Choke module wear

[Dave S]

I will be rebuilding my Strombergs over the winter. I have noticed that there is quite a bit of wear in the choke module spindle and/or bearing bush. Does anyone know if this will adversly affect the operation of the carbs?

I will be ordering a rebuild kit from Burlen but this does not include any parts for the choke module. Therefore, I am trying to decide if I need to find parts or source replacement choke modules or just leave as is. There is no problem starting the car.

Thanks

[jbuckl]

Imho these do wear, and sometimes stick too.
I don’t know of a source of spares.
You’re probably stuck with trying to buy less worn used from the usual used specialists ….
Or sleeve with thinwall brass tube and go undersized on the spindles (clean - up on a lathe)

One other possibility is to cut an o-ring groove in the spindles…. Never attempted that myself…. But have mused about it.

Did encounter this wear previously…. And small fuel leaks from them.

Was lucky enough to win a nos pair of complete carbs from eBay though for a bargain price….. so never refurbished the old chokes.

I have noticed fuel weeps from many choke mechanisms on strombergs in recent years. Nothing major and usually gone when the chokes are off.

[marshman]

Not convinced the spindles do wear. When I rebuilt my carbs I noticed that the spindles were a very relaxed fit so looked at swapping the choke modules for those off of some other new old stock carbs I had (not Stag ones). When I removed the new old stock modules the had the same "sloppy" or "relaxed" fit. The "seal" is formed by the choke "disc" being pressed against the carb body by the spring. More likely in my opinion is the spring "ageing" and not pressing the disc against the body firmly enough and causing some seepage, or the surface of the disc/carb body wearing. I would have thought wear on the spindle to be very low - how often does the choke get operated compared with that of the throttle spindle??

[APS]

Not sure if the OP has this problem, hence why they want to replace the choke spindle but ....
When I refurbished my stroms a couple of years ago, I had problems with one of the chokes leaking a little fuel.
The refurb kit came with gaskets for the choke, none fitted originally, but that made no difference to the leak. Forum wisdom says gaskets not needed.
On further investigation the new float needle valve I had installed was sticking.
Put the old one back and no more leak. Renewed the needle valve a second time, just so I know the carb is fully refurbed, and it's been good since.

[Dave S]

Thanks for the comments, food for thought. There is a slight weep of fuel from teh choke module on the carb with the worst movement/wear. I will investigate further when I take them apart.

There is also wear to the main throttle spindles/seals/bushes, both along teh axis of teh spindle as well as vertical to the spindle - so new spindles and butterflies required. I think this is the main issue with trying to get a steady tickover. From the comments made I am deducing that the choke assembly is unlikely to affect this. Once the engine is warm and the choke is off you can wagle the offending choke spindle without apparent affect to the engine.

[jbuckl]

Good to hear that slop isn’t actual wear….

However modern fuel systems are far more sealed than in the 70’s….

Hence the o ring suggestion.

[trunt]

I feel that the disk and surface on the carb body that it runs against is the most important thing. Before any fuel gets to the shaft then that interface has to leak first. Also that shaft needs to be free so as to to fully apply the spring tension to that interface, if it binds then leaks may occur, maybe even air leaks.

I’m pretty sure the fuel level is below this device and the fuel is only drawn up by the depression in the Venturi so it shouldn’t leak otherwise

[Philip Wardle]

Don't forget Richard's excellent video, it gave me confidence that mine were fit for service ...

https://youtu.be/LlrVi6Y2wx8?si=-mvS6Nf-aX4zfr7C

... and this one by Chris ...

https://youtu.be/DnR-ysCLy44?si=ZMes8y-0W7qx-7g1

[MikeParker]

I feel that the disk and surface on the carb body that it runs against is the most important thing. Before any fuel gets to the shaft then that interface has to leak first. Also that shaft needs to be free so as to to fully apply the spring tension to that interface, if it binds then leaks may occur, maybe even air leaks.

I’m pretty sure the fuel level is below this device and the fuel is only drawn up by the depression in the Venturi so it shouldn’t leak otherwise

+1. Slight play or even air leakage past the shaft will not do any harm providing the mating surfaces of the metering disk and the carb are smooth and flat. That is the only path for the air - between those surfaces. If they do not mate properly, then air leakage is not your main problem; excessively rich mixture is more likely. I did wonder when I refurbed mine whether there was a good way to flatten them and remove any scratches? 1200 grit wet and dry on a machined flat steel surface perhaps? In the end I decided I would probably do more harm, so did nothing.

Check the metering holes in the disk as well as the free movement of the disk along the shaft. The finest hole in the metering disk is very fine and looked blocked on one of mine. I used a fine piece of wire (one strand out of a multi-strand electrical cable core is good) to poke them through.

[Philip Wardle]

I found that old-style fuse wire is good for cleaning metering holes because it's made of soft alloys.

[mole42]

Accepted wisdom is to use only compressed air to clean the holes in the start device. On mine (1970 spec 3382) the holes are 0.5mm, 0.5mm, 0.6mm and 0.7mm in soft alloy, so you don't want to risk enlarging them with anything mechanical.

[marshman]

^^+1 a stiff bristled brush and your favourite cleaning solution then blast with compressed air. I would never "clean" or "unblock" any small holes/jets/orifices in any carburettor with a hard "mechanical" item.

[richardthestag]

Carb cleaner every single time.

Easy enough to separate the 2 discs from the shaft to give them a good clean with carb cleaner and the wife's toothbrush. Reassemble and then give the shaft a very light tap with a thin screw driver and hammer to secure it in place.

Be sure that the disc with the holes in it it perfectly flat and do try to reinstall it back onto the shaft the right way around..

Similarly when you refit to the carb body and before the control arms are attached it is possible to get them 180degrees out.

Don't bother with the ring shaped paper gasket. Never yet had one leak fuel after refitting, a smear of hylomar is usually enough. Factory never used a gasket, that I have been able to find anyway.

Fuel should never get as far as the bush that the shaft runs through

Once everything is back together be sure that you can fully open the cold start module and that it springs fully closed. If is doesn't then there is something wrong.

[Dave S]

Thanks all for the advice, very helpful. I am waiting for Burlen to get back to me so I can order the correct refurb kit. Of course no tags on my carbs. From the state of the dashpot screws they have been attacked many times, or wrong screwdriver bit used. New set of screws also ordered.

[richardthestag]

Stag carb models from Burlen website.jpg

in fairness to Burlen but the majority of rebuild and service kits for the Stag will be much the same.

The only issue I have encountered is that the throttle shaft on the RH carb is shorter on the stag than the majority of installations .. i.e. the stag carb forward throttle shaft is blanked. All you need to generally do is shorten the shaft required with a hacksaw