Classic cars forum & vehicle restoration.

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

I may not be much good at electrics but I think I can get away with a bit of welding. The top weld has been ground back ...and there is one anxiously awaiting it's turn !

This is the extended leg of the front side screen frame being mig welded.

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

The problem of the engine running far too rich (even when warm) persists. The single carb attached to the supercharger is an SU H6. I was advised that this would give better performance than the H4 as found on other similar installations.

The carb was supposed to have been new when supplied with the supercharger ...but I am not so sure now. Burlen's instructions for checking the petrol level in the float chamber say that with the lid inverted, a 7/16" bar should just pass between the float arm while resting on the sides ..but there is considerably more clearance than that! The level must be too low ...so I have adjusted the arm to the desired position as suggested.

I have a suspicion that this carb has been tampered with.! Surprised

Following lengthy telephone conversations with Burlen I have chosen to purchase a new needle. The present one is a D1. After some research, I have been advised to fit a KK needle. This has the benefit of a leaner mixture up to 3750 RPM and a richer mix thereafter. The important thing to watch with a supercharger is not to run lean at speed. This needle should prevent that.

The current spring is an unknown quantity as there is no colour coding on it... but if I still think the mixture is too rich, I will be changing to a blue (leaner) spring.

This is a step by step; trial and error business so we will see how things turn out. I await the postman!

JC T ONE · Joined: 30 Oct 2008 Posts: 1172 Location: Denmark

alastairq · Joined: 14 Oct 2016 Posts: 2181 Location: East Yorkshire

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

Hi Alastair. The system is with an H6 SU carb attached to a supercharger ,,,so I guess the air is sucked through the carb before being blown into the engine.

The H6 carb would normally have a 4.5 Oz spring (Burlen red) but as there is no colour code I thought I would check it out. With a 2.6" cardboard distance piece (as recommended) in the spring mounted on the kitchen scales, It measured an incredible 12oz. This is three times what I was expecting and in my opinion would be a contributing factor in rich running.

The blue spring that I am getting may be too lean with the new KK needle; I will have to fit it and see. Maybe a red one would be sufficient.

I am using 20/50 engine oil in the dashpot. If it starts to run lean I may use a heavier oil.

More than one way to achieve the ideal mixture, I am sure.

I have an old copy of the SU manual some where but can't seem to find it at the moment; no worries ... it is all "on line" . Rolling Eyes

alastairq · Joined: 14 Oct 2016 Posts: 2181 Location: East Yorkshire

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

Over the last couple of days I have been experimenting with different combinations of needles and springs but without much success.

It seems the mixture is either too weak or too rich. . The new KK needle that Burlen sent is too weak.

Strangely, the best running mix is with the original R1 needle and a 4 1/2oz. spring... but where I am confused is that the engine seems to "hunt" as if it were running rich ...but then backfires through the carb/supercharger as though it is running lean.

At one point I was convinced that the engine was misfiring but a few checks revealed that the plugs were all sparking and there is 105 PSI on all the cylinders.

At the moment I am left scratching my head; especially as Steve Baker (MG specialist) set the electronic ignition timing. Confused

ukdave2002 · Joined: 23 Nov 2007 Posts: 4309 Location: South Cheshire

If only we could have a device that measures the oxygen content of the exhaust, the amount of of airflow, together with the temperature and position of the throttle, analysis all this and then, then trims the correct amount of fuel to be injected!,😜😜

On a serious note, Electronic ignition is timed in exactly the same way as points, the only service difference is that the plug gaps can be opened up a tad to take advantage of the improved spark.

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

JC T ONE · Joined: 30 Oct 2008 Posts: 1172 Location: Denmark

ukdave2002 · Joined: 23 Nov 2007 Posts: 4309 Location: South Cheshire

Ray White · Joined: 02 Dec 2014 Posts: 7418 Location: Derby

alastairq · Joined: 14 Oct 2016 Posts: 2181 Location: East Yorkshire

IF...you can 'borrow' a trailer...or know of a trustworthy vehicle transporter...then you might do well to get in touch with Bogg Brothers at East Lutton, near Malton[or Driffield, or Bridlington....it's in the 'middle of nowhere!!].
Their dad, David Bogg, is a true magician with his rolling road, Sun tuner, long thin screwdriver, and the ability to fettle an SU needle 'by eye!'

Older cars are his forte, but he's equally happy with an ECU.
[Mind, it's a few years now since I popped in, so I'm not sure of his health situation, as such]..
It would be a 200 mile round trip, but not going anywhere near any sort of urban or metropolitan area.....all countryside...!!

Whilst there will be 'nearer' rolling roads, not many in the country will be a match for David Bogg....and his prices were very reasonable indeed..David, who must be now in his 80's, did the job for 'fun'....

https://www.boggbros.com/
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.