Exhaust "popping" on overrun?

[Colin Reed]

HI Joe,
Regarding setting Electronic distributor, What make is the one you have as they should not be any more difficult to set than Points.

Cheers
Colin
NZ

[Joe eck]

Hi Colin,
I think the unit is an Accuspark one.
It isn't so much that the timing is difficult to set on the electronic unit as I have become reasonably proficient at setting it by ear, but once set to prevent pinking , I think the static timing becomes very retarded.
I am no expert but there is certainly a big difference between my two units.

Looking at the centrifugal weights on both the electronic and standard distributer and moving the points cam by hand to simulate advance, the standard DK4a takes a lot more effort to move to the fully advanced position than the electronic unit so I am assuming that the advance will be quicker ?

Thanks to all for the help
Joe.
In the hills of West Yorkshire.

[Chris KC]

Other way around Joe, the more resistance it puts up the slower it will reach full advance.

if you have a DK4A which is hard to advance it is either gummed up with muck or you have a rare good one! Most of them have tired springs which don't put up much resistance, thus they advance too quickly.

Of course the rate of advance and the total amount of advance are two quite different things...

[Ian Williams]

In DK4 distributors I have rebuilt the thing which affected the working of advance mech most was not so much weak springs but wear in the spring mounting eye on the toggle. I fill and re drill these, rebore the toggle if the swivel hole is worn, and fit new or oversize pins on the cams and base plates. There are a number of DK4 variants all with different amounts of total advance, this is controlled by a hole on the base plate, these can also be worn increasing amount of total advance. I you have a selection of old units then you can take say a 4 degree baseplate with a 1/4" hole and open it out to 21/64 which will give you 8 degrees, or to 3/8" which will give you 10 degrees. If keen you could also turn up a top hat insert for the base plate to reduce the total advance.
Note; the figures are distributor degrees rather than crank degrees.

[Chris KC]

Funnily enough only yesterday I adapted a later action plate marked 17 degrees - I agree an insert would have been a nice solution, and I did consider sleeving the pins instead of altering the hole; but it responded fairly well to a dab of MIG on the outboard sides of the holes, which was then ground flush and gently filed to give the desired amount of advance; in my case I settled on 8.5 degrees and got it more or less by sheer luck at first attempt. I used a DTI on the rotor arm to double-check the actual amount of advance.

One observation I would add is that I have stripped a number of DK4A's which have at some time been re-bushed; but have yet to find one where the oil supply hole had been re-drilled through the new bush!

[Ian Williams]

A genuine Lucas DK4 bush is made of a porous oilite material, and so should not need a drilling, however many get replaced by solid brass with no lubrication hole and quickly fail. Accuspark seem to have attempted to overcome this by fitting the top bush so far down the body it is actually below the oil hole, they have also made the bush from steel, I suppose the thinking is to reduce wear??But then they thoughtfully compensated for the lack of wear by providing extra clearance in the bush!!!