1976 Merc 85 hp- won't run at full throttle

[alrednek]

I recently replaced the water pump impeller and the cylinder cover gasket on my 85 hp Mercury. When I took it to the lake it ran really rough and would only run at about a fast idle- it wouldn't plane the boat out at all. I had not run it in a couple of years and tried to crank it on the old gas which was a mistake. When it wouldn't crank I emptied out the tank and found quite a bit of water in the tank. I don't know if I have screwed up the throttle linkage somehow when I replaced the lower unit or if I have carb problems. I am wondering if the carbs could be gummed up and just need cleaning or if there is some way the water in the gas screwed up the carbs. I sure would appreciate some diagnostic help or suggestions on how to find the exact problem. I can likely fix the problem if you guys can just help me determine what it is. Thanks for any help you can offer.<br /><br />Mike Hannah

 

[Yepblaze]

Re: 1976 Merc 85 hp- won't run at full throttle

Take the carbs off and drain the bowls. Check that the jets are free of restrictions.

 

[jim dozier]

Re: 1976 Merc 85 hp- won't run at full throttle

Do what he said, and after 2 years of inactivity and a bad tank of gas I think while you have the carbs out and the bowls off you should thorough clean with carb solvent and compressed air and rebuild them. And what exactly is a cylinder cover gasket and why did you replace it.

 

[alrednek]

Re: 1976 Merc 85 hp- won't run at full throttle

The cylinder cover gasket was bad allowing coolant water to leak out around the spark plugs. The cylinder cover is the plate that covers the water jacket/spark plug boss area of the block.<br /><br />So, Yepblaze and Jimd, it sounds like you both think it is likely a carb problem from my description instead of something I might have screwed up doing the other repairs. Right?

 

[tmcalavy]

Re: 1976 Merc 85 hp- won't run at full throttle

don't know how you coulda messed with throttle linkage or timing just doing a water jacket gasket. that's probably all right unless someone has jacked with it without your knowing. if in doubt, pull #1 plug, put it in N and turn flywheel until #1 piston is at TDC (right up against the plug hole). now see if the timing mark on the flywheel lines up with the one under the timing belt pulley cover. if so, timing ain't it. if not, needs to be timed again and carbs synched. i'm betting its your dirty carbs....pull them and rebuild them. lucky you its a fun job, but worth it. do a fuel pump rebuild at the same time.

 

[alrednek]

Re: 1976 Merc 85 hp- won't run at full throttle

Thanks Tim...I'll check the timing. Yeah, I know how much fun it is to take the carbs off and rebuild them. I just rebuilt them about 4 yrs ago and don't look forward to it again, but if I gotta... <br /><br />I'd sure like to know an easy way to synchronize the carbs and how to rebuild the fuel pump if you have the time to respond again.<br /><br />Thanks, Mike

 

[tmcalavy]

Re: 1976 Merc 85 hp- won't run at full throttle

never seen a 76 85hp Merc, but I run a 73 Merc 500 so fuel pumps may be similar. On mine i just remove three small bolts, pull the pump off and replace the rubbers inside...just ordered a rebuild kit from boatingsolutions.com for a whopping $2.60. shipping was more than the kit. as for synching carbs, don't know...just rebuilt mine, took it out and it ran like sh*t so had to drop it with the boat guy on the way home. on mine you have to pull the dist. , coil, etc., etc, etc, etc, to get the carbs off...what a pain.

 

[alrednek]

Re: 1976 Merc 85 hp- won't run at full throttle

OK Tim, thanks for the info. I'll get a kit and rebuild the pump along with the carbs. I appreciate the response.<br /><br />Mike Hannah