40HP Yamaha loses rpm - fuel pressure?

[Tobias]

I have a 14ft boat with an '86 Yamaha 40 (3cyl). When I bought the boat it idled fine, but when I took it out on the water it lost power after 10 min of running. I took it in, the carbs ended up being clogged with salt water. I added a 25gph racor water separator/fuel filter about 2 ft before the engine. When running, the plastic bulb on the racor is only half full with fuel, somtimes less and sometimes more. When cold, the engine will not respond to throttle, but will eventually rev up if you keep the throttle open. It ran well for about 2 Hrs of use on my first day out. Then, today it ran fine for 2 1/2hrs, then would not respond to throttle again, I was at 2K rpms at full throttle. I putted to a bay, and anchored near shore and decided to bypass the fuel filter. It then ran fine for the next 1/2 hr, but I decided to return to shore to be safe. QUESTION: I have seen posts that the filter should be between the bulb and engine, and vice versa. Obviously, mine does not work with the filter between the bulb and engine. I plan to relocate it between the tank and bulb, but I just want to know if that is right?, or if the Racor (025-RAC-02) is just not going to work with this small an engine since the filter is so fine (10micron)? OR, is my fuel pump going bad? (the previous owner just had a fram inline fuel filter between the engine and bulb.)

 

[JB]

Re: 40HP Yamaha loses rpm - fuel pressure?

Mahalo, Tobias.<br /><br />Welcome to the Board.<br /><br />I will move this to Yamaha Troubles, where it should get more attention.

 

[Elmer Fudge]

Re: 40HP Yamaha loses rpm - fuel pressure?

Those filters tends to work better between the tank and the bulb.since you mentioned water in the carbs,if it got there via the fuel pump,installing a new diaphram kit should help,if not it's possible that you may have a sticking float or carb needle.

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

Thanks Elmer, I just ordered a new fuel pump assembly (only $25), and I will relocate the filter/water separator between the bulb and tank to see if that helps.

 

[Jammu]

Re: 40HP Yamaha loses rpm - fuel pressure?

Do You have the o-ring in place on the engines original filter

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

Ya-Man - Yes, the O-ring is in place, but I did find a small crack in the top of the original filter assembly near the mounting bolt that will leak fuel if I prime the fuel system. I have ordered a new filter assembly and fuel pump, but they have not arrived yet. In the meantime, I relocated the racor filter in between the bulb and tank. Thanks for your advice!

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

Ya-Man - Yes, the O-ring is in place, but I did find a small crack in the top of the original filter assembly near the mounting bolt that will leak fuel if I prime the fuel system. I have ordered a new filter assembly and fuel pump, but they have not arrived yet. In the meantime, I relocated the racor filter in between the bulb and tank. Thanks for your advice!

 

[rodbolt]

Re: 40HP Yamaha loses rpm - fuel pressure?

hello<br /> I bet you found the problem. if it will leak fuel it will suck air. pumps, bass and me, laziest things about.<br /> that pump is a lot happier pumping air then fuel. the sight bowls on the fuel filters will always have air in them when running. in fact they usually show to be only half full when WOT. the primer bulb,as it is on the suction side will NOT stay hard and full of Fuel. never ever ever. wont matter which side of the racor you put it on. if you suspect a filter or bulb a simple test with a vacum gauge can pin point what and where a restriction is.yammi says that engine can have no more than 4"hg of vacum when checked between the pump and the engine filter.<br /> good luck and keep posting

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

Well, I changed the fuel pump, fuel filter assembly and tested it again. It was still weak, couldn't get past 2K rpms. Took off the carbs to find them full of salt. It must have got in during the brief time that I ran it with out the racor. I took it out again, and it seemed a lot stronger, but couldn't get past 3K rpms, and still ran rough (stutters). I took off the carb during the trip to check for salt, but there was none. On the way home it got weaker and weaker, and couldn't get past 2K rpms again, and stuttered more and more. I have de-carbed with sea-foam (straight through the fuel line), and the plugs are only 2-3 months old. Could the reed valves be clogged? I haven't checked compression or timing since I don't have the tools for that, but the motor did run fine the first time I cleaned the carbs (4K rpm and lots of power). could the coils be causing this?

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

By the way, the engine is a "40ELJ" 1986 40 Hp

 

[Larry Sapp]

Re: 40HP Yamaha loses rpm - fuel pressure?

Tobias, try new spark plugs also...it helped with a similar problem on an 86/70 hp..<br /> L.E.S.

 

[akriverrat]

Re: 40HP Yamaha loses rpm - fuel pressure?

assuming both your posts are about the same engine i would take twenty minutes and do a compression test. fuel/air, compression, spark. spark has been eliminated. fuel has recieved a lot of attention but the compression has been ignored entirely. eliminate it as a possibility.

 

[Tobias]

Re: 40HP Yamaha loses rpm - fuel pressure?

I posted in a separate thread that one cylinder was not working since I believe I had two issues, 1. The fuel pump and salt water in fuel (this has been fixed), 2. The middle cylinder not firing - I believe this to be due to a bad pulsar coil since I swapped the ignition coils and the problem stayed at the middle cylinder, and the Ohms reading for the pulsar coil that corresponds to the middle cylinder was lower than the other two. I've ordered a new stator assembly. I still agree that I need to check the compression, but I will do this in addition to the stator.