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how do I set the idle timing on a '75 850 merc?

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after a motor overhaul, which didnt run correctly to begin with, I am trying to get the timing set correctly... it is supposed to be set at 4 BTDC at an idle, and the max is supposed to be 27 BTDC....

the engine starts and runs but it seems to load up... I have a smart tach to set the idle speed with, and I found top dead center with a dial indicator and adjusted the pointer so it points to "0" on the flywheel.
the distributor index marks are as close as they can get (the dist gear mark is slightly to the left of the index mark on the case)..... when I place a timing light on the motor at 900 rpm, the flywheel shows its running at 1 degree BTDC.... How do I adjust it so that I get 4 BTDC?.. Thanks
 
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Okay. First of all, this is NOT an auto engine! Timing at idle is irrelevant on a two stroke engine; the only thing of importance is WOT timing, which is 27 degrees on this motor (though I'd run a degree or two less thanks to our crappy gas). Idle speed is attained PURELY by reducing spark advance, with the carbs already fully closed.

If the motor "loads up" in gear and under load, that's usually one of two things: The carbs are set too lean (yes, too lean), or the carbs are opening before they should--the motor should see nearly full spark advance BEFORE any significant carb opening. Again, this is NOT an auto engine.

Good luck.

Jeff
 
I understand fully that it is not an automobile engine:) and that is why I dont understand how to adjust the timing at idle.... or at WOT for that matter. but I do know its not right.

the previous owner of this motor had the distributor out of it and adjusted things that shouldnt have been adjusted in an attempt to make it run right with broken rings, NO restrictors and out of sync carbs....and now that I own it I am trying to get it right.

timing may not be as important on these motors at idle as it is at WOT, but its still out of its preferred range at idle.
as much as I have been able to understand from reading about the subject, if you dont make the proper adjustments in the correct procedure, the later adjustments may not be able to be dialed in at all.

I have the carbs opening at the same moment, but im not sure how to get the timing set correctly.... do I turn the distributor until I get it to read 4btdc, then, DO I LOOSEN the screws in the plate at the top of the distributor to get the carbs back to idle speed?.......


and as you said "the motor should see nearly full spark advance BEFORE any significant carb opening" do you mean the advance should go to the full 27btdc just as the carbs begin to open, and then climb to WOT?.....

the timing is off for whatever reason, and it needs to be set right so the motor will run correctly and develop the power to push a 17ft boat on to plane... it didnt do it before the rebuild, and it doesnt do it now and the only thing that I can find that isnt right is the timing... and possibly the sync of the carbs, if I understand you correctly...
 
FACT-----------Idle timing is the point where throttle plates open !!-----------So it is NOT a timing adjustment.----------It is a carburetor / linkage adjustment.-------------Set the full throttle spark advance and you are done with TIMING ADJUSTMENTS !-------AS stated you need to fully grasp this concept .-----------It is not the same as setting the idle timing on a 1964 chevy 283 motor.
 
ok.. I grasp the concept that its NOT an Automotive engine, and I can grasp the concept that is NOT a timing issue, but it is a timing advance issue... still, NOT one of the experts on this site is willing to describe how to set the throttle linkage to the proper idle, after I set the distributor advanced to where it needs to be.... surly someone has had to set up the advance to the carbs at sometime in the past

I can get it to the proper idle speed but at that time its only running at 1btdc.... I can also get it to the 4btdc that im looking for, but then its running at nearly 1900 rpm.... where do I make the adjustment to separate the advance from the throttle plates so it will be at 4bdtc at the proper idle speed?...
 
You're doing it again! FORGET the idle advance measurements and set the WOT advance only.

Get the carb mixtures adjustments best as you can, then retard/ advance the spark enough to have her idle where you want it.

Jeff
 
Once more , you do not care what the timing is when the motor idles smoothly.-----As timing advances when motor speeds up the throttle plates are still CLOSED.-----------------The throttle plates open up when timing reaches 4btdc.----------Get the AUTOMOTIVE setting thing out of your head.------You are getting good help here , but you need to accept what is preached.
 
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