Square 4 Starting issues

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Andyozz
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Square 4 Starting issues

Postby Andyozz » Thu Mar 14, 2013 11:15 am

1343754580157-002.jpg
my 1959 Mk2 SQ4
1343754580157-002.jpg (31.69 KiB) Viewed 2138 times
Hi All
Being new to the world of square 4's and learning rapidly over the past 2 years all about them having rebuilt my 1959 Mk2 I am now in desperation for some help.

I have covered approx 1200 miles since the rebuild and all is well apart from one major niggly problem....... Starting.
My body is now starting to become deformed with a right leg that looks like it could kick start a Jumbo jet!!!!

To date what I have done......
Re torqued head (Twice.. fitted with Otto head gaskets)
Checked and re checked the tappet clearances. All OK at .008" & .010"
Checked, double checked, tripple checked ignition timing. spot on at TDC #1 in compression stroke with points just starting to open at fully retarded position.
Changed all the HT leads to copper leads with new plugs, caps etc.
Had the MC2 carb off more times than the preverbial knickers to check for air leaks, debris, float levels etc etc. The jet is centralised to the point where it will fall to the bridge under gravity without the spring being fitted. I have aslo fitted a service kit from Burlen fuel systems with new spring,needle, jet etc etc. I even took it to Burlen fuel systems who put it on their test rig and pronounced a fully serviceable carb (Thanks to Phil and Ross :D )
Compressions are good in all 4 cylinders with a total max difference of about 10 PSI between all 4 pots.

And Yet it will not reliably start. Once you eventually get it fired up, it runs well on 20 -30 mile runs.
I am pretty much convinced that it is fuel problem, but open to other suggestions.
Burlen had some good advice which I will pass on to other unsuspecting riders....
Ethanol in modern fuel ie it attacks not only rubber fuel lines and corks but also soft solder!!!! Beware all those with brass floats in the float chambers..... A long walk home is awaiting you.....

Anyway, back to my dilema.... I have been advised that the fuel level should be within 3/16" of the jet orifice (ie where the needle enters) when the mixture lever is in the fully run position. Can anyone confirm this? I know about the 3/8" gap under the float chamber needle valve fork. But again is this with the spring in the fuel needle valve compressed or with the fork just resting on it.

Any advice or help would be greatly appreciated apart from screaming at it and beating it with a big stick!!!!

Andy

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Postby roger.fellows » Thu Mar 14, 2013 9:39 pm

Seem to remember timing mine at 1/4 inch before TDC, but that is only from a failing memory. Don't have Waller to hand. Air leak between inlet manifold and head? Or at mounting stud?

Roger

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Postby nevhunter » Fri Mar 15, 2013 12:23 am

Have you tried flooding it for starting? Less when hot of course. Your fuel level may be a bit low. Running with the ignition firing at TDC is a position you should never need to use even when idling or starting. Nev

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Postby ismohautala » Fri Mar 15, 2013 7:26 am

Hi Andy

When I adjusted my SU carburetor(Square -55) the cap under the valve fork was 7/16 approx 10,94mm (valve compressed).

When cold ,jet lever down , some kicks , ignition on and it starts first kick.
Nuts for rusty nuts

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Re: Square 4 Starting issues

Postby david.anderson » Fri Mar 15, 2013 8:46 am

Andy
Try this thread for float height.
viewtopic.php?f=4&t=1330
You will find the bike a little easier to start if you advance to 1mm btdc retarded which should give 9mm at full advance. After advancing my ignition starting was improved but just remained difficult if the bike was left outside during winter.
Then after I converted to 12v electrics point burning became an issue so I used a Ford TFI unit to fire the coil, using the distributor points as a trigger. Since I did that the bike starts first kick, cold any time of year.
David

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Postby john.whiting » Fri Mar 15, 2013 9:54 am

Any one with problems with a Lucas distributor should check for clearance in the advance part of the cam setup,see if the point gap is easily altered by putting a bit of side force on the camshaft with your fingertip.preferably put the dizzy on a testing machine with an oscilloscope.The only cure for this is new parts,dont be conned into expensive repairs that last five minutes running.Or remove the whole point setup,and substitute an electronic trigger.Regards John.

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Postby Andyozz » Mon Mar 25, 2013 1:20 pm

Hi Guys
Thanks for all the usefull input.
Some info I have found out, that may help others.

