Setting up Strombergs

[Pete G]

After many years of painfully slow recommissioning I have finally started the engine. The ignition system is original OPUS but moved to the picture frame by a PO. The engine has not been "opened". New oil & filter and new coolant. Carbs rebuilt by me.
I turned the key and she fired up almost immediately. I followed the ROM for setting up the carbs but could not get the idle speed below about 1000 RPM on the tacho. with the idle screws turned all the way out. No choke on with the water temp gauge showing mid scale. Vacuum to dizzy disconnected and plugged, all other vacuum lines either connected or plugged. I could not find any vacuum leaks.
Any advice on what I may have done wrong to cause this and where do I go from here. I really do not want to remove the carbs. again if at all possible.

[chris420sa]

Hi Pete - your problem is by no means unique and I would strongly suggest that you trawl the forum for ignition and carb set up posts of which there are many. You'll soon work out which of the members' posts are the most reliable.
First thought is to check whether the choke cable (inner & outer) on each side is allowing the choke to be fully off when the choke lever warning light goes off. i.e. ensure that the choke operating arm stops firmly against the "square" on the choke assembly
It's commonly said that most tuning issues are ignition related and that really seems to be the place to start.
If you've disconnected and plugged the retard vacuum pipe connected to the rear LH carb underside and rear of dissie, that's good but may have impacted the timing at idle, which may have been set when the retard was operating (only operates at idle). After some 50 years your original OPUS is somewhat overdue for retirement and I would recommend it should be replaced by the SNGB "look-alike" BUT strongly suggest you also fit an advance vacuum diaphragm (the replacement ignition system is sold with the original type of retard diaphragm evidenced by the vacuum connector tube facing forwards) with vacuum pipe connected to an outlet on the the LH rear inlet manifold (not to the retard vacuum connection on the carb). Then set the timing (most probably with some help as Sir William L didn't worry too much about access to the crankshaft pulley when the Etpye was designed)- there's more about the advance diaphragm and timing setting with it connected on the forum by Jagwit and others.
The Operation Manual does not address mixture adjustment - there's a very good step-by-step set up guide by Jagwit which he posted in response to my question in 2019 - I think it was under my post titled Series 3 Idling (or similar) - you'll need a suitable air flow meter. In my case I found that the depth of the jet seat (not the jet itself) below the carb bridge (0.1 inches is the correct setting if I remember correctly) was insufficient to allow adequate adjustment of the air-fuel mixture - please let me know if you experience that problem as I can point you in the right direction.
If all that fails you may need to remove the carbs (elastoplast at the ready) and a) check/replace the seals on the thermally controlled side inlets and check the opening and closing temperatures b) seal off the " anti-pop" valves by replacing the gasket with a home-made blank gasket and c) check the mating surfaces of the choke assemblies for such wear as would allow fuel to by-pass the series of smaller holes (can often be sorted out by rubbing surface over a piece on newspaper on a flat piece of glass), as well as the more obvious butterfly closing fully, spindle seals in good shape and not too much "stickiness" in the throttle system. I'm sure you're aware of the Stromberg overhaul guide in the forum's Knowledge Base - it's well worth a read.
It's a somewhat tedious process but the pleasure after getting it right makes up for it - honest!
Good luck and please let us know how it all went.
Chris

[Pete G]

Thanks for the response Chris. I have searched for and read what I could find on Stromberg tuning but could not find anything specific to being unable to reduce idle revs. The chokes are fully off. I have tested the OPUS in accordance with the ROM and all checks out ok. All the seals, gaskets etc. in the temp. comps and air valves have been renewed and adjustments made to operating values. When I rebuilt the carbs I followed the Buckeye Sprite write up. If I remove the carbs again I will blank off the "anti-pops", I actually made some gaskets for this purpose when I rebuilt the carbs but used the ones that come in the rebuild kits.
I felt quite elated when against all my expectations it started in just a matter of seconds after not running for the last 10 years or so but that soon changed when the revs wouldn't come down.
I'll reconnect the vacuum to the dissy retard for a trial and see what happens. I wanted to get it going in its original configuration before I started to upgrade it. I haven't decided yet to go for a replacement for the OPUS
with dissy advance or go EFI.
I'll go and have another read of the forum posts to make sure I've not missed anything and give it another go. I have done nothing (I think) which would alter the timing, other than remove the dissy vac. nor have I played around with the jet seats.
I will let you know how I get on.
Pete

[madjack4]

Hi remove the carbs sell them on ebay ,convert to fuel injection ,or as i did SU carbs so much better the strombergs are total crap not worth spending money on .As for vac retard u may find tickover drops when retards is piped up but it should shut off when hot when piped through thermo valve on end of o/s inlet manifold . As said in previous post fit a vac advance unit with vac pipe to a ported vac far better makes for better MPG as runs cooler.Have a look at British vac advance co website read what they have to say about ported vac
Regard Rob :

[abowie]

Caveat: I have little experience with S3 cars or Strombergs. So I, like you, am assuming that your rebuilt carbs are working properly.

If this is the case I would be looking at the timing.

A fast idle can be caused by excessive advance. Of course the confounding factor will be that at 1000rpm you will be getting some mechanical advance as well. So if you measure it at 1000rpm it will probably be high.

