Page last updated July 17, 2008



Timing 650

This particular engine was a pain in the !@#$@ to get timed, at least for me.

You need to make sure the idle RPM is set according to Mercury's recommendations. For this engine, IDLE should be around 500 - 600 range.

You get there by placing engine in water and placing gear in FORWARD. Depending on propeller size and varoius other conditions (carburetor), your idle speed will differ. I currently have an 11 pitch prop installed and after adjusting the carburetor, I managed to get the idle to 600 RPMs.

But also, you must adjust the primary pickup to just "barely" touch at 3º - 5º BTDC . Primary pick up point is where the arm starts to touch. See pic above.

So the first thing you must do is select a good prop size. Propeller diameter and pitch will determine resistance.

Higher pitch usually means higher speed and lower RPMS (more resistance and prop goes through more water than a lower pitch prop, this is great for speed, getting there in a hurry and more fuel efficient)

Lower pitch means higher RPMs and lower speed at WOT (great for bigger loads or lots of people, no hurry, just need to push a heavy boat, less fuel efficient)

RPMs for the 650 should be at 4800 - 5300 at WOT (wide open throttle). If you find you are higher than that 5000, you should consider increasing the pitch of the prop to decrease the RPMS (higher RPMs tend to wear engines down)

Generally, increase / decrease of pitch by 1 will increase / decrease RPMs by 200. THEN.....


OK. a few preparation steps before you time engine. The black mark needs to be aligned with the timing pointer tool. If you don't have one, they are very hard to locate. Ensure the timing pointer is pointing at the THICK black mark. Then......




Make sure the tab on the pulley is aligned with the mark on the distributor adapter. If it is not, pull the pulley cover off the pulley and slip the belt so that everything is aligned. now the engine is ready to be timed. It is impossible to time the engine unless you are operating with resistance, meaning you need have boat in water to time it.


1. While in FORWARD gear and with engine in water or barrel full of water (only forward, not neutral)

.. Adjust the distributor screw until desired RPMs of 500-600 are obtained. Please note that if you have a higher pitched prop and when you adjust idle with forward gear engaged (more resistance) the engine will throttle higher RPMs while in neutral (less resistance).

NOTE: You must adjust the idle while in FORWARD gear or you will stall engine everytime (FORWARD has more resistance than NEUTRAL) If you adjust idle in neutral, you will achieve 500-600 RPMs, but when you switch gears, the RPMs alway drop around 200 RPMs (based on PROP size), so your FORWARD idle will now be at 400 RPMs instead of 600 RPMs and it will stall engine.

2. Adjust primary pickup... CAUTION - WAIT FOR A CALM DAY - NON CHOPPY WATERS DAY - if choppy, then you chance being thrown out of the boat. As the boat skips along the lake, it will bounce up and down. Very Dangerous... Ok, not that dangerous, it can be accomplished by anyone as long as you are careful and not stupid about it. Fly wheel is turning since cover is off...DO NOT TOUCH FLY WHEEL Area, if you do, you are retarded and you will lose fingers or be careful..don't do this if you have had a few beers.

NOTE: This is dangerous....extreme caution is advised. You must tie or secure yourself so that if you slip, you stay inside the boat. You really don't have to be very close to motor in order to time it. Point / Head the boat so that your "shadow" hits the motor. This will allow you to see the flash of the timing light clearer than with the sun directly on the engine (so high noon is not a good time) .Also, make sure your partner that can hear / see you. If you slip, you don't want to slip out of the boat.

After all safety measures are in place, while in open water, place gear in forward and slowly increase throttle until primary pickup just barely touches throttle cam(see picture above). It should be reading at 3 - 5º BTDC while it barely touches. If it does not, the you must adjust the idle stop screw accordingly.

NOTE: If your timing is way off, you may find yourself having to adjust the idle stop screw because you need room for the IDLE STOP SCREW to get it at 3-5º BTDC. You'll see. If you find yourself messing with the idle stop screw position, you will need to VERIFY the DISTRIBUTOR idle position again. It mess up the idle settings. You may find that adjusting the primary pickup or getting it in the ballpark FIRST may be a better solution, then adjusting the distributor idle screw.

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