Sport Jet 175 x2 with low compression

[rossman21]

I am having problems with my 1998 Sea Rayder with a Sport Jet 175 x2. It idles extremely low - around 800 rpms. I have tried a number of things, but just can not increase the idle. I did a compression test and all 6 cylinders are at 105 psi. Is this engine now worthless???

 

[Dukedog]

"I have tried a number of things, but just can not increase the idle."

what have you tried?.. do you have an OEM manual for it?

 

[rossman21]

I have rebuilt the carbs, replaced the reeds, verified that the electrical fuel primer and fuel pump work, verified that the push button enrichment valve clicks and works, replaced the spark plugs, verified spark to each cylinder.

I have also adjusted the primary pickup screw and idle stop screw.
The oil mixer was removed years ago and the engine runs on 50:1 pre-mix. I am using brand new gas.
I have not adjusted the timing (I don't own a timing light).

I was told the sport jet 175x2 compression should be 125 psi. At 105 psi, is my old engine a goner?

 

[rossman21]

Yes, I have the Sport Jet manual from Mercury.

 

[QBhoy]

Hi. I think you’re just about ok with that compression and gauges can be a little low or high sometimes. As long as they are all similar across them all. So for now…rule that out I’d say.
As for the low idle. What’s it meant to be ? Are you reporting this as in the water or out the water idle speed ? There is a fair difference between the two on a jet drive. Is your wear ring to prop clearance ok ?
What idle rpms are you aiming for ? Is the issue that she stalls ? Have you tried to adjust the idle settings at Tick over underway ? Or adjust the minimum throttle position setting ?

 

[rossman21]

It idles at 800 rpm in the driveway with a garden hose. I would like it to idle around 1500.
I took it to water and could not get it to run at all - she would die after a few seconds. (In the water I would love if it idles around 1,000).

Of the 3 main adjustment screws, I have "played with/adjusted" the middle screw and the bottom screw - the bottom screw increases the idle from 500 to 800, but not enough for the engine to run correctly (idle is too low to sound good)

Thank you for suggesting looking under the boat - that is something I never thought of! Anything touching that impeller is definitely going to slow that engine down.

 

[Scott Danforth]

It idles at 800 rpm in the driveway with a garden hose. I would like it to idle around 1500.
I took it to water and could not get it to run at all - she would die after a few seconds. (In the water I would love if it idles around 1,000).

Of the 3 main adjustment screws, I have "played with/adjusted" the middle screw and the bottom screw - the bottom screw increases the idle from 500 to 800, but not enough for the engine to run correctly (idle is too low to sound good)

Thank you for suggesting looking under the boat - that is something I never thought of! Anything touching that impeller is definitely going to slow that engine down.

first, your compression is low verify your gauge and retest
second, 800 RPM is spec for idle
third, wanting it to idle at 1500 is just trying to band-aid issues

fix your fuel system issue. do a proper link-n-sync

you may have to go thru the carbs again paying attention to the chokes and verifying clean passages to the jets

there is a reason the searayder / sportjet combo died and get small jet boats went with proper jet setups yanked from the PWC world after that.

 

[rossman21]

800 RPM is spec for idle
third

I do not believe this is true (minimum of 1,000)

there is a reason the searayder / sportjet combo died and get small jet boats went with proper jet setups yanked from the PWC world after that

This might be true - but this is boat that I have and this is what I am stuck with. I am hoping to get it running so I can take the kiddies out and have some fun.

 

[QBhoy]

Hi. Ok. So your idle will be low for sure then. When she is in the water. You really want to be setting the idle up when in the water really. Is the fuel definitely good ? Carbs clean ? Lots of things can effect this. Needs to be warmed up and in the water to set up properly.

 

[rossman21]

Hi. Ok. So your idle will be low for sure then. When she is in the water. You really want to be setting the idle up when in the water really.

I tried to setup (adjust) in the water, but when I took it to the water, it would not start in the water (my sport jet only starts with the garden hose in the driveway). I can't adjust it if I can't start it

Is the fuel definitely good ?

Brand new pre-mixed 50:1 gas.

Carbs clean ?

Rebuilt the carbs last week (and replaced the reeds). Also has brand new spark plugs.

Lots of things can effect this.

I understand that lots of things can effect this - that is why I am here looking for help/recommendations.

Needs to be warmed up and in the water to set up properly.

I live 40 minutes from the water - and there is no hose at this boat ramp. I am unable to warm it up before putting it in the water. I would love to be able to adjust it in the water, but my sport jet will not start once its in the water.

