1975 Merc 650 65hrs 3cyl ?????

[jfholijr]

Hi guys, first of all I just want to say THANK YOU ALL VERY MUCH FOR HELPING ME GET THIS MOTOR RUNNING AND ON THE WATER!!! I took it out twice and it ran good and strong. It's on a 15 ft bass boat and 4 people and it accellerated nicely and planed well. <br /><br />Now first question. Why in God's name is it so loud? especially when backing off from wot at about mid throttle it is very loud. Is that normal for this motor? I am missing the sound dampening material that was glued to the inside of the cowling but still it really seems louder than it should. If I need to replace the material what can I use as replacement and what should I glue on with?<br /><br />Secondly, my plastic timing indicator is gone so I had to fabricate a replacement using a wire cloths hanger that would point to the timing mark. Now my motor is supposed to have a max advance of 23 degrees, if it is only 21, or 22 will that be much of a problem? if so what damage will it cause being off a couple degrees? also is it better being off on the low side rather being to high (21 degrees instead of 25 degrees)?<br /><br />Lastly, I think I'm only getting about 3-4 miles to the gallon. Is this normal?<br /><br />I appolagize for all the questions and do sincerely thank you all for your help. This obviously is my first boat so please guys be understanding. Thanks

 

[agrazela]

Re: 1975 Merc 650 65hrs 3cyl ?????

Whoohoo,<br /><br />I own a 1978 Merc 3cyl...70 hp, but I believe it is essentially the same motor.<br /><br />This is the LOUDEST motor in this hp range I have ever heard, bar none. To me, it is especially loud in the 2000-4000 rpm range on either acceleration or deceleration.<br /><br />My cowling has no sound dampening material either...if you do add some, please post so we can see how it works out (I have been considering this idea myself). With the clamshell design, I am not sure there is any way to prevent sound from "leaking" out somewhere; then again, I think alot of the noise is vibration in the clamshell, so who knows?<br /><br />I recently did a decarb on this motor (may have been the only one it has ever had), and it is much quieter now (though still quite loud!) It is especially more quiet now on the deceleration...I think my gunk deposits were causing pre-ignition and causing all kinds of nasty vibrations...especially on deceleration. If you have not decarbed recently, I highly recommend it.<br /><br />As for timing, I would say ever-so-slightly retarded (say 25 degrees BTDC) is safer than advanced (21 degrees)...better some slight wet-fouling than running too hot/burning a piston.

 

[agrazela]

Re: 1975 Merc 650 65hrs 3cyl ?????

Oh, and yes, by the way, I have been getting about 3-4 mpg on this motor, but with alot of stop-and-go, short burst running. I do not know what I would get if I ran it flat-out for an hour.

 

[jfholijr]

Re: 1975 Merc 650 65hrs 3cyl ?????

hello agrazella, thank you for your reply, are you sure that it's safer to have it on the 25 degree side rather than the 21 degree?<br />About the sound dampening, I'm considering putting in some foam (poly urithane i.e. foam rubber) but not sure if it is a good idea or what to glue it in with.<br /><br />Also have a question about the tach I bought today. I have the mercontrols and the tach's harness just plugs into the mercontrols but the merc machanic here said to disconnect the brown wire from the switch box and connect it to one of the yellow wires coming from the stator. Can you or anyone else confirm this form me. I'm paranoid for sure and I know it. Thanks

 

[jfholijr]

Re: 1975 Merc 650 65hrs 3cyl ?????

^

 

[Ben Konopacky]

Re: 1975 Merc 650 65hrs 3cyl ?????

whoohoo; that is exactly what i did with that brown wire on my 75 850. make sure you set the tach. for the correct # of poles/or cyl. for a correct RPM reading.

 

[andrewkafp]

Re: 1975 Merc 650 65hrs 3cyl ?????

I think your motor has the 2 pce (Not wrapper) type cowling.<br />If so,the sound deadening pads are still sold as spares<br />61631 BLANKET, SOUND ABSORBING (UPPER) <br />61632 BLANKET, SOUND ABSORBING (LOWER) <br />61634 BLANKET, SOUND ABSORBING (LOWER) <br />61633 BLANKET, SOUND ABSORBING (UPPER) <br />Most likely Left and Right.<br />If it has the 1 pce wrapper type.. they are<br />31935 BLANKET, SOUND ABSORBING - WRAP AROUND COWL <br />25234 GLUE, ADHESIVE - SOUND BLANKET FASTENING <br /><br />From here<br />http://www.dougrussell.com/partscatalog/collections/index.cfm?fuseaction=colle ctdetails&colid=01

 

[jfholijr]

Re: 1975 Merc 650 65hrs 3cyl ?????

Thanks Ben Lucky and Unicorn. Ben Lucky I set the tach to 6p according to what I could understand from the instructions that came with the tach, does that sound right? The tach is a quick silver brand. Is this motor a 12 pole? <br /><br />Unicorn those parts aren't available anymore.

 

[Ben Konopacky]

Re: 1975 Merc 650 65hrs 3cyl ?????

whoohoo; just checked my setting in my maint.log.(every thing i do to the boat)it is set at 6p.had to tweek the tach.a little to calibrate it to master. But it should be close enough..

 

[jfholijr]

Re: 1975 Merc 650 65hrs 3cyl ?????

Ben Lucky what did you use to compare the tach readings with to calibrate your tach? I know where the adjustment is but have no way that I know of to compare it to.