Logo
FULL SITE MENU

Yamaha 115 loses RPM on top end

8

8kgold69

New member
I have a 2004 Yamaha 115 4 strokeF115TLRC. It idles great. Press the button in on the shifter and rev the throttle, the RPMs jumps up to 6K. Changed the water/fuel separator filter, fuel filter,all the fuel lines, new spark plugs, etc... When I have the boat in the waterand take off, it planes out. When I throttle up to 38-3900 RPMs it is okay.When I give it more throttle it acts like it starves for fuel and the RPMsstart to drop and I start losing speed. Anyone experience this with theiroutboard? Checked the gas in the fuel filter looked clean. The fuel in the water separator was clear. Appreciate any help.
 
I had the sameproblem with my '02 F115. You have a fuel restriction somewhere... It run'sfine until you try to feed serious fuel under load and then the problems start.The fact that it will rev to 6K in neutral means nothing as there's no load onthe engine and you can reach 6,000 RPM with minimal true fuel flow as you justgive it a shot of throttle to get it there. Check your fuel flow starting from the gastank back. I'd suggest you pull the fuel line that exits from the fuel filterthat is under the cowling of the engine at the left rear of the engine. Stick atowel in there and squeeze your primer bulb a few times... with each squeezeyou should see a significant, unrestricted shot of fuel squirt easily out ofthat outlet each time you squeeze the primer bulb. If not, replace the filter in that littlehousing and see if it then squirts with each squeeze. If it is stillrestricted, you could have a clogged fuel pick up line in your fuel tank. Somepick-up lines in fuel tanks have a filter on the end of them where they sit onthe bottom of the fuel tanks. If you have a filter on the end of your pick-upline in your gas tank, pull it out or cut it off & toss it. They causeproblems and never should have been put there with all the other filters inline. That should eliminate any potentialproblem with flow from the gas tank to the outlet on that fuel filter under theengine cowling. You replaced the fuel/water so that shouldn't be the problem.Hopefully, that will fix it. If not, your problem is probably where mine wasand it will be in one of two places. One is easy (clogged fuel injectors), theother is not (the filter that sits on the bottom of the high pressure fuel pumpin the VTS tank that is BEHIND the intake and manifold pretty deep inside theengine. Pull the fuel injectors and send them to Fuel Injector Man (www.fuelinjectorman.com) (thecheapest place I found that cleans injectors). He replaces all gaskets,o-rings, the internal filters in the injectors, cleans the injectors withultrasonic and sends them back to you sealed with all the old parts so you knowthey were changed as well as before and after flow and spray readings from hisequipment. Put the injectors back in (put a little oil on the o-rings on theinjectors first) and see if that fixes it. If that doesn't fix it... you'llneed a good set of tools and about 5 hours to get in and out (the first time)to get to that filter on the bottom of the High Pressure Fuel Pump that sitsinside the VST (vapor separator tank). The Yamaha engineer who put that filterthere was an idiot. The filter itself is about $30 but getting to it is a PITA.It is a tiny little assembly and the filter is a little micro screen about3/8" across. You'll pay serious money to have it changed at a Yamahadealer so grab your tools or someone who has them, a shade tree and somebeverages. The job isn't horrible but there is one bolt (I believe it is thelowest on manifold) that will take a great deal of time playing around withvarious ratchet extensions and such until you find the right combo that works. That one bolt will take you a great deal oftime as it did me. Again, wonderfuldesign. If that's where you end up, Google "Yamaha 115 VST filterchange" and such as I did until you find instructions and photos posted byothers who've had the pleasure of replacing that friggin’ thing. Because it isjust a screen in a little assembly, you could probably blow it out and be finebut for $30 for a replacement... If I'm going to spend 5 hours getting to itand back out I'll spend the $30 to have a new one. There is also a crazy shapedgasket on top of the VST housing that costs about $45. It is recommended to be replaced when you goin there. I didn't replace mine and itworked fine but I did pull it, cleaned everything up well with carb cleaner(not the gasket), and put all back together without any problems since. Thatlittle filter on the bottom of the high pressure fuel pump can often be cloggedby gummy messes thanks to the crap ethanol fuel that has been forced on us or byfibers from that filter under the housing on the left rear of the enginefalling off over time if it isn't changed at regular intervals. Hopefully itisn't that filter in the VST tank but if it is... take comfort in knowing thatothers have gone there before and saved themselves $700+ in labor to replace a$30 filter.
Lastly, If youare using gas blended with ethanol as I do as I refuse to pay for 100% gas thatis available at many marinas... use the green marine Sta-Bil ALL THE TIME. Not just for storage but ALL THE TIME. The detergents in it help to keep ethanolrelated problems to a minimum.
 
