Spring Size

[AlanBartlett]

What size spring do I need for the butterfly flaps on the carb? Or does anyone have one I could purchase



from what I can remember of it, it was mounted where the line points

[Keith Andrews]

The carb butterfly spring...any engine , should be light as possible.
This pulls sideways on the butter fly bushes, causing wear on unlubricated surfaces, resaulting in air leaks, lean mixtures....often shown by popping out of the exhaust when one lifts off the accerator.
If you require a heavier accelerator, do not increase the throttle return spring, but increase the spring, or add a spring on the accelerator pedal linkages.
This is why accerator linkages are designed not to link directly to the butterfly, and often have the main spring for the pedel, under the dash.

[AlanBartlett]

So in simple terms your saying use the spring which is mounted to the floor where the pedal is?

[AlanBartlett]

So in simple terms your saying use the spring which is mounted to the floor where the pedal is?

[Keith Andrews]

u have to have a light spring on the butterflys, to be able to just hold the butterflys closed, without accessive loading on the bushes....

IF the accerator is too light for your preference THEN the underdash linkages spring should be increased or srtonger spring added there.

[Tony Fearn]

I think that Keith and Alan are at cross purposes here, perhaps because Keith has never seen the mediaeval choke arrangement on the pre-war Jowett carb.

Keith is probably talking about springs involved with the internals of the carburettor, whereas Alan is just talking about the little spring that fits at the bottom of the 'closure plates' on the "elephant's ear" bolted onto the 30VEFH carb used on the 1934 Jowett saloon.

I have found that if the wire in the choke cable (the former being a bit like a stiff piano wire which is soldered into the choke button on the dash) is set up properly using the fastening screw on the right hand 'closure plate' of the "elephant's ear", then the pull and push of the choke button in its slide on the dash board will open and close the choke without any need for a return spring.

The accelerator pedal linkage return spring, fastened at one end to the floorboards and to the linkage at the other, within in the engine compartment, has nothing to do with the choke arrangement, and as Keith has said can be changed for preference of a light or heavier accelerator pedal "feel".

If this spring breaks or comes loose then the butterfly within the carb will "failsafe" to fully open. This will of course unleash the unbridled power of all those 17 BHPs, so just stick your toe under the pedal and ease it back until you can stop and remedy the problem unless you want to experience the Maclaren F1 feeling!

Tony.

[Keith Andrews]

The accelerator pedal linkage return spring, fastened at one end to the floorboards and to the linkage at the other, within in the engine compartment, has nothing to do with the choke arrangement, and as Keith has said can be changed for preference of a light or heavier accelerator pedal "feel".

If this spring breaks or comes loose then the butterfly within the carb will "failsafe" to fully open. This will of course unleash the unbridled power of all those 17 BHPs, so just stick your toe under the pedal and ease it back until you can stop and remedy the problem unless you want to experience the Maclaren F1 feeling!

yes thats what Im talking about......similar to the bradford setup...
"will "failsafe" to fully open." for saftey reasons, and is an essentual part to prevent 'panic 'situations. and 2nd light spring should also be attached directly to the carb butterfly shaft.
If a linkage/spring breaks/disconnects, the carb returns to idle, and one dosent run to a powerpole a person or other cars at a run or display.
This also takes up any slack in the linkages and holds the butterfly shaft idle adjusting stop lightly against the idle speed adjusting screw.

[george garside]

I get the feeling that some are talking about the throttle butterfly Whilst the original quetion related to the two side flaps on the horn, cows ear, elephants ear or whatever that formed the' medieval' choke on mid thirties onwards pre war twins, i.e. there was no choke butterfly in the venturi as used in Bradford. Therefore fail safe not relevent - if on the other hand we are talking about the throttle butterfly it is! The only frunction of the 'choke' spring is to keep the flaps away from the orifices during normal running so precise strength of spring prabably not important & if all else failed a piece of knicker elastic could be pressed into service

[Keith Andrews]

yes, correct
Alan is a keen young lad...and from what see of the guy desersves every bit of support..
And maybe Im a bit baised....
A young lad , no Dad...in retrosect I know what thats like, have them pass on just when u realy need them...
He is working on the carb, knowing how and why all linkages work is important for young guys. That way they they dont make mistakes, get it all right 1st time around....and dont have their cars, unexpectedly take off into a row of classics.
The important thing is not who is interpeting the question correctly but that he has as much info AND whys.

[AlanBartlett]

I get the feeling that some are talking about the throttle butterfly

Yeah, although my diagram isn't clear that is what I'm trying to find out. So from all the info provided here your saying it needs one but can get away with the choke cables tension, and that the spring mounted on the floor board is enough to allow movement of the flaps on the carb. Am I correct would you like me to post pictures up... Or bring some along too the national at the weekend?

[Tony Fearn]

Alan,

It's good to know you are coming to Warrington. From the numerous replies to your queries it's obvious that quite a number of us are re-living our early involvement in the pre-war Jowett scene, many years ago, through an interested young man.

Bring all the pictures to the NJW. Write down your questions in case you forget some of them. There will be quite a number of pre-war vehicles for you to look at and photograph so bring some spare batteries for your digital camera. I think KC will have a laptop there so he can do the Skype thingy to the rest of the world. I'm sure he could show us a CD of your pictures on which you need advice, on the machine.

There will be a lot of people there who can give you proper answers as many of them have engineering backgrounds.

Seek out Ian Priestley. He is the Pre-war Registrar and if he doesn't know, he'll "know a man that does".

My car is a 1934 Short Saloon as I've probably previously said. It has 'Mary Ellen' written on the bonnet, so please make yourself known.

If you are VERY serious about keeping the car for many years, and there is something you need that isn't in your father's spares box, let me know asap via the private mail facility and if I have it (unless it is a heavy total drive train) I will bring it to Warrington gratis.

I have very fond memories of your dad.

Tony.

[Tony Fearn]

This is a P.S.

My son Richard is home at the moment for another day, and if you email me the picture of your car that 's been on this site later today (Wednesday), if you don't know how to create an Avatar of it to be used when you post on Jowetttalk, he's said he will create one for you so that I can email it to you. Of course, if you aren't "bovvered" it doesn't matter.

Tony.

[Keith Andrews]

photograph so bring some spare batteries for your digital camera.

And a tape measure.....
This is often very useful when taking pics for future reference....
Ride heights, spring rates, stuff like that....

A friend in the States made the mistake putting a new headliner in in his Camaro a few yrs back...
Forgot to locate holes for seat belt mounts, seat bely hooks, coathangers etc...
Fortunaltly I had pics on my web server
http://www.kakariki.net/camaro/HoodLine/