HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

BrettNC

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I have a 1985 75 HP Mecury. I'm trying to determine the correct timing at idle just as the carbs begin to open. I have contradicting information:

Clymer Service Manual: 2 ATDC-2 BTDC
Seloc Service Manual: 7-9 BTDC
Sticker on air silencer cover: "4 ATC when running"
Clams' link and synch guide: 4 BTDC

At the point where the carbs just begin to open, the most that I can advance the timing is 2 degrees BTDC.

What is correct?
 

hkeiner

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

If you provide your motor's serial number, I am sure someone can look it up in a Mercury shop manual. A Mercury shop manual would be the most definitive source for the correct timing specs.
 

Laddies

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

The 75HP is 1 to 5 degrees ATDC according to a Mercury manual but what do they Know
 

ICEMAN

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

The manuals you have are generic. The manufacturer has placed a sticker on the air silencer. Hmmmm, would they spend the money for this sticker, just to throw you off? Or, could this be what the manufacturer suggests as the correct setting, for your motor? I would go with the sticker, after all, mercury did not print the manuals you have.
 

BrettNC

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

Lose the sarcasm. The silencer cover may not be the original one with the engine. Manufacturers sometimes change the specs at a later time. These manuals have specific values for this specific motor. That's not what I would call "generic". The motor idles better at 1 ATDC than it does at 4 ATDC. I just wanted to make sure my timing is acceptable and that I'm not detonating.

Most people come to this forum for information and to ask questions. Lifeless dolts come here to act in ways that make them feel superior. If that is your deal then get lost. Your post was useless.

The sticker obviously didn't give all of the information needed.

Good thing I asked, huh?
 

hkeiner

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

When I first attempted to do a link and sync on my motor, I got confused over what the Mercury shop manual's specified IDLE timing spec really meant. The idle timing spec was shown as a range (e.g., 2 to 9 degrees ATDC) rather than as a specific timing value, like that provided for the WOT timing spec (e.g., 21 degrees BTDC). As a result, I didn't know where exactly to set the idle timing. I too was concerned about setting the idle timing wrong and causing engine problems.

What I learned was that the manual's SPECIFIED idle timing range is just to get you close and within reason of what it should be. The ACTUAL idle timing is adusted again later in the link and sync process to achieve a certain engine RPM at idle with the motor in gear and in the water. The ACTUAL idle timing should end up somewhere within the specified range. This somewhat obscure (to me) bit of knowledge was a big help to me in understanding the idle timing specs and timing adjustment process. In short, as long as all the link and sync steps are followed in the correct sequence and the engine idle speed is at the correct RPMs, then the ACTUAL idle timing is set OK. Funny that my Mercury shop manual (and my Seloc and Clymer manuals) did not explain this. I had this explained to me by someone on this forum.

I hope the above is helpful to you. However, it is possible that your motor's link and sync process is different than for my motor and that my above comments do not apply to you.
 

domains

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

Just depends what your doing with the motor,setting timing ahead will give more power but harder on motor.
 

ICEMAN

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

sarcasm woops, my bad....



Anyway, according to Mercury manual # 90-86134-4, which is for this motor. (unless you supply serial number which will let me check if there is a different manual) On page 2C-1 in the chart on the top of the page it states: throttle pick-up timing 1-5 ATDC (75) If we turn the page in our Mercury manual to page, 2C-2 it states: 2. Pre-set carburetor idle mixture scres at 1-1/2 turns out from lightly seated position. 3. Connect Timing Light to No. 1 (top) spark plug. 4. With engine running in forward gear, move throttle lever so that throttle primary pickup cam just touches primary pickup on carburetor cluster, as shown in figure 3. Then without moving throttle lever, adjust primary pickup screw(figure 4) so that the timing pointer is aligned specified throttle pickup on timing decal. retighten nut on adjusting screw.
Step 5 goes on to tell you to set high speed timing. (again, located on timing decal)

So I don't know about the (YES GENERIC) manuals you are using, but the Mercury manual states to use the timing specified on the decal.

If these two manuals are so good, why do the two of them give conflicting information, as you state in your post.

Numerous times, people have come to this forum and asked what is the best manual for thier motor. The answer is the one from the manufacturer.

If the intake silencer was changed, someone should have been more careful
 

hkeiner

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Re: HELP! Clymer says 2 ATDC-2 BTDC, Seloc says 7-9 BTDC for idle

3. Then without moving throttle lever, adjust primary pickup screw(figure 4) so that the timing pointer is aligned specified throttle pickup on timing decal. retighten nut on adjusting screw.

Since the idle timing spec is a range, do the the link and sync instuctions include another subsequent step to RE-ADJUST the idle timing to achieve a specificed RPM? Something like the following step out of Mercury Manual for 75hp motors with serial numbers S/N 0A996142 thru 0D283221?

I ask because I want to know if my current understanding of how to set FINAL idle timing (as described in my previous post above) applies to this motor as well. If not, then I know to be more cautious in providing my comments to others on this subject. If yes, then I am more reassured that I pretty well understand how to set idle timing on outboards in general. I am in learning mode too but I believe that while correct idle timing on a 2-stroke is important, correct WOT timing is much more important. Thanks.


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Idle Adjustment - Holding throttle arm at idle position, adjust idle timing screw to attain an engine idle RPM of 650-700 RPM in “Forward” gear. Tighten locknut and turn off engine.

NOTE: On this type of engine, idle RPM is adjusted exclusively with ignition timing.
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