04 Yamaha 115 Four stroke fuel problems.

I have a 04 Yamaha 115 four stroke, starts and runs great. After traveling 4 or 5 miles then stop for about 20 minutes, motor starts back up and runs for about 100 yards and stops like running out of gas. Pump primer bulb, starts and runs fine untill I stop for a while, then same thing. I replaced check valve and pick-up tube at tank, replaced fuel line and primer bulb and bypassed fuel/water seperator. took out for test run, first day no problem but next day same problem.

Need help.
Jerry b

You need to get a fuel pressure gauge and attach it to the top of the fuel rail to check the fuel pressure. Behind the intake manifold is the VST(Vapor Separator Tank) . There is a filter inside that needs to be serviced. There is also an inline fuel filter between the fuel pump and the vst.

On top of the fuel rail is the fuel pressure regulator. How rusted is it?

I checked fuel pressure at idle, it was 35 lb. there is no rust on pressure regulator. next step is to pull intake and service filters.

Thanks

My experience has been that when my 115s had plugged VST filters they wouldn't ever run great and then intermittently run bad. They would idle great and then get up to a certain rpms and slowly back down. I think the VST has junk in it that gets sucked up into the filter and after stopping sometimes it would run a bit better but eventually bog down. 35 seems a bit low for pressure at idle but it's what happens to the pressure under load/higher rpms that better defines the VST filter plugging. When I had a bad pressure regulator it wasn't an intermittent problem either. Changing out all your filters is a good idea regardless of your problems, but checking fuel pressures under load would be worthwhile.

If you can pump up the primer bulb and things work fine it may be the mechanical pump on the back of the engine that's bad........as if you can keep things running great by continually pumping fuel to the VST via the bulb it sounds like a fuel supply problem and not plugged filters. These motors should top out at 5000+ rpms and if yours will do that and stay there by pumping the bulb I'd look upstream from the filters. Although changing them isn't a bad idea either. As for the 35 psi......it may be your gauge is off, but if it holds at 35 under load I'd say your VST filter isn't the main culprit.

Good luck

I checked the filter between pump and vst, it was clear. I connected a clear hose from primer blub and filter at pump. Ran for about 4 miles, ran great, turnning about 5800 rpm, stopped and watched clear line. About fifteen minutes air bulbles started to apear comming from pump side of line. The longer I let it set more air came in. Started motor and ran for about 1/4 mile the air cleard up. Stopped again and same thing happend. Going to get a 6 gallon tank and connect and see what happens. The main problem is loosing prime with motor turned off, Onece its primed up its runs great