Engine hesitation (S2 triple SU)

[ralphr1780]

Last summer, have converted my S2 from twin-Stromberg to triple-SU (brand new kit from Burlen).
Tuned the SUs as per the wsm, and after numerous sessions and almost 2000km later, I still have a slight but very noticeable constant engine hesitation. It is there on acceleration or cruising and at all rpm.
Clearly not a miss, but a hesitation.
Ignition is EDIS, plugs are new (BPR5ES), and timing map is stock unchanged.
Electronic SU pump, filterking pressure regulator set at 2.5, UM needles.
Car pulls strong, plugs look all similar brownish tint so no obvious signs of poor mixture.
I did not have this on the Strombergs.
Looking for wise advice, should I change timing map? needles positioning?
Thanks,

[mgcjag]

Hi Ralph.....had a similar problem.....took ages to find.....was just a loose wire in one of the crimp connectors on the coil.......from the ignition switch......i had tested all the wireing with a meter and all was ok....finally used a wire direct from battery via a switch in the cabin to the coil to eliminate all the wireing......when the car stumbled i flicked the switch on to give a direct circuit...stumbling stopped.... Steve

[ralphr1780]

Thanks Steve, in my case the coilpack (for Edis) is not fed by the white wire coming from the ignition switch but from a separate line from the fuse panel. Nevertheless, could add a parallel wire and switch to test.

And forgot to add that I do have some little exhaust poppings when decelerating downhill.

[Heuer]

Sounds like it is running too rich if you are getting popping on thew over run. There are several SU guides in the Forum KB which may help you:

Balancing SU and Stromberg Carburettors: https://www.dropbox.com/s/6pmcaqykapw7n ... e.pdf?dl=1
SU Carburettor Notes: http://www.jcna.com/library/tech/tech0006.html
SU Tuning Guide: https://www.dropbox.com/s/tc0k3pac07y3m ... 1.pdf?dl=1
SU Carbs.com Tuning guide: http://www.sucarbs.com/tuning2.html
SU Search (SU needle comparison spreadsheet):
https://www.dropbox.com/s/svh1qj4xr1rqw ... s.xls?dl=1
WinSU: SU tuning software: http://www.winsu.co.uk/

A quick and dirty test is to remove the plenum and air filter and take the car for a run. This will cause the engine to run lean (more air getting through).

[christopher storey]

The popping on overrun is also a classic sign of insufficient advance on the ignition. Only 2 or 3 degrees of retardation from the ideal is needed to produce this, and it would also fit with the hesitancy during normal running. I should try advancing the ignition curve in 2 degree steps to see whether it helps

[ralphr1780]

Thanks David, I had already downloaded and explored all these for the tune up.
Christopher, I will try the 2 degrees advance, should be easy to do with the MJ-Edis by just changing the trigger offset from 0 to -2. Will report shortly results.

[Mich7920]

Hi
Begin by the Jaguar service manual.
I found that it was the more simple and usable set up guide for our 3 SU.
Mich

[Ropariva]

Hi
Just wondering if this issue was resolved?
I am here as I also had a hesitation as described. After much contemplation I was convinced my issue was ignition so I ordered a 123 distributor. Once fitted the difference was immediate. The idle was smoother and the hesitation was gone. It’s a different engine.
My engine had been freshly rebuilt, carbs fully refurbished and a Pertronix insert fitted to the original distributor. The distributor had been dismantled and checked and there was no issues with it with points prior to the rebuild. When I checked the timing on cylinders 1 and then on 6, they was about three degrees difference between them?! This was what convinced me to get the 123 dizzy.
Cheers. Alan

[christopher storey]

Alan : the difference between cylinders is a classic sign of a bent distributor shaft or worn bushes on the shaft . The result is that the shaft runs eccentrically and gives inconsistent points gap with resultant inconsistent timing

[ralphr1780]

Alan, I tuned the 3 carbs a little leaner and the slight poppings at deceleration have gone. But I had still the constant hesitation all time, so have followed Christopher's advice and put a 2 degrees advance offset: idle is more stable and response is immediate when pressing throttle. But could not take the car out yet for a run for various reasons...
However, I had meanwhile been running with my 3.8 S1 and facing an irregular idle which couldnt cure with carbs tuning. Finally decided to change advance offset by 2 degrees: idle is rock steady now as it should be with edis ! Thanks Christopher