SportJet 90 PWC transplant

[WCTori]

Hello all, Allow me to introduce myself. My name is Tori, and i'm coming here to ask a few questions regarding the SportJet 90 (Merc/Force) engine and Jet unit. I am trying to transplant this combo into a vintage PWC. I'm attempting to put in a Wetbike. I have lots of experience with vintage PWC and have done a few engine swaps before so this isn't anything new to me, bu this motor and jetpump are.

I know this isn't a highly loved engine, but i'm very limited on physical size and engine/jet pump options. The Wetbike came with an almost identical set up, so this isn't too far fetched. The Wetbike came with a Suzuki DT50/60 2 cyl. perched atop a similar Jetpack. In fact the thru-hull is identical. I've managed to shoehorn the 3cyl. Force motor into the hull, and the only thing at this point fouling things up is the water supply line that runs from the engine mounting plate to the engine. I lack about 3/16" of the fitting on the block clearing the hull.

Question: Can i downsize this fitting and supply line. Its a very large hose, maybe 1" O.D. From my experience, i can't see this motor needing or using this amount of water to keep it cool, but i want to be sure. I might be able to downsize to 3/8" i.d. and solve my problem.

Here are a couple pictures of what i have going on.

 

[WCTori]

I've also got questions regarding the mechanical trigger advance. I have to control the throttle via a twist grip which wont be strong enough to also work the advance. My thoughts are to put the advance on a finger lever on the left handle bar. Or maybe not use the advance at all. I could maybe just put it in a fixed state.

Anyone have any thoughts on this ?

 

[WCTori]

Nothing ? Anybody ? Am i posting in the wrong section ?

 

[jbcurt00]

I can't answer, but you might try the PWC forum
PWC (Jetskis, Waverunners, etc.)

 

[WCTori]

Thanks, i saw that section but figured since my questions were on the boat side of the transplant, this section would have been a closer fit.

 

[jbcurt00]

looks like nobody else has attempted it.

Sounds like an interesting project, not real fond of some of the boats people choose to transplant jets into, esp vintage boats, but I do like following along and trying to learn something when I see one.

You might find this info helpful

 

[achris]

I've also got questions regarding the mechanical trigger advance. I have to control the throttle via a twist grip which wont be strong enough to also work the advance. My thoughts are to put the advance on a finger lever on the left handle bar. Or maybe not use the advance at all. I could maybe just put it in a fixed state.

Anyone have any thoughts on this ?

As the advance is a very integral part of throttle and engine speed control, any change in relationship between carb movement and spark advance outside the manufacturers design is not going to work. As is putting the advance in a fixed position. Once the carbs are fully closed, the spark advance is what controls engine idle speed.... Maximum spark advance also effects the ultimate power output of the engine too...

Chris......

 

[WCTori]

Hi Chris, thanks for the response. I planned to operate the Trigger with a finger lever. I could easily go full throw of the Trigger when going full throttle with the other hand (twist grip) and conversely, when i need idle, release the finger throttle to allow the Trigger to move back (it is spring loaded) Do you feel this will not work ? I realize i may effect max. power output if it isn't just right, but i'm thinking this may not be a worry since the engine is now only pushing a 250# hull instead of a 1000# boat hull, and will have a lot less drag.

 

[achris]

No, the amount of advance must be carefully adjusted according to the amount of throttle. You can't just wack it full advance.... Instead of trying to re-invent the engine, work on getting a twist-grip that will do the job properly...

 

[sixfigures]

It has been about 14 years since I fooled with a 90 sport jet it's a force O B engine.I don't know about the trigger but the charging system will blow your brain if the rectifier goes out. Look for a post from years ago explaining how to install a relay switch that isolates the power when the engine is turned off. I know everyone says that the new stator will fix the issue but it won't always do the job, isolating the positive from the battery when the ignition is turned off never fails. Use a relay switch that is only on with the key . I used a starter relay. you can also get a p w c rectifier/regulator and use that in place of the factory regulator since it works better.

 

[ondarvr]

I'm not quite sure why you're saying the twist grip can't control both the throttle and spark advance, it does on every tiller motor with no issues.

 

[WCTori]

Good point on the tiller equipt motors. I expect it to be too much drag. That was my only concern. I'll set it up with a twist grip tonite and see what it feels like. One thing i did notice in it's current boat configuration, is it will not return to idle on it's own. Not enough spring tension. Adding more will just make the twist harder.
I'll let you know how this works out......

 

[WCTori]

Alright, had a little time to fab up some brackets and a throttle pull. The twist grip i have to use will work although it's fairly slow due to the stiffness, and it doesn't give me the full throw i need. I presume i can only get so much pull from a twist grip. It works well enough to allow me to proceed with the project. One problem is since i cannot get full throw of the linkage, i cannot get full throttle. 80% of the sweep is used in an immediate advance of the timing. I've recorded and uploaded a video to show you what i mean. It doesn't get full throttle until the last little bit. The final arch in the belcrank is what finally moves the throttle plates.

My thought for a fix was to make an adjustment to the timing or linkage so that some of the advance was already done before the cable started to pull. Hope that makes sense.

Thoughts anyone ?

Here is the link to the video: http://youtu.be/9F86BIEvRPg

 

[ondarvr]

Your vid is marked private.

I have done this before, just move the connect point of the cable so you get more travel on the throttle and advance linkage.

 

[WCTori]

Crap. Okay, try it now.

Moving the cable won't help. There is only "X" amount of travel with the cable. The twist will only pull a cable so far. I need "Y" amount of movement.

 

[ondarvr]

You can't just change the how the throttle and spark advance are synched, they are designed to work together in a precise movement.

From the vid I can't see where or how the cable connects to the linkage, but you just move the mounting point of the cable end for more movement (normally closer to the center of rotation) or get a different twist grip.

 

[ondarvr]

Edit

You can't just change how the throttle and spark advance are synced, they are designed to work together in a precise movement.

The increased throttle advance at the very end of its travel is normal for outboards.

From the vid I can't see where or how the cable connects to the linkage, but you just move the mounting point of the cable end for more movement (normally closer to the center of rotation) or get a different twist grip. You can mount the cable end in different locations by making a small bracket, I've done this before when going from remote controls to tillers. There are many twist grips out there to choose from, some allow much more cable travel than others.

 

[WCTori]

Thanks ondarvr, I follow you now. I'm thinking if i move the cable connection point inwards toward the pivot point of the linkage, i'll loose leverage and make the pull even stiffer. I don't think i'll be able to have it any stiffer and still be able to comfortably use the bike.

I'm also trying not to modify anything on the Sport Jet set up so that i couldn't put it all back in the boat and return things to normal if my transplant doesnt work out. I'll play with it more today and see what i can come up with.

 

[WCTori]

No Title

Ok, i was able to make some progress today. I drilled a hole in the throttle pivot arm closer to the pivot which has gotten me the throw i need to achieve WOT. It's stiff, but will do for now, and for initial testing purposes.

 

[WCTori]

I think my biggest problem at this point is where the throttle comes on. Too far at the end of the twist. I need more control than this. I'm afraid i'll have to go back to my initial plan to operate the timing independantly from the throttle.
See this video for a better explanation.
https://www.youtube.com/watch?v=flWN0Er-EcI

No one has given me a solid reason why i couldn't do it that way other than "that's how it was designed.... " The Suzuki DT60 motor we run, is set up with a two stage timing curve. 8* @ 1000 rpm, then 25* @ 5000 rpm. I know you may say, "that's how it was designed" but they're just 2 strokes. I don't see it being an issue.

Feel free to prove me wrong.....