auto choke still playing up

[jeffdub]

hi everyone im having a bit of a problem with my auto choke . When i start it from cold it just about ticks over and seems to be running rich as you can smell petrol , i havent got a rev counter but i would guess its around 500 rpm . after driving it for about 2/10 ths of a mile to the petrol station it seems to be working as its doing about 1500 rpm. I depress the accelerator as ian hulley told me to do and ive checked the flap in the carb and its closed im a bit stumped and wondered if anyone could help me please ? thanks jeff

[fairwynds]

Have you checked the Wiki for the explaination of how the choke works? Reason I ask, is that when I dismantled mine, learning heaps about the choke as I did so, it works by means of a bi metal strip, which closes the choke when engine cold (ie - turns choke ON). So, when you engine is stone cold - have a look down the throat of the carb, by taking of the black cover. Is the choke flap closed? if so, thats a start. Now fire up the van and over the next few mins, watch to see if the flap moves at all (it should as the van warms up, but remember, these vans take a while!).
It MAY be that your choke is not coming OFF (ie. opening) because the shaft/spline is sticking?
Take a peek at the Wiki pics to see what I mean.
My particular problem watch the tiny 12v heating element within the choke housing....so choke was not coming off early enough, and causing engine to run rich until it was FULLY up to temperature.
Hope this makes sense.... keep posted..

[kevtherev]

is the choke closed FULLY when cold?
no gaps or anything.

[jeffdub]

thanks fairwynds i'll check that out hi kev, no i dont think it was fully closed now i come to think of it , is there a way to adjust it ?

[kevtherev]

Thats good it shouldn't be fully closed there should be a 3mm gap when idling on a cold engine.

Does the gap widen when you press the accelerator?

[jeffdub]

i think so kev but to be honest i cant remember probably best if i take a look in the morning and see what happens

[kevtherev]

OK lets assume it does... I just wanted to rule stuff out.

Now I assume that you started the cold engine by depressing the accelerator once and releasing it, then cranking the engine till it fires.
Is that correct?

Correctly set up, the engine should start and idle at 2000 rpm without any accelerator being touched.
once touched it will drop to 1500.

Do you know what the fast idle cam is?

[jeffdub]

yes kev ian hulley advised me to do that so first thing i depress the accelator a start it soon as i remove my foot it drops to about 500rpm , sorry dont know what the fast idle cam is

[kevtherev]

i depress the accelator a start it soon as i remove my foot

no.. depress it and remove your foot ....then crank it, when it starts touch the acc
if you do that like I have described.. it drops to a very low tickover.. almost stalling?

[jeffdub]

sorry kev i didnt explain it very well. i press the accelator remove my foot and then crank it

[kevtherev]

OK
well without seeing it I can't help much more.
But the fast idle cam operates the main butterfly valve in the carb (throttle) when cold, it holds it open to keep the idle speed up while the engines warming up, once warmed up it has no function.
Only when the engine cools down and the bi-metal spring turns the choke and the cam to engage the throttle stop once again.

try some WD on the springs it may just be sticky

you can see the springs here and the fast idle throttle stop below which engages the cam

[jeffdub]

thanks kev what i did notice when i looked at it is the springs seemed a bit slack if you know what i mean ?

[pfield69]

Hi guys, I'm having problems with could starting too. It looks like the fast idle cam isn't working as I would expect.

The Van starts fine but you have to keep the throttle pressed a little.

If I turn the cam anticlockwise with the throttle open, I can engage it and the van starts and idles fine.

More photos and a guide to fix/ set this would be much appreciated.

Or if antone know a good carb enginer in the Woking/ Surrey area that will do just as well (I need a gasket between carb bowl and carb top)

[fairwynds]

Hi
I used these guys when I did my rebuild, and found them very good indeed...
Southern Carburetters in Crawley, West Sussex. 7 Priestley Way 01293 533843.
Bit far from you maybe, but worth phoning...
FW

[kevtherev]

If I turn the cam anticlockwise with the throttle open, I can engage it and the van starts and idles fine.

the stepped cam rotates clockwise as the engine cools, also closing the choke flap and opening the butterfly as the stepped cam comes into contact with the fast idle screw

look at the autochoke housing, it is secured by three screws, the screws allow some rotational adjustment.
Undo the screws, and turn the housing clockwise about an eighth of a turn and then re tighten.

here you can see the range of movement
the housing viewed from the inside out




do this until the cam rests on the step that allow the engine to run in the ambient temp after the throttle is set for cold start.
You might have to re adjust the choke flap gap after this

cam set up



There are 2 scenarios to debate on:

A - IDEAL case (aka "this I would like to happen")
Cold engine (-10 deg. C outside) -> The choke flap is closed and the fast idle screw (3) rests on the highest cam of stepper (2). We start the engine without touching the throttle pedal. Engine starts at fast idle (2300 rpm), the bi-metal coil heats at 12 V and then is shut off while bi-metal coil is now heated by coolant as the engine is warming up. The bi-metal coil forces the choke flap to open gradually and in the same time the stepper cam (2) rotates anticlockwise and screw (3) 'slides' to lower and lower cam thus lowering the rpm to 900.
So far we NEVER touched the throttle pedal and waited in neutral for the engine to warm up. Now we go for a short trip, park and stop the engine. Basically all happens in reverse, the bi-metal coil contracts closing the choke flap and forcing the stepper (2) to rotate clockwise and raise the screw (3) to highest cam, ready for a new cold start.

B - REAL case (aka 'semi-automatic')
Same as above with a couple of major differences: the spring that drives the stepper has no force to overcome the friction between the screw (3) and cams while the engine is warming up, respectively the bi-metal coil has no force to raise the screw to the highest cam while contracting after the engine is stopped.
We have to do 2 things:
1) drive after a cold start without waiting for the engine to fully warm up and so by using the throttle pedal, we raise the screw from cam each time allowing the stepper to rotate and the screw to rest next time on a lower cam;
2) before a cold start, we press the throttle pedal 1-2 times fully to allow the stepper to rotate and position the screw on a higher cam.