Thanks for the response. I apologize for not responding sooner. I pulled the intake manifold unit off, not that tough of a job, disassemble the VST tank, checked the filter on the bottom of the pump motor, some debree, but nothing that would restrick the fuel flow. Pulled spark plugs to see if any were gas fouled. All were dry which indicates none of the injectors are leaking. Checked the inline filter that goes from the fuel pump assy to the VST tank, clear. Made sure all fuel lines are clear. Checked the pickup in the fuel tank, not clogged. I've changed all the other filters. No difference in motor performance. Now looking at some of the parts diagrams on line I notice a couple of other parts that I think maybe causing a problem. After pulling up some parts websites I notice there is a Pressure regulator. It is under the FUEL INJECTION NOZZLE category item # 9. Then looking under the FUEL 1 category #14, fuel pump assy, there are two diaphrams. And then under the INTAKE 2 category, #13 is a filter assy that mounts under the fuel control valve assy. Could someone tell me if they have experience any problems with these items? I would appreciate any help.
Thanks
 
Injectors may not be leaking but they could be clogged or restricted.

Ironic... firstday taking the boat out this memorial weekend for the season and I again havethe same problem as you (which I had 2 years ago). Ran fine for about 1/2 hourand then became starved for fuel. Can only reach 2700 RPM and push the throttlefurther she gets a bit deep throated. Vibration and fuel flow rattles all kinds of gunk lose beginning of the seasonso I know it’s another restriction in filters somewhere caused by the 1[SUP]st[/SUP]running. So, I am starting the sameprocess again as I did 2 years ago. I've pulled the fuel injectors and will besending them out for cleaning as I recommended you try in my prior post. Atleast your VST filter is cleaned and you know that isn't the problem. Thepressure regulator you mention... I've looked at it and researched as well inmy past experience. I read that if it looks to be in good shape with nocorrosion on the top/outside etc. it should be good. I believe some models hadproblems with water draining under the top of the cowling that would drop onand rust the top of it but mine looked good so I wasn't about to pay $220 for afuel pressure regulator on a ghost hunt. Pull the fuel injectors and send them outfor cleaning to Fuel Injector Man (where mine are headed this week). I'm alsoordering a new VST filter because I won't put cleaned injectors in if there's aprob with my VST filter so I'll go in and out and replace that before I put myinjectors back in. If you want to try it, you can try to clean/clear theinjectors yourself. There are lots of youtube videos on how to clean themyourself that require screwing around a great deal... I just bought a few cansof carb cleaner, gently held the injector in a vice and attached 12V +/- to thefeeds. You'll hear the injector click open and then you BACK BLAST through thespray nozzles NOT FROM BACK. You want to drive any junk out the back and out ofthe filters, not ram it from the back up through the filters and into into thespray nozzles. I believe a short 3/8" ID piece of hose about 3" longwill fit perfectly over the nozzle housing. Then stick the thin jet spray tubefrom the carb cleaner can into the 3/8" hose and crimp the hose off tightwith a pliers to hold some pressure while you back spray. Blast away. Gothrough all 4 injectors and then put them back in and see if that helps theproblem. It may fix it but if it at least gives you a significant improvement,you prob found the problem and can then send all out and have them fullycleaned with filters replaced. Let me know how it goes. Fun Fun. Rule of life... Never have more toys than you care to take care of!
 
OH... before you put the Injectors back into the fuel rail... pull the rail and balst it with carb cleaner as well. With the lower fuel line off that feeds the rail off, turn the key several times to the on position and back off to flush that well or squeeze the fuel bulb a few times to manually flush that line just in case there is gunk in there.
 
I have the same problem on my 2008 F115. Changed the fuel filter. Changed the VST filter. It's not that hard I put a drop sheet underneath to catch anything that might fall out. Glad I did because there are spacers on the VST canister mount that fell out. I stuffed rags around the base of the motor so nothing could fall in there. Took lots of pictures. I have read that you can just remove the screen from the VST filter. I decided to put a new $30 VST filter in and changed the fuel pump (Quantum brand) while I was in there.

I still have the problem. It happens when I have disconnected the gas line and ran off a brand new portable tank with premium no-ethanol fuel and brand new Yamaha brand gas line. It is like it has two speeds at full throttle. It withholds 10 percent of top end RPM and once in a while gives all she's got. I have ordered a diagnostic software kit but will need to wait till May now as it has gone into storage for the season. Sea Foam did seem to help but only temporary. i guess fuel injectors are next. What a PITA!
 
8kgold69 said:
Thanks for the response. I apologize for not responding sooner. I pulled the intake manifold unit off, not that tough of a job, disassemble the VST tank, checked the filter on the bottom of the pump motor, some debree, but nothing that would restrick the fuel flow. Pulled spark plugs to see if any were gas fouled. All were dry which indicates none of the injectors are leaking. Checked the inline filter that goes from the fuel pump assy to the VST tank, clear. Made sure all fuel lines are clear. Checked the pickup in the fuel tank, not clogged. I've changed all the other filters. No difference in motor performance. Now looking at some of the parts diagrams on line I notice a couple of other parts that I think maybe causing a problem. After pulling up some parts websites I notice there is a Pressure regulator. It is under the FUEL INJECTION NOZZLE category item # 9. Then looking under the FUEL 1 category #14, fuel pump assy, there are two diaphrams. And then under the INTAKE 2 category, #13 is a filter assy that mounts under the fuel control valve assy. Could someone tell me if they have experience any problems with these items? I would appreciate any help.
Thanks
Click to expand...

Have you tried priming the fuel bulb when you are at WOT to see if it gets the rpm? Low pressure fuel pumps are often the cause of the symptoms you are having.
 
Back
Top