SQ4 Misfire

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simon.holyfield
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Re: SQ4 Misfire

Postby simon.holyfield » Thu Oct 11, 2018 12:02 pm

Thanks Keith, there are some good tips there. The plugs are relatively new, but the bike uses a pair of VRLA batteries in parallel, which must have been there 5 years or so.

I've ordered some new advance springs from Drags - if I get those in the next day or two I'll charge the batteries and see how I get on.
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

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Re: SQ4 Misfire

Postby john.bebb » Thu Oct 11, 2018 4:14 pm

Marvelous paraphrasing Paul! - I realize that many will object to the following remedies for misfires (for sake of "originality") - but do remember that when our bikes were first built - "petrol" was a quite different liquid concoction! - so, notwithstanding the modern petrol variants: -
Ignition; - send your distributor to Kirby Rowbotham for conversion to pointless & use a Boyer Bransden electronic ignition...
This mod replaces the mechanical retard advance with a far more reliable electronic system.
((Odd springs? - what matter?? - Think of the physics & mechanics - the spring of higher torsion will ALWAYS prevail)).
Such can all work at 6V but if the pennies can run to it, the same is better if fed at 12V via a modded (Kawasaki) Alternator c/o Iron Horse Motors...
((to the best of my knowledge; - such is the ONLY 12V alternator conversion truly capable of meeting its claims)).
This has the added bonus of being able to see & be seen at night!
Fit a NEW ignition coil - there is little hope of identifying internal insulation breakdown which may only occur at certain running temperatures.
Carburation; - Scrap the old Solex (maybes keep for posterity) & fit an Amal 626 @ 1". Flare the head inlet manifold to remove the step.
Fit such carb with main jet = 220... anything smaller and you may well be overheating - wasting a bit of fuel far outstrips the costs of a major rebuild!
Cheers, John

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simon.holyfield
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Re: SQ4 Misfire

Postby simon.holyfield » Mon Oct 15, 2018 8:50 pm

Right, my fellow Squarielisti, I have news.

First, the open circuit battery voltage is 6.2 V, on a bike that has not run for a week or two. I'm happy with that.

Second, removing the tank, rocker covers & HT cabling reveals that the tired rocker cover seals (no one should use fibre gaskets at those temperatures) have released enough oil to fill up the HT connections on the coil:

IMG_20181015_202705.jpg


My bike does not have the rubber sock over the distributor...

Next, I know that these odd springs are correct for my 40426A distributor - what I doubt is that they are fitted in the correct holes, since the heavy spring never exerts any restraint on it's bob-weight (too much clearance when fitted in that hole). The smaller spring on the other side is always under tension, even as you see it in this picture:

IMG_20181015_201204.jpg


The B5HS plugs are a good colour and have done a few hundred miles.

The capacitor looks good. Using a multimeter set to ohms, one can observe the resistance rise to some 25 MOhms over a period of a few seconds - a smaller capacitor (new) I have for a Lucas 25D4 distributor rises to a similar figure in much less time.

The coil also checks out - 10 MOhms or so to earth from the HT connection, and suitable low resistance in the primary; 10,000 x that in the secondary. I didn't record those readings, stupidly.

Obviously those are cold figures - they may be quite different when hot.

Lastly, some of the valve clearances seem tight; I have not checked the ignition timing yet.
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

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Re: SQ4 Misfire

Postby nevhunter » Mon Oct 15, 2018 10:42 pm

The lighter spring controls the initial advance which comes in just above idle speed. The heavy one has to be slack at this time (has lost motion) Yours may be incorrectly set up . The only way to really know is plot the advance curve on an appropriate machine. While these things may cause a power loss and a bit of hotter running, It's not likely to cause a misfire Might be worth checking the valve spring tension and guide wear and for any valve sticking and of course the tappet clearances are worth checking always. Nev

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Re: SQ4 Misfire

Postby paul.jameson » Thu Oct 18, 2018 9:41 pm

Your advance springs are in the correct holes. Go to the Draganfly website and find their advance retard springs. Click on the link to fitting instructions and you will find useful information. I did, earlier this week as I am currently working on the distributor for the Healey.
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.

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simon.holyfield
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Re: SQ4 Misfire

Postby simon.holyfield » Thu Oct 18, 2018 11:42 pm

Latest news : I have discovered that a fast idle, charging voltage struggles to exceed 6.8 volts... Should be more like 7.2 in my mind.
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

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Re: SQ4 Misfire

Postby nevhunter » Fri Oct 19, 2018 3:06 am

A good battery will hold the charge volts down until nearly fully charged, Nev

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simon.holyfield
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Re: SQ4 Misfire

Postby simon.holyfield » Fri Oct 19, 2018 7:17 am

nevhunter wrote:A good battery will hold the charge volts down until nearly fully charged, Nev


Sorry Nev, I'm not sure what you meant by that. Are you suggesting that if the batteries are fully charged the voltage controller won't let the charging voltage rise too high?

It's an AO Services V-Reg2 charge controller.
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

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Re: SQ4 Misfire

Postby nevhunter » Fri Oct 19, 2018 11:28 pm

A good condition battery has a low resistance and acts as a limiter of surge voltages . If you disconnect the battery you usually blow the stop lamp bulb Voltage regulation usually responds to voltage and current limiting parameters. Once the battery reaches the voltage where it's fully charged the current drops right of in the charge system. as the field current in the generator is cut right back, by the action of the regulator points . The ammeter will just kick a bit now and again unless you put the lights on where it will drop momentarily then centre again. (If you are going fast enough Engine RPM). Nev

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Re: SQ4 Misfire

Postby MARK.WALSH » Sun Oct 21, 2018 10:55 pm

Hi Simes
I have an AO working well but on fast tick over I'd be very lucky to get 6.4 volts.
My voltmeter is direct across the battery so possibly some juice is diverting and working the ignition (meaning the voltage output from the dynamo is higher)
Either way it doesn't misfire or cause problems, but on normal tick over I would go down to under 6v as the unit would not kick in - I prefer not to let it tick over for no more than a few minutes to avoid discharge problems (running 6V 12AH Battery).
Mark


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