115 Johnson -- Problems at higher rpms??

deedledog

Cadet
Joined
Feb 16, 2002
Messages
12
I recently purchased an 2000 Wellcraft with Johnson 115 with low hours. The first time I put it in the water it would run fine up to the high 3000s. At rpms from about 3900 up it would continuously bog and surge. Sounded like it was not getting fuel, like when a tank starts going empty. When I got it home, I removed the fuel filter and cleaned it, and there was some trash in it so I thought that was probably it. Yesterday I took it back out and it did the same thing.<br /><br />Today I checked all lines for kinks, then disconnected the fuel line and blew it out with air from the tank back to the motor, then from the fuel filter back to the boat. Blew out the bulb at low pressure. Removed and inspected shutoff valve on tank and blew out the drop tube into the tank. I placed the ends of the hoses where I could see anything that came out and they all appeared clear and I didn't find any trash discharged. I'm afraid that I didn't accomplish anything.<br /><br />My question is, am I barking up the wrong tree? Could this be a timing problem? A carb problem? Motor idles great, responds to throttle great, just will not run smooth at higher rpms.
 

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: 115 Johnson -- Problems at higher rpms??

Welcome to the forum, Deedledog.<br />So far, you haven't wasted your time,as it is a possable fuel-starvation problem. 90% of the time, it is a real process of ellimination. Form this point, try pumping the primer bulb when it acts up, to see if it is soft (#1), and if the performance improves (#2).If it does, it's time to move on to the fuel pump. These work off engine compression,so check the compression first. Then (if comp is within spec), order a rebuild kit for the fuel pump. If it still acts-up, time to pull the carb.<br /><br />There is the possabilty that a plug is fouling on the extra fuel when you gun it.<br /><br />There is a possability that a timing is out.<br />This would be a rare situation,as nothing has been moved. But if you have struck something, the possability exists that the flywheel may have twisted on the crankshaft at the key.
 

lakerunner

Seaman
Joined
Jan 14, 2002
Messages
57
Re: 115 Johnson -- Problems at higher rpms??

Did you drain the fuel tank are is this the fuel that was in the boat? Also drain the carb-bowls and see if any trash made it passed the filter.
 

jegervais

Chief Petty Officer
Joined
Jan 18, 2002
Messages
646
Re: 115 Johnson -- Problems at higher rpms??

You're on the right track - This is this the 60 degree V4 (year 2000 also) right?? This motor uses a a fuel vapor-seperator to supply fuel to 2 fuel rails (1 port/1 starboard). The rails feed fuel into a passage of the throttle bodies and then to the carb bowls. Its also possible some trash is plugging the passage in the throttle bodies as there are screens in them. The other (and easier to deal with) possibility is that the main jets on the carbs are a little gummed up, or there is trash in the bowls - drain them as lakerunner suggested. <br /><br />If this is a year 2000 motor, your issue is not likely timing or a sheared flywheel key (as the flywheel is bolted with 5-bolts to the top of the crankshaft). Timing is controlled via an optical sensor which uses infra-red light beams and an "encoder wheel" which "tells" the logic circuitry in the power pack when to fire the spark plugs.<br /><br />Lastly, don't overlook the possibility of the boats fuel system - before you decide to dig into something major, get a portable 6-gallon tank, hook your engine up to that and try it. I've seen plenty of problems from anti-syphon valves, plugged pick-ups and collapsed hoses in the boat.<br /><br />-John<br /><br />BTW - The next time you're out in the boat, when it starts surging, push the key in and hold briefly for a few seconds. This activates the primer solenoid and will dump fuel in behind the carbs. If she picks up and goes, you know you've got a fuel delivery issue. It won't be the fuel pump either, because the primer is fed from the pump too.
 

deedledog

Cadet
Joined
Feb 16, 2002
Messages
12
Re: 115 Johnson -- Problems at higher rpms??

Thanks for the help guys.<br /><br />This is the fuel that was in the boat, but it only had about 1/4 tank so I filled it completely up when I first tried it, and topped off again before the second time. I added a little oil to the gas until I could get it out and make sure the oil injection was working OK, but not enough to hurt anything.<br /><br />I forgot to mention that I had pulled the plugs after the first time out and there was no evidence of fouling. It doesn't run like a fouled plug or missing cylinder anyway. Like I said before, it sounds like its getting starved.<br /><br />Thanks again!<br /><br />Deedledog
 

deedledog

Cadet
Joined
Feb 16, 2002
Messages
12
Re: 115 Johnson -- Problems at higher rpms??

Oh yeah,<br /><br />While I was running about 4000 rpm, I pumped the bulb, which seemed soft at first but was hard by the third pump. I kept pumping to keep it tight but didn't notice a change. In retrospect, I might not have taken into account the lag in time that it would have taken that to actually effect the engine.<br /><br />Chris (Deedledog)
 

tn

Cadet
Joined
Aug 21, 2003
Messages
21
Re: 115 Johnson -- Problems at higher rpms??

Deedledog, <br /><br />This sounds a lot like the same trouble I was having on my 96 115HP. Started great and would idle OK but when I wanted it to go at WOT it would surge and cut out but still go. I ran a can of OMC engine tuner through it and it made all the difference in the world. It's probably the cheapest thing you can do before you start on bigger projects like carb rebuild etc. It's only about $8.00 a can and even if it's not your main problem it sure won't hurt to try it. You want the OMC tuner that has the hose on it. You just screw it onto your primer valve. It's the unit up on top of your carbs,looks like an air hose valve on a tire.
 
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