4.2 3x45 Webber’s running 12 deg advance?

[Paul bow]

Hi guys, struggling here..
A fully rebuilt 4.2 stock engine but new everything, rods pistons the lot. Anyhow running 5 hole progressive Webber’s 45dcoe (also brand new) been on a rolling road, (£800!!) and still struggling with it, not going back to the rolling road have zero confidence in them.. the problem is when it left there it had 4 deg advance, I was told that it should be at least 10 anyhow did that changed the plugs to bp5es (Ngk) run much better but a lumpy tickover at 8500/9000 rpm.
So advanced the timing to 12, goes like a scalded cat but pops and slight backfire at idle, also if u slam the hammer down from 1k rpm it’ll miss a beat or two before taking off.. my question is with today’s fuel (super plus unleaded) a 123 dizzy set at 7, what would u say maximum timing should be??
Thanks for any help in anyway
Paul

[bitsobrits]

I'm thinking you should get your carbs fully dialed in, then optimize the timing. Just because someone has a rolling road doesn't mean they know anything about Webers. Out of the box Webers WILL need hardware changed (jets, jet holders, perhaps emulsion tubes, maybe chokes) to tune them to your exact application. Takes some time (and money, even if you do the tuning yourself), but essentially perfect running across the rev range can be achieved, especially with the 5 hole progression circuit. So many people give up before they get there, then blame the carbs...

Also, it's not just the initial timing advance that's an issue, but the advance curve as well. Typically with Webers you may start with a slightly higher than standard initial timing, but also want to limit the total advance somewhat.

[mgcjag]

Hi Paul....if i remember correct a while ago you posted that you were looking for an engine.......what engine do you have.....its timeing details will be in the service manual under distributor and give the curve details.....the standard 123 with selectable pre programmed curves isnt really great as none of the curves are ideal....if your setting up webbers tben you will also want to acuratly set up timing....a 123 tune would give much more flexibility......you really need to find via reccomendations someone to tune your webbers.....I heard good things about Northampton motor sports......Steve

[christopher storey]

Paul : DCOEs are notoriously difficult to get right in relation to part throttle response . The progression is largely governed by a. the choke size ( no more than 36 is desirable for a road car ) and b.the emulsion tubes, and from memory F9 or F16 are the most usual for Jaguars. However, in relation to timing the problem of part throttle progression is that there is no vacuum advance facility on Webers . Your original rolling road setting of 4 degs BTDC at idle is unquestionably too far retarded , and even 10 degs at idle is a little low. We need to know what distributor you have ,what advance curve is being used, and even better would also be the DCOE settings, choke sizes , idle jets, main jets, emulsion tubes etc etc to see if your setup now corresponds to what might be reasonable or not

PS I should add that "slamming the hammer down at 1000rpm" is not a reliable test for any purposes because there will be an inevitable transient mismatch of airflow and fuel delivery and in an extreme case you can get backfiring leading , particularly with DCOEs , to a carburetter fire . Try feeding the throttle in gradually over a period of perhaps 1 to 1.5 seconds .

[Paul bow]

Thank you guys for your feedback..
much appreciated..
So the car went to atspeed rolling road in Rayleigh they changed on the carbs the jets , tubes and choked to..
Choke 32, mains 1.45, f16 tubes, air correction 220.
I drive the car out happy, however after 100 miles the car was backfiring, and sluggish,took out the plugs and they were all covered in soot .. thick soot.
Took it back to them, they didn’t put it back on the rolling road just changed out the idle jet on the pavement (?) and sent me on my way. Mmmmm
Anyhow after speaking to rob beere, I advanced the timing from 4 to 10.
The 123 ignition has I think 14 settings mine is set in 7, swapped the plugs from ngk bp7es to bp5es, do a hotter plug, balanced all the carbs on an airflow meter reading around 6 on that. It runs much better, albeit still a bit rich, yet the mixture screws are only out between 1 and 1/12 turns...the car had a bit of a lumpy tickover, like it was out of time , yet it revved effortlessly.. checked the crank damper just a thought perfect. This is where I wondered if 12 deg or more would be too much advance, albeit at 3000 rpm I only get the timing at 29 deg, no more I believe it should’ve around 34?
the plugs are cleaner, it seems to run hotter at 12deg is this to be expected.. so many variables!
Am I missing something here.
Thanks again

[abowie]

The long and the short of it is that as said above you need to take it to someone who can tune Webers and do it properly. This is what I would do were it my car and I wanted to keep the Webers.

WRT advance, I agree your 29 degrees sounds a little small. You could try the old quick and dirty method of advancing it 2 degrees at a time until it starts to ping and then pull it back until it stops, but without objective dyno numbers you risk engine damage if it's lean. Does the 123 offer a curve with more (32 to 34) total advance starting from idle at 10 degrees?

Again, if you were keen to try tuning it yourself you could fit a couple of O2 sensors and make adjustments based on those numbers, but this is something I have zero experience with myself.

