Series 3 idling

[chris420sa]

I'm aware that a similar topic has previously been posted but would greatly appreciate assistance/direction to previous pertinent correspondence.
A previous owner had attached an "external spring" on each of the rear RHS throttle lever and front LHS throttle lever, each spring being then attached to a makeshift metal plate. This seemed to provide the correct tension to ensure that the engine quickly returned to normal idle speed. Being a great believer in getting back to the original, I removed the carbs, replaced all 4 throttle return springs (and have the cuts and bruises to prove it :lol), refitted and set the carbs up, using a flow meter to synchronise. However the engine does not return to normal idle (650-750 rpm) but remains at about 1,000 rpm until I give the throttle a quick "blip".
Could it be that the throttle return spring (C34301) on the pedestal is the problem? If so, it seems that such a spring is not available from any of the usual UK Jag parts suppliers. Any ideas where I can get such a spring?
Of course my learned brethren may also offer some alternative advice as to how to resolve the problem.
Look forward to hearing from you.
All the best, enjoy the weekend.
Chris

[Whitact]

Hi Chris,
I had a similar problem on my OTS, which got progressively worse as the engine got hotter. It was particularly annoying in slow heavy traffic as the idle speed would just keep creeping up.
In the end I sorted it by dismantling, cleaning and oiling the capstan and refitting with as many turns of pre-tension on that spring as I could manage. After carefully adjusting and lubricating all the rest of the linkage I managed to get it set up so that it would snap shut every time to a regular 650 rpm idle.
Cheers

[MarekH]

Dear chris,

If you look at the throttle pedastal from above you ought to see that the spring end protrudes through the top through a little hole.

If you need more tension, then simply drill another tiny hole in the capstan top some way further around on the same radius and you can operate with more tension without resorting to an unsightly external spring or having to throw any money fixing the problem.

kind regards
Marek

[chris420sa]

Dear Marek and Adrian - many thanks for your advices. I have done as you have suggested. There were 2 holes in the capstan (probably for LHD's?) so I moved the spring to increase the tension. Unfortunately that has not solved the problem and the idling remains fast until I kick down on the throttle and wait quite a while (patience seeming to be a necessity when owning a Series 3).
Both chokes are fully off.
Would appreciate any further advice/s which you can kindly provide.
In the Repair Operation Manual under 19.20.05, Item 3 requires: "check that the angle across the top of the LH bellcrank equals that of the RH bellcrank; if not...etc"
That seems to be easier written than done as I am not sure what the reference point is to measure the angle with any reasonable accuracy.
My throttle linkages onto both of the rear carbs have quite a bit of play at the operating cranks on the throttle spindles and I wonder if I should try to take up (some of) the slack by adjusting the lengths of the vertical links?
Look forward to hearing from you.
All the best
Chris
PS Can you access the photo of my etype which was taken with an infrared camera by a friend of mine. Interesting that the Signal Red (and the grass and leaves) come out white.

[MarekH]

Dear Chris,

From your description it sounds as though the linkage is binding at some point and it should not.

Once the engine and linkages are warmed up, if you disconnect the linkage connecting rods then it should not affect the idle and you should make sure that all four carburettors are adjusted individually for equal airflow. Verify that the throttle spindles are not binding.

Then you can reconnect them so the front and rears are connected. Verify that the linkage can move and return without binding on each side.

Next reconnect the vertical links, removing free play and retest. It is surprising how many cars do not have the linkages moving in a single plane and this makes them bind. This is probably where your problems lie.

Finally reconnect the two long links and remove the free play. The throttle should move without sticking.

There is a similar write up on the AJ6 website for later v12 engines and you should be attempting to do roughly the same but with the four carburettors rather than two six cylinder plenums.

kind regards
Marek

[Whitact]

Chris,
In addition to Marek's comprehensive guidance one more thing to double check would be the fast idle cam clearance and adjustment of the "choke" cables to ensure that these are not contributing to your problem.
Cheers,
Adrian

[chris420sa]

Dear Marek
Many thanks for the valuable advice which I'll apply this weekend.
Just a few questions for clarity, if I may:
1. The importance of the Manual's 19.20.05 check that the bell crank angles are the same on LH & RH?
2. How does one check that angle? And at what stage in the linkage adjustment process?
3. It would not seem that the throttle capstan return spring can assist the LH and RH throttle spindles return to slow idling speed (please see 4. below) but essential that the horizontal links from the capstan do not prevent the return to slow idling?
4. When the horizontal links from the capstan are disconnected from each of the bell cranks, the levers from each rear carb throttle spindles attached to the vertical links can move freely and do not cause any tension to result in the capstan return impacting the throttle spindles
5. Could you please provide a link to the AJ6 website to which you refer.

