90 hp sportjet wont rev past 4200 rpms need help

[tyler ordway]

i have a 1994 seapro renegade with the 90hp sportjet engine. i bought this from in auction, so i dont know prior history. I cleaned the carbs set the idle screw 1.5 turns out. boat runs really good just revs out at 4200 rpms. with jolts to 5000 rpms. it only goes 10 mph, but with the jolts i got it up to 30mph. its runs good and doesnt stall. occasionally there a loud clacking noise coming from the engine bay. i have spark on all 3 plugs. the third carb on the bottom overflows with gas i put a new float valve in and adjust the float to shut it off sooner. im thinking its running on 2 cylinders and the third works occasionally and revs up to 5000. need advice would be greatly appreciated


what i have done so far

cleaned carb
new plugs
changed gear lube
compression test all 3 at 120

thanks tyler

 

[tyler ordway]

im also thinking the timimg might be off

 

[itsdgm]

Hi @tyler ordway welcome aboard.

A few things that come to mind right away:
1. Fuel starvation. Possibly fuel filter, carbs need more cleaning/rebuild, bad fuel pump?
2. Low battery voltage
3. How do the air cleaners look? Could be starving for air if the filters are dirty or full of oil.

Also, what kind of engine is in your boat? More info might help with the diagnosis. Good luck hopefully it's a simple, quick and cheap fix. Keep us posted.

 

[4x15mph]

@tyler ordway , show us a pic of this renegade!

I would look at all of what @itsdgm (Dennis) pointed out as well as:
1. Fresh gas?
2. a rebuild of the carbs to include new OEM parts (i.e. diaphrams). It sounds like you may have just cleaned them
3. spark plug wires, replace since they may be from 1994 and affecting the spark. You may have spark like you said but it may not be consistent/strong.

 

[Speedling]

Yup, if the spark is good you look at air and fuel. This is a 4 stroke right?

 

[tyler ordway]

Sorry the engine is a 90 hp Mercury sportijet. Oil injected 2 stroke. There is no air filter in the air box. I will take a couple pics and post them and a couple mins.

Thanks guys

 

[tyler ordway]

 

[tyler ordway]

I'm going to check the fuel pressure from the pump. The carbs seem really simple compared to other carbs I've cleaned no diaphrams. I sent a pic of all extra parts left in the boat. Im gonna look for any gunk in the exhaust. The impeller looks to be in good shape.

 

[bronze_10]

There are people far more knowledge that me on here but I will share an issue I had once incase it relates.... years ago I had a 1996 seadoo 2 seater jetski i bought with 20 hours on it in 2006.... it was white with purple accents.. don't remember the modle... it had a 787 cc motor or something like that.... the first year it ran great.. the second year not so much.. for 30 min it would do perfect, then it would go into this weird loaping thing with the engine... it would only go at about half throttle and then jump to full and then back to half... I spend so much money on that thing with full lines and oil lines and new carbs ... nothung helped until I read on line how the engine coil worked.. the coil fired off spark on both plugs at the same time one cylinder was in compression and made power while the other was in exhaust with no fuel to burn.... I replaced this coil with one I bought on line and the ski ran flawlessly......... then I sold it cause it pissed me off so often...

I have no idea if this will help BUT my ski is close to the same year as your boat.... sooooo

 

[Speedling]

Ever check the reeds?

 

[tyler ordway]

lol I may sound like an idiot but I don't think there are any reeds

 

[Speedling]

http://www.pwcengine.com/products/Mercury-90-hp-Sport-Jet-(3-cylinder)-Boysen-Reeds-1993%2d1995.html
Hint: they aren't in the carburetors

 

[tyler ordway]

Ok thank you. I'm definely going to check the reeds later on today. I'm hoping that's the issue.

