Home › Forum › Ask A Member › TDC timing tool recommendation › Re: TDC timing tool recommendation
zul8tr that is a great write up on getting the timing nailed down. The same process that I was going to use more or less. I was planning on using my analog dial gauge for this process as well. The mag will be locked at the full advance location as you stated as well but my motor has a recoil on it so I should have better luck with kick backs not throwing the rope at me. Right now it is a very easy starting motor even with it not being adjusted properly yet.
Does anyone have a good place to start with the timing for btdc? I have been told by an old racer that I want it between 0.350 and 0.400 and I will just have to play with it until I find what it wants on my boat and altitude etc. Does that sound right? The main thing is getting the two cylinders to fire at exactly 180 apart from each other. I know the service manual for a mark 28 calls for 0.275 but I am not using this block for what it was intended so further advancement makes sense.
Thanks again for the help
ryan
Ryan
I recently set the timing on an engine like that for a friend. His engine had a lot of wear slack in the linkage and that needed to be fixed before doing the timing. How is your linkage ❓ Once linkage fixed I set his at .235" since a stocker used for fishing and it runs great. For you I suggest not to start too aggressive. Not knowing what rat work was done I recommend .320", .400" is way too much, perhaps work uo to 0.350"with testing. To determine the best timing for your engine and rig I do a run for about 3000 ft top speed with a tach and speedometer, when rpm and speed peaks and does not fall off I go a bit more. When fall off is noticed back off.
Timing also a function of how you will use the boat, when I raced APBA best top speed does not always win it’s how quick you go around the race course. Carb jetting, fuel ratio and octane is also a function related to timing. I run 87 E free in the Merc 25ss and the Yamato Y80 at 16:1. Always over 7000 rpm. These engines are low compression with effective compression ratio measured based on the top of the exhaust port, they usually fall around 6.5:1. You want fuel that burns fast.
What plugs are you using, projecting with cut back ground electrode recommended ❓
Once the points and timing is set like I described above you can always advance the locked mag and timing of points balance should still be very close. Can always check with buzz box and dial gage without pulling the flywheel if you have a 2 wire kill switch with a wire to each set of points terminal. Then just connect the buzz box to the exposed kill wires put the dial gage in the cylinder and check BTDC. Note timing the engine as I note is the best way to get the points to fire at exactly the same BTDC position and takes into account that there is some wear and looseness in the connecting rod, pin and crank bearings assembly. Put a kill switch on the mag and have the lanyard attached to your wrist in case you cartoon out 😮 , that will kill the engine electrically. Do you have a full butterfly in the carb to stop the air flow when you let go of the deadman throttle ❓
To save the recoil broken rope from kick back with locked full advance my process is to pull out about 12" of recoil slack before pulling over the engine. In case of kick back there is enough rope slack to deal with the kick back and prevent a broken rope from the handle going into the recoil. Get the tools 😡
Pete