As ever, your advice is much appreciated.

Adrian - thanks for the reminder re the chokes, will ensure that does not interfere with the set-up.

Looking forward to a successful "idle" weekend!

Best regards and thanks again.
Chris

[MarekH]

Dear Chris,

1/ The importance relates to geometry. The levers will move in an arc.
This means that the amount of "useful" movement is related to angle and you can get your old maths notebooks out and look at your sine and cosines to work that out. If the angles are different, then one side's throttle plates will move disproportionately to the others initially and then they will constantly be out relative to each other as their motions overlap.

I'll bet most owners have never checked this or even knew it was in the manual. What I think is more important is that every force acting on that spindle acts in the same plane. If not then this is one of the prime causes in your throtle return sticking slightly and I'd more focus on that part of the geometry than the exact angles.

2/ You'll have to attach a straight edge to something and estimate. If you are higfh tech, two of those little laser pens that pilots at Heathrow complain about will assist. Failing that get a cat and sooner or later your will buy a laser pen cat toy so your cat can chase the red spot across the living room. Attach the mouse shaped toy to the throttle and proceed as before.

3/4/ It sounds as though the vertical links and their relationship to the pivots are not in the same plane. None of the throttle linkage should be binding or resisting moveemnt anywhere.

The general way to solve this is to start at the carburettor and work your way back to the capstan. If for example, the throttle spindle bushings are buckled and twisted on the throttle spindle in one carburettor, then not fixing that will always result in a sticking throttle. Once that is verified working well, then slowly work your way, link by link back towards the centre of the car, reconnecting and testing step by step.

5/ No - use a search engine and enter "aj6 website".

kind regards
Marek

[jagwit]

Chris, in response to your request above, I've decided to write up the method I use to set the 4 carbs on a V12, for what it may be worth. If anyone spot a flaw, please let me know. I've written this from memory (blond, blue eyes, 55, male etc...) without reference to any other methods. I believe your questions should be answered herewith.

1. Remove the two long throttle rods from the bell cranks and capstan and loosen the nuts at both ends and check that both ends can adjust freely. Adjust them to their shortest position (both ends screwed in) but do not lock the nuts. (Note that one end has reverse thread!!)
2. Loosen the lock nut of the fast idle screw on Part # 12817 and turn it in to be well away from the choke arm – both sides;
3. Loosen the bolt (or nut) of part # 12843 on both sides of the engine. Check that the butterfly shafts of the two carbs can move freely and entirely independent of one another;
4. Set the screw on part # 12860 so that the tab of #12843 presses the spring loaded pad below it to sit at about 50% of its available travel. This is to allow max adjustment between the two carbs once the bolt on #12843 is fastened again;
5. Check that the bell cranks have the longer arm closest to the throttle capstan (These where wrong on a car I worked on and resulted in the carbs not opening the same amount and also could not be opened to full throttle on one side) and all ball joints should point rearwards. The shorter arm of the bell crank should have the short throttle links to the carb actuator arm; ;
6. As with long throttle rods loosen both lock nuts on the short throttle rods on both sides and adjust them to their LONGEST length leaving enough thread to be locked with the nuts and lock the nuts. Leave them connected to both carb and bell crank. The angles of the bell cranks should now be the same to the the naked eye;
7. Now start the engine, let it warm up fully and then, using the idle set screw (that presses on #12862), set all 4 carbs to draw the same amount of air, whilst also getting the engine to idle at the correct idle speed. (I suggest 950rpm for auto and 850 for manual, add 50 rpm if fitted with A/C.) After having set each carb’s air open just that carb and let it snap shut, measure again that the air drawn is still the same. (they can be somewhat sticky in this “almost closed” position.)
8. Now set the fueling on each carb by adjusting the needles. This may affect idle speed and the amount of air being drawn and now it becomes an iterative process, balancing air & setting idle speed, adjusting fueling, balancing air etc. Adjusting one carb could affect all three the others!! There is a good video on how to set the fueling here: https://www.youtube.com/watch?v=wenBlytGjSI
9. Once you are happy that all 4 carbs draw the same air, idle speed is correct and fueling adjusted correctly, we can now tighten everything up. First is the bolt on #12843 which now locks the two butterfly shafts of the two carbs together – on both sides. Check that air drawn has not changed. Open each side using the bell crank and let it snap shut again checking that air remains balanced all round. The idle screws on all 4 carbs SHOULD still be determining where the butterfly shafts stop.
10. Now turn out the idle screw 1 turn of the FRONT carb on both sides. Idle speed on each bank is now determined by only the idle screw on the rear carb. Check again that air drawn is the same all round. Open and let them snap shut and test again. If not, air is now BALANCED between FRONT and REAR carbs on a bank by using the screw on #12860 - very little adjustment should be necessary. Use the idle screw on the rear carb to balance between LEFT and RIGHT banks once front and rear are again balanced.
11. Now it is time to connect the long throttle rods and adjust them. Connect each throttle rod to the pedestal and while holding the ball joint at the other end, adjust the rod length (by turning the rod, not the ball joints) so that the ball joint will go over the bell crank ball joint but leave play in BOTH push and pull directions. IF the throttle rod can not be made short enough, shorten the short throttle rods until the long rods can be connected and still have some measure of adjustment (shorter and longer);
12. Now increase the length of the long throttle rod until all play from the pedestal to the carb actuator is taken up. The tiniest rotation of the pedestal should NOT cause the throttle arm to move, but anything beyond that should cause the butterfly shaft to move. The same amount of free play should be set on both sides.
13. Now you should have all 4 carbs balanced, idle speed correct, fueling correct and it should idle sweetly. (IF your ignition system is good – but if its OPUS or even REOPUS, good luck…)
14. Now you can set the fast idle screws (when choke is activated) on both sides to your preference. The closer to the choke arm, the faster the engine will idle when choke is active.