 

[QBhoy]

I tried to setup (adjust) in the water, but when I took it to the water, it would not start in the water (my sport jet only starts with the garden hose in the driveway). I can't adjust it if I can't start it

Brand new pre-mixed 50:1 gas.

Rebuilt the carbs last week (and replaced the reeds). Also has brand new spark plugs.

I understand that lots of things can effect this - that is why I am here looking for help/recommendations.

I live 40 minutes from the water - and there is no hose at this boat ramp. I am unable to warm it up before putting it in the water. I would love to be able to adjust it in the water, but my sport jet will not start once its in the water.

Ok. Understand. Will it not even start with some throttle on ?
I’d definitely check the pump isn’t getting locked up on something like the wear ring or something around it or in the intake before it. Intake it when you run it at home, you turn the water on after it’s started and off before it stops ? Just in case you’re getting water into it from doing it the other way about. That would afffect things. Just thought I’d ask

 

[Scott Danforth]

Run some ring free or power tune to see if your compression comes up

Perform a link-n-sync

Check for spark on all cylinders

Use an ir thermometer to check for all cylinders firing

 

[rossman21]

Ok. Understand. Will it not even start with some throttle on ?

With the throttle in neutral, I pull the neutral lock button out, then throttle it all the way forward - this is the only way I can get it to start
As a test, I removed the throttle cable - with that removed, it is much easier to manipulate - I have tried more throttle, less throttle, tried everything I can think of by pretending my hand is the throttle cable. Still can't get higher rpms.

I’d definitely check the pump isn’t getting locked up on something like the wear ring or something around it or in the intake before it.

Looking under the boat is a GREAT suggestion!
I have not been able to get under the boat yet (basically monsoon weather all day). I am hoping there is a chunk of seaweed somewhere or maybe something wrapped around the prop shaft - i know if the jet pump is not working properly, it would definitely slow up the engine. That would be an easy fix!

Intake it when you run it at home, you turn the water on after it’s started and off before it stops ? Just in case you’re getting water into it from doing it the other way about. That would afffect things. Just thought I’d ask

I run the water from the garden hose before starting and always running water while the engine is running. I have not tried running the engine with no water - I know the manual says never do this - not even for one second.

 

[Scott Danforth]

Should not need full throttle to start

 

[rossman21]

Run some ring free or power tune to see if your compression comes up

I have not used these - which product/manufacturer do you recommend?

Perform a link-n-sync

Sorry, but I do not know what this is. I noticed there are so YouTube video on this - I will try to educate myself.

Check for spark on all cylinders

I have 3 spark testers - I plug all three on one side of the engine and they all light up. They also light up the other side. It seems I am getting spark to all the plugs.
But - I have heard that the cheapo spark testers I have can be misleading - a tiny little charge will light up the tester, but that might not be enough to create the needed spark (just learned this today).

Use an ir thermometer to check for all cylinders firing

What a great idea!
I don't have one of the professional automotive type ir thermometer - I am hoping my wife's thermometer that she bought during Covid and uses on the kid's forehead will work.

 

[Scott Danforth]

Read the factory manuals on setting the carbs. I don't trust any video on youtube unless done by a trained mechanic

A spark tester is a gap test. The spark must be able to jump a 3/8 gap

 

[rossman21]

Should not need full throttle to start

My Sport Jet has always been cold blooded. Once it starts it has always puffed out a nice cloud of white smoke. Once it warms up - it will easily restart in neutral without throttling up. But the first start has almost always been difficult.
I would love it if it just started when it was cold

 

[rossman21]

Read the factory manuals on setting the carbs. I don't trust any video on youtube unless done by a trained mechanic

I will read up on my settings my carbs.

A spark tester is a gap test. The spark must be able to jump a 3/8 gap

I was lied too! I was told those testers were worthless.
No matter what, I am going to use an ir thermometer.
If some of the cylinders are not firing, that would be an obvious reason the rpms are low.

 

[Dukedog]

............. that motor has "electrionic" electrical junk.. it has a single box that replaces switch boxes and it also has an electronic ecu.. these can be a PIA ta diagnose ('specially ona computer)... you need to go by what your manual (if its tha right one?) tells you ta do for carb, linkage, timin' adjustments.. test spark and etc.. if it does not have these things in it its tha wrong type manual...

 

[QBhoy]

Hi. So don’t quote me on it…these may be different from any other jet craft I’m used to…but if it has a cooling feed off the jet pump itself like normal jet systems. You usually start the engine first before turning water on. And turn off water before stopping. Or you end up with water getting into the engine with not having exhaust pressure to keep it out. Yours may differ…but certainly this would be the norm