V12 not running right - new SNG Barrat ignition

[rycymru]

1973 E-type v12 Roadster, manual, with 87k miles, owned for the past 6 years. I'll try and be thorough and give as much information and background about my E-type not running right.

I've been working on cars for over 10 years; rebuilding engines, suspension, transmission, electics, etc on Land Rovers, Audi's, and modern Jaguars. But my experience with carb and distributor cars is limited to my 1973 e-type, and i need a bit of help and advice.

After 18 months-2 years of sitting in the garage, i have the time again to get the jag up and running (clogged radiator, hot start issue and then no start issue when parked). I just replaced the ignition system with the SNG Barratt kit. I followed the manual and set the fine adjuster in the middle of adjustment before installing the distributor at 12 degrees BTDC.

The car will start with the full choke on but i need to keep my foot on the throttle for it to stay running for a few minutes until it warms up, otherwise the rpm will drop and then die. After 5-10 min or so, i checked the timing at 700-800rpm (vaccum port on distributor is capped), it was at 28 degrees BTDC, so i adjusted the fine adjustment, but it reached the end of travel and the car is at 18 degrees BTDC at idle. When revving to 3000, the timing is at 26-28 degrees BTDC. The large rebuild manual i have says idle timing should be 4 degrees ATDC, which doesn't sound right. What should the timing be at idle? I can always remove the distributor and reset the adjustment screw before setting it at 12 degrees BTDC static again.

When revving the engine it seems to hesitate until the engine hits 2k rpm, then after that it revs like it should up to 4-5k rpm. Also, it doesn't have much power under load. I haven't driven it outside my driveway.

I rebuilt the stromberg carbs a few years ago, new gaskets, needle, jets, and all. The car seemed to run great afterwards, until other issues popped up. I followed a procedure of setting fuel mixture by using the allen tool in the top by turning the needle screw all the way to the right then turn to the left a 1/4 turn. then try and balance each carb with the tool over the air inlet and adjust the idle screw. Not sure if this is correct, so please let me know if i am off.

I'm not sure if its an ignition timing issue, or maybe fuel issue? Gas tank was cleaned out, new pump, new fuel filter several years ago and gas is reaching the carbs. Should i redo or look into the carbs as well and see if that is an issue? As with most large projects, i can focus so much on the large items, that i miss something small/or obvious.

Considering the car won't idle without me hitting the gas until its been running 5-10 minutes, what should i look into first? Thank you for any help you can give me.

Ryan.

[christopher storey]

I have to say that your timing sounds strange . Are the bob weights in the distributor working correctly and are the springs in good order ?

The other aspect which is notorious for causing poor running in a V12 is vacuum leaks from the various breather etc pipes . Have you tried a vacuum gauge on the inlet manifold(s) to see whether it will pull steady vacuum?

[jagwit]

I believe the SNG kit comes with a vacuum RETARD module (vacuum connection on dissy side of the "flying saucer") on the dissy as per the original V12 setup. This vacuum retard setup was Jaguar's solution to meeting the emissions targets OF THOSE DAYS, and is, in my view, an abomination just as scandalous as VW's dieselgate. The only difference is that VW's tricks only applied during emissions testing, whereas the Jaguar solution stayed with the car for all its life - at the expense of the owner and to the detriment of the engine.

So, the first thing you should do, is disconnect the vacuum to the retard module. Plug the pipe you disconnected and never connect it again. Unless... Better still is to obtain a vacuum advance module JLM519 and install that, I'll come to this later.

First thing is to get the timing sorted. Since you have run out of vernier adjustment, you will need to adjust the base of the dissy, by loosening those 3 allen cap screws in the base of the dissy and turn the entire base.

"The Books" is always based on meeting emissions targets - OF THOSE days - not what is best for the engine (and your pocket). 12degBTDC at idle is a good figure to go with since the E-type V12 is a low compression engine. It should then advance at least another 15degs (not sure of the actual value) when revving it up to around 3000rpm. Timing MUST be correct before you do final carb tuning.

Your method of tuning the carbs for fuelling is good , to start with, but it requires further tuning to get it to optimal as now its most likely running (idling) very rich. The idea is to set the carbs as lean as what the engine will tolerate. What makes tuning a bit tricky is that both carbs feeds into a common plenum, so effect of adjustment of one carb is somewhat blurred by the other carb. Do not turn anti-clockwise by more than 2 full turns from fully clockwise.

Now, I HIGHLY recommend fitting the vacuum advance module. If you do, timing is still set with the vacuum line disconnected but once correct, you can connect the vacuum line to those very small nipples between the front and rear intake manifolds. EDIT: You should notice the idle speed increase when you connect the vacuum line (due to improved efficiency resulting from more advance) which may require having to re-set idle speed.

The choke mechanism should open the throttles for you when active. Having to apply foot only means the choke mechanism may not be set correctly.

