MK3 Spitfire SU Carbs, Tuning and other oddity

[Pete Lewis]

do you know what piston springs are fitted ???

 

Pete

[68spitfire]

Hi Pete,

 

Yes they are RED which by my Haynes SU carb manual is correct along with BO needles.

 

I believe the jet is correct, need to check, but it was all supplied when I had the carbs re-furbished i.e. bushed etc.

 

Been trying to get my head round this all day at work ahem!

 

Tune with colortune ok, lifting pin test fails (weak response) and car runs like a kangaroo.

 

Tune with lifting pins ok, and colortune responds with a rich yellow at idle, but car drives ok.

 

So I am trying to figure out if the manifold is leaking somewhere.

 

Trying to work out if colortune is ok, and I have a vac leak, then that carb must be over rich?

 

Cannot figure out why the discrepancy between the two tests.

 

I think I can rule out the Aldon Ignitor now as the drive I took the other day in full rich condition the car ran well.

 

The car will have to wait until the weekend now and I intend to take the carbs right off, and renew all gaskets on manifold. Oh and inspect the manifold as well for cracks etc.

 

So not able to make the New Forest Run next Sunday   and probably the Drive it day trip to the Haynes Museum the following week!   

 

Such is life,  stay tuned and thanks again.

 

Rich.

[Pete Lewis]

A pump oil can with some petrol in and squirt around the faces and joints, if the idle climbs its found a leak

 

and it wont catch fire never use brake fluid, that can go up a treat.

oil is less responsive

some will think this a little mad but in the emmission dept I ran it was std bit of kit

(Before H &S rules)

 

 

This is all a bit odd, with rocker box off are the valve guides all in same place, no loose ones going up and down withthe valves ?

 

 

Pete

[68spitfire]

Hi Pete,

 

I had the rocker box off the other day and checked the tappets which to my surprise had not moved at all since the last time.

 

Did not notice any valve guide issue though I was not looking for it.

 

I did suspect the emissions EGR system thing with the diaphragm on the inlet manifold, but the diaphragm is in tack and only about 18 months old, the unit is clean and appears to work fine, even the little flappy valve down in the base of the unit.

 

With the engine running and removing the rocker filler cap the revs rise about 500-600 rpm, then replacing the cap they go back to normal, so I guess thats normal?

 

Will try the petrol/manifold test at the weekend before stripping it all down.

 

Rich.

[68spitfire]

Fresh update on the saga.

 

Checked the valve guides and nothing seems out of order, besides if I had a loose one I would expect blue smoke through oil induction.

 

Done the pour neat petrol ( read: carefully dribble fuel ) over all of the gasketed joints on the carbs to manifold and manifold to block.

Also dribbled petrol over the throttle spindles and around the engine breather connection.

No response to any of that so I am assuming I have no vac leaks.

 

Checked the float chambers again and float heights. I did find that one was about a millimetre to 1.5mm out ( high fuel level ), cannot remember it being like that before.

The front carb has always had a damp appearance in the bore all the time, even when the car was running ok.

 

Done a carb reset by the book.

Levelled jets to top of bridge and down two turns.

Ran up car, balanced airflow then adjusted mixture by lifting pins.

Initially I lifted one carb and when rich moved both carbs leaner by the same amount until I got close as I was concerned about one over rich and the opposite cylinders feeding off of it via the balance tube.

 

Got near on the correct lifting pin response and then done carbs individually.

I then checked the results with colortune.

 

Only had to move about 1 flat leaner to get the colour tune to look more or less right, just a slight hint of yellow.

Did not go to far as it made the lifting pin test read weak.

 

At least now the lifting pin test and colour tune results are very close, unlike previous when they were totally out of wack.

 

Have not taken the car out on the road yet as no room to move my other car out, to much traffic parked.

 

The car does seem to idle better now, so it could have been the front carb overflowing a tad making the false reading via balance tube.

 

Need to get the car out and report back. Oh and if it pulls ok, get a long run in so I can check the plug colours.

 

Rich.

[Pete Lewis]

We will all hold our breathe

 

 

pete