Motor won't run at high rpms.

[JeffGoldberg]

I have a 1963 75 Hp Vfour Starlite Electric shift.The motor will idle but when I try to bring up the rpms it seems to starve for fuel and stalls most times. Sometimes I can bring it back to an idle and it will continue to run. But if I try to keep the rpms up it slowly goes down in rpm untill it stalls.I can pump the tank ball up and it will start and idle.I tried the same gas ball and hose on my 6 hp evinrude and it runs fine and the ball stays hard so I dont think its the check valve in the ball.So I rebuilt the fuel pump but I had done that only a few years ago and all the O-rings and diaphram looked good.I still have the same problem after the rebuild. I tested the fuel system as my manual says by disconecting the line going to the carb and pumping the ball on the gas tank and fuel flowed freely out of the line. Next i turned over motor and monitored the fuel line to the carb and I saw no fuel comming out thats when I rebuilt the fuel pump.Now when I turn over the motor I get a steady SMALL flow of fuel out of the line that goes to the carb.So i says yippe I got it. I start the motor and I have the exact same problem at high rpm.Should the tank ball stay hard once it is pumped up and the engine is running?I also understand roughly whats driving the fuel pump, "crank case pressure" but I have no way of telling if its working correctly. Someone also mentioned putting a small electric fuel pump in to assist or take over for the original pump. Has anyone done this and had it work?I would like to fix it right rather than monkey rig an add on pump. I look forward to your input. Thanks in advance.

 

[jtexas]

Re: Motor won't run at high rpms.

Engine running, the primer bulb will be full of fuel but not necessarily "firm". when you squeeze it, it should open right back up, otherwise there's an obstruction upstream. It should be firm when you shut the engine off and stay firm all day.

Try this: prime the fuel line and tilt the engine full up far as it will go. if you see fuel draining out the carb throats, then your carb float valves aren't seating properly. Could be worn out, or could just be misadjusted. Either way, they're flooding the engine.

Carb rebuild will cure that.

 

[JeffGoldberg]

Re: Motor won't run at high rpms.

Tried that no fuel comes out the carbs. The fuel ball is hard. Rebuilt these carbs three years ago. So you think its flooding not starving for fuel? I guess I will need to check the plugs right after a stall from high rpm and see if there wet? Didnt think of that as I thought it starving.

 

[jtexas]

Re: Motor won't run at high rpms.

I thought it might be -- it was pretty easy to rule out though, eh? Difficult to gauge whether a persons idea of a "small flow" is adequate or not. But after your pump rebuild established fuel flow I thought it worth a try.

I'm not clear on whether the primer bulb is still hard after it stalls out -- if so, then the carb float valves must be closed. If the bowls are empty and the valves are closed then obviously you have sticky float valves.

Have you replaced the fuel fittings on the tank and engine? Could be sucking air. If that's not it, then you must be right about inadequate pressure from the fuel pump. Just can't keep up with demand at higher RPM. Sorry if I sent ya on a wild goose chase.

I'm not convinced the right people are reading this thread -- I'd start another, with a specific title that mentions the year & HP, and low fuel pressure -- there's guys around here who know more than me about this vintage of motor.