3.8 auto choke.

[blackbeltuk]

Hello.
Some more help please. My auto choke
Has been disconnected. So I would like to put
It back. I have been told that there should
Be two wires that will make the choke
Operate. I have seen that one cable runs from
The otter switch. But where to. And could
Someone point me in the right direction
About a second wire where I should
Look and again where it should connect to. I am
Aware one wire is attached to the distributor.
Thanks in advance Ricky.

[piman]

Hello Blackbelt,

the choke solenoid is permanently live with the ignition on, according to the workshop manual is linked to the live side of the brake light switch, green wire, with the second wire green/black, going to the otter switch at the front top of the inlet manifold, when cold this earths the solenoid. As it warms up, the switch opens and the choke is switched off. There should be no connection to the distributor. It was quite common for owners to fit an internal switch inside the car to over ride or by-pass the otter switch so be aware of this.

Alec

[blackbeltuk]

Cheers for that Alex. I'll have a look today (sat) And what workshop manual have you got.
I have an original s type manual. But can't find anything about the choke,
Ricky

[piman]

Hello Ricky,

the manual I used was a Haynes one I keep in the house, the information was taken from the wiring diagram.

Incidentally I have two proper Jaguar workshop manuals for the MK 2 and I'm happy to pass one on if someone needs one?

Alec

[oldtimer]

Ricky,
I have my Jaguar Cars Ltd 3.4 and 3.8 S type Service Manual (2nd Edition) on my knees.

Index to sections - at the very front says- CARBURETTORS & FUEL SYSTEM Section C

Turn to Page C2 Index Carburettors

Auxiliary Starting Carburettor
Description Page C10
Adjustment Page C11
Thermostatic Switch Page C12

I have just had a quick read and it is all there.

This devise is not a choke in so far as restricting the air flow, as the name implies, it is in fact a fuel enrichment device.

It's performance from new was flaky at best. I guess the problem is that there is no compensation for the range of temperatures that it has to operate at. The engine will ALWAYS start but requires the throttle to be tickled to keep the engine running. Left to it's own devises for a few seconds it will choke it's self to death ( grossly over fuel the engine)

A common modification even on my new one back in 1966 was to have a switch in the cabin to override the thermostat. In fact I isolated the thermostat altogether.

Nothing more annoying than nipping out of the car for something and the engine has choked it self to death. You try starting a flooded engine after that!

Hope that helps a bit

Oldtimer

[blackbeltuk]

Thanks for all your help. Yesterday I was taking my car to the yard from home which is just under 9 miles to replace the speedo cable. needles to say I didn't make it. after about 5 miles
the car started to splutter and the revs dropped. manage to get to the side of the road then a
plume of smoke came from the engine. not a lot. I then decided to call the AA who arrived in
about 30 minutes. started the car and all was fine he then followed me to work then about a couple of miles the car done the same but this time white smoke from the exhaust. The AA man reckoned the car was running rich so he set the carbs which cured the smoke. So this time I said
we go home. anyway cut it short we didn't make it but this time the smoke from the engine
appeared again. that turned out to come from the breather pipe. so we took the pipe off and I
noticed a green cable sitting under the metal pipe not connected to the otter switch. So I reconnected that. but in the end it was decided to recover the car and take it home. So this is what the first AA man thinks. That the crankcase breather is blocked which is building up pressure which is affecting the fuel to the curbs. the smoking is oil coming from the breather
pipes. the starts fine after a while. which he said is the pressure is released from the breather pipe. Anyway Cant fault the AA for there response time. So off to my mums with some flowers then home to see if I have reconnected the choke and to strip the crankcase breather and clean the mesh filter.
I let you know how I get on. Cheers Ricky.

[piman]

Hello Ricky,

white smoke is either steam or brake fluid from the servo being drawn into the engine through the servo vacuum hose. (Check the brake fluid level)
I don't see how high crankcase pressure affects the fuel flow to the carburettors, it just tends to increase oil leaks, and as there were fumes coming out it can't be blocked totally?
I bet the AA man doesn't see many HD SU. carburettors either?

Alec

[Martec]

Hi Ricky,

What year is your car, and where does the breaker pipe go to, to atmosphere or to the inlet manifold/air filter?

Brian

[blackbeltuk]

Hello Brian.
My car is a 1965 3.8. The breather pipe runs to the air filter.
Ricky

[Martec]

Hi Ricky,

Sorry to start with a few questions, how long have you had the car and was it working well up to this point?

You started your post with asking how to reconnect the Otter switch to operate the 'starting carburettor', How have you been starting it to date?

I am coming from the position of having run my 1961 3.8 MkII for the last 14 years. Like 'Oldtimer' I by-passed the Otter switch from day one with a cabin switch in the earth line from the 'starting carburettor'. I also run it most of the time on LPG.

As Alec has said white smoke in the exhaust is usually either steam or hydraulic brake fluid. If I start on LPG in the winter it creates a lot of steam until it is warm, but very little on petrol. I hope you have taken Alec's advise and checked your brake fluid reservoir for loss (I went to France and back with a slight servo leak but I wouldn't recommend it).

Smoke from the breather! if it was connected how did it leak smoke?

I have found it impossible to start my engine from cold without using the 'starting carburettor' (unless it is on LPG) so if the starting carb is in operation all the time it would start, and then become increasingly more difficult to keep running as it would be so rich (the starting carb throws petrol in with a very big bucket). If the starting carb is on you will hear it, HISSING like mad and the idle revs will be quite high.

Can I suggest you disconnect the breather from the air filter and block up the hole in the air filter and run the breather down to the road (same as the early ones) also remove and clean whatever gauze/filter is fitted to your engine to ensure there is no crankcase back pressure, refit when the problem is solved.

The HD carburettor is different to the cheaper later HS carbs in that the central jet is sealed to the carb body with an integral rubber diaphragm. The early diaphragms are suitable for leaded fuel but not unleaded and will go hard, so the jet height can't be adjusted (rich or weak) even though it may appear so.

Assuming your air filter is clean and doing its job muck still gets into the carb and often up into the carb cylinder and restricts the piston movement resulting in the car stalling, particularly at idle. The piston and cylinder need to be cleaned with a soft cloth and maybe carb cleaner, NEVER an abrasive. When refitting you should be able to hear the piston clack onto the bridge after you have lifted it and let it drop (pushed down by the spring). Also the dashpot should be part full of engine oil, who's job it is to restrict the lifting of the piston so the increase vacuum draws in more fuel for acceleration enrichment.

With clean carbs and a clean air filter the mixture can be set for warm/hot running and the staring carburettor only used for starting, I usually only run this until the water temperature gauge shows 30 degrees, then switch it off.

I got into Jaguars when I went to see a guy's XK150 with a 3.8 ltr engine, he would start the car run it out onto his drive for 10 minutes then back in the garage. I sorted his engine by him dumping the sump twice (it was way over the maximum mark with petrol from the starting carb), and a change of plugs. Is your oil level high and does it stink of petrol?

Best of luck Rick, please keep us informed of your progress.

Brian

[piman]

Hello Brian.

"I got into Jaguars when I went to see a guy's XK150 with a 3.8 ltr engine, he would start the car run it out onto his drive for 10 minutes then back in the garage."

A pet hate of mine yet I read about it all the time by owners who think they are doing the engine a favour by starting it up periodically without really warming it up, which in my view means a reasonable drive on the road.

Alec