Sportjet won't Plane

[Stormjet90]

94 Mercury Sportjet 90HP in Dynasty Jet Storm
I can not get this boat to plane. I can only get about 10-15MPH .
I suspect low engine RPM but no tach so I can not be sureÂ…
engine starts easy, throttles up quick and runs smooth.
Below is what I have done so far:
1. Flushed and refilled tank with 50:1 Premix.
(This one is NOT oil injected)
2. Verify tank vent operation-OK
3. Verify proper operation of check valve in primer bulb-OK
4. Verify Compression 130-125-135
5. Verify spark at spark plug –OK
(Plug reading look fine after running for 30 Min)
6. Replace Fuel filter between tank and pump
7. Replace fuel pump.
8. Replace hoses from tank to pump & pump to carbs.
9. Drained old fuel from carbs.
10. Verify at full throttle position, carb butterflys fully open – Horizontal
11. Replace Fwd- Reverse cable -
(Veryified the Reverse gate is fully out of the way when in forward)
12. In the jet drive, I replaced wear ring, installed rebuilt impeller,.(checked clearance installed .028” blade to wear ring)
I am pulling what little hair I have, out.....Any suggestions on the boat?
-Mark

[572Daytona]

You really need to find out what your RPMs are to see if the problem is the motor or the jet. You can get an inductive tach such as this:
http://www.esitest.com/cart/325.html
Or an engine analyzer with an inductive pickup such as this:
http://www.etoolcart.com/index.asp?PageAction=VIEWPROD&ProdID=6688
These will allow you to measure engine rpm by just clipping the sensor over a plug wire.

[centerhill condor]

have you ever seen the boat run right? This guy came into the shop with a boat he got a good deal on and it idled okay but had no power at wot.... Now realize I'm no boat mechanic but the guy had the wrong flywheel. took a long time to find it out because it had good spark and the proper voltage drops etc... the give away the flywheel was a different color than the rest of the engine.
what about the air filtration system? have you run it with out the air filter? sometimes they get gummed up as well. also, what about adding some carb cleaner? these two strokes get all gummed up just like the others. does it smoke alot? could be an air problem such as vacuum leak.
does it have mixture screws? in the old days they get screwed in somehow and don't get screwed back out.
sometimes, you can run it wot and it will, over time, clean out the crud and pick up and run like a banshee or burn a piston. at some point you won't care which!
also, check the exhaust these two strokes clog the exhaust and it has to be manually cleaned just like a weed eater! this problem causes good idle and a little more but no wot!
this impeller, did it look just like the old one? they come in a wide array of pitches, blades, ratings, etc and if you have one for 350 hp you'll never spin it fast without the 350 hp. the pump is the perfect dyno.
good luck.

[Stormjet90]

Thanks for the quick replies.
I just picked up a teleflex in dash tach but have not hooked it up since last on the water. It's now on my priority list to install !
I have not seen this boat run right- only owned for a month. Another bargain purchase....
Flywheel appears to be OEM/stock - color and wear match rest of the engine.
I have ran the boat without the airbox - this one has only a USCG "air box" - No filter. It runs the same either way.
The impeller was the stock OEM impeller had a few nicks in the leading edge, as this is a threaded impeller and as far as I have been able to reasearch, is the only impeller offered for this application. The edges were cleaned up, surface refinished, diamater checked. This was done at Performance Propeller of Nashville (TN) whom I was referred by several of my friends. They do great work- as witnessed in others boats. The wear ring had some pitting as it had been ran in brackish water and when mounted was at about .038-040" to impeller before rebuild. Thought for sure that replacing wear ring and a proper diam impeller would fix it as it was cavitating something awful.
I hadn't used the carb cleaner, yet. When I took the bowls off the carbs they were shiny and clean so I passed on the carb cleaner. It does smoke a bit more than I think it should ...but it is a 2-stroke. Maybe I will look at the exhaust side, now.
Assuming it is low RPM's, where should I look next?
-Mark

[centerhill condor]

come out to centerhill and I'll let you pull my boat around sometime!

[Old Guy]

I fixed a 2 stroke motor that had a sheared key on the flywheel. Same kind of deal. It would start and run, but very little power. Somebody had taken it apart and put a small piece of key stock in there instead of the proper key. I'm guessing that it backfired and sheared the key. Or they hit something with the prop. Anyway, somehow the key got sheared.
Also check the spark advance. Good luck.
old

[Sin City OLDS !]

Hmmm i have looked at your list there, have you checked for a Clog in the Exhaust? it's a two cycle they do that .... I have had then idle fine ,but when you nail it it just falls flat ..

[Stormjet90]

GOOD NEWS.......Good News..........
Thanks for all the posts!
As a result, Got the boat to plane and its starting to run right.
Top speed of about 40 MPH with 225# Driver.
SO you ask...What was the cause of the problem??
A couple of things:
Last seasons gas left in the carbs and fuel system had gummed up the orfices inside the carbs and was causing fuel delivery issues even though the carb bowl and floats were as clean as could be (fooled me).
Just as prescribed, A 16 oz can of Sea Foam in the 20 Gal tank and a can of Sea Foam's Deep Creep sprayed in the carbs while running on the lake were just the ticket. WOW what a difference, Thanks!!
On top of that problem, with the choke off, the choke butterflies were horizontal on the top carb but just slightly closed on the middle carb and about half closed on the bottom carb. (HOW DID I miss that?) ATTENTION TO DETAIL! I thought I had checked all of the butterflies position but I must have overlooked the kower ones somehow. Why didn't that show up as rich on the lower 2 sparkplug readings? I still do not know. <I'm Kicking myself in the @$$ for overlooking the obvious>
Thanks again everyone,
Safe Boating!
Mark

[centerhill condor]

congrats...don't beat yourself up for the obvious. We've all been there and lived you will too! You'll catch a bunch of debris in the fuel filter in a tank or two... just be prepared... now how 'bout that tow? Had a great last couple of days on centerhill... did some skiing and swimming! Come see us....bring some rope!