enigine lacks power

[atticus3600s]

I have a 1968 6HP Johnson outboard, and it does not seem to be achieving full power. The compression is 85/95 and the spark is fine. The fuel pump and spark plugs/wires are new, and the carb has just been rebuilt. I am also wondering if I should put a 3-bladed prop on it, as it has an old two blade right now. Any help is greatly appreciated!

 

[Paul Moir]

Re: enigine lacks power

Welcome to iboats, mercury!<br /><br />The two bladed prop is most likely a speed prop. Check to see if it's got any numbers written on it anywhere. What kind of rig have you got this engine attached to?<br />Does the engine seem to be running at half-power? Spark may appear to be good but failing under compression - a very common problem with these engines. Check to make sure you can draw 3/8" long sparks. Or try disconnecing a plug wire and running on one cylinder.<br />Who do the spark plug firing ends compare? What do they look like after running them?<br />Did you use automotive (ie, supression) wire to replace the old wire? Or metal core stuff? Sometimes on this type of magneto it makes a big difference.<br /><br />EDIT: I see that your engine originally came with a 8 x 7.25" 2 bladed prop. Could this be the prop you have?

 

[BF]

Re: enigine lacks power

Hiya,<br /><br />I'm not sure if your '68 is the same as the 70's vintage ones I'm familiar with (I have one, my Dad has one). I have 2 bladed weedless prop on mine, my dad's has a 3 bladed regular prop on his. I'm pretty sure the pitch is the same on both (8x8 ?). I have thought about trying the prop from his on mine, to see what difference it makes, but have never got around to it (doesn't help that the motors are in different places). I have also had the feeling that mine isn't running to full power (esp when compared to my Dad's). His will easily plane a 12' boat with me & 65# dog... Mine will only sometimes plane a lighter 12' boat, and doesn't come close to planing my light 16' aluminum when it's used a kicker. It runs good & smooth. Idles down nice, and mine is definately running on both cylinders (I've checked). Given that it runs well, I haven't done much more checking into it... <br /><br />Not much help I know, but your description sounds a bit familiar to me (like mine).<br /><br />If the points & cam followers are worn out, will the timing be retarded and cause a loss of power??

 

[atticus3600s]

Re: enigine lacks power

The prop is the original 8x7.25. The plug wires were replaced with automotive suppression wires. After running the spark plug ends are slightly damp and black, but it is not gummy. What is the compression supposed to be for this engine anyway?<br />The sparks look good coming out of the wires. I have it hooked up to a 12-foot aluminum V-hull, and it dosent get anywhere near planing with me and a trolling motor and battery in it (about 180lbs.) My cousin has a 1994 6HP and it gets a 14 foot aluminum boat on plane with the two of us in it!

 

[Terry H]

Re: enigine lacks power

mercury89...someone is gonna come on and tell you to change the plug wires back to marine wire...you know, the ones that have wire in them, not carbon. Well I would just have to agree with them, I don't know if it will make much diference, but it will help...just a thought