Link and sync

[shadowrider]

I'm back. trying to start over. Motor is a 73' merc 850 ( ser.# 3495920).
I recently aquired, have triple checked tdc, pulley/flywheel alignment. It is right. Compression is 140 on all 4 cyls. Max timing was set around 34 Deg. My spec is 27 Max. The spark adv screw is not long enough to stop dist at 27 deg. It is original screw with red tip. Just does'nt make any sense to me, that a factory screw is not adequate. Any thoughts ?

 

[emckelvy]

Re: Link and sync

Something is set up wrong or something has slipped. 34 deg is way too much and will burn up the motor from detonation.

Even the factory setting is too much for today's fuels. You should back it off at least a couple of degrees. The most common cause of way-too-far-advanced max timing is being off by a tooth or 2 on the dist belt setup.

The other thing I've seen happen is the drive pulley (on the flywheel) gets cracked then with wear/vibration moves back and forth, affecting timing. This is a very difficult problem to diagnose and usually you have to pull the flywheel to see it. Definitely has to be pulled to replace the pulley if it's bad.

Something else, how's the timing lite? If it's one of those with an adjustable timing bias, maybe there's something wrong with it. I'd check it against a known good lite and see if it reads differently.

BTW the factory spark-advance screw normally doesn't have to be turned-in more than about half-way to get the correct timing setting. So you're gonna have to look beyond that to find your solution.

Last thought, have you run it yet? How's the idle speed adjustment? Usually if the timing setting is all out-of-whack the idle speed screw will be way in or way out. It normally sits in the middle-range of its adjustment, too.

HTH..........ed

 

[shadowrider]

Re: Link and sync

Before messing with it, It seemed to run ok. Timing light is an older version from the 70's. Dont think it is 1 tooth off belt, as that throws alignment way off. Idle jets are at about 1&3/4 turns from seat. I have another timing lite about same vintage I could try.

 

[shadowrider]

Re: Link and sync

I tried my other timing light and it reads the same. With adv. screw all the way in I am getting 30.5 deg. I guess I can move it one tooth on belt to see if it comes to a more normal setting on the screw.

 

[shadowrider]

Re: Link and sync

I should mention that this motor has a jet pump.

 

[shadowrider]

Re: Link and sync

O.K. I moved dist. pulley 1 notch and that did it. Was able to complete link and sync. However, arrow on pully does not point to center of crankshaft. Will have to take it out and see how it runs now.