94 Johnson 70bhp dies at full throttle

[young think]

appriciate some advice here..1. engine idles nicely 2. but when in the water, upon throttling it will die at high rpms.3. prime the fuel line and restart4. starts off and dies after a while againsuspect fuel not going to engine, lost of fuel flow..prior to this I changed the fuel connector from tank to outboard engine..iginition, compression all alright.. anything I missed out?

[fireman57]

Could have a float stuck in a carb. When you say engine idles nicely, is that on muffs? I ask because then you say "when in the water". You will need to set the idle up on muffs because once on the water the back pressure will make it idle lower. If you are losing your prime you could have an air leak somewhere. When you say it dies after a while again how long is that? BTW, welcome to iboats!

[andy6374]

Sounds like a fuel problemo.Start with the tank and inch your way up to the carbs, checking the fuel line, primer bulb, and fuel pump along the way. Make sure the tank vent is open. -andy

[young think]

Thanks for the welcome folks.The engine idles nicely on the muff and in the water, I suspected a leak to the fuel system.On the move, I can't get max power, it will die off exactly after a few minutes of travellingI've just overhauled the fuel pumping system , and when I cover the 3 carbs inlet, fuel flows out fine. I've yet to try it in the sea.When I depress the new fuel bulb it feels firm but bouces back quite slow. When it dies off , I notice the bulb doen't collaspe..

[young think]

fireman57 , noticed you are from Indiana.. which part.. I lived in Kokomo few years ago..

[TimMattson]

You can point a timing light into the carbs while running to see a "picture" of what your high speed jets are putting out ....you should see equal cones of fuel spraying like crazy at higher rpms.Hook the light to any plug wire and also a battery.You do have to run it with the cover and carb cover off.Also verify WOT on the throttle while in there. Tim M

[duke3]

Im 99% sure, the motor is running out off fuel.Control/clean or change fuel-filter.Also control, that there is no wacoum in your fuel-tank, just after the motor dies.

[TimMattson]

Fuel pumping system changed or did the fuel pump get changed? It can be rebuilt or swapped for a new assy with the thick gasket behind it that supplies the pressure that drives it.Purge all lines as a new one goes on(if not already) and maybe look for a split line that only acts up on higher pressure.

[SLEEPY1230]

What kind of boat is it on? I had a bowrider with a built in tank with a anti-siphon valve that went bad and would not give enough fuel at full speed. If tank has anti-siphon valve be sure the primer bubble is not anti-siphon also and make sure the buble is pointed in the right direction.