Finally, not wanting to sound like an arse but I have 3 E types all running SUs, standard plugs and standard distributors with points. They all run perfectly.

[Tom W]

Reading the problem you describe, there’s several things going on, and it can be tricky to determine what the root cause is for each problem. With Weber’s, nearly every setting changes at least 2 things so it makes it very difficult to tune out specific faults without affecting something elsewhere.

You can get some way towards setting things up on the road by feel, but to get it spot on you need some way of objectively measuring what each change does to the performance. Ideally you need to be able to overlay other engine parameters (lambda etc) against power. Possible with a data logger and timed runs down the same stretch of road, but easier on a rolling road. Be aware that as you get everything dialled in, the natural variation you’ll see run to run is greater than the difference in performance you’ll expect to see from a given change.

Firstly, you need to determine the maximum ignition advance your engine needs. This is more a product of cylinder head design and effective compression ratio than carburettor manufacture. Also, more isn’t necessarily better. It’s more a case of keep adding it until the engine either pinks, or fails to make more power, then come back a bit. This is very difficult to do precisely on the road. Also, get it wrong and you risk engine damage. Jaguars book figures are a safe starting point, but are quite conservative compared to what conventional wisdom suggests a hemi head needs. I’m not sure why, so exceed it at your risk. If you’re using curve 7 on the Jag123, set at 14 degrees at idle, you already have 40 degrees at 3300 degrees.

If you’re adding more low down advance, you need to select one of the shorter curves, so you don’t keep adding more at the top end too. I.e work from the top back, not the bottom down. The challenge with the Jag123 is finding a curve short enough.

Returning to the carburettors, Weber’s are good at masking errors at the top end. At wide open throttle once the main jet comes on they usually go well irrespective of whether the settings are spot on or not. Performance low down and at transient throttle are far more sensitive to errors. First you need to make sure all the basic settings are correct. Are all the float levels the same? Is the linkage set correctly so all 6 butterflies open the same, do all 6 chokes flow the same. Don’t assume the professionals will have checked all this unless you’ve seen them do it. In my experience not all of them go back to first principles, some seem happy to try tuning the car in the condition it’s handed over!

You describe the engine stumbling slightly on snapping the throttle open. This adds an extra level of complexity as the pump jet comes into play here. As you open the throttle and for a moment after the mixture is temporarily enriched (as it should be). Over this period the actual mixture is controlled by so many factors, it’s difficult to determine which ones are incorrect. You can see how the pump jet settings are by experimenting rapidly the throttle open from a steady cruise at higher RPM, say when overtaking etc. Does the engine pull cleanly if you open the throttle wide more gently?

You need a methodical approach to determining where the engine doesn’t run right, and where it does run right, and what the parameters are in those situations. E.g. throttle position, RPM, load, transient or steady throttle.

[Paul bow]

Thank you for that informative post.
I couldn’t agree more with the Webber’s at full chat, she absolutely flys along not missing a beat.
However on an over run (ie throttle closed) it’ll pop and bang out the back, it never bothers me at first but it’s a little too much, I’m taking it to goodwood in a few weeks and that sort of behaviour is just not ‘cricket’ up there!
Maybe I’ll just have to bite the bullet one last time and perhaps try Northampton motor sport as recommended. Just after my last experience (at a rolling road costly too) I’ve kind of lost all confidence in them, also the car seems so close.
My fear was that all 12 deg advance I could be doing damage? The engine is not pinking, however it seemed to run a bit hotter, at least the plugs removed where nice n clean after a 40 mile run.
So 12 deg advance at idle, with no pinking is ok and maybe a tad more too??
Thanks for the help

[mgcjag]

Hi Paul...back to basics.......double check you initial timeing pointer setting engine at tdc and pointer set to it.....cam timeing....who set it...is it correct......initial static setting of 123.....are u useing the green led to set it.....curves.....beware whats printed per the curves....one of our members measured the various curves.....7 i think gave 41 deg.........if your on a 4.2 basic engine your start point should be 10deg btdc......then about 21 deg max mechanical and 9 vacume so total about......so around 31+9......you can look at the dizzy curve figures in the jag service manual........i assume your useing a timeing lamo to check your advance........Steve

[Tom W]

Unfortunately trying to recommend a non standard ignition setting by diagnosing a car over the internet is a gamble at best. All anyone can do is say what’s worked for them, or repeat what they’ve read elsewhere.

I found my car on Weber’s responded better low down to more ignition advance, but that’s just my experience on a 100k mile engine with a few other non standard bits.

However the important point to understand is whatever you add to the bottom, you add everywhere throughout the rev range unless you select a different “length” curve. If you want to add 2 degrees at the bottom end, but don’t want to change the advance at the top end, you need to select a curve that has 2 degrees less total advance than the current one. With the pre-programmed distributor there are only 16 choices though, grouped into 5 different “lengths”, so there’s only so much you can do. This makes more sense with the 123 instructions. If you have a programmable distributor, 123Tune etc, then you can draw any curve you want.

