TUNING THE 7HP AUSTIN ENGINE FOR BEST ALL-ROUND PERFORMANCE

PART 2

Click here for Part 1    -    Click here for Part 3

 

 

 

The Distributor.

Now remove the top of the distributor; clean the points and set at .018 in. to .020 in.  On the latest type of engine remove the flywheel cover, and on the earlier models the starter from over the flywheel, and now check the ignition timing.

 

Ignition Should Not be Over-advanced.

This is an operation which should he carefully done as the 7 h.p. engine is of the 2-bearing crankshaft type and too much stress cannot be laid upon the danger of an over-advanced ignition on this type of engine.  The timing position may be anything from 11/4 in. to 2 in. B.T.D.C. fully advanced.  If you set the markings 1 and 4 on the flywheel dead in line with the oil pipe which runs from the crankcase, you will find the ignition is set at 15/8 in. B.T.D.C., which is an excellent position to start your tests from.  When replacing the starter do not forget the long screw fits into the near side.  Any other adjustments can be made on the road.

 

 Refill Radiator and Sump.

Fill the radiator with water—and it is a good idea to open the tap at the bottom and flush out the water system by letting the water run right through for a short while.  Refill the sump with oil to the required level (approx. half gall.).  Remove the plugs which cover the oil jets on the off side of the crankcase.  Poke these out with a piece of fine wire no thicker than 1/16 in. (This is a matter which is too often neglected.)

 

 Warm Up and Pull Down.

We are now ready to start the engine, and this we do, letting it run at about 1,500 revs. After about ten to fifteen minutes, pull down the cylinder head nuts.  Repeat the operation after another 15 minutes.  We are now ready for the road.  If a thorough job has been made of the aforementioned work, it is surprising how few adjustments are necessary to get the desired results. 

 

ON THE ROAD

We now fix a small 1-pt. petrol tank on the cylinder head for consumption test purpose. 

 

 A Final Check up.

After travelling about five miles we stop and again pull down the cylinder head nuts and tighten the exhaust and inlet manifold nuts and adjust the valves to the correct .004 in. clearance.

Now for our first test run! Choosing a fairly flat section of road without much traffic we will try for speed first.  There appears to be a slight flat spot in getting away from the standing position, but that can be attended to later, without upsetting the carburation, at a higher rate of speed.  When once we are over that the accelera­tion is excellent.

Yes, we can reach 32 m.p.h. without any valve bounce on third speed.  That seems about the limit without hanging on and straining the engine. 

 

Is the Ignition Timing O.K.?

Now top.  Yes, going up nicely— 45-6-7-8. That seems about all.  Well, she’s quite smooth.  I think we can try a fraction more ignition.  We’ll see.  We are already set 15/8 in. B.T.D.C. on the flywheel.  There is no need to remove the flywheel cover or starter.  Each degree on the vernier markings on the distributor equals 3/8 in. on the flywheel.  We’ll mark where we are now, first, on the vernier, in case it slips while we are adjusting it.  A lead pencil will do.  Now half a degree is all we move it.  Try the run again.  Good 35 mph. on third.  No undue roughness.  Now for top speed.  Yes! going up nicely— 45-6-7-8-9-50-51, yes, and 52.  That’s the limit.  If our consumption is good we shall be satisfied.

We now stop and adjust the slow running to overcome the slight flat spot.  It does not appear to be quite all gone, but we will try a run for consumption.

First, we disconnect the pipe from the petrol tank to the pump.  Now run the engine to use up the petrol remaining in the float chamber.  Turn the tap off at the bottom of the test tank and connect up to the carburettor.  Now fill up the test tank (exactly one pint).  Set the speedometer at zero, or make a note of the mileage if it is not a “trip“ type instrument.

Now we are ready.  We will choose a little traffic and a couple of small hills, but no congested areas.  Good! We have covered five miles and still going strong.  Now we have stopped, with the speedometer reading 5.5.  That’s 45 mpg.—all that the makers advertise—but I think we can get a bit more than that without interfering with speed.  A word here about the latest type of carburettor fitted on the 7 h.p. Austin— the Zenith 26 V. carburettor.  It is extraordinarily flexible and will adapt itself to the engine conditions in a remarkable way.  The standard setting is: choke 17, main 57, comp. 50, and slow running 60.  This setting undoubtedly gives the best all-round results.  The earlier models were fitted with an 80 slow-running jet.  The only jet which can sometimes be changed with advantage is the slow-running jet.  We’ll try a change on this car.  Yes! This one is fitted with an 80.  We’ll put in a 6o.  That gets rid of our flat spot, too.  Now for another test.  Don’t forget when testing for petrol consumption to try and keep as near to 35 m.p.h. as possible.

Good! Exactly six miles.  We will try a run back in the opposite direction.  Yes, 6.1 that way—49 m.p.g.  We will connect up the petrol pump, go over the head and manifold nuts again, make sure our valve cover plate is oil-tight and then for home.  The earlier model 7 h.p. cars were fitted with a Zenith carburettor type 22 F.Z.  The best setting for all-round performance on this type is choke 15, main 70, comp. 75.

Continued next month ..........