6 replies to this topic

[fenghuang]

Problem 1:

Start engine and the accelerator pedal needed to be held down or the engine would stall almost immediately.

Sollution:

Adjust the Throttle Stop Screw. (I think that's what it's called.) This obviously opens the butterfly valve a little, and the engine will then idle relatively smoothly.

Question:

Is this a legitimate solution, and is there something like a specific RMP (I'm guessing soewhere around 800) that this needs to be set for?

 

Problem 2:

The jet adjuster has been wound down aprox 12 flats.

If I push the Piston Lifting Pin up by about 1mm, nothing happens.

If I push it up as far as it will go (I gues 3 or 4mm), the revs drop.

I can wind the jet both up and down from this position by 4-8 flats, and it makes no difference: a small lift of the piston and nothing happens - push the pin up all the way and the revs drop.

Question:

In a few weeks I hope I will have been able to get to all my tools and dig out a Colourtune and a Tacho, but in the meantime, any ideas what's going on here?

[David128]

Check oil in dashpot and check carb piston is dropping with a click.. Sounds like piston at the moment has lifted already

[fenghuang]

The dashpot is correctly filled with SU carb oil.
Re the click. Is that the sound of the piston bottoming out, or something else?

[David128]

yes the piston bottoming out

[carbon]

Fenghuang, with a carb you need to pull out the choke before starting the motor. Particularly when cold.

 

The first half inch or so of choke cable movement opend the throttle very slightly, to prevent cold engine stalling. The next half inch or so is when the main jet is lowered. If you can start from cold without needing any choke out then chances are your idle mixture is too rich.

 

Using the piston pin for mixture checks needs a bit of practice. When lifting the pin there is a few mm of movement before the pin makes contact with the underside of the piston, and only when you have made this contact do you then lift by another mm or so to check the effect on idle speed.

[fenghuang]

Did I neglect to mention that I first drove a car before fuel injection was commonplace?

In all fairness, I wasn't aware there was a gap between the resting positions of the pin and the piston, so that useful to know, thanks.

Edited by fenghuang, 18 March 2016 - 03:31 PM.

[gazza82]

Showing my age now but the first car I drove had a side-valve engine!! Try adjusting the valve clearance on one of them!

 

Piston should rest on jet shoulders .. I've had a couple of SUs in the past with bent lifting pins which jammed up and held the piston high .. No I don't know how the owner did that either unless his favourite tool was a hammer!

Edited by gazza82, 18 March 2016 - 04:04 PM.