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Setting timing with strobe.
fogrider:
Strange differences indeed ! Most 4 cylinder cars with a standard .012" to .015" points gap are set around 50 deg dwell. I have used my old 4 cyl dwell meter on a few 4 cyl hondas' and 25 on the 4 cyl scale is 50 on the bike. That's a good figure for spark production and always works a treat. My 550f is set at that and I'm very happy with the performance
Always interesting to hear what others are doing though.
Regards all.
Seabeowner:
I think the actual dwell on the Hondas is about 50% (180deg or 45 on a 4 cyl scale) Correct me if I'm far out.
What I am not clear on is that the dwell is set to give the inductive coil sufficient time to fully "charge" and also not over tax the coil. But is it set so this is sufficient time at maximum rpm? (3.3ms at 9000 rpm) And therefore an overly long time at lower revs.
Also are electronic ignitions set so the give a fixed charge time at all rpms? So power drawn will be a lot less at idle say.
K2-K6:
The relationship of dwell to the effect it has is quirky and worth looking at.
Dwell being geometric and represented as an angle, but the effect it has on the coil is purely time based.
When you set dwell at X rpm it gives the coil a time period to charge based on that rpm. But as you increase speed of crankshaft the dwell is still a constant geometric angle, but with the time base now decreasing. The coil just gets less time to charge.
As most points fired cars are going to see a maximum 5000 rpm generally it doesn't get too short.
But these fours see twice that, with attendant reduction in coil charge time. Effectively you need to set dwell as much as you can get away with for these bike engines, hence the difference in views above.
It's one area that electronic systems can control more effectively, they generally are designed to produce a dwell they control as the same time throughout the engine rpm range, triggered at timing for both on and off coil cycles independent of geometry.
K2-K6:
--- Quote from: Seabeowner on May 12, 2021, 10:26:41 PM ---I think the actual dwell on the Hondas is about 50% (180deg or 45 on a 4 cyl scale) Correct me if I'm far out.
What I am not clear on is that the dwell is set to give the inductive coil sufficient time to fully "charge" and also not over tax the coil. But is it set so this is sufficient time at maximum rpm? (3.3ms at 9000 rpm) And therefore an overly long time at lower revs.
Also are electronic ignitions set so the give a fixed charge time at all rpms? So power drawn will be a lot less at idle say.
--- End quote ---
Crossed over with you there while typing :)
They accommodate error with coil resistance on these systems, using 5 ohms to avoid overheating them at low rpm but sufficient to cope with charge rate at the higher end as I understand it.
As example, if you put 3 ohm coils on there they'd overheat at low rpm use (ignoring system switching requirements) but may be ultimately better at continuous high rpm when needing less time to fully charge them.
fogrider:
Seabeaowner uses the correct terminology for dwell, %, not degrees, I've said degrees from the year dot, no idea why !
50% is the way to go for a points gap of .015."
I've had old Fords that have the points at .025", dwell for them around 40% I seem to remember.
A bit of discussion is good education, great forum this one.
Regards all, Terry
East Yorks.
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