Sport jet 90 problem

[Epic Sport]

Hi all, I have a problem i'm trying to troubleshoot with my 1994 sport jet 90 - 0EO78309........
I just bought it a few weeks ago and the first time I took it out everytime I swiftly went to WOT it would loose RPM then die. I took it home and scrutinized the motor (you know how we do when we don't really know what we're looking at) and started researching the motor and problems others have had with it. I (with my own amiture deductive reasoning) thought it could be a fuel delivery problem. To see if I could do a quick fix I added a can of Sea foam in the gas tank, sprayed the carbs down good with carb cleaner and changed the plugs. I took it out again and pushed the throttle very slowly, gradually to WOT and it worked for about 10-15 min and did the same thing, RPMs dropped and it died.
I'm starting to think this is a problem when it warms up because I took it out yesterday, fishing. I would start it, go fast to my next fishing spot and stop for 30-60 min then do the same thing. It seemed to do fine.
FYI, the motor starts right up, everytime! Hot or cold.
Please advise, any input would be greatly appriciated!

 

[aksor]

Re: Sport jet 90 problem

Check your fuel pump, remove feed to carbs and crank engine fuel flow should be a steady flow not pulsing, fuel pum p repair kits are cheap and should be done yearly to avoid problems. Use a putty knife to hold spring compressed when reassembling fuel pump and don't forget to replace the gasket between fuel pump and engine. Also ensure your carb vents are free of gunk and the hoses going to the silencer are clean.

 

[Epic Sport]

Re: Sport jet 90 problem

Check your fuel pump, remove feed to carbs and crank engine fuel flow should be a steady flow not pulsing, fuel pum p repair kits are cheap and should be done yearly to avoid problems. Use a putty knife to hold spring compressed when reassembling fuel pump and don't forget to replace the gasket between fuel pump and engine. Also ensure your carb vents are free of gunk and the hoses going to the silencer are clean.

Thanks for the response! I actually found a pump and rev limitor on ebay for pretty cheap so I went ahead and bought both, if for nothing else than to have an extra around. I will conduct that test and keep you updated!

 

[Epic Sport]

Re: Sport jet 90 problem

Okay, the fuel pump is replaced along with all three ignition coils. I took the boat out today and had it at WOT for about 20-30 minutes. Right when I was getting excited it started acting up again, the RPMs drop as if I am backing off on the throttle and it dies. :facepalm:

It seams to be spuratic with the only constant being that it only happens when the engine warms up ;
- A few times today when I was at WOT the rpms dropped and stayed around 2ooo with the engine running rough. I then put it in neutral and it was running rough and idling high, 1700 rpm approx.
- A few times the rpm dropped and it died.
- It does need choked to start up again (more times than not) but 8 times out of 10 it starts within a second of turning it over. The other two times of ten it takes several attempts to start again and this, again only happens when I keep running the engine after it starts acting up.

I will welcome any suggestions anyone has. It would sure make a good birthday present to myself to be able to enjoy this POS this coming weekend!

 

[Anders67]

Re: Sport jet 90 problem

Hmm. Have you checked so its free and clear hoses/ pick up, from tank to fuelpump?. So nothing is clogging the free flow sometimes?. Filter in fulepump lid clean?. Fuelpump lid in right position with intake in 4-o clock position. Check valves (3) and membran ok?. You checked the vacuum line/hose to pump and fitting so clear, and hose not cut or clogged?.

Check the thin airline om left side of carbs (between carbs and up to airbox) so its free, and blow through so its open in to carbs too. Carbs cleaned out?.


Is that?s okay. Over to electric.

You should check the spark on all cyl. when it?s happen. I took out the timing lamp with me and hooked it on to the high power lines, and checked if it lighted as it should (not missing). There you can see if one cylinder is falling out.

If it?s not overheating (engine) it?s normally on electric for a coil ore condensator to fall out when heated up, if broken.

 

[tednv]

Re: Sport jet 90 problem

Identical boat, identical problem... here's what i've tried so far...

( 2 = me buying two of the same item to make sure it wasn't new defective, so now i have a ton of spares)

ride plate gasket
gear oil on both ends
2 stators
2 triggers
2 voltage regulators
2 switchboxes
2 flywheels
tygon tubing throughout
fuel pump rebuild
all new coils
3 starters (i keep burning through them trying to get it to run)
2 different types of plugs

tools i've used for sanity:
compression tester
voltmeter
timing light
permanently installed fuel pressure gauge

compression good, voltage good, fuel pressure good, timing good

still having this problem...

 

[tednv]

Re: Sport jet 90 problem

also rebuilt the carbs 4 times, trust me, they're clean...
forgot, + new batteries

 

[tednv]

Re: Sport jet 90 problem

also forgot new head gasket, exhaust gasket, cleaned and adjusted reed valves (which helped slightly with compression)

 

[Anders67]

Re: Sport jet 90 problem

Check all the way from bottom of pick-up in gas tank to fuelpump if all other things is good. So nothing clogges it .

Check evapor hose on left side of carbs. So it?s open in to floater chambers ,and all way up to intake.

All grounding from electrical. Especially from the CDM if you have that. They work on low volt to trigg, so it need?s not mutch to disturbe them.

I had 1-2 CDM modules that died on high rpm, and after a while.


I also had a idiot problem on mine, to do the similary prob.. I was a little piece of debris in fuel , on the inlet side of the needle jet to carb. So when WOT the debris shut of the fuel in to the lower carb.. Make the engine first go up as i shuould and then fall back and died on that carb an the two lower cyl..

 

[Anders67]

Re: Sport jet 90 problem

And another thing it can be. Whater in comb. chamber on higher rpm.

Kill the engine and take out the plug on the cyl that dies, when it happen. And see how it looks in color.

 

[tednv]

Re: Sport jet 90 problem

Solved the problem, it ended up being a bad rev limiter. I ended up changing EVERY other electrical component before I got to the rev limiter, so that's a positive I guess since now I don't have to worry about all the other stuff failing. And now I have a box of spare old parts in case it does go bad