What do you have your tach set at for 40 hp?

[Mark42]

The Teleflex tach I bought indicates that for all Johnson/Evinrude twin 2strokes set the adjustment to 5p. The Evinrude manual indicates that 6pole 12amp models use the 6p, and the 5pole 4amp models use the 5p setting.<br /><br />I believe my model should be set at the 6p setting, but I am getting confused. <br /><br />Mark.

 

[DJ]

Re: What do you have your tach set at for 40 hp?

Your engine is NOT a 12 amp. Use the 5P.

 

[Mark42]

Re: What do you have your tach set at for 40 hp?

DJ,<br /><br />How do you know it is not a 12 amp? This is a critical piece of info. The OMC manual has pictures of the 12 and 4 amp alternators. They look quite different. From what I can see under the flywheel without removing it, it looks like the 12 amp, BUT I AM NOT SURE.<br /><br />This has me confused.<br /><br />Not knowing for sure which alternator I have, in conjunction with the different RPM limits for differnt models has me really conserned about my tach accuracy. I am trying to get the proper prop for the boat, and having doubts about the tach setting is really messing things up. <br /><br />Any more info you can share is greatly appreciated.<br /><br />Mark.<br /><br />PS: someone indicated in a different post that the 6700 rpm limit for the 40 may be a typo. The manual lists 40 and 50 Recreational as 6700, 25DR, 40R, and 48 as 6100 and 40RS, 45 and 55 as 5800. Think the OMC manual has a typo there?<br /><br />Thanks,<br /><br />Mark.

 

[Mark42]

Re: What do you have your tach set at for 40 hp?

ttt

 

[stsmith]

Re: What do you have your tach set at for 40 hp?

Hi Mark<br />I am having the same problem. '78 55hp Johnson.<br />I dug up these 2 sites but still left me with the same question. It may help you. Check it out.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=024624;p=#000002 <br /><br />Smitty

 

[stsmith]

Re: What do you have your tach set at for 40 hp?

Hi Mark<br />I am having the same problem. '78 55hp Johnson.<br />I dug up these 2 sites but still left me with the same question. It may help you. Check it out.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=024624;p=#000002 <br /><br />Smitty

 

[Mark42]

Re: What do you have your tach set at for 40 hp?

Thanks Smitty,<br /><br />Sorry to see we are in the same boat. (couldn't resist). I guess I will switch the setting to be 5p, and see what the tach reads next time out. <br /><br />What I really need is a mechanical tach like machinists use where the tach is held against the end of a spinning shaft and it reads out the RPM. With one of those, I would hold it against the prop nut and see what the real RPM is.<br /><br />Anyone else with any info please feel free to chime in here. Could really use some expertise!!!<br /><br />Thanks,<br /><br />Mark.

 

[lark2004]

Re: What do you have your tach set at for 40 hp?

prop nut isn't same speed as engine. You forgot the gear ratio inside the gear case. Any way, how are you going to find rpm at wot with a tach on prop nut? shouln't it be in the water? and don't say with muffs, because you should never rev your engine without the proper exaust backpreasure. Just do as DJ has suggested, as to how he knows? I don't know, but I do know that he does know what he is talking about.

 

[Mark42]

Re: What do you have your tach set at for 40 hp?

Sorry, I meant flywheel nut. It doesn't have to be at WOT, just at mid throttle. With cowel off, and crusing at steady speed on calm water, the engine RPM should be able to be safely taken off the flywheel nut, then compared to the tach on the dash at the same time.<br /><br />Mark.