'72 merc 1150 timing clarification

[monk-monk]

Im confused about something, i've read the timing sync page where it states the amount of retardation determines idle speed, and then goes on to say when the throttle arm is advanced the timing advances toward TDC and then to before TDC and just as it is passing TDC it should just begin to pick up the carb cluster....are you telling me the initial engine timing is actually AFTER TDC!!? And if so how far ATDC should it be timed...just don't get this sequence...!!

 

[AMD Rules]

Re: '72 merc 1150 timing clarification

Hey monk..haven't heard from you in a while...

The emphasis for primary timing event is that the timing is essentially moving from slightly retarded timing (ATDC at idle) to slightly advanced timing just as primary pickup makes contact (BTDC for primary pickup). As you've read, this is typically around 3-4 degrees BTDC.

Max advance is 21 degrees or less.

Hope that makes sense.

 

[AMD Rules]

Re: '72 merc 1150 timing clarification

Suppose I should mention that the factory manual says to set primary pickup at TDC to 2? BTDC ,for the '72 1150

 

[monk-monk]

Re: '72 merc 1150 timing clarification

thanks, now i believe i have an issue. when i remove all plugs except for #1, put the timing light on it, crank it, it is not slightly retarded, it is probably more like 10 or 12 degrees retarded, i have to advance the distributor nearly 1/3 around in its rotation to get to passed TDCand the primary pick up has already engaged the carb cluster. but it seems to start very well! what do you think?

 

[AMD Rules]

Re: '72 merc 1150 timing clarification

Are you investigating timing to cure a performance issue, or just trying to review it to ensure its okay?

This is when I ask if you've confirmed your timing pointer and piston TDC agree with each other, verified?

I wouldn't be concerned with how much the spark is retarded with the throttle at the idle position. Its variable motor to motor, and changes based on where your idle stop is set to achieve the desired idle rpm. These things will start with the idle timing all over the place, and will run with only a few plugs firing but certainly won't run well at any significant speed that way.

I would aim for primary pickup (0-2?BTDC), and maximum timing (21?BTDC) , as that is what should give you the most reliable, safe performance. The motor needs to be slightly advanced before hitting the primary pickup for good throttle response, and at maximum advance just before the secondary throttle pickup kicks in, to yield a good hole shot.

 

[monk-monk]

Re: '72 merc 1150 timing clarification

Im trying to get it to idle better when i put it in gear. i have worked with the idle mixture screws and have achieved good results (1-7/8ths out on all) i have turned them out to about 2-1/4 but when i throttle up it sounds funny and i really don't know how to describe that sound. i have a pretty good feel and ear for how its doing when i make adjustments. i have it as close as i ever have, its about a 50-50 when i put it in gear, it might do good one time and will stall the next time i put it in gear. i do know that the max advance is 21 and it idles in neutral at 950 RPM's. from what you tell me, and what i observed from the timing light it seems like it might be engaging the primary pick up BEFORE that 2 degree BTDC, it was engaging ATDC...not 2 BTDC

 

[tashasdaddy]

Re: '72 merc 1150 timing clarification

hey, ole, clams, left this for us. i have used it worked great. http://forums.iboats.com/showthread.php?t=168855

 

[AMD Rules]

Re: '72 merc 1150 timing clarification

That's the procedure Monk already quoted in the first post, and is already trying to follow.

 

[Moody Blue]

Re: '72 merc 1150 timing clarification

Is it possible that the distrib timing gear is out of "sync" with respect to the crankshaft, thus creating a false timing situation?

Could be it has jumped (or been moved) a tooth or two from what it should be.

 

[daveswaves]

Re: '72 merc 1150 timing clarification

Is it possible that the distrib timing gear is out of "sync" with respect to the crankshaft, thus creating a false timing situation?

Could be it has jumped (or been moved) a tooth or two from what it should be.

Good thought MB, but not likely on this engine. If you are off by a tooth on the drive belt the problems would be much more dramatic. Good luck on the lake tomorrow with your 80 hp.