Model B Ignition Timing

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tony.barnett
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Model B Ignition Timing

Postby tony.barnett » Fri Apr 03, 2015 2:06 pm

Just about to put my mag back on and started to wonder about what to set it to. As its a blind head I have nothing to poke a stick down to set it advanced, so was planning to go TDC fully retarded (I know how that feels...).

Any thoughts?
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Re: Model B Ignition Timing

Postby dave.owen » Fri Apr 03, 2015 3:18 pm

Generally works well for OHV, for SV may be a bit more retarded..not sure how to set with a blind head.but you could set as you say and use the advance /retard to find the sweet spot.

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Re: Model B Ignition Timing

Postby tony.barnett » Fri Apr 03, 2015 3:35 pm

I'll have to whip one of the valve caps off Dave. Should be able top see the piston for setting TDC but setting fully advanced might be tricky.
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Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
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Re: Model B Ignition Timing

Postby tony.barnett » Sat Apr 04, 2015 10:22 am

Just read the 1930 Owners Guide on the Knowledgebase - it says to set timing fully retarded at TDC for both SV and OHV bikes. Gives approx. 7/16" advance, apparently. Don't know why I didn't think of looking there before.
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Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
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Re: Model B Ignition Timing

Postby Knud.Degnbol » Sat Apr 04, 2015 3:22 pm

Don't it have a primer, you can unscrew? My model A have.

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Re: Model B Ignition Timing

Postby tony.barnett » Sat Apr 04, 2015 7:05 pm

No it doesn't Knud. That would make it easy ;-)
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Re: Model B Ignition Timing

Postby leon.mitchell » Sun Apr 05, 2015 8:35 am

Hi Tony,
Points just opening at TDC fully retarded is a good recipe for the side of the road, but there are many reasons to set the timing so that fully advanced corresponds to normal running. For most vintage side valves 35 degrees before TDC fully advanced should be about right. A degree disk on the end of the crank will do the trick.
The nominal "swing" between advanced and retarded on a magneto is 30 degrees. If it runs at half engine speed the TDC/fully retarded technique will give 60 degrees advance when the lever is set to full advance. If someone has been at the magneto with a file, the spark could be anywhere when fully advanced.
Cheers
Leon

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Re: Model B Ignition Timing

Postby keith.hodgenia » Sun Apr 05, 2015 8:46 am

Has anyone every checked how accurate the "sweet spot" an experienced can feel actually is?

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Re: Model B Ignition Timing

Postby leon.mitchell » Sun Apr 05, 2015 11:50 pm

I think it varies from bike to bike - some seem very sensitive to ignition setting, others not. I once set my 1914 Rudge to 40 deg BTDC (the argument was that modern fuels should allow more advance) but that seemed over-advanced compared with the usual 35. Of course I knew what the setting was, which is why testing drugs is done with one group on placebo! My guess is that settings within +/- 5 degrees of the correct setting would "feel" OK to all but the most expert.

However there is only one place the magneto gives its strongest spark - when the points open at the maximum flux point. On a new or properly rebuilt magneto this is the full advance setting on the magneto. That's why it's best to time the ignition on your motor to use the best spark (full advance on the magneto) at normal touring speeds.

Leon

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Re: Model B Ignition Timing

Postby tony.barnett » Sat May 23, 2015 8:37 pm

Bit of feedback - I set the ignition TDC fully retarded as suggested in the literature. Bike runs a treat. You do have to search for the sweet spot with the ignition lever but it seems to respond fairly well. And the mag modification has resolved the problem starting. No problem last weekend starting it no matter how hot. And no need to bump it at all. Very pleased about that.
KOBI
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Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
Velocette MAC
Honda C70ZZ
The Offroad Fleet - Fantic 200, Bultaco Pursang, Beta Rev 3


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