1979 70hp stall and kills under a load

[jo jo]

hi i am new to the forum, I just bought a 1979 70hp mercury 700 it came off of a 15ft bass boat. i put on a 16ft flat boat it runs good come's out the water fast and runs about thirty mph at half throttle. it only has a 13 pitch when give it full throttle rpm come up the speed does not. is there a round about way to find out which pitch i should have. also would like to no what might make it stall and kill only when trying to run it up on the trailer. i am kind of at a lose compression reads at 120 psi per cylinder. any info would be greatly appreciated.

 

[rndn]

Re: 1979 70hp stall and kills under a load

Welcome to the forum!!
There are several sights that offer a prop calculator, so here is a link to just one of them.
http://www.turningpointpropellers.com/
If it is stalling when loading on the trailer you may have a fuel issue. Maybe the float(s) are not adjusted properly in the carb(s). Another option is when you go to trailer it do you trim out the motor so it doesn't hit the launch? If you do maybe you are are pulling the connection from the boat to the motor and pinching something.

 

[jo jo]

Re: 1979 70hp stall and kills under a load

thanks for the reply the first time it was trimed up a little the second time it was down. i did have trouble with the number two plug no fire,changed all the plugs an it fix the problem. the plug wires look pretty shabby i am looking for a set right now. i drained the bowls on the carbs the guy i bought it from did say he had some bad gas in the tank

 

[wildbillhemphill]

Re: 1979 70hp stall and kills under a load

Welcome to the forum!!
There are several sights that offer a prop calculator, so here is a link to just one of them.
http://www.turningpointpropellers.com/
If it is stalling when loading on the trailer you may have a fuel issue. Maybe the float(s) are not adjusted properly in the carb(s). Another option is when you go to trailer it do you trim out the motor so it doesn't hit the launch? If you do maybe you are are pulling the connection from the boat to the motor and pinching something.

These motors have a switch on them I call it the upsidedown switch it cuts off the spark if the motor jumps in the boat if it is in the wrong position it will kill the motor on a steep boatramp, It is located just behind the startermotor at he top of the powerhead and should be at about a 60 degree angle it's alittle round blackthing with 1 wire on the top. Its worth checking out I had one eat me alive before I figured it out.