high rpm fuel problem

[wylie catter]

Hello everyone. Today I took out my new motor for the first time. It is a 1975 15hp johnson. I recently cleaned the carb, replaced all the fuel lines and installed a new water pump and spark plugs. It idles perfect in the barrel or in the lake but as soon as I opened it up it hesitated then got up to about 3/4 of wot and ran there a few seconds before it died. It would crank right back up on the second pull. I found out that it would run better with the choke on running wide open. But it won't idle good with the choke on. So it would idle perfect with the choke off and when I'd give it gas I would pull the choke out and it would stay running. But it defenetly wasn't running at the full high rpm that it should.

A side note is when I first got this motor running at home I had to adjust the idle adjuster on the outside of it all the way up to get it to sound like it was idling at the correct rpm's. In hind sight that should have told me something wasn't right.

So what does that sound like to you guys?

Thank yall in advance for the help. This place is awesome.

 

[wilde1j]

Re: high rpm fuel problem

Fuel starvation appears to be what's happening. Check fuel pump output by removing output line and cranking motor. Should get strong fuel pulses. Make sure motor can't start when doing this by disconnecting spark plug wires. If pump stream is NG, replace fuel pump. Other possible causes are crap in carb, air leaks into suction side of pump, tank pickup screen plugged, tank not vented properly, etc.

 

[Will Bark]

Re: high rpm fuel problem

If, after checking everything that Wildej1 sugggests; you might try setting your float drop to the full 1&1/2". That is what I had to do to cure the exact same problem on my 1977 Rude. Good luck.

 

[wylie catter]

Re: high rpm fuel problem

You mentioned tank not vented properly. Well the tank and lines are all new, (but) I know I overfilled it. It happened before I knew it. So at the boat ramp when I opened the vent, gas came out. Man I'm gonna feel stupid if that's the reason.

Does that idle adjuster on the side of the motor being in the full screwed in position seem like a cause for concern?

If it is the fuel pump then what is recommended? Rebuilding it or replacing it. I've rebuilt one on a mercury before and it was a major pain in the but. And later on a boat mechanic told me I had put the wrong parts in it anyway.

Thanks for the responces. Yall are a big help.

Terry,

 

[wylie catter]

Re: high rpm fuel problem

If, after checking everything that Wildej1 sugggests; you might try setting your float drop to the full 1&1/2". That is what I had to do to cure the exact same problem on my 1977 Rude. Good luck.

How do you determine your float drop?

Thanks

 

[wylie catter]

Re: high rpm fuel problem

Happy Thanksgiving everybody!

I was wondering what you meant by float drop? Do I set the float with the tip of it 1.5" from the bottom of the carb with the bowl off and the needle in the open position?

Or maybe I take the bowl off and turn the carb upside down so that the needle is seated, and then set the end of the float 1.5" up from the carb?

Any advice or help is certainly appreciated. I'm hoping to fool with it tomorrow.

Thanks Terry

 

[Will Bark]

Re: high rpm fuel problem

With the carb bowl removed, hold it in the upright position and let the float drop down making sure the needle drops with it; measure the front of the top of the float to the bottom edge of the carb; gently bend the metal tab on hinge so that you get a drop of 1&1/2". You do have a clip on the needle to the float that pulls the needle down as the float drops don't you? Hope this solves your problem. Good luck.

 

[amen0037]

Re: high rpm fuel problem

Same thing happened to me. Check your gas line that connects into the motor. The piece that connects look into it and if its a plastic valve get rid of that line and use something with a metal ball valve for the gas.

 

[wylie catter]

Re: high rpm fuel problem

With the carb bowl removed, hold it in the upright position and let the float drop down making sure the needle drops with it; measure the front of the top of the float to the bottom edge of the carb; gently bend the metal tab on hinge so that you get a drop of 1&1/2". You do have a clip on the needle to the float that pulls the needle down as the float drops don't you? Hope this solves your problem. Good luck.

Alright, got it. I'll set that. And yes I'm pretty sure has a clip on the needle. I'll double check though.