Austin Healey 100/4 - SU carburettors

[Sam99]

Hello All

Any SU Carburettor experts on here , please ??

Long story short - Austin Healey - 100/4 - twin SU’s , cold air box.
It was running fine all last year , last time on the road was October 2022.
Unfortunately , I haven’t started it since. My fault.

This last week - it will not start. It's not even trying. Just turns over.
All electrics are OK. Plugs are sparking.
Electric fuel pump is OK
Fuel through to the carbs.
Fuel in the float bowls.
No luck.
Scratching my head time - I poured little fuel into each cylinder , using a syringe , and it starts immediately.
Ran it for around half an hour - all seems OK.
Turned it off.
An hour later , it starts without the throttle.
Did this a few times - starts OK - Happy days.
Not so. This morning , a cold engine , and it won’t start again.
Fuel in cylinders and away it goes.

Any suggestions , please ????

[spikeyhead]

probably gummed jets

https://www.howacarworks.com/fuel-systems/checking...

[finlo]

Sam99 said:

Hello All

Any SU Carburettor experts on here , please ??

Long story short - Austin Healey - 100/4 - twin SU’s , cold air box.
It was running fine all last year , last time on the road was October 2022.
Unfortunately , I haven’t started it since. My fault.

This last week - it will not start. It's not even trying. Just turns over.
All electrics are OK. Plugs are sparking.
Electric fuel pump is OK
Fuel through to the carbs.
Fuel in the float bowls.
No luck.
Scratching my head time - I poured little fuel into each cylinder , using a syringe , and it starts immediately.
Ran it for around half an hour - all seems OK.
Turned it off.
An hour later , it starts without the throttle.
Did this a few times - starts OK - Happy days.
Not so. This morning , a cold engine , and it won’t start again.
Fuel in cylinders and away it goes.

Any suggestions , please ????

Have you pulled the choke out?

[hidetheelephants]

Modern fuel is garbage, it turns to varnish very quickly which blocks small passages and jets and if you're lucky it will start attacking the pot metal and causing horrid corrosion. A few blasts of carburettor cleaner into nooks and crannys(and follow up with compressed air if you have it)may clear the problem. If not the carbs may need removing for ultrasonic cleaning.

[Sam99]

Thanks for the replies

[RichB]

I agree modern fuel is crap and do suggest you heed the suggestion to get some carb cleaner and have a good clean up. That said two things... what fuel are you using? May I strongly suggest you use Esso Supreme 99+ when yo can, especially when you're planning to store the car for a period of time. In most areas of the country it is zero ethanol (not 5%) and I think Esso deserve our support. And... although you are getting a spark it may be worth replacing the condenser, it's only a one-pound part and it helps generate a really strong spark. I once had a very frustrating issue on my brother's Midget that I was convinced was a carb problem and it turned out to be the condenser! Good luck.
p.s. I very nearly bought a Healey 100 back in the day but went for an MGA instead which made me an MG person for years until my brother bough a Healey 3000 MkIII - smashing cars

[ARHarh]

Unlikely to be blocked jets on Sunday carbs. Check out how they work.

I would unscrew the caps and check for oil in the car piston. Whilst there use the plumber at an angle to.lift the piston it should lift easily and fall back. Not much else going on in an su. Take a plug out and check for traces of fuel.

As above far more likely to be points or condenser if it doesn't start.

[Gary C]

hidetheelephants said:

Modern fuel is garbage, it turns to varnish very quickly which blocks small passages and jets and if you're lucky it will start attacking the pot metal and causing horrid corrosion. A few blasts of carburettor cleaner into nooks and crannys(and follow up with compressed air if you have it)may clear the problem. If not the carbs may need removing for ultrasonic cleaning.

but SU's dont really have small passages in comparison ?

Sounds as if the pistons aren't sliding up.

Stick your finger in and manually lift iand see if it starts. Probably the fuel is firing it, it revs and sucks hard enough to unstick the carbs pistons and then it runs fine until they stick again.

[Gary C]

BTW, nice car

pictures please.

[hidetheelephants]

RichB said:

I agree modern fuel is crap and do suggest you heed the suggestion to get some carb cleaner and have a good clean up. That said two things... what fuel are you using? May I strongly suggest you use Esso Supreme 99+ when yo can, especially when you're planning to store the car for a period of time. In most areas of the country it is zero ethanol (not 5%) and I think Esso deserve our support. And... although you are getting a spark it may be worth replacing the condenser, it's only a one-pound part and it helps generate a really strong spark. I once had a very frustrating issue on my brother's Midget that I was convinced was a carb problem and it turned out to be the condenser! Good luck.
p.s. I very nearly bought a Healey 100 back in the day but went for an MGA instead which made me an MG person for years until my brother bough a Healey 3000 MkIII - smashing cars

If it's an infrequently used vehicle Aspen alkylate fuel will avoid the bad fuel scenario, although it is pretty expensive.

[Maxdecel]

finlo said:

Have you pulled the choke out?

^ ^ ^ This, have you checked it's working ? Found a similar problem with a Westminster recently but someone had butchered up the choke mechanism resulting in the same non start when cold.

[RichB]

hidetheelephants said:

RichB said:

I agree modern fuel is crap and do suggest you heed the suggestion to get some carb cleaner and have a good clean up. That said two things... what fuel are you using? May I strongly suggest you use Esso Supreme 99+ when yo can, especially when you're planning to store the car for a period of time. In most areas of the country it is zero ethanol (not 5%) and I think Esso deserve our support. And... although you are getting a spark it may be worth replacing the condenser, it's only a one-pound part and it helps generate a really strong spark. I once had a very frustrating issue on my brother's Midget that I was convinced was a carb problem and it turned out to be the condenser! Good luck.
p.s. I very nearly bought a Healey 100 back in the day but went for an MGA instead which made me an MG person for years until my brother bough a Healey 3000 MkIII - smashing cars

If it's an infrequently used vehicle Aspen alkylate fuel will avoid the bad fuel scenario, although it is pretty expensive.