Do you have the vacuum advance connected anywhere, assuming you’ve bought a 123 with that facility? There’s an awful lot of miss information surrounding Webers and vacuum advance.

Regarding popping on overrun, there’s a few other things that can contribute to that beyond carbs and timing. What exhaust do you have and are you running standard camshafts and cam timing? Are all the exhaust joints gas tight? Mine pops and bangs too, and so far I’ve not been kicked out of Goodwood.

[Paul bow]

Thanks again I love this forum such a wealth of knowledge..
Yes it’s all standard cam timing, I did it my self and spent a lot of time getting it absolutely spoton, Hayward Scott exhaust and headers..
I’ll start again today and let u know where I end up, prob with a booking at Northampton motorsport or Tom Barclay who also now has a rolling road and well recommended by rob beere, been here once before a really nice n knowledgeable guy
Thanks again

[abowie]

Best of British and keep us informed!

[Paul bow]

Well guys, with the recommendations on here about Northampton motorsport I spoke to Steve up there today, most helpful and decided that with so many variables trying to get this infinite balance was really past my knowledge, so booked it in there, although they are so busy, earliest date was 1 November!
Anyhow it’s booked and I’ll live with a few pops n bangs till then...
thanks for all the great advice as usual guys, great forum of knowledge here..

[abowie]

.
So 12 deg advance at idle, with no pinking is ok and maybe a tad more too??

The issue with pinging is where you are at full advance, not where you are at idle. The dizzy curve is set up to offer a maximum number of degrees of advance past the set (static) starting point.

It is much easier to measure the advance at idle than at 3000rpm at full throttle, so this is why ignition timing is set statically, with no mechanical advance on the dizzy.

Once it's set to the base setting (say 10 degrees) the distributor controls the advance curve and the maximum amount of advance, stopping when the cam hits the stop on the plate (say 28 degrees).

With a mechanical distributor, to get more advance at the top end you need to advance it at idle. So to get 32 degrees, you end up having to set it to 14 degrees at idle. The extra advance at idle is not ideal but that is all you can do, short of modifying the cam stop point or the weights/springs.

With your 123 you can choose different curves, so if you want another 4 degrees at the top you should be able to use a curve that is the equivalent of starting at 10 degrees static and advancing to a total of 32 degrees.

[Paul bow]

Abowie, thanks for that, well explained ..
The 123 with preset settings is a bit of a pain to adjust having to keep removing the dizzy to adjust the settings I understand the tune version is much better as it’s fine through an app on your phone so I think I’ll upgrade to that also .
Although at 3000 rpm the total advance is around 29 (the idle at 12) fitted with the Webber’s it absolutely flys right up to 4500rpm where it then it’s about all in, albeit I wouldn’t take it past that anyhow for all the obvious reasons !

[malcolm]

You don't have to remove the dizzy on a preset version now. The latest versions have a window and switch on the side to change curves. However, none of the preset curves are a perfect match for the e type, as i found out by measuring each curve with a lamp. They don't give enough initial advance, and too much total. So the tune version is still better, although apparently a bit of a job to set up.

[frank77]

Hi Steve,
coming back to your post some 2 years ago.
I have 45 Webers with 3 progression holes on my 69 S2.
Car runs fine, idle and full power is not an issue. But to get the lower progression range in between ok, I have to run this range a bit fat. And still there is a little flat spot at ca. 1500.
I read about the 45 Webers with 5 prog. holes. Would you expect to get an improvement here ?

Cheers, Frank

[mgcjag]

Hi Frank....if its me your refering to me....i know nothing about webbers...my posts above were just related to the 123 distributor.....Steve

[frank77]

No problem, just saw that there a 2 Steves around.
I meant the other one: bitsobrits

[bitsobrits]

Generally speaking, a 5 hole progression circuit should be better for a street car, giving the possibility of a more linear transition from the idle to the main circuit, assuming the jetting is otherwise correct. However, there may be other factors at work here, such as exhaust system or timing. Are you running factory exhaust manifolds or aftermarket? If aftermarket, what is the design of the manifolds? (I.e. short tube or long tube header). The short tube 3 into 1 headers which are a fairly common offering these days (with the side by side i.e. wide collector design) tend to create a mid range flat spot. Long tube headers with primary tubes that are not too large (1 5/8" or 1 3/4" max on a mostly stock engine) are the way to go here.

When you say the transition range is a bit fat, are you getting there with a somewhat rich primary or main circuit? You can get there either way, and via jets or air correctors, so unless you have explored all those options, you may want to spend more time testing other idle/main jet/air corrector combos before you splash out for different carbs.

As for timing, Webers (when correctly dialed in and compared to standard carbs) tend to like higher initial advance (like 12-14 degrees) and a somewhat rapid advance curve, but no more than standard total advance.

Getting Webers (or Dellortos for that matter) truly dialed in takes time, money, and a methodical approach, but once done correctly can be perfectly tractable and actually fuel efficient if you can control your right foot.