Be patient, have fun!!

[baganz.sven@web.de]

Hi,

my carb specialist JPA, close to Hamburg Germany, has recommended to me to use stronger springs on all 4 carbs. They fit without any change to the carbs.
I have just finished the complete overhaul of all carbs but have not mounted them again so it will take some time until I can report about the behaviour but I‘m sure that the springs are now strong enough to close quickly and completely.

Sven

[chris420sa]

Dear All - many thanks for the very helpful advice. Have just completed the task and will do a road test tomorrow. I found that the bell cranks had indeed been installed the wrong way round by a previous owner.
Of course,it's also possible (?) that one of the carbs has an air leak around the rubber seal on the throttle spindle - will test by spraying some carb cleaner in that direction and see if the revs increase. Hope that's not the case as the cuts and bruises from removing the carbs previously have not yet healed!
I also moved the throttle return springs along the actuating levers a bit which seems to have increased the tension.
Just out of general interest, the airflow meter which I recently purchased from Burlen works fine except on the rear LH carb where the heater fan casing gets in the way. No 90 degree bend adaptors are available from the German manufacturers for the CD175 carb, so had to improvise with some vent tubing.
All the best and thanks again
Chris

[garry.james@arcor.de]

Guys,

this high idling when the engine is hot has nothing to do with the pedestal spring or the throttle linkages, as the carburators are only pushed open by the linkage and they return to closed independently of the linkage. To show this you can open the butterfly valve using a screwdriver on the idle screw cam lever and the linkage will not move.

I have the same problem on a V12 and have tracked it down to the right rear carburator. It moves perfectly freely when the engine is off but the vacuum acting on the butterfly valve presses the butterfly vavle spindle towards the engine. This increased friction on the rubber seals on the Butterfly valve spindle causes the Buttefly valve to stick open. The springs on the Butterfly valve spindle seem to get old and after 50 years they cannot cope with putting new seals on the butterfly valve spindle. With a quick blip of the throttle the valve closes properly, this is due to the higher spring tension at higher throttle position and then the inertia of the faster closing valve pushing it to fully closed.

I have another E-type V12 which I still need to restore and on that one someone has fitted additional tension springs from the idle cam lever to the bracket holding the throttle linkage cam. That does the trick but it makes the throttle opening worse because the additional spring rubs on the idle screw lug on the carburator.

So on this issue I can only agree with Sven and his Carb expert in Germany. Fit new or stronger springs on the spindles. Or don't put new seals on the butterfly valve spindle.

Cheers,

Garry