1967 Mercury 95hp 6cyl not reaching full RPM's

[75GlastronMN]

I have a 1967 Mercury inline 6 95HP. 950SS. yes it has the thuderbolt ignition system.

It is mounted to a 1967 Glastron V172 runabout. 17' boat. About 1000lbs.

I can not get the boat over 30mph or over 4000RPM's. Red line for this engine should be around 5000RPM

I verified that the tach is accurate.

Compression is 135-140 across all cylinders.

I also tried several props ranging from 15 to 19 pitch all stop at 4000 RPM's with varying speeds.

i have also gone through the sync n link procedure and made a couple adjustments with no positive results. Yes the carbs are fully open at WOT and the WOT timing is at 36.5 degrees as noted on the engine.

The engine runs pretty good the entire RPM range and never cuts out. Has a good strong hole shot too. I bought the boat this way so it's hard to say if it's always been like this or not.

oh yea, new spark plugs. 76A I think......

So my question is, Where do I go from here?

Should I pull the carbs and give them a good cleaning? Fuel pumps? Anything else you can think of?

Thank you for your help.

oh yea.. Is there something holding the plug wires on to the dist cap or in the coil? I can not get them off and am scared they will break if I pull harder.

 

[johnny howe]

Re: 1967 Mercury 95hp 6cyl not reaching full RPM's

i have the same motor. when taking off the wires i take off the cap and all

 

[paintbal55]

Re: 1967 Mercury 95hp 6cyl not reaching full RPM's

i have the same motor. when taking off the wires i take off the cap and all

the wires are threadad into the holes with a brass crimped on end

 

[paintbal55]

Re: 1967 Mercury 95hp 6cyl not reaching full RPM's

I have a 1967 Mercury inline 6 95HP. 950SS. yes it has the thuderbolt ignition system.

It is mounted to a 1967 Glastron V172 runabout. 17' boat. About 1000lbs.

I can not get the boat over 30mph or over 4000RPM's. Red line for this engine should be around 5000RPM

I verified that the tach is accurate.

Compression is 135-140 across all cylinders.

I also tried several props ranging from 15 to 19 pitch all stop at 4000 RPM's with varying speeds.

i have also gone through the sync n link procedure and made a couple adjustments with no positive results. Yes the carbs are fully open at WOT and the WOT timing is at 36.5 degrees as noted on the engine.

The engine runs pretty good the entire RPM range and never cuts out. Has a good strong hole shot too. I bought the boat this way so it's hard to say if it's always been like this or not.

oh yea, new spark plugs. 76A I think......

So my question is, Where do I go from here?

Should I pull the carbs and give them a good cleaning? Fuel pumps? Anything else you can think of?

Thank you for your help.

oh yea.. Is there something holding the plug wires on to the dist cap or in the coil? I can not get them off and am scared they will break if I pull harder.

try a premium higher octane fuel in your mix and run some carb cleaner spray through the three carbs use as the can directs
also the lower the pitch on the prop (14-17 p)the higher the rpm and hole shot torque
the higher the pitch(18-21p) the less torque in the hole but greater speed the rpm will only max out on high pitch props after you come to a plane on the water

 

[CV16]

Re: 1967 Mercury 95hp 6cyl not reaching full RPM's

I'd say to buy some carb kits and have at it. I have a 66 850 that spins up to 6000 with a 15 pitch on my CV16.

 

[CharlieB]

Re: 1967 Mercury 95hp 6cyl not reaching full RPM's

While cleaning the carbs it is always agood idea to also rebuild the fuel pumps.

ANY fuel restriction will limit WOT RPM and can burn pistons by running lean at high RPM. Check EVERYTHING just to be sure, fuel tank pick-up tube, fitting, all fuel hoses, primer bulb, connector to motor. Alcohol in todays fuel deteriorates fuel hoses, they should be changed every few years, it is cheap insurance against a possible melt down.