Timing 2.25 2a

[the big fist]

HI all,
I have a Series 2a 109 with the 2.25 (7:1 compression) and Pertronix electronic ignition.
The car has sat for a few years and I am giving it a bit of a tune up.

I have always tuned it with the timing light and by the marks on the flywheel.
Problem is I can't remember which Marks are which. I marked one with a paint marker but can't see what it is, just a vertical line.
My memory also escapes me. Do I plug the vacuum port so no advance and then time for TDC or for 6 deg BTDC?
My timing mark jumps around a fair bit, would this be play in the timing chain / tensioner or in the distributor ?
What rpm should I try to set the car at ? If I set it around 850, it will stall, if it's around 900-1000 it's ok.
I have read a fair bit on timing these motors and the general consensus is to go by ear. I am not that keen on the by ear method but have previously found it fairly successful. Other option is should I try the vacuum gauge method ? Do I just plug this into the carby port ?

Lastly, I did have it running nicely, but on acceleration (in neutral) it would stutter, then pop and fart and take off. Easy acceleration it would be ok.
Does this sound like the accelerator pump in the carb ? These Zeniths are a bit of a pain.

Lastlty, is there any easy way to check that my idle mixtures are correct ?
I've just been doing the screw in and then out 2.5 turns (i think) to get it approximately right.

Phew, lots of questions !

Cheers,

Peter

[JDNSW]

HI all,
I have a Series 2a 109 with the 2.25 (7:1 compression) and Pertronix electronic ignition.
The car has sat for a few years and I am giving it a bit of a tune up.

I have always tuned it with the timing light and by the marks on the flywheel.
Problem is I can't remember which Marks are which. I marked one with a paint marker but can't see what it is, just a vertical line.
My memory also escapes me. Do I plug the vacuum port so no advance and then time for TDC or for 6 deg BTDC?
My timing mark jumps around a fair bit, would this be play in the timing chain / tensioner or in the distributor ?
What rpm should I try to set the car at ? If I set it around 850, it will stall, if it's around 900-1000 it's ok.
I have read a fair bit on timing these motors and the general consensus is to go by ear. I am not that keen on the by ear method but have previously found it fairly successful. Other option is should I try the vacuum gauge method ? Do I just plug this into the carby port ?

Lastly, I did have it running nicely, but on acceleration (in neutral) it would stutter, then pop and fart and take off. Easy acceleration it would be ok.
Does this sound like the accelerator pump in the carb ? These Zeniths are a bit of a pain.

Lastlty, is there any easy way to check that my idle mixtures are correct ?
I've just been doing the screw in and then out 2.5 turns (i think) to get it approximately right.

Phew, lots of questions !

Cheers,

Peter

I have always used the static setting method from the manual, fine tuning from this by advancing for fastest idle, then retarding if this results in pinging under load. The moving around of the marks with a timing light is almost certainly wear in the top bearing of the distributor or in the centrifugal advance mechanism. No real solution except to overhaul or replace the distributor.

The idling mixture is best adjusted again following the book procedure, with the 2.5 turns only the starting point. The stutter from idling could well be incorrect idling mixture in my experience. A quite likely problem is that wear on the throttle shaft makes the idling unstable in that both the air leakage along the shaft and the throttle restriction are slightly different every time the throttle is opened and closed, making correct idling adjustment impossible. Failing a carburetter overhaul, it is likely to give better driveability if the idling mixture is set slightly rich. Note that this adjustment needs only a small fraction of a turn to make a difference.

If the top and body of the carburetter are not matching, you are unlikely to ever get it adjusted properly. These can be corrected by lapping flat, using wet and dry on plate glass.

john

[chazza]

Check also the vacuum advance to see if it is working, by sucking on the pipe, whilst looking to see if the base-plate moves in the distributor.

Popping in the exhaust on the over-run, can be put down to a rich mixture and a plug that is whitish, rather tan, after a hot run with the choke in, might be indicating too lean a mixture.

If it won't idle at about 600rpm, there must be something wrong with the valve clearances; ignition timing; or fuel delivery, so check them in that order.

To find out which timing mark is which, set No. 1 cylinder at TDC on the compression stroke - it might be easiest to take the rocker cover off to observe the valve position - and observe which mark the pointer is referring to. 6 deg. BTDC is fine for petrol of 90-96 octane,

Cheers Charlie

[the big fist]

Thanks guys, much appreciated.
It's a new pump that's on there. I had a quick look last night and it doesnt look like I am getting a jet of fuel down the carb when I push the throttle.
Sounds like I could have a whole series of issues.

With regards to the timing light and Vac plugged. Should I set for TDC or recommended 6 deg ? More so for the knowledge, but what is the correct way of doing it ?

Cheers,

Peter

[JDNSW]

Thanks guys, much appreciated.
It's a new pump that's on there. I had a quick look last night and it doesnt look like I am getting a jet of fuel down the carb when I push the throttle.
Sounds like I could have a whole series of issues.

With regards to the timing light and Vac plugged. Should I set for TDC or recommended 6 deg ? More so for the knowledge, but what is the correct way of doing it ?

Cheers,

Peter

I would set it at 6° stationary, but tdc is probably closer with the engine idling and vacuum plugged - problem is you don't know what centrifugal advance is present, particularly on a worn distributor, but whatever you set it at is a starting point. If it is too far advanced, it will ping under load, and I would try (with vacuum reconnected) adjusting from this point for maximum idling rpm.

The ideal of course would be to recondition both distributor and carburettor before even trying to set it up, but for most this is not realistic. One thing I would do, unless the high tension leads are near new, I would replace them - suppressor leads are a potent source of problems, and are not very expensive.

John

[the big fist]

Thanks John,
I am interested though in engines in general, or lets say mine was running 100% new. When setting the timing, do you plug the vac and set to TDC or 6 deg ?
I've seen some cheapish distributors on Ebay, I might grab one of those and swap the petronix over.

Cheers,

Peter

[JDNSW]

Thanks John,
I am interested though in engines in general, or lets say mine was running 100% new. When setting the timing, do you plug the vac and set to TDC or 6 deg ?
I've seen some cheapish distributors on Ebay, I might grab one of those and swap the petronix over.

Cheers,

Peter

I set the timing with the engine stationary using a 12v light on the points. This bypasses the whole question of both vacuum and centrifugal advance. Not sure whether you can do this with the petronix, although if this uses the original points for timing, you can restore the ignition to standard, adjust the points and timing, and then reconnect it.. As indicated above, I use this as a starting point to adjust by ear, similar to the idling adjustment.

At present my distributor seems to be in pretty good shape, but I have doubts about the throttle spindle, although it is running pretty well at the moment.

Hope this helps,

John

[the big fist]

Thanks again John.
Much appreciated.