120 Sport Jet losing power

[bustedstuff]

'97 120XR in a SeaRayder F14. I think that I have solved my fuel flow problem but the boat will not run on plane. The engine starts and idles well but when throttled up to get on plane will begin to surge and stall with the problem getting worse at higher throttle settings. At WOT the boat will run 5 to 10 seconds then stall out completely. It will restart immediately. The carbs have been cleaned out and adjusted. I have installed a water separator and filled the tank with fresh 93 Octane and Sta-bil Ethanol treatment. The stator was replaced by the dealer about 5 years ago.

It feels like the lower carb is starving for fuel but the bowl is full. This thing is driving me crazy!

What do I check next?

 

[calledinsick]

Re: 120 Sport Jet losing power

Does it run rough/missing (ignition) or does it bog out/fuel starvation (fuel)? Check approriate below if you can tell one way or the other.

IGNITION:
I'd start by checking the ignition system posted in the sticky at the top of this forum. Make sure that's all performing correctly.

Rev limiter could be failing. There is a black/yellow wire that can be disconnected to isolate the rev limiter. (Small box on the starboard side of the engine nearest the carb bank.) Once disconnected try running at higher throttle and see if problem goes away.

If all the above look good I'd check the coils. They are easily removed and often have a broken magnet (easily visible once removed) that will often cause sporadic problems.

FUEL:
If I remember correctly you rebuilt the fuel pump and verified the fuel flow was not pulsing. If you haven't already you might also install a clear fuel filter near the carbs. I have added one and like the additional
check point.

Make sure the vent tubes and connections are cleared out. There are numerous posts on this.

Who cleaned/adjusted the carbs? Floats could be set wrong.

Synch the carbs- Looking down carb throats all butterflies should be flat at full throttle. If some go past flat they will reduce power. (They should all be closed at nuetral)


If these all check out we can dig a little deeper.

 

[bustedstuff]

Re: 120 Sport Jet losing power

I went through the carbs myself. I do all of my own work on this boat and my 39' twin inboard. I have fought problems with the carbs on this boat since ethanol was introduced here several years ago. The bottom one has to be cleaned out every 4 or 5 hours of use or the vents stop up and the bowl fill with fine sandy trash. The inline fuel filter has had miminal effect on this problem. I dropped the bowl off and turned the engine over without starting it to test fuel delivery but I guess the bottom carb needs to come off again.

Thanks for the tips. I will get back to you with my results.

 

[calledinsick]

Re: 120 Sport Jet losing power

I'll add that I replaced my fuel lines with USCG alcohol resistant lines (I added the see-thru filter at the same time). I was getting the same 'fine black sandy trash'.

Search USCG fuel A1. Around $3.50/ft but worth it if you don't have to clean out the carbs all the time!

I think I've said it before but replacing those fuel lines should be standard now (15-18 year old lines anyway)!

 

[bustedstuff]

Re: 120 Sport Jet losing power

I like the idea of a see-thru filter but is violates the USCG rules and we have a VERY heavy presence here. ( the chances of a USCG boarding and inspection are higher than 50%)
I worked on the engine carb sync and adjustments while running the boat but at one point it began missing badly, slowed until it fell off plane and threw a rod through the side of the motor.
I pronounced it dead and called for a tow.

Any way to put in a newer motor with fuel injection?

 

[calledinsick]

Re: 120 Sport Jet losing power

Wow! Sorry to hear about the blown engine! Have you done any diagnostics to determine the cause?

From my experience, the most common issues with these engines is the ignition components, then fuel delivery, and I'd say overheating/piston melting third.

I'm not familiar with an injected engine that could be a direct replacement.

I haven't noticed any of the sandy-trash since the fuel line replacement (or anything for that matter) in the filter so it will now come off! Thanks for the info!

 

[kend301]

Re: 120 Sport Jet losing power

I like the idea of a see-thru filter but is violates the USCG rules and we have a VERY heavy presence here. ( the chances of a USCG boarding and inspection are higher than 50%)
I worked on the engine carb sync and adjustments while running the boat but at one point it began missing badly, slowed until it fell off plane and threw a rod through the side of the motor.
I pronounced it dead and called for a tow.