 

[Cobra Jet Steering LLC]

What is the compression? absolutely change the plug wires they break down internally and run a bit better when cold but fail when warm, also remove and replace the fuel lines and be sure there is no trash inside them, those are bowl carbs and they can get trash in the fuel lines that will block of the carb needles, check the fuel tank for trash or water since you purchased it where you did there could be all sorts of trash stale fuel or water in the tank causing issues.
Do not just add fresh fuel to what was in the tank, clean it thoroughly. Add a good filter with a glass sediment bowl so you can see what is going on.
Clean ALL your ground wires especially the ones on the coil and brain.
And be sure they are still good, those will rot from the inside also.
If the reeds are bad you will see fuel blow out the carbs when you try to run it. If the needle and seat is leaking in a carb , pumping the primer will show fuel leakage from the carb that has the issue.
Did you replace the base gaskets when you pulled the carbs, if not you should.

 

[tyler ordway]

Thank you very much for the reply cobra jet steering. It's because people like you and everyone else that make forums. Such a powerful tool. I'm been working and thinking about this boat for a couple weeks now. I've put new valves in the carbs. And cleaned them. Right now I'm waiting for the new reeds in the mail. Ive cleaned the fuel lines and fresh gas with sea foam. I'm really hoping and about 70 percent sure it's the reeds. Clyinders 3 was spitting a lot of fuel out. I'm guessing that it's running on 2 clyinders and when it gets to cylinder 3 the compression is blowing the fuel right out of the chamber. And not firing. I hope that's the case. I haven't messed with the grounds or could yet but I'm going to go threw them while waiting for the reeds to get it here. The compression is at 120 each. The gaskets on the carb seem to be ok. I blew all the jets out with a air hose and carb cleaner. If the reeds do t fix the issue I'll get the new plug wires. After that I don't know what else the issue could be. It runs absolutely great idles great. Starts easy. Just doesn't rev out. Really hopping it's a dead clyinder.

Now on there other hand should I fix and sell this boat and get something a little more modern. Because I have heard that sport jets are a dying breed. If so who makes the best and reliable jet boats.

Thank you all very much. And no matter what I'm working on. Or what the problem is. I can usually get the answers thru forums such a valuable tool.

 

[Cobra Jet Steering LLC]

Well the symptom sounds like a bad reed where the fuel is blowing out the carb. As for sport jet it is actually a Force outboard engine mounted on a jet pump. They had a big problem with the brains blowing when you turned off the ignition, this would occur if the rectifier went bad, people would change the field windings with a newer style but that was not the real solution to the problem and the new field windings still blew the brain if the rectifier went out.
You can replace the rectifier with a jet ski voltage regulator, the wiring is the same and the amperage is also. Or you can wire in a relay on the red wire from the rectifier to the battery to open the circuit when you turn off the key that is a simple way to prevent the issue.
The problem is if you blow the brain and you do not fix the rectifier issue the new brain will also blow as soon as you shut the motor off.
The stator produces ac current the rectifier changes it to pulsating DC current when the rectifier goes bad it allows ac current to back feed in the field windings and that creates a bastard charge to the circuit for the ignition thus blowing the brain, it happens when the engine is still spinning after you turn the key off, it just takes a second to cause the problem. There is no warning either ,everything is just great and when you go to restart the engine NO SPARK and you are dead in the water.

 

[tyler ordway]

Thanks very much nothing worst then being dead in the water lol. I got the reeds today I'm going to put them in tonight and is I get done early enough I'm going to test it tonight. If not I will tommarrow. If all works out I would mind upgrading the steering and the rectifier. I'll keep you guys posted

 

[Cobra Jet Steering LLC]

Ok also NAPA auto parts HAD or may still HAVE what they call a small engine book that lists a bunch of parts for those engines like coils and brains so any time you need something have your local store check and see if they still carry them.

 

[tyler ordway]

Ok so I got the new reeds put in a got a chance to test the boat out. Seems to accelerate better. Plane fast and go faster. But the fastest it would go is 25 based off a speed app on my phone. Does this seem right. Other than that I can't see an issue with the way it runs starts or idles. The rpms didn't go up any either thou. But the rpm gage could be broken. Because it says 1000 without the boat running. Compression is at 120. And it does shake a little which I think might be normal. I got the boat cheap and don't want to just throw parts at it. I've read on other forum people saying there 90 hit 43. Mph. And others say there dogs.

 

[Cobra Jet Steering LLC]

well 40 is about correct so keep doing the things I suggested with the plug wires and grounds etc