'91 70 HP Johnson #2

[fish4fun42]

I had my '91 70 HP Johnson overhauled in 2001. Bored .030" over, <br />new pistons, carbs cleaned etc. Engine was overhauled due to galling <br />in #2 cylinder. Carbs were not re-jetted. Engine has VRO.<br /><br />The boat is now in the shop and the #2 piston has a pencil sized hole <br />down the exhaust port side. #1 and #3 cylinders have 120 PSI compression.<br /><br />Mechanic does not know root cause of problem. <br />This concerns me since I don't want to go through rebuild again <br />if I have it fixed. <br /><br />Questions: <br /><br />1. Do 70 HP Johnsons have a history of #2 cylinder problems? (is it worth fixing?)<br />2. Should the VRO be disconnected since the unit is 12 years old?<br />3. Any ideas as to why the piston burned? advanced timing? fuel starvation? VRO?<br /><br />Thank you for your comments.

 

[clanton]

Re: '91 70 HP Johnson #2

If engine being repaired by dealer, tell them to check the service bulletins, then check the engine to see if the mods have been done, if not then do the mods described in the service bulletins, Try search your engine the bulletins are on this board. They increased jet size, retarded timing, inproved waterpump, relocated tattle tale nipple to top of block, upgraded thermostat, thermostat seat, and temp sensor. Then prop close to 6000 rpms

 

[Dhadley]

Re: '91 70 HP Johnson #2

Were you using something besides Champion plugs?

 

[fish4fun42]

Re: '91 70 HP Johnson #2

Thank you for your quick reply's. I don't think any of the service bulletins have been completed on this motor. The current service is not being performed by a dealer. What is the best way to look up the bulletins on this site? <br /><br />Concerning the plugs, I cannot currently confirm the brand or heat range since the boat is in the shop.