Any way to put in a newer motor with fuel injection?

Ypu can do anything you want if you will spend the $$$$$ There is no standard replacement other than seeing what motors will fot the driveshaft spline for the crank and go from there

 

[bustedstuff]

Re: 120 Sport Jet losing power

Solved the stalling problem when a rod came through the side of the motor. Pulled off the carbs and reed valves and found all kinds of broken parts. Now looking to replace the powerhead.

I have pulled the motor out of the boat and began to disassemble but am stuck with getting the exhaust manifold and flywheel off. I have sprayed and pried and tapped on both without results. Of course four of the exhaust manifold bolts heads had to snap off.

Any helpful ideas would be greatly appreciated!

 

[calledinsick]

Re: 120 Sport Jet losing power

Sounds like a project!

Need to tap/strike the forcing/center bolt with a hammer...never hit the flywheel: top or bottom!! 1/4 turn...strike again...repeat. I may have let it sit overnight with pressure...not sure. Then continue the next day.

The exhaust manifold came off pretty easy for me. No bolts broke. Remember it gets hot and cold a lot, maybe a rubber mallet? I'd use caution if you decide to pry, must be a smooth surface to seal!

 

[bustedstuff]

Re: 120 Sport Jet losing power

I soaked the bolt with penetrating oil for a couple of days then tried the harmonic balancer puller like yours and left it under pressure for a couple of days. All I accomplished was to break the impact wrench I was using on the puller and to strip the threads in the bolt holes. On the manifold I have tried penetrating oil too along with using a utility knife blade to try to separate the parts by cutting into the gasket as well as lots of prying but no luck. I hate to break the manifold since a new one is $1900!

Any other suggestions?

 

[calledinsick]

Re: 120 Sport Jet losing power

Impact wrench should only be used on the shaft nut, not on the puller! Then install the puller. Should be minute turns of the forcing bolt followed by strikes on the forcing bolt head with a hammer (it took some pretty good strikes with little turns inbetween). I'd look at re-tapping the threads if needed. Don't strike or pry the flywheel.

For the exhaust manifold, make sure you have all 10 bolts out (I know a couple broke off).

 

[bustedstuff]

Re: 120 Sport Jet losing power

This thing is really a mess. I finally got the flywheel off with a huge pulley puller powered by the impact wrench with lots of hammering. The flywheel had spun on the shaft after the engine locked up and sheared through the square key. Still no progress on the manifold but I am using long bolts threaded into the block to support a plate that can be used to apply pressure on the manifold flanges to try to separate the parts. My manifold has 25 bolts.

 

[venxxxxx]

Re: 120 Sport Jet losing power

When I took my 120hp powerhead's flywheel off, I was hitting it with a metal hammer and shattered the magnets. After a few very hard hits, it came loose. But if I were to do it again, i'd spray some of the bolt-off penetrating oil and let it sit for a few hours and tap just on the crankshaft.
The rod that threw damaged the sleeve on the crankshaft as well, so it's gone. Not sure how good your shaft is, but thats a hard piece to locate.

Btw, where/how much did you find your engine casing ?

 

[bustedstuff]

Re: 120 Sport Jet losing power

I guess since the flywheel had sheared off the key and continued to spin it had extra metal jammed between the shaft and flywheel. I pounded in the thing from several angles while applying pressure with the puller. I had to apply so much pressure that the steel flywheel is bent slightly at the edges and it still only came off when I hammered the center bolt of the puller with a sledge. The only damage was a chip out of one of the magnets but they are all still attached and seem to have retained their magnetic properties. Never did get the exhaust manifold off. I am having the block repaired.

 

[Anders67]

Re: 120 Sport Jet losing power

if you bent the flywheel, replace it.

Otherwise it maybe vill be unballanced , and kill your new crank or bearings.