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| Explain the spark control on old engines |
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narrabay
Member
Username: narrabay
Post Number: 12
Registered: 02-2016
| | Posted on Monday, February 15, 2016 - 04:39 am: | 
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I understand the basics, but how does it work in practice. Where to set for starting, and what to do with the spark advance lever when running? I would guess you move the throttle and then adjust the spark timing? Thanks! |
miro
Senior Member
Username: miro
Post Number: 845
Registered: 11-2001
| | Posted on Monday, February 15, 2016 - 07:57 pm: |
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Most of the old 2 cycle marine engines vary the speed by changing the timing.
The throttle setting is more or less left alone.
To start, you set the spark timing to be retarded,i.e. after top dead centre (TDC).
You can then prime the cylinder, and flip the flywheel over TDC and it should start. If you have a compression release, use it.
If however you have good compression, it might be a bit of a chore to get the piston over TDC.
Alternatively, you prime the cylinder, retard the spark, and then flip the flywheel back wards, against compression so that the igition fires. That should cause the engine to turn forward and hopefully, keep running. It's called bounce starting.
Once the engine is running you can advance the timing so the engine runs better ( and faster) .
Running the engine fully retarded for a long time is not good - usually overheats the engine and exhaust areas.
You can check You Tube for bounce starting - there are several good examples there.
Miro |
eric_schulz
Senior Member
Username: eric_schulz
Post Number: 103
Registered: 01-2007
| | Posted on Monday, February 15, 2016 - 09:07 pm: |
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Opening the throttle on an engine and then slowing it down by retarding the spark is like setting the speed on your car engine at 2000rpm, putting it into drive and controlling the speed with the brake pedal. Just horrifying. Just because some people did this 100 years ago, we should not do it now. It is a good way to waste fuel.
Timing, even for starting, never needs to be after TDC. You tune an engine by ear, both fuel and spark. Set it where it sounds the happiest.
Eric |
johnoxley
Senior Member
Username: johnoxley
Post Number: 153
Registered: 04-2010
| | Posted on Monday, February 15, 2016 - 11:57 pm: |
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Miro may be talking about pre-carby engines - The vaporiser or lift valve mixers were sensitive to fuel adjustment and required adjustment at every speed. Controlling speed with the timing allowed control of revs without the constant need to adjust the mixture. You usually only had a range of say 100 to 400 rpm anyway. I could get my old 5" bore Union to idle at 60 rpm but this required exacting adjustment of mixture + timing and you had to get the low compression setting correct (via exhaust tappet clearance).
Andy |
narrabay
Member
Username: narrabay
Post Number: 16
Registered: 02-2016
| | Posted on Wednesday, February 17, 2016 - 09:02 pm: |
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Found this video of spark control in action, and is that a vaporizer or carburetor? and reversing on the fly, pretty cool. Another question, this is a 2 stroke engine?
https://www.youtube.com/watch?v=1FbLzBkH4Ic |
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