Stalling at full throttle

[amishboy]

Running a 1973 Rinker 15' fiberglass with a 73 Mercury 65 hp outboard on probably the original portable gas tank. At full throttle, she would slow down and stall as if out of gas. Valve was open on tank cap and bulb was not flat. Started right back up. Did this several times. Tank was about 1/3 full. At about 1/4 full she shut down at low throttle as if it was out of gas and would not restart.
Switched over to brand new plastic tank and did not have stall problem at any speed. I think obviously this has to do with the old tank. Could a lose cap do this? Tank gunk? Any suggestions?

 

[usskydvr]

Re: Stalling at full throttle

Good job troubleshooting. You are probably right that it is the old tank. Not a loose cap (a tight cap with the vent screw closed would cause fuel starvation). Sounds like gunk. ( one outside possibility would depend on the configuration of the new vs old tanks, it could be that the fuel pump is having a harder time pulling the fuel from the old tank vs the new one, that might explain why you were only having problems with the old tank when it started getting lower. but gunk can also cause similar issues)