74' mercury 850 no power???

[tomkatesam]

i have a 1974 merc 850. when im on the water the engine starts, and idles, but when we open it up it tops out at 7mph. the compression is good (all cylinders 100-105) the engine has spark, and i just put a new prop on it??? what else could be wrong, i just rebuilt the carbs, cleaned out the distributor cap, and replaced the fuel lines. i have noticed some air bubbles in the fuel line coming from the fuel pump, could the this be the problem? what can i fix next??? thanks!

 

[erniex]

Re: 74' mercury 850 no power???

hi,<br /><br />What kind of RPMs are you getting at 7 mph? IS the engine running smooth and only going that fast, or is it stumbling, spitting, coughing, etc. Air in the fuel line is always a problem. Make sure all your hoses, connections, primer bulb, etc. are in good condition and the tank vent is open.

 

[papasage]

Re: 74' mercury 850 no power???

i have a 1974 65 hp doing that . tried chocking and sprey into carb. it didnt do any good . checked new hose and the inlet end of bubble was loose. dont know it that is it but the carbs wer cxlean afte second time pulling them . will know when i put it in the water . maby this weekin. papasage

 

[Chris1956]

Re: 74' mercury 850 no power???

Tom, It you over prop a merc, they will not rev up. Is it possible the new prop has too much pitch to allow the motor to rev up. Try the old prop and see if it revs up.<br /><br />Also, 100-105 PSI is not a lot of compression. Is it balanced between the four cylinders? Is the timing correct? Are the fuel pumps working properly?<br /><br />We need some additional in order to assist!