Yamaha f115 4 stroke running bad

[MILLSMAN]

2003 Yamaha F115 barely running. It starts fine and will run OK if under 1500 RPM but will not go when you push the throttle. It stammers and misses. Went to a portable gas tank with new gas and that did not help. Gas is not the issue. It will also start to buck and run rough at 1000 rpm. If I shut it off and then restart it will run OK at the low RPM. Checked the plugs and they are OK. Electrical? Fuel Pump? Injectors? It always starts right up???? Thanks ...........for your help

 

[racerone]

Look for strong spark on all leads.------Checked all filters ?

 

[Snoopy11]

Agree check all plug leads. Also, check any air intakes and make sure nothing is partially blocking air flow. I had similar issue once and after exhaustive checks a friend put his hand in the air intake and pulled out a clear piece of thin plastic that was blocking air flow..

 

[WIMUSKY]

X2 on the filters

 

[MILLSMAN]

Well, worked on the motor much more and here is where I stand: Motor runs fine at idle and up to 4,200 RPM, but can't get it past the 4,200 mark. It runs fine up to the 4,200 RPM but sometimes will spit and shudder at slow speed (1,500 RPM). If I shut it off and restart it will run fine at the lower RPM. I had some water issues in the gas so I got an auxiliary electric fuel pump and pumped the gas for 20 hours through the Siera filter and back to the tank. Then installed a new filter. Removed the injectors and replaced them with new ones. Checked the intake manifold to make sure there was no obstruction. Runs great at low RPM'S but can't get it over 4,200 RPM. If I push the throttle more it will run rough and loose RPM's. Looked at the first fuel pump and it looks fine. What should I do/ look at next??????

 

[racerone]

You have not reported on the spark !--Does spark jump a gap of 3/8" or more , yes or no ?--Check compression too.----Sounds like it might be running on 3 cylinders.

 

[WIMUSKY]

Coil(s)

I had an I/O that ran fine idlinging around until I tried to get on plane. Then it spit, sputtered etc...

 

[fafuto92]

Having the same issue here. Twins F115 starboard one is going thorugh this same issue. going to check the coils too

 

[MILLSMAN]

Well, finally got the F115 running fine. Turned out it was the VST filter that was plugged. Had to take off the entire intake manifold to get to it, but it was worth the effort. Not really that hard, but time consuming. There is a Utube video on how to do it, but it does not include all the grunts. There was a bunch of crap in the VST resivor and filter. Thus, when i would hit the throttle it would plug the filter because of the additional suction caused by the injector pump. Everything else on the motor was fine. Compression, spark, etc.
Based on the fact that it takes 6 - 8 hours to replace the VST filter, I decided to remove it and throw it away. It takes only 20 minutes to replace the fuel injectors, 6 hours VS 20 minutes. hummmmmmmmmmmmmm. No more VST filter!!
Motor runs great now. Thanks for all your suggestions

 

[Capt Ken]

First off, if it took you six hours to replace the VST filter, don’t quit your day job. 1.5 hours at best. Now for the bad news. Without that filter, the likelihood of a piece of trash going through the HP pump and leaning out an injector, is pretty high. Leaned injector equals a melted piston. The crud in the VST tank was due to the water corroding the coating inside the tank. You can clean it out but it will soon corrode again.

 

[vjsimone]

Which brings me to ask the question, how do you manage the water in the tank? Where is it coming from? Are you talking about Ethanol or Non-Ethanol fuel ? thanks.