Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

eric21

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Jun 30, 2011
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Hi everyone, I just installed a new powerhead because the last motor blew 2 pistons and cracked the exhaust ports so I couldn't bore it out.
So I installed it and it started right up :), I was using the dealer flushing kit with low water pressure. As told by the motor manufacturer I am running 25:1 pre-mix, I also throughly cleaned the carbs, reeds, new themostat, fuel lines, and fuel filter.

Here's the things that are concerning me:
1. Engine idle rpm is around 1900 (tried adjusting the linkage and looks correct)

2. Lack of exhaust smoke (this bothers me because i'm running 25:1)

3. I havn't played with the timing yet (I tried to keep it exactly as it was when I took it off the other motor - I plan on timing it properly)

4.I am planning on checking the fuel pump pressure to make sure its in range.

My feeling is that the pump is not providing enough gas which is causing a lean condition which is thus causing the rpms to shoot up and also the lack of smoke. I didn't touch the idle screws because it ran good before it blew up, so it don't think that
is the problem. This thing starts on the first turn but I don't wanna blow it up again, so let me know what you guys think
All advice is greatly appreciated
Thanks
Eric
 

eric21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Ok here an update, checked the fuel pump pressure - 3.5psi at high idle (its the 2 stage pump so it should go up to 6psi at wot)
Looked at the spark plugs and they were all nice and brownish tan slightly moist (its just been idleing on the hose)
Those 2 things make me feel better but i'm concerned with the high idle and the engine seems to be running hot.
Could a too far advanced timing cause this issue that i'm having or is it something else?

Please let me know what you think
Thanks!
 

donaldson21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

I have a 1993 jazz with the 90hp mercury(force) sportjet in it and it says on the gas tank filler to mix at 50:1 ratio and my seadoo mixes at a 42:1 ratio so I would say there is not enough oil in the gas is where the lack of smoke is coming from and also maybe the lean mixture.
 

GA_Boater

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

If you can move parts from one powerhead to another and put everything in the exact right position, you are a better man than I am. Seriously - you have to check everything because no two motors have exactly the same tolerances and you have no reference. Timing, carbs and linkages need checked. Timing and carb settings could cause the high idle and lack of smoke.
 

kend301

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Rebuild / clean the carbs , SET THE TIMING to 30 deg at WOT !!!!! improper timing will blow one up !
Reset ALL your timing and throttle linkages to factory specs and adjust idle air mix and idle to factory specs .
GA_Boater speaks the truth about just swapping stuff , besides everything was set properly for a motor ready to blow up , not for a new motor .
 

eric21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Thanks you guys very much, I brought it to the shop to have it fine tuned because I don't trust myself. They are going to fully re-build the carbs and adjust the linkage and set the timing, its gonna cost me but its worth the piece of mind.

On a side note: when they checked out the motor (tried it in the water not just on the hose) he said water was comming out of the exhaust manifold and he heard a slight knock.

When I started it up there was no knock what so ever and not a drip came out of the exhaust manifold, he said that could be because there was no load on the engine... does that make sense to you guys?
He said the knock could be from the timing being off or possibly a little water in the cylinders from the leaky gasket but he seems to think the engine is ok and will be good to go when adjusted properly.
Does all of that sound correct to you guys?
Thanks
 

Fireman431

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

I have a 1993 jazz with the 90hp mercury(force) sportjet in it and it says on the gas tank filler to mix at 50:1 ratio and my seadoo mixes at a 42:1 ratio so I would say there is not enough oil in the gas is where the lack of smoke is coming from and also maybe the lean mixture.

FYI: 25:1 is TWICE the oil in the gas as 50:1. (25 parts gasoline to 1 part oil vs. 50 parts gasoline to 1 part oil)
 

calledinsick

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

I did have a similar issue with the water coming out of the exhaust gasket. I couldn't figure out why there was water on a lot of the enigine components. I started it on a hose and it was fine. Finally I got brave and opened the engine hatch while on plane and there was a stream of water spraying out of the exhaust manifold against the starter!

Turns out a small rock had lodged in a water passage in the manifold/gasket and the manifold gasket had burnt in that spot causing the leak at higher rpm's.

A pretty easy repair. There is also a pattern to tightening the manifold bolts when re-assembling.

For a 94 SJ 90 this should be the part number for the gasket: 27-8190354
 

eric21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Thanks man, I had used a new aftermaket gasket but it seemed really low quality and thin. I torqued all the bolts in the proper sequence and tightened to 13 N-M (which seemed loose to me but thats what the book said) and made sure the mating surfaces were clean.
Do you think it could have been the qualitity of the replacement gasket?
 

calledinsick

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

13 is what the manual says. I think I used a Sierra, but I don't remember...mostly I use QuickSilver parts. I also put the gasket in dry (no RTV/Copper).
 

kend301

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

FYI: 25:1 is TWICE the oil in the gas as 50:1. (25 parts gasoline to 1 part oil vs. 50 parts gasoline to 1 part oil)

When breaking in a new Sport Jet Engine 25 : 1 is the recomended mix for new engine break in
 

iraqvet70

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

where did you buy the remanufactured powerhead?
 

eric21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Look on ebay for "sportjet powerhead" they are a place out of Kentucky. They have all types for the 90 & 120 sport jet. I'm still waiting for my shop to go over the boat so I can get my warranty.
 

eric21

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

Well I finally got the boat back last week :) I taken it out 5 times since then and have been breaking the engine in per the recomended procedures. It starts perfectly and seems to run pretty good, but I find myself opening up the hatch every couple minutes to look and listen to engine ( i'm super paranoid now lol). My boat needs to be at about 4800 rpm to get on plane and I know i'm not supposed to rev it that high yet but i've done it a couple times for a very short time and it feels good (its tough to put around at 10mph lol).
I don't remember how hot the engine is supposed to get but I can hold my hand on it for about 3 seconds at its hottest. Does that sound ok?
 

Fireman431

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

When breaking in an engine, I've always read to run the throttle throughout the range, avoiding a prolonged run at WOT. the idea is to let it break in at different RPM's not just idle. Run it and have fun, just vary the throttle constantly.
 

CharlieFoxx

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Re: Installed remanufactured Powerhead 1994 sport jet 90 - high idle rpms??

.......

A pretty easy repair. There is also a pattern to tightening the manifold bolts when re-assembling.

For a 94 SJ 90 this should be the part number for the gasket: 27-8190354

Can you speify that pattern please? I'm thinking about changing that exhaust manifold gasket.
Thanks for the info...
 
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