sport jet 120 fuel starving at wot

[btanner]

Just purchased this 97 Ranger Rebel 158 with Mercury Sport Jet 120. Great condition and well card for. Last time ran, late summer 2010. Previous owner used Sta-bil ethanol additive and Mercury fuel conditioner before parking it. I put in new plugs, fresh fuel with Sea Foam and ounce of Sta-Bil ethanol treatment. After firing up, idled around a couple of minutes and then took off. Any throttle above 1/2 would cause fuel starving, drop back on rpms and then catch back up. Started doing better after 30 minutes of running. Parked over night and hit again today. Had to use fast idle at fast to keep it running for more than 3 seconds. After 20 seconds idled back and did okay. Took off and had a little fuel starving for the first 10 or 15 minutes, especially if I went to WOT, it would bog way down and I would have to pull throttle back to let it catch up. If I held it at WOT it would surge up in rpm, bog down, try to catch back up. Finally got it running fairly smooth at about 3/4 throttle. Anything above that and it would start bogging some, smooth out and bog again. Feels like fuel starvation. Not feeling any misfires or sputtering or rough running. Just acts like you pulled the throttle back and then back up again. My first thoughts are trash in the fuel filter screen or carb(s). Any help or previous experience much appreciated. Going to the lake next weekend and can fiddle with it..:-}
Also a little hard to start after running awhile and then off awhile. Thanks

 

[calledinsick]

Re: sport jet 120 fuel starving at wot

The 97 should be a Sport Jet 120XR, I've got a 95 SJ90. The XR's were a little more advanced with ignition...so you're better off there.

*Don't try to start this out of the water without a dealer type flush kit installed*

The fuel could be a couple of things or a combination of things. These are the most common.

Take the air intake (sound attenuator) off and look down the throats of the carbs. At nuetral, they should all be closed. Push the shifter to full throttle and look down the throats. They should all be flat. If any of them are not flat you should re-synchronize the carbs. Easy to do. (This has the effect of the butterfly opening too far and starting to restrict fuel/air flow).

Pull the fuel line off where it enters the carb bank and put the end of the line in a bowl/jar. Watch the fuel flow while cranking the engine. It should be a pretty steady flow. If it pulses, the fuel pump will need to be rebuilt (diaphragm). I think the kit is about $20.

Next step would be to pull the bowl off the bottom carb. Look for black/dark sandy crap in the bowl. This is a sign of the fuel lines being 'eaten' by the alcohol. If you have that you'll need to take the carbs off and clean/rebuild.

The 'hard to start after sitting for a while' is a common issue (at least it is for me. I believe it to be the 'auto-enrichner'...it cools off partially compared to the engine but not at the same rate. Then it either over or under enrichens for a semi-warm engine. I think this is a 'live with it' issue.

I'm to the point now that I recommend people replace their fuel lines with USCG A1 alcohol resistant type - but that's up to you. St. Charles Boat and Motor has this. A little pricey but it's easy and a one time fix.

Good luck!

 

[calledinsick]

Re: sport jet 120 fuel starving at wot

You can identify the Black Stator by the wires coming out of it on the starboard side of the engine. The Black Stator will have 2 yellow wires, 1 red, and 1 blue. The Red Stator will have 2 yellow, 1 white/green, 1 green/white.

If you need to crank/start the boat out of the water with a hose attachment, use very little pressure or you'll fill the cylinders with water. This should be ok for pressure holding the hose straight out in front of you:

 

[btanner]

Re: sport jet 120 fuel starving at wot

Just to pass along, replaced the fuel pump diaphragm and all is well. Ran like a new one. Thanks all.