Mercury 650 3 cyl Link N Sync Questions

gholmesjr

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I am hoping you all can help me with this. I have some questions while going through this procedure, my questions are in RED:

This basic procedure will work for all the 2/3/4/6 cylinder inlines from 1960 to 1988. It's not for the newer 3 and 4 cylinder loopers.

Engine off

Disconnect throttle cable

Pull throttle arm to full throttle and verify carbs open fully. Adjust main throttle stop so that the carbs are JUST hitting thier own little throttle stops. The idea here is that you want the screw stop and NOT the carbs acting as the "final stop" for your throttle lever.

Return the throttle to idle, carbs should be closed. Set all idle screws to 1 3/4 turns out from lightly seated.

Remove all plugs except #1, hook a timing light to #1. Then follow the narritive.

When the throttle is in the idle position the carbs should be fully closed and the ignition retarded. It is the amount of retardation that determines your idle speed and is set later with the idle stop screw.

QUESTION: Retardation of the ignition, what does this mean exactly? Does this mean that the distributor is rotated forward, thus slowing down the RPMs? On this motor the further back the distributor rotates the quicker the motor spins as the throttle is also pulled. So my thinking is the retardation of the ignition is slowing the RPM by moving the distributor forward.

Timing Event One - throttle pickup.
As the throttle is advanced, the spark timing advances toward TDC and then to before TDC. As the timing is just passing TDC the 1st (minor)throttle pickup should hit and start to open the carbs. Use the timing light. Adjust the tang or trigger screw to make this a reality. All of them are speced different, but if the 1st pickup hits at 3-4 degrees BTDC advance - you win. Use the timing light with a friend cranking it to complete this setting.

QUESTION: Is this the sticker that is on the flywheel, I should be hitting 3-4 deg on that sticker on the indicator?

Timing Event Two - max advance.
As you continue to advance the throttle the timing will advance while the carbs slowly open a bit more. The next adjustment is max advance, this is the point where the distibutor (or trigger) can advance no more. Set the max-advance stop to 21 degrees for "direct charge" crossflow inlines and 34 degrees for the older plain vanilla crossflows. Use the light, - err to the side of caution.

QUESTION: Is this done with all the plugs in or still just the first one? Is this basically at WOT getting it to that 21 deg but with only one spark plug? Or is this not WOT, but before the steeper pick up on the cam for the throttle? If the ladder, are we saying that before at the 3-4 deg we should be at the beginning (just hitting) the first pick up on the throttle cam and then by the time we get to the second larger pick up on the throttle cam we should be at 21 deg and we continue to be at 21 deg while we go to WOT?

Right after max advance, further throttle motion should cause the second throttle pickup to hit and open the carbs to full. You already set that -now verify it.

Leave the throttle cable disconnected and go to the water. Leave the boat strapped to the trailer and back it in so it's deep enought to run. Have a friend crank it while you operate the choke and throttle. Warm it up at 1500 rpms's.

When "warm" adjust the idle stop screw for about 800 rpm and then ajust your idle needle(s) in (one at a time) till the motor stumbles. Quickly backing it out 1/2 turn from "stumble" will usually save it from needing a re-start. Do that for all the idle screws. Re-set idle stop for 800.

Now have your friend put it in gear (make SURE you are on the transom NOT in the water) and reset your idle stop for as low as you can get it. 500-600rpm is great if your old reeds will let it idle that low in gear. Now, re-adjust the idle screws, in to stumble, then 1/2 turn out. When you've gone back and forth with that a few times and have it "perfect" - adjust each one out 1/4 turn.

Reset the idle stop so that it's about 700-800 out of gear and 500-600 in gear. Sometimes bad reeds won't let you get that low, you've GOT to get it under 1000 in neutral (worst case) to avoid beating up your lower unit when you shift into gear, even 1000 is "bad" but like I said "worst case".

QUESTION: Idle stop is the lower screw that puts pressure on the joint that hooks up to the throttle cable?

Now adjust (and hook up)the throttle cable so that with the shifter in neutral, there is light to moderate pressure holding the throttle arm against the idle stop.

Take the boat off the trailer and go out in the water. Try the hole shot. If it falls on it's face try adjusting the idle screws out 1/4 turn at a time (all of them together) till you can get a hole shot. You can kind of do this on the trailer at the ramp, but it's not really safe for you, the boat, or the tow vehicle.

You're done.

-W



Thanks for your help, I've gone through this motor and this is the last part. I am finding it hard to find someone around town that works on these anymore.

