Just can’t keep her idling

[steeleman]

So I have had my 68 Mercury 650 out twice now this year. Completely rebuilt the carbs because I was having these symptoms last summer, it would stall out and kinda act like it was loading up at idle, especially when transitioning from low idle and giving it any sort of gas at all. It’s like it floods out almost. If you are cruising and throttle down to idle, it will idle for about 60 sec then die.

So, carbs rebuilt, definitely overall running better. Anything above idle it is absolutely stellar. But I just can’t figure out what is up with it. I have two tanks and it will do it on both, new line from tank to motor. Just can’t seem to get it.

Any preliminary thoughts?

[dave-bernard]

did you adjust the idle screws and idle stop. did you go thru the mag and set it right?

[billw]

There is an adjustment on the bottom carb link. Make sure this is set so that both throttle plates begin to open at exactly, as in EXACTLY, the same time. Also, Dave is right about making sure the mag is all set up right, especially primary pick up.

Long live American manufacturing!

[dave-bernard]

Mag setup not just externally but internally well cleaned and gap @ .008.

[steeleman]

Thank you for your responses. What is the best way to tell if they are opening at the say time? Just by eye? And how do you setup the mag? What is proper procedure

Would mag cause it to die after it idles good for a minute? Feels like a fuel issue? And that is idling good under load without moving the throttle at all

[outbdnut2]

quote SteeleMan:

Would mag cause it to die after it idles good for a minute? Feels like a fuel issue?

Can you keep it going by pumping the gas line primer bulb? If so, look to a weak fuel pump.

If your carbs are running too rich at an idle, after a bit your spark plugs may be getting wet with gas and fouling – when it quits, pull the spark plugs and see if they are wet to check for this.
Dave

[dockbuster1]

Assuming your mag is timed right your carbs are set rich not too lean and the squeeze bulb keeps it running I would guess the sealing ridges are worn or the reeds are chipped if so the fuel pump won’t work at low speed

[Mumbles]

quote SteeleMan:

What is the best way to tell if they are opening at the say time? Just by eye?

You need to make yourself a set of these simple amplifiers which magnify any motion of the butterfly shafts. Alligator clips with some of the teeth ground out and a small rod attached is all they are. They get clipped onto the end of the shaft opposite of the linkage. This way they don’t give a false reading and only move when all of the backlash is taken up and the butterfly is actually opening. They also work good for doing a link n sync on single carb OMC motors.

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[billw]

Nice amplifiers, Mumbles. I will have to make a set! I have to say that thus far, I have just watched the shaft movement very, very closely. In the case of the 650 Merc, with only two carbs and vertical throttle shafts, they are pretty easy to see all at once.

I was also thinking, about the stalling issue, that if you have not installed a new set of fuel pump diaphragms, now would be a good time. A pin hole leak in one of them would cause a symptom such as the low speed stall after a short time….It may not end up solving it….or it may…..but either way, it’s a cheap fix and a good investment of time. Definitely worth a shot.

Long live American manufacturing!

[steeleman]

I will try new fuel pump diaprams I think. That is what is feels like to me, a loss of fuel pressure at true idle, or also air getting into the fuel somewhere.

My gut says it’s the pumps. Carbs appear to be in sync, but I will make some sweet clips like mumbles as well! Those things are sweet.

[Author]

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