Medallion 152 jet boat 1996 120hp..need help

[theo]

:bonk: :nilly: I just bought a Medallion 152 jet bought for tooling . I always loved Donzi and so was attracted to this immediately. I'm sure(from what I'm reading....it isnt a "true' Donzi but it seems to be put together really well!It is in good condition and got it very cheap $1200 with an untitled trailer. I was searching the web for days trying to find info before the purchase and couldn't find anything of value. the owner bought it from a female recently divorced , he didn't know anything about boats or this boat. He stated "This listing is for my friends 1996 120hp Donzi Medallion Jet Boat. She has owned it for years and stored it in her garage. Times are tough for her and she hasn't been using it. It has been sitting for about 6 months. It is in terrific shape, all the gauges work, very clean, nice CD Player with working speakers. I borrowed it from her last week to take it on the Peace River, I put in half a tank of new fuel, and it fired right up and idles great. However when we took it out on the water it wouldn't go above 28mph, she said it used to go almost 50. I drove it around for about an hour, it seemed like it got a little better, but not like it is supposed to be.."
I purchased the boat and took it out ...the engine sounds good and spotless engine compartment...It started right up and got right on plan and went to 34mph(according to the speedo) then I couldn't get above 32mph..in very calm water, by myself at 220lbs and 1/4 tank of gas...It was a fun little thing and figured i could get it up into high 40's with some tinkering(guessing)...then after 30 minutes in the dark ..I started doing 360's and the boat wouldn't go...ran great but nothing ..as the boat drifted I noticed I was in 3 feet of water and grass was to the top of the water, figured clogged but I know in jets the impellor doesn't reverse...the boat does not go at all...but just revs...After rowing home for over an hour(fun,fun,fun)the boat is docked and trailer is not accessible....help, how to clean out,I was going to dive under boat...but this is fresh water,in south florida ,at night,and I would rather admire gators from afar....tommorrrow is a new day....please help...:beer:
clean out or big problems...shouldn't the boat move alittle if clogged...how do I clean out >the jet is under the boat? can I do while in the water? Does anyone own one ..cannot find anyothers! Oh... by the way great site!!!!

[harbormaster]

You can retro fit a 120hp powerhead on that thing. The 90hp sucked. I am not sure about the 50mph speed though. All they are is outboard motor powerheads.

[erikshube]

Try rocking it side to side in the water. I know thats the way to do it with ski's.
When you get it out of the water, check the impeller and wear ring (pvc like "pipe" around the impeller).If either are nicked or scored the slighted bit, it would drastically reduce the speed and power of the boat.

[smbarcelow]

I'm not real familiar with self-bailing jet boats, but don't they have an impeller access cover in the engine compartment? If not, you should find adequate access from under the boat. I'd suggest disconnecting the battery before reaching in, since there's no real neutral. If enough seaweed was wrapped around the impeller, it would be completely ineffective at moving water. The engine may rev and turn the impeller, but it will just spin in the water without moving it through the drive. Good luck. Sounds like a good buy.

[Just Say N20]

You will have to get under the boat and pull the weeds out of the intake grate. There is NO access from the top on the Mercury Sport Jets, and there is no clearing mechanism on the SJ 90 or SJ 120.

That boat running correctly should be a low to mid 40s boat. With jets, the clearance between the impeller and the wear ring is critical. On my 175, it should be between .038 - .052. Once you get outside the the .052, the performance falls off exponentially.

This is probably what you will find. In this situation the boat barely moved forward. I only had about 100 yards to go at this point. You have to be careful because the engine is cooled by diverting a small portion of the pressurized water from the pump. When the pump intake is clogged, there is very little cooling water going to the engine.

http://i26.photobucket.com/albums/c111/streb2005/Reflexxweedsintake.jpg

[BUIZILLA]

I had a 175 sportjet

anything less than 18" of water it vacuumed the bottom clean, it would suck weeds right out by their roots....

[zelatore]

This is probably what you will find.
http://i26.photobucket.com/albums/c111/streb2005/Reflexxweedsintake.jpg

Salad. It's what's for dinner.

[Drox]

I bought a 1995 152 Medallion with a 120 Sport Jet earlier this summer and thought I would report my problems and solutions thus far.

Problem #1 - Random air cavitation of the jet pump... It did not appear that the bottom cover under the jet impeller was loose - but that was the direction that all of my research pointed to. Solution - I roamed around town until I found the exact screws that fit on the outside cover under the impeller. (Some of the heads were worn out from past owners tightening them - so I replaced them all.) Someone had used 3 course threaded screws in place of the fine threads and I had to match the right threads to the right holes, but once I had the right screws in place I tightened up the cover plate and the cavitation was gone.

Problem #2 - Boat Porpoising. I installed Smart Tabs... They work unbelievably well!! The boat handles great... It no longer walks back forth at low speed, planes out in a heartbeat, and it takes on major chop without a problem! Also, I did not notice any speed loss.
http://www.nauticusinc.com/smart_tabsSX.htm

Problem #3 - The boat engine would cut out as though the fuel filter was clogged or fuel pump was going out. It was primarily a problem at low speed. I installed a fuel pump kit and cleaned the vent lines between the carbs... but it turned out to be a faulty rev limiter. It was intermittently cutting out various cylinders. (Dealer had to figure that one out! $220)

Happy Boating!