The gap under the fork for the float chamber is stated by many publications as 3/8" (9.5mm ish). This what I have been setting to. However, when I took my MC2 to Burlen fuel systems, I was given some hand written notes from 1956 on MC2 setup proceedures. (If I could find a way of attaching a copy of it to this forum to share I would)
And as always there is a one liner at the bottom that states " Fuel level should be within 3/16" (4.76mm) of the jet orifice".
Now, wIth a 3/8 test bar under the forks this gives a float level of approx 10-12mm below the orifice.
I checked again with Burlen Fuel systems who checked another MC2 from there refurbished stock and this gave a similar measurement of fuel under the orfice.
By trial and error, I adjusted the float chamber to give me approx 3/16" fuel level under the orrifice jet (Normal running position of Mixture lever), which gives a gap under the float forks of approx 5.5mm.

With this seeting the engine starts first or second kick when hot.
Additionally there is no tickler on the MC2, only the mixture lever which lowers the main jet in the fuel level and a thinner part of the needle, great once the the engine is running creating a partial vaccuum over the main jet to suck fuel up, but not much use when there is no air flow over the venturri bridge in the carb which can cause the very cold starting problems.
However, I found that if you lean the bike to the right hand side as far as you can with the fuel tap on for a second or two, this will artificially flood the main jet due to the float chamber being on the left hand side (float chamber fuel level is higher than the main jet orifice) . This I found aided the cold starting by effectively floading the venturi with fuel the same as tickling a good old AMAL carb.

With regards to the ignition timing, Points opening at TDC is the maximum retarded position. Does anyone have any info on the max advance position or at what RPM max advance should be reached?.

These modern ethanol fuels are here to stay I am afraid, and I have been reading about retarding the ignition slightly to compensate for the faster burn rate of ethanol. Has anyone any info or comments on this. I think this is going to be a pain in the preverbial for all us vintage bike nuts especially when they increase the amount of Ethanol in fuel the years to come !!!. For those that are technically minded here is a usefull link about Ethanol and how wonderfully good it is for the green policies but really bad for us vintage engine nuts, especially the water absorbsion, corrosion, and generally nasty nature of this stuff.

http://ethanolrfa.3c...c_rbm6bdgh3.pdf

For those still awake thankyou for reading, I have now amassed a large amount of info on this, so if you need any help or advice, please PM me.
Regards
Andy

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Postby john.whiting » Tue Mar 26, 2013 9:49 am

Advance of a Lucas dist is 15 to 18 deg.This means full advance will be 30 to 36 deg usually at fairly low revs,say under 2000,when the stationary setting is tdc.I would suggest you try more static advance ,try up to 10deg in stages.Relying on measurements made to microns is unnecessary with old low compression engines,and many owners used to tune the bikes by turning the dist .while revving the motor,listening for the best sound and least vibration.Someone asked for advance curves here once before,but Lucas did not give out such info to the public .I have advance figures for Lucas dist used in International trucks ,but no others.Regards John.l

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Re: Square 4 Starting issues

Postby david.anderson » Tue Mar 26, 2013 9:36 pm

Andy
The information I have for the SU states that with the lid upside down bend the tab so that it will just touch a round 7/16 bar placed under the curved section of the forks. With my carburettor and others that I have checked that gives me a fuel level 3/16 below the bridge.
Is the 5.5mm figure that you are quoting measured under the round of the forks or at the ends of the tabs.
David

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Postby Andyozz » Fri Mar 29, 2013 10:21 am

John
Thanks for the timing info. I think when the weather warms up a bit, i'll do it by trial and error.... Little bit at at time!!!. I'll post on here what I find if anything. With reference to your earlier post the distributor is good ie no lateral play in the shaft, points are about .002" difference on all 4 points, in my books thats good enough.

David
The measurement was taken under the curve of the fork and against the location lip of the lid (as per the picture in your link above). As I said before, these are the same measurements that Burlen were finding on a refurbished carb at their works. I can only assume that possibly the new float bowl fuel needle jet (and possibly the new "stay up" float) are giving slightly different measurements. However, I tried it with the old Brass float and this gave similar results.
A mystery, but the engine starts and runs now, so the proof is in the pudding. I just hope that this info will help preserve others right leg for a bit longer :-)


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