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fuel problem

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krackrjack

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I have a Evinrude 7.5 hp outboard that was built in 1956. model no. 7520. I cleaned and rebuilt the carb. It cranks and runs good after I pump the fuel ball. It will run for a few seconds, surge and quit. It will run as long as i keep priming the ball. It has a external pulse fuel pump. What makes a pulse pump work? I put a new one on it but it still won't pull the fuel to the engine. Also what is the correct oil to fuel mixture for that engine. Need help
 
Fuel pumps work / operate by a positive pressure pulse from the crankcase.------Where / how did you mount the new pump ?-----Are you using the air hose that went to the old pressure tank as a pulse hose ?
 
The pulse pump is mounted on the side next to where the air line comes from the crankcase. The air line goes into the top of the pump.
 
When that motor left the factory the airline going to the tank was NOT a pulse line.-----What modifications have you made ( remove check valves ? ) from that airline if any.
 
Thanks a lot. I'll give that a try. What is the correct oil/fuel ratio for that motor. Under the cover it says to use 8 oz of oil to each gallon of gas. It will not run with that much oil in the gas. I tried a 32/1 ratio and that was better but it still smokes like hell and don't run too smooth. Is 40/1 too lean? thanks
 
8 oz per gallon is correct If it won't run at that, something is wrong. Sure, it'll smoke. 1956 technology, remember.

There's more to it than removing the check valve. One of the passages has to be blocked. Or did you remove the valve but not block one of the passages? That might be why it won't run.
 
Thanks guys. Your help has been good. I followed the link I got and found out what was wrong. Ever who it was that put the pulse pump on it did a incomplete job. The check valves were still in the motor. I removed the check valves and blocked the left side. I put everything back together and pumped the ball and started it up and it ran until i cut it off. I bought this motor cheap and now I think I got a deal. Thanks again
 
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