J.T.
 

gholmesjr

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Bueller? Bueller? Don't mean to be pushy, but does anyone have some incite before I break down and take it to the shop?
 

gholmesjr

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I'm going to try and work on this tonight before succumbing to taking it in to the shop.
 

merc850

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Here are the manual steps and the top plug (Nr.1) is the only one you reference. 19756501.jpg 1975650.jpg
 

gholmesjr

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Thank you Merc. This is far more detailed than the instructions I have. I will hopefully be trying this out tonight!
 

merc850

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Good idea to buy the 1975-1978 Mercury manual, got mine on ebay.
When it's timed set the low speed needles 1 1/4 turns out from seated then warm up engine in lake and set the final settings in water; underway.
 

gholmesjr

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Ok, so I followed the instructions. I dialed in the timing. It was really hard to get it to time the idle while in gear t the 3-5deg. I was able to deadlock in on the 23deg easy. The GOOD news, the motor doesn't die anymore. The BAD news. I have really no power. Can't do a hole shot at all. It just feels lethargic. I have a video of the motor if you don't mind taking a look and letting me know what you think. Part of me is wondering if the prop size is wrong. But I don't know.
 
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merc850

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Sounds like it's not running on all cylinders are both carbs opening all the way? With motor not running advance throttle all the way and look at butterflies.
New plugs L77V? Do you have a tach hooked up?
 

gholmesjr

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Thanks for getting back to me Merc. Both carbs open all the way. I replaced the plastic couple between the two to ensure that both open the same amount. New plugs are in and all are getting spark. New (salvaged) dist. cap as the old one was cracked. Done the carb kit and float settings, fuel pump diaphragm replaced. Getting good gas through to the carbs. None of the plugs look fouled. Lastly, I do not have a reliable tach hooked up. I have one that wraps around the first cylinder wire, but it doesn't read correctly, so I've been going off sound mostly. I know I should have a tach hooked up, but I've been trying to cut cost a bit. Also, I tested the rectifier per Z-man instructions here: http://www.myoutboardengine.com/rectifier.html I think that the rectifier is shot. Would that make things cut out?
 

merc850

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The rectifier is for battery charging only you should see across the battery 12v at idle and the voltage will increase as the motor speeds up. You can get an alternator driven tach (I get them from my dealer for $25 - they pull them out of old boats) set to 6p to get an accurate reading and put you in the 5300 top end, it's important to not run at a lower rpm. What pitch prop are you using?
Have you run it with the cowling off to see if spark wires are shorting?
 
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gholmesjr

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How would I be able to tell by looking that they are shorting out? Can you explain how an alternator driven tach is hooked up? Is it hooked up to the rectifier and counts the pulses from the stator? I will look into getting one of those. As far as the prop goes, it doesn't say much on it, but there is a number that says 14P. It has 48, then a long number that I can't make out and then a 14P.

Merc, if you were in Omaha, I'd buy ya a beer!
 

merc850

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If you can run it in the driveway at night with water hooked up you'll see any arcing. Yes the tach connects to one of the YELLOW leads on the rectifier and has terminals for + and - power. The 14 Pitch prop sounds right for a heavy boat with 2 persons aboard.
Too bad I live 2,000 miles away!
 

gholmesjr

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Hey Merc, can you tell me where I can find a 6 pole tach for my motor? I am looking and a lot of them won't work with it.
 

gholmesjr

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Thanks Merc. While I'm waiting for the new rectifier and the tach to come in, I've been doing some research on the issue. On another forum they suggested that a replacement of the upper crank seal and the upper housing O-ring could help as it is old enough to be brittle and cause some air leakage which causes bogging. What's your thought on this?
 

merc850

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Yes replacing all the seals might help, if you pull the flywheel you'll need the Mercury thread-in puller, available on ebay, etc.
 

gholmesjr

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Got the rectifier and the tach installed last night. The old rectifier was completely shot compared to the new one. What should I be looking for now that I have a tach that works hooked up? Should be going out tonight to test it.
 

gholmesjr

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Have another question, the throttle response. When we kick it into gear, it takes a bit for the resistance from the motor to be felt in the throttle stick. Meaning that it takes some distance in the throttle stick to open the butterflies on the carbs. Is this normal? I have an illustration attached that shows what I am talking about. The numbers aren't exact, but give a good basis of what I am talking about. Other motors I've had pick up right as it is in gear, this one has a lull period where the boat goes forward in gear, but doesn't pick up until almost half way down.
 

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