Firstly, double check you have the dizzy statically timed at 10 degrees. See if this helps.

If it doesn't, try retarding the distributor a couple of degrees and see if this drops your revs. Check your timing with a light. Rinse and repeat until you have your desired idle. Now check the timing with the light again. If it's not within a degree or 2 of 10 BTDC I'm wrong and you need to look at the carbies again.

WRT fuel injection. My 1975 XJS runs four 2" SUs. Beautifully.

[Pete G]

Thanks Andrew, Bob. All info/opinions gratefully received.
Bob for info. early S3 V12 did not have a thermo valve or the facility to fit one in the o/s manifold nor for that matter in the water rail.

[71 V12]

Nothing wrong with Strombergs on the V12.

I have mentioned this before in other posts, are you sure there are no leaks in the induction/ engine breather system? Air leaks could be your problem.

There are a couple of 3-4mm pipe fittings on the inlet manifolds which were vacuum ports for the inlet valves in the air filter cases. These should be blanked. Check all of the engine breather pipe connections (there are quite a few) including the big grommet on the left bank and the cam chain inspection grommet on the right bank for splits or cracks.

When sorted you can get a V12 to idle at 500-600 rpm comfortably.

[Pete G]

I reconnected the vacuum line from the LR carb to the dissy and when warmed up the revs were at 800ish on the tacho. I only needed the choke to start the engine and could push it right in within a few seconds. The revs were at 6-700 and rose to 800 as it got up to temp. I followed the adjustment instructions in the ROM and It now ticks over at 1000 with the idle screws turns out. I suppose that a further search for leaks is required.

71v12 what/where is the big grommet on the left bank? I must be looking in the wrong place as one is not obvious to me. The cam chain inspection grommet has been replaced and is secured with the spring clamp.

Propane gas does not seem to have any noticeable effect on the revs/engine note.

[Signmman]

Not familiar with s3 cars
Do the carbs have heat compensators on them like the series 2 cars
There is an idle trim screw on them used when the engine is tight one on each compensator
I believe when seated will cause engine to increase rpms , open up to decrease fuel

[71 V12]

The large breather grommet on the left bank should be a good seal with clamps. The other area circled on the front of the right bank is approximately where the cam chain adjuster grommet is. No clamps on this one, just a firm push to fit.

My car needs fuel choke to start and run for a minute or so, I can then reduce the choke to half for about 1-2 miles until a little warm and run without hesitation.

When warm idles at about 600 rpm. Sounds like yours may be running rich. Are you sure the small vacuum ports underneath the inlet manifolds are blanked? There are 1 or 2 each side.

Regards,

Kevin

[Pete G]

Signmman - the s3 Strombergs do have temperature (heat) compensators but whether they are like the s2 ones I don't know. Each compensator has a nut which can be adjusted to alter the temp. at which the bi-metal strip operates. Each carb. has an idle Trim Screw but not on the Temp. Comps.

Kevin - yes my engine breather rubber elbow is new and firmly clamped. With you saying grommit I was looking for a rubber bung,DOH.

I haven't had chance to get back at it for a few days. When time permits I'll have another check on all the vac. connections. The lines that go from the plenums to the inlet trumpet vac/temp. switchs are plugged at the air filter ends. I'll remove the tubes all together and blank them at the manifold end, see if that helps. I was sure that all the vac. ports were plugged but I should check again to be sure I'm sure.

[chris420sa]

Hi Pete - just to check that you set the air-fuel mixture when you adjusted the carbs? If the mix is not correct it could be (??) that when she comes off choke the mix is causing the fast idle and no adjustment on the throttle idle screws? Did you manage to find the Jagwit article on setting up Strombergs which I referred to in my previous post? If not I could scan and PM it to you.
Also does the timing remain OK when things warm up a bit? I had a dicey reluctor which worked OK when first setting the timing and then went badly wrong with random chages to the timing - to the benefit of SNGB's profits when I replaced the whole ignition system.
Good luck
Chris

[FlyBoy]

Hi Pete,
Have you resolved your high idle problem?
Carb overhaul kits do not have parts to overhaul the bypass valve assemblies! The diaphragm and gasket kit must be purchased separately. Do to age and heat soaking the valve diaphragm becomes had and doesn't allow the valve to seal. Hence, an air leak resulting in a high idle. There is also a thermal valve, another emissions item, that can be adjusted not to open. That will eliminate another "problem" area without sacrificing any performance.
The bypass valves are an emissions component and not needed (unless you have to pass an emission test). Best course is to remove the valve, make a blanking gasket and reinstall the valve(s). Rebuilding a bypass valve is an effort in futility IMHO. The internal spring looses it effectiveness and contributes greatly to the problem, even when a new diaphragm/gaskets are installed. Better off without operational bypass valves!
If you car is an automatic I'd start at the transmission rear and replace ALL rubber vacuum lines if you suspect one (or more) may be causing a vacuum leak. If you have a smoke machine (easy DIY project) that will greatly help in locating leak areas.
Let us know your progress and if the idle issue is resolved.

Happy Trails,
Dick

Bypass valves connected with small vacuum line