1975 Merc 650 (2000-3000 RPM requires choke)

[72Glastron75Merc]

I have a 1975 Merc 650 with a few problems... 1 identified, with 2-3 still lingering. Once started, it holds an idle fine, I can play in the 1000 - 2000 rpm range with no problem... once I hit 2000, I need to tap the choke every 200 - 300 RPMs until I reach 3000... then everything is fine from 3000 - 5500... As for the other issues, I realized there was a pin hole in the fuel line between the fuel filter and the fuel pump... I have that part on order for this week, however, i think the rpm issue is unrelated. Additionally, I get some smoke at low rpms... (1200 - 1600, and only when in gear).... and while I have you hear... I have the idle set at 1000 RPMs... anything lower than that stalls out... Please help me fix my baby!:redface:

 

[72Glastron75Merc]

Re: 1975 Merc 650 (2000-3000 RPM requires choke)

Any thoughts?

The smoke and 1000 rpm are my minor concerns... All I really care about is that dead-zone from 2000 - 3000 rpm. It basically prevents me from ever pulling a skier.

 

[emckelvy]

Re: 1975 Merc 650 (2000-3000 RPM requires choke)

What color is the smoke, blue or white? If blue, could be a rich idle mixture adjustment.

On the other hand, you're running lean between 2000-3000 so I'm wondering if the carbs have ever been worked on. If not, sounds like something's plugged up. Or problems with the fuel pump, or primer bulb.

If you have white smoke, could be a cooling issue and checking the impeller would be first on my list.

BTW, a pinhole leak in a fuel line is Never a good thing! Depending upon your fuel system's configuration, it's either blowing fuel or sucking air, neither condition conducive to your or your motor's longevity!!

I'd be very wary of running this motor lean, it's already on the verge of failure by design! Your idle issues very well could be just a matter of mixture & idle speed adjustment, but I wouldn't run it much until the lean-running issue is fixed. Maybe you'll note an improvement once the bad fuel line is replaced.

HTH & let us know what you find.........ed

 

[72Glastron75Merc]

Re: 1975 Merc 650 (2000-3000 RPM requires choke)

The fuel line made a huge difference. No more lag from 2000 - 3000 and it seems that the smoke issue is also cleared up. Everything has been running fine for the past 2 - 3 outings... until yesterday. I was cruising at WOT, then all of a sudden a huge power loss... I was too confused to remember the RPM fluctuation, but I think it dropped relative to the speed (ie: from 5200 RPM at 30 MPH down to approx 1500 RPM at 6-7 MPH)... My first reaction was to pull back on the throttle, which lead to a stall. When I tried to restart, it would hold an idle, but would stall when put into gear. My temporary fix was to adjust the idle stop (a significant adjustment) about 25% in order to hold a strong enough idle to put into gear... The gas was fresh, all the lines looked good... I'm taking it out on the water today, but have no idea what to expect...
Any thoughts?