Square 4 MKI - more troubles

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john.bebb
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Re: Square 4 MKI - more troubles

Postby john.bebb » Sat May 16, 2020 1:07 pm

Hi Gui - (bother)!!! just spent ++10 mins writing a reply & the system has lost it! Congrats on fitting the Iron Horse alternator - it's a superb device!
I'm not aware of the Thorspark device - does in keep the points, capacitor & bobweights? - or are they binned for Hall effect pick-up & electro mapped adv/ret?
Is the sporadic miss momentary - or longer lasting - is recovery instant or slow?

Do remeber that when running-in - it should not be all "softly softly" - the moving components require stress to bed in - make it work under stress intially for v. short bursts & gradually increase the length & severity of the stress periods...
On similar premise; - I trust you're using Morris oil or equivalent to bed the lump in - using modern super-slippery is totally counter-productive.

My first draught was far more thorough - but tough luck!
Cheers, John

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Re: Square 4 MKI - more troubles

Postby paul.jameson » Sat May 16, 2020 8:11 pm

Not wishing to be unhelpful here but my experience with Square Fours is that whatever the problem is, the symptom is a misfire. The good news is that by the time you have solved the problem, you have a pretty good idea of your way round the bike and the condition of its various parts.
Paul Jameson
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Now Archivist once more - but not Machine Registrar.

Gui.dorey
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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sun May 17, 2020 1:45 pm

Happy to report that after a longer run today, she is running much better without the misfires (almost...).

But going back to some of the questions above. The Square four, although still in the run in stages, was running very well before. Last year she did about 200 miles, but at the start of this years season I blew the head gasket. This led to the current repair, and after that I had the misfires. Nothing was changed except pulling out the head and reassembling it again. Granted, with all the messing about, the carburetter settings were certainly changed and affected.

The main problem was a partly blocked petrol tap, which I also solved. Now after a longer run she seems to be running well again. However, I still feel some hesitation when accelerating from close to idle, as when I'm just rolling along with no effort and then open the throttle to accelerate. This is the range when she seems to hesitate and misfire a bit. So it seems to be in the range just between about 1/8 throttle to 1/2 throttle. After that she clears up. This leads me to believe it is indeed a mixture problem and in the transition from idle to mid range.

So what are the opinions? Pilot too rich or too lean? Or something else entirely?

Cheers,
Gui

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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sun May 17, 2020 1:55 pm

john.bebb wrote:I'm not aware of the Thorspark device - does in keep the points, capacitor & bobweights? - or are they binned for Hall effect pick-up & electro mapped adv/ret?

Cheers, John


John, thanks for the help. Hopefully I answered the rest of the questions in the previous post. As for the Thorspark ignition, it is just a magnet and Hall sensor which replaces the old points. After removing the original points and base plate, it just fits into the distributor without modifications. There's is no mapping to do as it still uses the original advance mechanism with the bob weights and springs. Very simple and easy to install. Until now, I am happy with it and is working reliably, although the time and mileage in service is still quite low.
Cheers
Gui

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Re: Square 4 MKI - more troubles

Postby adrian.hannam » Mon May 18, 2020 6:37 am

This may have nothing to do with your problem, but I have been looking at the valve timing on my bike lately. The notes say: "Retarded timing will cause a loss of power at lower revs so the engine will feel sluggish." Did you touch the timing chain?
'48 KG outfit, '51 VH, '51 4G (in bits)
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john.bebb
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Re: Square 4 MKI - more troubles

Postby john.bebb » Mon May 18, 2020 6:51 am

Hi Gui, pleased to here it's running respectably.
If it was perfectly OK before the blown gasket - and you're absolutely certain that the electrics & sparks remained unchanged; -
then it can only be carburration...
As I recall; - the Solex Bi-start has no less than SEVEN fuel or air jets - all of which need to be completely clear for faultless running.
I suggest you strip the carb & give it a really thorough cleaning - air blast each jet (don't poke with wires!).
Xylene is one of the few solvents which will dissolve petrol deposits - maybes soak all parts overnight before air blast & reassembly.
Petrol deposits??? - yes such do occur - particularly if laying dormant over winter - and far more prevalent with the modern high ethanol content crap which comes out of today's pumps - it leeches various components out of the Mazac / low grade aluminiun trash that Solex used for post-war manufacture.
I replaced my Solex with an Amal 626 - the "sticktion" as is rumoured to be caused by high induction pressure is simply avoided by overstreaching the return spring. (Note: I do not concur with Draganfly wrt jet sizing of this carb on a Mk1 Sq.).
Final suggestion; - try the occassional use of Tetraboost http://tetraboost.com/product-info/ every third or fourth tank refill...
Cheers, John.
PS. Stuff the Covid "crisis" - gonna 'phone Hamlin's today to chivvy them wrt progress on my short block refurb...

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Re: Square 4 MKI - more troubles

Postby simon.holyfield » Mon May 18, 2020 8:24 am

Gui, I would wind the pilot adjuster out half a turn - it's too lean in that transition zone. I'm assuming you have cleaned the ports around it and satisfied yourself that the seat is not damaged?

I know that some Solex users fitted a modified screw (I think with a longer cone) that David Jones had made, to good effect - this would give you more resolution (less area variation per turn). Mine is happy with the standard screw.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Wed May 20, 2020 4:07 pm

Dear Simes,
I think you‘ve got it. Turned the pilot screw out 1/2 turn and she ran much better. All the hesitation and misfires are now gone and she ran beautifully. Very happy. Thanks again for all the help from everyone.
Cheers,
Gui

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Re: Square 4 MKI - more troubles

Postby john.bebb » Wed Jun 10, 2020 3:15 pm

Hi Gui, the Amal spring streach may not necessarily procure a permanent resolution.
Plz refer to viewtopic.php?f=4&t=10688
where I state my intention to develop a more suitable spring...
Cheers, J.


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