1978 Merc 800 bogs

[cajun1957a]

"Compression is 145 psi in all

"Compression is 145 psi in all four holes. Had a tune up on it and all cylinders are fireing. It idles fine. When i throttle up, whether fast of slow, at about 2500 rpm it will die out and stall. If i can get past that rpm range it will get up and dance across the water. Pulls you back into your seat in fact. This motor just screams once Im into the higher rpm. In fact, i need a different prop because it is reving 5800 rpm with a large diameter 15P prop. It starts fine, idles fine, runs at full bore phenominally, but what can be causing that dead spot?

Also, what recomendations can you make on props. I was going to go to a 17 P but others have said perhaps to go to a four blade 15 or 16. I am getting 34mph by gps on a tri-hull bow rider and would like a little more. I have the revs and horsepower for it i think

randy"

 

[beckerjs]

"if the carbs are clean and th

"if the carbs are clean and the gas is good, sounds like the idle mixture is set just a bit lean. Each carb has its own mixture setting, turn the idle mixture 1/8 to 1/4 counterclock wise to richen the mixture, this will help the engine accelerate through the transition of idle to main jet. Carb adj 101
http://www.themarinedoctor.com/cgi-bin//YaBB.pl?num=1150170058"

 

[beckerjs]

"stay with a 3 blade prop, go

"stay with a 3 blade prop, go up 2 pitch sizes or 1 pitch size if the boat was empty and light. If you use the boat to pull tubes then you want a prop that will let the engine rev"