Logo
FULL SITE MENU

Link and Sync 1972 mercury 650 timing belt question

F

franklenz

Contributing Member
I've been pulling what little hair I have left out of my head. The belt alignment procedures in almost everything I've read says to line up the nub on the rotor to the flat raised area on the rotor housing when the timing pointer is lined up with the belt alignment mark on the timing sticker on the fly wheel - after confirming top dead center matched tdc on the flywheel timing sticker. I got this concept and down to a science...... but,

But when I do this, there is not enough adjustment (not even close) to dumb down the timing to 0-3 degrees while idling in gear in a tank. It can only dumb down to 21-23 b/f tdc at best.

Then, I read a post that stated to align the cam, the rotor pulley center, and the arrow on the rotor pulley to "timing line" on the flywheel. (I assume that means where I want the idle timing to be at) I did this, and here are some pics...

I can only align it after tdc or 4 degrees btdc. Which one should I run with before I make adjustments? It will run at both spots, and I have room to adjust to the accurate timing from both spots.

What's your opinion or experience? Is the 1972 timing belt alignment different than the 73-75 engines? Or, is there something completely wrong with my engine.
image_225188.jpgimage_225189.jpg
 
As a follow up....
I can't remember which one I went with, but I got the timing perfect. I adjusted the carbs starting at 1.5 turns out (because the carbs are slightly dirty) - adjusted these for a smooth idle at about 900 rpms. Then, I adjusted the idle stop screw to keep the motor running good while in forward gear. Everything was solid. I took it out to the lake for a test run, and the motor runs fine at wot, and at idle, but....

another issue - while attempting to do hole shots, the engine will bog down and eventually stall - unless I tap the choke flaps a couple of time. When I tap the choke, the rpms go up as normal, and then a nice wot. I assume that tapping the choke causes the motor / reeds to suck more fuel through the carbs, which compensates for the dirty carbs.

There are no air leaks in the fuel lines. Also, the fuel pump is new and pumping well. There is no leaks in any engine gaskets, and the reeds have a solid vacuum pulling through the carb.

The motor will not idle in a tank at 0-3 btdc with the carb throttle completely closed. The throttle flaps have to be slightly open in order for the motor to maintain an idle.

Shouldn't the motor run at idle with the throttle flaps closed? I know that there is multiple holes in the throttle flaps to allow just enough fuel through the system to maintain the idle.


My only guess is that the carbs are gummed up and need to be cleaned / soaked? Agree?
 
Last edited:
As a follow up....
I can't remember which one I went with, but I got the timing perfect. I adjusted the carbs starting at 1.5 turns out (because the carbs are slightly dirty) - adjusted these for a smooth idle at about 900 rpms. Then, I adjusted the idle stop screw to keep the motor running good while in forward gear. Everything was solid. I took it out to the lake for a test run, and the motor runs fine at wot, and at idle, but....

another issue - while attempting to do hole shots, the engine will bog down and eventually stall - unless I tap the choke flaps a couple of time. When I tap the choke, the rpms go up as normal, and then a nice wot.

There are no air leaks in the fuel lines. Also, the fuel pump is new and pumping well. There is no leaks in any engine gaskets, and the reeds have a solid vacuum pulling through the carb.

My only guess is that the carbs are gummed up and need to be cleaned / soaked? Agree?
 
Adjusting the idle mixture screws "1 1/2 turns out" is just a preliminary guesstimation of where they should be--that's all.

You need to warm the motor, put it in gear, and tie the boat down so it can't move (and trick you). Then find the best idle, taking your time and letting the motor settle out after each tiny adjustment.

When you find the best idle, add an additional 1/4 to 1/2 turn OUT (CCW) on both adjustments and she'll ran like a raped ape.

Jeff
 
Yeah, I'll play with that on the water next time I'm out. I'm pulling the cabs today to clean them. On the water, it wi shift into gear and idle and puts along with now issue. I can accelerate with no issue - unless it's a hole shot. The secondary pickup hits right at the spark advance stop at 23 degrees. It just doesn't make sense why I would have to tap the choke a couple of times to bridge the gap between 3000 and 5500 rpms. Once the motor starts to take off - yep it screams. It's gotta be dirty carbs....u think?
 
Nope; too lean an idle adjustment.

On my Mercs, I get the spark advance as close to maximum as possible BEFORE the carbs begin to open. That helps prevent bogging (and improves gas mileage).

Jeff
 
Thanks. I will try that. I just finished taking the carbs off, but I have to go to work. No time to take them apart. I would attach pics, but this site doesn't like my iPhone.
 
