Mercury 850 not running right

[Kootenay Cruiser]

Hello all, I seem to be having a problem with my Merc. It's a '75 Mercury 850 with Thunderbolt ignition, the problem I'm having is it runs fine but will not rev up past about 3400 rpm in the water, out of the water it will rev up past 4000 rpm. Any suggestions as what I should be looking for? I changed plugs, wires and cleaned up the distributor.

 

[kazek]

Re: Mercury 850 not running right

kootenay...do not rev engine that high on muffs.your problem might be throttle plates not opening all the way.check that first.with engine off push throttle lever all the way,and look through carbs .linkage should hit its stopper(or just).u might need sinc and link.

 

[Chris1956]

Re: Mercury 850 not running right

Since you have distributor ignition, it is probably not the ign. Check spark plug wires for arcing to the block. Check compression. What pitch prop do you have and what kind and size of boat?

 

[Kootenay Cruiser]

Re: Mercury 850 not running right

Just replaced plugs and wires. The boat is a '76 Larson manta 17.5' not sure of pitch of prop but it looks kind of rough

 

[Kootenay Cruiser]

Re: Mercury 850 not running right

Prop is 14" In diameter not sure how to find pitch

 

[aussieflash]

Re: Mercury 850 not running right

Just replaced plugs and wires. The boat is a '76 Larson manta 17.5' not sure of pitch of prop but it looks kind of rough

How rough?That could be your problem.
Check all cylinders are firing.Have you done compression test yet?
Could also be Carbs or fuel pump.

 

[Kootenay Cruiser]

Re: Mercury 850 not running right

Well it looks like its seen a few rock,and I haven't done a CT yet but it runs smooth doesn't feel like its missing

 

[kazek]

Re: Mercury 850 not running right

diameter will give you a "kick"on take off.too big of diameter will drag eventually.pitch is your speed.with similar set up i am running 17p now.getting 4600rpm(could go lower with pitch to 15p thou).went through 21p@3600 rpm,13p@5900 rpms.just to give you an idea about propeller issue.