Mercury 650 problems – is it worth an overhaul?

[shoestringmariner]

Travis, the guys here have been very helpful. I hope I haven’t been leaning too much on everyone

[Pondrocket]

ShoestringMariner, you are doing a great job carry on.

Travis

Travis
AOMCI VP Communications
AOMCI Webmaster
webmaster@aomci.org

[mercuryspecialist]

[/quote]Thanks for your input. I mentioned that I was planning on rewiring it over the winter. He said that I had to use the exact same gauge and length of wire had to be identical as the wiring in this system is resistance sensitive.

As for the tach, a sticker under the hood said to make sure the tach was “quicksilver compatible”. Truth or fiction?

Also,I was told the top and bottom carb are different sizes because one carb feeds one cyl and the larger one feeds 2 cylinders. This is the strangest thing I have ever heard.

Lastly, do you know where I might find replacement harnesses or someone who makes them?[/quote]

Although I would recommend the same gauge, color insulation, and length also, the system is not "resistance sensitive".
Yes, the tachometer would need to be Quicksilver compatible, if connecting to the ignition system. However, if instead connected to the battery charging system, then a modern alternator driven tachometer such as a Teleflex can be employed. Note that the engine wiring harness’ s tachometer brown wire must be then moved to connect to one of the AC side rectifier terminals to receive a signal from the charging system instead of the ignition system.
The carburetors are not different in size. The top feeds the top cylinder, the bottom feeds the bottom cylinder, and both carburetors feed the middle cylinder.
CDI does state to offer to rebuild your original. In the past when I have spoke about having a harness rebuilt, it was said to be six or more weeks to do so. They do show a new replacement for the 1980 to 1990 models. This harness seemingly could be employed on 1976-1979 models also, but would require the matching plug type remote control harness as well. 1972 to 1975 models have instead a battery powered CD ignition, so the wiring differs somewhat.

Regards,
Joe
info@fergusonpoolemarine.com

[shoestringmariner]

quote MercurySpecialist:

Thanks for your input. I mentioned that I was planning on rewiring it over the winter. He said that I had to use the exact same gauge and length of wire had to be identical as the wiring in this system is resistance sensitive.

As for the tach, a sticker under the hood said to make sure the tach was “quicksilver compatible”. Truth or fiction?

Also,I was told the top and bottom carb are different sizes because one carb feeds one cyl and the larger one feeds 2 cylinders. This is the strangest thing I have ever heard.

Lastly, do you know where I might find replacement harnesses or someone who makes them?[/quote]

Although I would recommend the same gauge, color insulation, and length also, the system is not "resistance sensitive".
Yes, the tachometer would need to be Quicksilver compatible, if connecting to the ignition system. However, if instead connected to the battery charging system, then a modern alternator driven tachometer such as a Teleflex can be employed. Note that the engine wiring harness’ s tachometer brown wire must be then moved to connect to one of the AC side rectifier terminals to receive a signal from the charging system instead of the ignition system.
The carburetors are not different in size. The top feeds the top cylinder, the bottom feeds the bottom cylinder, and both carburetors feed the middle cylinder.
CDI does state to offer to rebuild your original. In the past when I have spoke about having a harness rebuilt, it was said to be six or more weeks to do so. They do show a new replacement for the 1980 to 1990 models. This harness seemingly could be employed on 1976-1979 models also, but would require the matching plug type remote control harness as well. 1972 to 1975 models have instead a battery powered CD ignition, so the wiring differs somewhat.

Regards,
Joe
info@fergusonpoolemarine.com[/quote]

Perfect, thanks so much. I thought the carb size thing was way off.

One thing I need to mention is that I corrected my original post. I believe that this motor is actually a 1975, so I guess the older style ignition…

And about the carbs. I went out last night for 2-3 hours and it ran ok. When I tilted the motor at the launch though, gas was dripping out of the engine (assuming carbs – front plate was closed. I’m guessing I’m getting into these carbs sooner than expected. Stuck float or bad gasket maybe?

[mercuryspecialist]

[/quote]One thing I need to mention is that I corrected my original post. I believe that this motor is actually a 1975, so I guess the older style ignition…

And about the carbs. I went out last night for 2-3 hours and it ran ok. When I tilted the motor at the launch though, gas was dripping out of the engine (assuming carbs – front plate was closed. I’m guessing I’m getting into these carbs sooner than expected. Stuck float or bad gasket maybe?[/quote]

Thank you, but you had mentioned that it was a 1975, and this is why I mentioned that there is some differences in the wiring due to the differing ignition systems.
Tilting the outboard for trailering or beaching would cause the carburetor floats to move, and therefore the leaking. There is no repair needed, but simply normal.

Regards,
Joe

[51seahorsetn27]

Well since your pulling the flywheel to do the transom, you might as well do anywiring under there while its off and either get a new harness or redue yours while the boats down. As far as the prop and over reving go, if you have the old prop still get the part number and cross it with a new prop number from say mercury or a nos vendor. If the prop was to big an you went to a smaller prop it would "seem" to be over reving because you had gotten used to hearing it bogged down. Honestly if the electronics and wiring are not on par trying to diagnose anything else is pointless. So many fuel and other "problems" have veen faulty electronics and wiring, and have ended more motors in the melter when wiring can be cheaper and faster than scratching my head rebuilding carbs and fuel pumps only find one bad wire, module, or switch that cost an 1/8th of rebuilding other components was killing performance and fun time. Just my two cents.

[shoestringmariner]

You guys are the greatest. Thanks again. Glad to know the carb leaking is normal. I was scratching my head at it, wondering how on earth I was going to get at them. I think I’m going to have to address this wiring sooner than later. It was acting up on me last night. It was a fight to get it going several times. I would’ve chalked it up as not knowing it’s idiosyncrasies yet, but it was bogging hard and dying when I was trying to get it out of the hole.

So, in the search for a service manual. Also need to read up on the ignition systems on these things. This high-voltage thing concerns me. I don’t want to put my fingers anywhere near until I know what I’m doing.

And on that note, if the battery is disconnected will all the high-voltage be discharged? I’ve heard of people dying because of capacitors discharging while they’re working on old amplifiers or welders etc. I don’t see anything looks like a capacitor however I don’t know what’s in the switchbox

[mercuryspecialist]

As most outboard motor carburetors lack an accelerator pump, bogging can be a too lean setting of the low speed mixture screw. Carburetor float level can also be a cause (replacement of the inlet needle & seat assembly, and proper float adjustment would then be advised). There is no shock hazard with the ignition switch "off", but Do disconnect the negative battery cable from the battery, or both cables, to protect the ignition components when servicing (this is true for many outboards).

Regards,
Joe

[shoestringmariner]

Thanks Joe. I want to check the 1-1/2 turn open thing. Is the bottom screw the low speed needle?

[mercuryspecialist]

A picture would be best, but you would need to e-mail me directly for me to do so (info@fergusonpoolemarine.com). Here is a try at a written description. With the front cowl and clam shell cowls removed, looking at the carburetors like from inside the boat, the low speed mixture screws are approximately one o’clock in relation to the venturi or throat of each carburetor. The aluminum choke plate with attaches to both carburetors, has a matching hole for both mixture screws. The high speed mixture is controlled by a fixed jet. A brass hex plug must be removed to change sizes, and is at six o’clock.

Regards,’
Joe

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