Any clue on if the timing belt setting is different on the 1972's than the 73 forward? I know I have it right (dead on with tons of room to adjust), but my brain is boggled as to why I can't find the 1972 timing belt alignment instructions anywhere on line - mentioning that it is different than other years. It does follow the same instructions for older models. I wonder if my distributor is from an older 3 cyl. I did have a 1974 650 that did line up as the instructions state - tab, belt alignment mark, pointer, etc.
 
Also, I agree that it's too lean.....now. But, at that setting it ran great for the past three seasons. Also, compression is 150 on all three - solid! And the fuel pump is new with no air leaks anywhere.
 
Here is a hole shot with the settings I've always used.
https://youtu.be/-hH9dkmzNV8
It started to bog down between 3000-4500 rmps. That's why I believe the carb is getting gunked up. It started to do it at the end of the season last year, but always does it now. I went back to 50:1 oil mix after putting to much oil in it all year last year. I was told by a mechanic that "you can never have to much oil" - he forgot to say it would foul the plugs and clog the carb. Oh well.
 
I noticed this upon removing the carb...

The cap on the top carb is missing? I assume there should be one there. Could it be sucking in air and throwing off everything?

missing cap 2.jpg
 
Yes! You can epoxy a metal washer in there (with the hole plugged, of course). Then, you might find a freeze out plug that size ant a good auto store.

Jeff

PS: Got lots of spare carbs like those if you need a part.
 
Awesome! I can't wait to get it back together today. Everything else on the carbs is spotless besides some surface dirt from fuel run off from tilting the motor. There are no restrictions anywhere that I can tell. I going to give them a quick clean and put it all back together this morning. I will post the video when it's up and running. Thanks for the help.
 
Jeff, Do you have time to accurately measure the diameter of that freeze out plug? I don't want to pop out the one I have, and I have an Inside diameter of .444" for the hole. I just might use a 44 mag shell casing as a temp fix 😜
 
IMG_3811.JPGActually... I was running errands today, and I stopped by a lawn mower repair shop. They had a huge selection of welch plugs!!!! I picked these up for $2.08. Great find.
 
Jeff......"raped ape". All over a $1.04 welch plug - hours and hours of work for that little stupid part. I'm happy though! It'll be in the water tomorrow.
http://www.youtube.com/watch?v=HkGCVp01Huw
 
Put it in the water today, and tried to adjust the carbs under idle load by myself. It's not too easy. I almost got it, but it's still just a hair off. Idling too high in neutral - or, is idling to slow to maintain an in gear idle. Timing is set at 1.5 btdc on earmuffs. I will put it in a tub tomorrow and try to get it perfect. It is running a hell of a lot better though.
Here is some video - the audio is awful due to the gopro underwater housing, but you can still "see" that its getting decent hole shots.

http://youtu.be/PBWPk63RSq4

The boat is a 1967 starcraft super sport v. My son is the fourth generation owner - his great grandfather bought it Nee in the fall of 1967.
 
Here we go again! This is NOT an auto engine! The base timing is irrelevant, only the Wide Open Throttle timing.

Jefff
 
Thanks Jeff. I appreciate the info. Is there a thread you can point me to that has already addressed that issue? Or is as simple as hitting the idle adjustment screw? I definite don't want to aggravate you. Thanks for all of the help.
 
Got it Jeff. Thanks. I re-read the manual, and multiple timings posts with your concept in mind. So let me paraphrase and let me know if I've got it right....
i can static time or neutral time at 0-2degrees btdc.
Then, set the primary pick up.
Then, set my max throttle stop.
Then, set my spark advance to 23 btdc (I do it "static" with engine off, but the key in the run position - then I confirm it with the engine running.)
Then, start the engine and put it in forward gear while in a tub or a lake.
Then, adjust the idle stop screw and the idle mixture screws to get a good running idle at 550-600 rpm's - I may have to go back and forth between these two (card and idle stop screw) a few times to get it right.
So, ultimately I might be at 8, 5, 3, or 0 degrees btdc (or anywhere in between) at idle in forward gear.
Wherever it ends up does NOT matter - as long as it's smooth?
So, now that I go back and read all of the forums, and my manuals on the timing - it merely says "primary throttle pickup = 0-2 btdc". It doesn't mean/say idle in gear at 0-2 btdc, just set the primary pickup there.

Am I correct?
 
I took your advice and got everything just right Jeff. Thanks for the help. I got to thinking that there should be a significant difference in my spark plugs due to running on one carb (the bottom one) most of last season and half of this season. I replaced them this morning, and this is what I found. The above picture....
 
From left to right... Top / middle / bottom. 1,2,3. I'm lucky I did not blow the top piston. It's still got 150 psi and no melting/marring.
 
Back
Top