Hi there,
I fitted a 123 electronic ignition into my xk120 saturday, drove sweetly for about 25 miles. Started it today and its running very rough and lumpy! Noticed after the run yesterday it was quite lumpy on tick over but put it down to the fact that the car hasn't been driven in properly years (old distributer would fail after 5/6 miles hence 123) any ideas/?
Regards,
Scott

 

Hello,

What settings on the 123 did U use, the default does not match a 3.4 of the XK120.
On my XK140 I have put it on 3, but you have to test for the best settings.
Did you adjust it on 10 degrees before DTC, where that the green light goes on.
I have a 123 on all my 3 old jags ( xk140, xk150 3.8, s-type 3.8 ), never had a problem.

regards,
Peter Jan

 

Hi Peter,
I think it has been set to 4 as recommended by the people I bought it from for the xk120.. it's running very rich also..do the settings on the 123 make that much of a difference? Took it on a 40 mile run yesterday very smooth on the road but lumpy when meeting traffic.. I might adjust the mixture before taking out the distributor again..
Regards Scott

 

Scott,
The idle settings on the 123 are all similar, the curves start to separate at higher RPM. So if your at the recommended 10 degrees static setting, I would check plugs for fuel or oil fouling. Over rich at idle, would be more noticeable when engine is warm, vs cold engine on start-up.
Rgds David

 

Hi thanks for the advice.. I'm going to reset it to 10degrees before TDC...can you tell me how many degrees does a tooth on the fly wheel represent? I can't find my manual!!

 

If you have 132 tooth flywheel, then 3.66 teeth before TDC mark would be 10 degrees position.

Also with 10 degrees as initial setting, you may have to much max advance with "curve 4". If you get pinging between 2200-3000 rpm with hard acceleration, you will want to go to the "0" curve setting.

 

Scott

See attached listing for 123 curves. I don't have XK -120 manual, but 34 degrees at 3600 RPM was very close to XKE OEM maximum advance curve. XKE was 9:1 CR, if you have 7:1 or 8:1 CR, then 3 or 4 may be ok?

Rgds David

 

That's very handy. Thanks very much
Scott

 

Hi there.
Just to report..reset the timing from scratch and I'm happy to report that the car is running perfectly!! Took it in around traffic,no problems.
Brought it in an overnight trip of approx 120miles and the car behaved perfectly
My next question is this!!
It's the only xk120 I've driven and would like to know how they are supposed to handle..I took mine down the country roads of West cork in Ireland.. I found it quite giddy over the bumps... Is this to be expected? I thought it was quite 'juddery' at high speeds..
I'm used to old stuff but not this old.. I balanced the wheels, this made a slight impression but still it's not smooth..
Any opinion would be appreciated.
Best regards,
Scott

 

Scott,

Oh how I wish I were touring Ireland in an XK120. Glad to hear engine is sorted.

Is the "Giddy ...Juddering" felt in the steering column or are they a seat of the pants items?? I am more familiar with (twitchy to bone-jarring)

I maintained an XKE with similar front suspension, correct tires/ tire pressures and mostly new rubber bushings, ball joints, rebuilt steering rack, new tie rod ends, tight front bearings...needed to get all "slop" out of front end. Jack up front end from frame and wiggle wheel up & down front to back to see how tight!!! I had an old school front end alignment Tech, He dialed in Castor, Camber & Toe in + or - "0".

Notes indicate in 1950, the factory changed castor angle to positive 3 degrees from positive 5 degrees for the XK120, and the Tie-Rod bearings were changed to rubber; nothing else note worthy in suspension.

See attached article Page #3 for more specifics, from some one who knows the XK120.

http://www.guybroad.co.uk/download_c...RET-SHEETS.pdf

Rgds David

 

Hi David,
Sorry for the late reply.
I was onto a friend of mine who knows these cars and has said its the front wheel set up.. I'm waiting to get the time to bring it to him!
regards scott

 

Scott,
Good to hear you have front-end expertise locally. Most shops in my region with expertise have retired the expertise; shops that could work on RRs from the 30s to Jaguars in the 80s have been left in the hands of those that will not look at anything older than 2005. There are a few full-on restoration shops locally that survive, but they are looking for jobs between $5,000 and $25,000.
Thanks for the update... look forward to final fix.
Rgds
David