Mercury 650 problem

[Stumpys]

Hey guys, just found out about this forum and I think this place is great with a lot of very smart folks. Anyway, I have a 1968 Mercury 650 that when I go to throttle it, it seems like it is slow to build the RPM's. Once it goes on plane and I trim it, it runs pretty good, but it acts like there is no advance to the timing. It takes forever to rev up. This is on a 16'Bomber fish and ski tri-hull.<br /><br />I took it to the lake the other day and it has been idling fine and runnning pretty good other than the slow RPM's, but now it started dying when I throttle up. I have read some of the other post about bogging down and I am planning on working on this- this weekend. <br /><br />I don't really want to post too soon without giving any compression numbers or anything, but I just need a starting point. <br /><br />Now, I just bought this and I don't know anything about this motor, or what has been done to it. In fact, I don't know anything about marine motors!<br /><br />Thanks in advance...

 

[mellowyellow]

Re: Mercury 650 problem

welcome aboard,<br />sounds like a fuel related problem to me. maybe time to rebuild carb(s). <br />have someone squeeze the primer bulb when throttling up and see if she picks up for you.<br />good luck,<br />M.Y.

 

[rickdb1boat]

Re: Mercury 650 problem

My 67' 650 had the same problem. Rebuilt the Carbs(Bad idle, slow to respond) and went to a lower pitched prop and it ran like a beast... Do you know your WOT RPM's?

 

[Stumpys]

Re: Mercury 650 problem

Thanks for the reply...and I'm glad I found this forum.<br /> <br />No, I don't have a tach. I did bring the boat to work tonight so I can rebuild the carbs and do a compression test. If this does not solve the problem, I will let ya'll know.

 

[mercglass]

Re: Mercury 650 problem

I have a 1976 merc outboard 65 h.p. I wonder if anyone knows how to adjust the cable on the side of the motor that adjusts the shifting.It wont go into reverse

 

[Stumpys]

Re: Mercury 650 problem

Ok, I rebuilt the carbs, did a compression test...80 on all four cylinders. I did notice as I rev it up, the bulb starts to get really spongy. Could it be starving for fuel or is this normal? Is 80 psi too low on the compression?

 

[Stumpys]

Re: Mercury 650 problem

Ok, I rebuilt the carbs, did a compression test...80 on all four cylinders. I did notice as I rev it up, the bulb starts to get really spongy. Could it be starving for fuel or is this normal? Is 80 psi too low on the compression? <br /><br />Sorry alpharomeo... I'm just a novice here myself. I'm sure these folks will tell you how to do it.

 

[mellowyellow]

Re: Mercury 650 problem

80 is very low, usual min. is 100psi. how did you<br />check compression? get a new primer bulb.

 

[Stumpys]

Re: Mercury 650 problem

I have a screw in compression tester, and I cranked it over about 6 turns.

 

[mellowyellow]

Re: Mercury 650 problem

may be the tester itself? did you install new<br />needle valves and seats for carbs? while your at<br />it I recommend installing new fuel pump diaphrams.<br />easy/cheap. get a new primer bulb and re-test.<br />good luck,<br />M.Y.

 

[Stumpys]

Re: Mercury 650 problem

Ya, I guess I had better try another tester, and yes, I did go completly through the carbs.<br /><br />Thanks mellowyellow... Gonna get right on it today.

 

[cs1452nos]

Re: Mercury 650 problem

i agree with mellowyellow, replace the diaphrams. good way to test them is to pump up the prime bulb, it should get hard if they are good, and if they are bad, it will stay soft. i had similar problem on my 650 motor. replaced them, and she runs great. your compression is low, but get another tester and check again. mine are at 125 psi across the board. good luck... chris

 

[tflug]

Re: Mercury 650 problem

I think I might have the same or similar issue with my 1972 Merc 650. <br /><br />Here's a dumb question:<br />My throttle control panel has two levers. The first one, a larger one seems to control the gears and throttle. The second one seems to turn the cap and rotor. what is that for.<br /><br />BTW - the egine will only start and run with it pressed all the way forward. <br /><br />Ideas?<br /><br />thanks

 

[Stumpys]

Re: Mercury 650 problem

Ok guys...I rebuilt the carbs, cleaned the tank, changed the filter, replaced the primer bulb, and I took it out this weekend. It still does as before, but now, when it warms up, it dies when you try and take off. It will start and idle fine. Pumping the primer bulb does not help, but when you take off, it dies. <br /><br />The only thing I have not done yet, is to work on the fuel pumps. The carbs had absolutely no crud of any kind, and the screens were perfect. This thing is driving me and the ole lady @#@##@ nuts.<br /><br />Another thing I have noticed is that when idling, there is a lot of exhaust coming from under the water. I thought the exhaust was above the water line. Even running, there is a lot of bubbles from the exhaust. Is the what is is suppose to be doing???? I watched the other boats up at the lake yesterday, and they do not do like mine. Sorry to ask stupid questions, but I really don't know crap about these things. <br /><br />I agree on the compression... I really think this thing needs to be re-ringed.<br /><br />Thanks....

 

[Chris1956]

Re: Mercury 650 problem

Stumpy, The bubbles may be normal through the hub exhaust, hadr to tell from description. It also sounds like your carbs are set to a too lean idle mixture. Richen the top carb (CCW) 1/8 turn and try to accelerate, then richen the bottom carb and try again.(repeat if necessary) You want the idle as rich as possible and yet it will still idle reasonable well.

 

[Stumpys]

Re: Mercury 650 problem

Thanks Chris... I'll give it try. Anybody still thinks she needs overhauled???

 

[mellowyellow]

Re: Mercury 650 problem

re-check compression KC, if it's "really" 80 time<br />2 give up on all else. in a few cases "decarbing"<br />will un-stick rings.

 

[cs1452nos]

Re: Mercury 650 problem

stumpys, i would replace the diaphrams in the fuel pumps. i guarantee that will take care of the fuel problems. the other prob. is with that low compression. get another tester and make sure it is correct, and then go from there. maybe time to rering her. just my two cents. chris

 

[Stumpys]

Re: Mercury 650 problem

Thanks for all the help guys... <br /><br />Got the seafoam and letting it soak all night in the cylinders. Gonna run it through the tank also. Figure it can't hurt by doing that. Anyway, tomorrow she gets the pumps overhauled.<br /><br />Anything after this, it's time to break her down!