Ignition Timing Conundrum

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Ignition Timing Conundrum

Postby Andy E » Mon Mar 20, 2017 4:28 pm

Hi All

I'm after advice again please. My 1956 AJS 16MS (Now 500cc) is fitted with a Lucas N1-4 magneto in place of the SR1 which would have been fitted in 1956.

I have finally sorted out the poor starting problem of the last year or so when I realised that the spark plug gap suggested for the N1-4 is 0.015" to 0.18". I had set the various plugs that I had tried to 0.020 to 0.22" as shown in the handbook for the 1956 bike. It now starts as it should do.

I have recently carried out a top end rebuild and the original flat topped +0.040" wire wound piston has now been replaced by a new +0.060" piston from the club spares scheme. This piston has a domed top, so I presume that the compression ratio is now higher that it was.

My experience with the differing spark plug gaps and the potentially raised compression ratio now leaves me wondering what I should do about the ignition timing. The 1953 manual for the bikes fitted with the N1-4 shows that the timing should be set at 7/16" BTDC fully advanced. I have set the timing on my bike to 1/2" BTDC fully advanced as shown for the 1956 bikes.

I'm relatively new to these bikes, so any advice would be much appreciated.

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Re: Ignition Timing Conundrum

Postby Brad » Mon Mar 20, 2017 4:44 pm

Hi Andy.
Can't comment on your compression ratio query, but with regard to the ignition timing, many people here reckon that 7/16 before TDC is the way to go.
It seems that this setting is best suited to modern un-leaded fuel. It certainly works ok in my G80.
If it ain't broke, fix it till it is. ;)

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Re: Ignition Timing Conundrum

Postby raffles » Mon Mar 20, 2017 8:47 pm

I have been running my 1956 G80 for 37 years with 8.5 to 1 compression and timed 1/2 inch before tdc usually buying fuel from Tesco it has never failed to start within three kicks and has never let me down.
Tony

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Re: Ignition Timing Conundrum

Postby Andy E » Mon Mar 20, 2017 9:00 pm

Thanks Brad / Raffles

Hmmm, maybe I should set it at 15/32". :D

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Re: Ignition Timing Conundrum

Postby Expat » Tue Mar 21, 2017 1:13 am

Hi Andy,
Re ignition timing, used to set mine at half inch before, then a couple of wiser men than I on this forum reckoned that 7/16" or even 3/8" was fine with modern fuels AND was easier on the crankpin. :)

So, sympathetic pushover that I am, it is now at 7/16". :D

Haven't noticed any difference in how she runs.

Regards,

Steve
Keep shiny side up.

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Re: Ignition Timing Conundrum

Postby 56G80S » Thu Mar 23, 2017 7:30 pm

First, I do it the old fashioned fag paper way.

But I do err on the side of less before TDC than the full 1/2". Thing is if the points aren't spot on in the first place then it all turns into a bit of a lottery.

Points first, timing second.

Johnny B

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Re: Ignition Timing Conundrum

Postby Expat » Thu Mar 23, 2017 11:49 pm

Totally agree re the points gap John but now I use my multimeter on the resistance audio setting, one clip on the breaker spring, the other to earth and when it goes silent, the points have opened. :D

Regards, Steve.
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Re: Ignition Timing Conundrum

Postby Andy E » Sun Mar 26, 2017 7:00 pm

Well I reset the ignition timing method to 7/16" BTDC. Having just got back from a 25 mile test ride, I can honestly say that I didn't notice any difference in starting or running performance. I was taking it easy though due to running in the bike in after a rebore and new piston.

I really have got to like this bike and I'm looking forwards to putting some miles on it this year. Thanks for the advice on this and the earlier push rod tube issue. :beer:

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