I use Aspen 2 stroke in my chain saw but at that price not in all the bloody classics, Esso Supreme+ I tell you, perfect.

[Sam99]

Hello all,

Thank you all for your thoughts and comments.

I have a day off today , hence my post yesterday hoping for a fix today.
It's a tad chilly , suns out and 8 deg in my garage .
A day in the garage.

So - a couple of you mentioned my choke’s.
Im sitting in the drivers seat watching the Bowden cable outer sleeve flex as I pull the choke out and then push it in. My choke cable does not have a Bowden cable inner - its a solid length of wire.

I pulled the choke fully out - as far as the cable would let me and checked the chokes.
I found they would lift another inch or so by hand - This then left a slack cable with no way of holding it.
I found a small hand clamp , the sort you would use holding small things in a pillar drill and clamped it on the exposed inner cable.
My car started first time - I then ran round to slacked the clamped choke cable as It was not running too well on full choke. But it is running.

Two brains are better than one - in this case it was quite a few - Thank You all.

Last question.
Choke cables - what are yours made of ?
A bowden cable outer sleeve and a cable inner ?
Or as mine is - an outer cable with a stiff wire inner.
The thought being , I suppose , when the choke is pushed in , the rigid cable pushes the chokes off.

Any thoughts or comments ???


Oh , lastly , I have found a very local Esso dealer for the recommended Supreme 99+

[RichB]

Sam99 said:

Any thoughts or comments ???

Sam, it sounds like you carbs linkages need properly adjusting. The SU carbs are pretty simple to adjust but if you've never played with them it's worth getting a guide book to follow.

Obviously there are two controls - the throttle and the choke.

I assume you have adjusted the two butterflies so that they open together in a balanced fashion?

If so then firstly I would completely slacken the choke cable where it connects to the carbs and set the idle speed, l would suggest around 600 rpm but whatever you feels right. Ensure that it is the idle speed screws that are adjusting the speed and not not tension in the throttle cable. Then clamp the throttle cable so that it starts to open the butterflies as you depress it, i.e. so there's very little slack in the cable. At this stage you have balanced the butterflies (previously) and set the idle speed.

The choke on the SU has two stages; the first stage is to increase the idle speed, the second stage is to pull down the jets (there is a linkage joining the two jest so that they both come down as you pull the choke.

You need to clamp the choke cable so that there is little or no slack and as you pull the idle speed increases, there is (I seem to remember) a cam that achieves this with a rich idle speed screw bearing on the cam.

A small pull should increase the idle to say 800-1000rpm and then the further pull should start to pull down the jets. The idea being you can control the jets for a rich start with a full pull and then the idle speed while the engine is warming up by pushing the choke half way back in.

It sound complicated but that's just the way I've described it, it really is simple and works well if you have everything adjust correctly. The problem is that things go out of adjustment and people bodge it by fiddling with the wrong screws! e.g. bodging the choke instead of adjusting the jets or using the chick idle speed screw to set the correct warm idle speed!

p.s. a solid wire inner cable is fine and probably correct. There should however be a spring on the jet linkages that pulls them back to the normal position.

p.p.s. Sorry if you already know all this...

Good luck.

[Sam99]

Hello RichB

Thanks for your reply.
Im pretty certain the slides and chokes are all OK , as the car ran fine all last year.
My choke cable has always seemed a little on the short side , but has always worked up to now.
Maybe it's time to change my choke cable and set it up correctly.
BTW , the chokes do have a return spring fitted.

Thanks for you time and advise.

Regards

Sam

[RichB]

Sam99 said:

Im pretty certain the slides and chokes are all OK

Humm... SUs don't have slides and chokes...
They have butterflies, pistons and jets that pull down. Are you sure you've got SUs?

Overwinter a piston may have got stuck, have you put your finger in and lifted them?

[Huntsman]

I had a 100/4 with the cold air box. PXK319.

You need to check the choke cable is lowering the jets, you'll find the jets get stuck, then the choke cable slips, needs 2 people, one to operate the knob and the other to rummage under the carbs and feel for the jets gojng up and down.

[Maxdecel]

RichB said:

Humm... SUs don't have slides and chokes...
They have butterflies, pistons and jets that pull down. Are you sure you've got SUs?
Overwinter a piston may have got stuck, have you put your finger in and lifted them?

I'm guessing where he says "Slides" He means "Dashpot" & "Choke" is the lever mechanism that lowers the jet tubes as:- " BTW , the chokes do have a return spring fitted." That must be connected to the lever mechanism.
Judging by his description when it fired up it must be hunting, likely someone has reduced the fast idle activated by the

[RichB]

Maxdecel said:

... BTW , the chokes do have a return spring fitted." That must be connected to the lever mechanism.

Indeed, I tried to describe that in my lengthy post but it's hard putting it all into words

[Maxdecel]

RichB said:

Indeed, I tried to describe that in my lengthy post but it's hard putting it all into words

Took me a while to transpose, one mans venturi is another's choke
I'd not touched SU's for years until a couple of weeks ago, quite fortuitous as it refreshed my memory ........ Such as it is !
Coincidentally it was the very same problem, my mate was convinced the engine was Problem been he had his wife checking the choke operation, mind a piece of what looked like insulating tape had been sucked in and wrapped around #2 Carb. needle in a perfect "U" Starts great now but breathes a bit when it's warm he tells me.