may only get a few hours out of them before something goes bang. It may be made to run well today and won't get out of it's own way tomorrow, complete seizures after shutdown or low rpm operation at idle speeds are very common on low compression engines that get tuned to run out to WOT and used that way such as required to get a boat on plane.
Now maybe you understand why I linked to that other thread where I stated I won't work on a jet boat engine below a 15% loss of compression. If that doesn't make sense go back and read it again and pay attention to what I wrote and not just what's on the list. You're pushing a boat hull that's 2/3's more wetted surface than a jetski and has the ability for twice + the passenger weight load and have you seen how much extra weight some people cram into storage lockers and bring on board with them? There's more wiggle room in a twin engine boat with the extra HP, a single really has to be right to run the boat satisfactorily.
That's the difference between shadetree's and hacks tuning something to bleed out the last little bit of life left before it completely self destructs or someone responsible enough to cease using an engine to preserve whatever value is left.
You know your engines are well beyond their useful service life at this point and it's up to you to choose what to do about that.
Expect to have a pretty loud and destructive failure well before your motors continue running to a low point of 90 psi. and you already know the crank seals are bad.
Your piston skirts will come apart from oil film loss and extreme heat before you'll likely ever see 90 psi. on a compression test, and your crank seals are leaking coupled with low cylinder compression, that's plenty of information to draw the conclusion it's past time to rebuild them while there's something left to save.
Your carbs could probably be rebuilt and tuned on the boat after installation to compensate for outer crank seal leaks and make it run pretty well at this point with 120 psi of compression, the problem is things won't stay that way for long. You may only get a few hours out of them before something goes bang. It may be made to run well today and won't get out of it's own way tomorrow, complete seizures after shutdown or low rpm operation at idle speeds are very common on low compression engines that get tuned to run out to WOT and used that way such as required to get a boat on plane.
Now maybe you understand why I linked to that other thread where I stated I won't work on a jet boat engine below a 15% loss of compression. If that doesn't make sense go back and read it again and pay attention to what I wrote and not just what's on the list. You're pushing a boat hull that's 2/3's more wetted surface than a jetski and has the ability for twice + the passenger weight load and have you seen how much extra weight some people cram into storage lockers and bring on board with them? There's more wiggle room in a twin engine boat with the extra HP, a single really has to be right to run the boat satisfactorily.
That's the difference between shadetree's and hacks tuning something to bleed out the last little bit of life left before it completely self destructs or someone responsible enough to cease using an engine to preserve whatever value is left.
You know your engines are well beyond their useful service life at this point and it's up to you to choose what to do about that.
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Compression is the same on the other side so that's not my issue, although it is systemic which I will address at the end of the season. I just want to get the right side to perform like the left side for Labor Day weekend. I checked the small filter in the front carb and it was clean as a whistle. The rear filter would require removal, although I think my problem is the front cylinder evidenced by removing the spark plug wire while running and seeing a much smaller change. I'm thinking now that the problem may be electrical, like the MPEM. Any good tests to verify that they are operating properly?
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