[christopher storey]

12degBTDC at idle is a good figure to go with since the E-type V12 is a low compression engine

I'm not quite sure what your definition of low compression is, but the V12 in any of its guises is not in my book anywhere near low compression at 10:1 with the Heron heads and 12.5:1 with the May heads . However, I would not differ greatly from your 12 deg BTDC at idle, provided that it does not cause pinking under load

[jagwit]

I'm not quite sure what your definition of low compression is, but the V12 in any of its guises is not in my book anywhere near low compression at 10:1 with the Heron heads and 12.5:1 with the May heads . However, I would not differ greatly from your 12 deg BTDC at idle, provided that it does not cause pinking under load

My definition of "low compression" is anything from +-9:1 and less.

I would be interested to know which "book" tells you that standard E-type compression ratios are 10:1 and up. Your information is correct for later XJS. My '80 XJS pre-HE is 10:1 and my DD6 I had was 12.5:1

Engine number suffixes indicated compression ratios on the E-type V12s: I understand that LA and LB suffix was 7.8:1 CR and SA and SB suffix was 9:1 CR. I believe that 7.8:1 was more intended of the USA market.

[christopher storey]

Ah, well I stand corrected.

[rycymru]

Thank you for the responses and advice. The vacuum retard on the distributor is capped and will stay that way. The emissions parts were removed before i bought it. On the driver side intake, if i remove the small hose going to the carbs or remove the larger hose going to the vacuum tank, the engine idle increases as it should.

I adjusted the distributor to 12 degrees BTDC at idle as mentioned above. I also adjusted the choke as suggested, one side was way off which led to the cold idle issue; it is now fixed and revs at 1600-1800 rpm when cold and full choke is on. I have adjusted the fuel mixture, currently 3/4 to full turn from the full right position.

I was able to drive it out of the driveway and down the street and it has more pull than a week ago. But, it feels like it only has 40hp. When i hit the throttle it's taking its time getting moving up the rev range. I only drove it 4 houses down and back and forth so i didn't go far.

This could be nonsense, but i did replace the entire exhaust system with a Bell stainless steel system this winter. Could something have gotten inside while in the box / or when i had it laying on the floor before install and restrict the exhaust giving me this no power issue? The old exhaust was rotted and blew a hole in the muffler years ago.

I'm grasping at straws since the carbs seem to be tuned, spark plugs are good, new ignition system, and timed correctly. Any further help is appreciated.

Ryan.

[vee12eman]

Hi Ryan,

There is a possible solution, or at least something to check. Have you reconnected the throttle linkage to both sets of carbs? It's quite possible to connect only one bank, then pull away, noticing a distinct lack of power, although "40hp" seems low. Idle will still be fine, but effectively, you are only accelerating on six cylinders. Sometimes when you have been tuning carbs, you may have failed to correctly connect one linkage, it's not unheard of.

If you haven't actually tuned the carbs, which I'm not sure that you have recently, having re-read the thread so far (forgive me if I am have missed something), then it's probably wise to do so. I can send an article on how to achieve this that I wrote some years back for the E-type club, if you PM me your email address. If you are a member of the club, then it's in the May 2014 back issue available online. It should help you understand the process and do the job successfully yourself. It seems you have the necessary tools for carb adjustment.

Another suggestion is that the carb pistons may be sticking, since the car was sitting inactive for 18 months. Just check they are all free to move, both up and down.

Regards and good luck,

Simon

[jagwit]

Lack of vacuum advance typically makes an engine feel lethargic on partial throttle.

But with "only 40hp", I tend to agree with Simon that IF carb tuning and timing is good, most likely you have air supply issue. I had this issue when rebuilding a S3 for a friend. Turned out the vertical shafts were too short and the throttle "bits" were assembled incorrectly (by me ) resulting in the throttles not opening fully. On that same car I found some of the air valves (pistons) installed the wrong way round. Then they won't lift up effectively choking the engine.

Only other causes could be poor compression or bad cam timing.

[jagwit]

I only drove it 4 houses down and back and forth so i didn't go far.

I find that my car is also rather down on performance until its off the choke AND the carbs have some heat in them. So do not expect full performance with a cold engine.

[rycymru]

The throttle linkage is connected to both sides of the carbs. I have tuned them according to some things i've read along with the manual. Back off all the carb idle screws/carb balance screw and start with carbs in the back and get eh idle to 750 while having the pressure gauge over the air inlet the same on all 4. I may have missed something. All 4 pistons rise when the hitting the throttle, so they are not sticking.

But, on Saturday while playing with it, it starts on full choke, but dies after the choke is pushed in. Even after idling for 5 min and hitting the throttle didn't keep it running. I was frustrated with the car and called it a day. I'll try and make some time this week to have anotehr look and see if there is somethign i missed or explains the issue.