OK, I've returned to my normal state of "semi confused".... Just been reading my Haynes carb book and there are a few differences between the information in there and the normal Haynes. With the carb book, in section 5 (if you have a copy) it gives a diagram of the pushrod for hot idle, starting and deceleration(overrun cutoff), there are no measurements though so it's only relative movement. Here it says that the "...pushrod holds the engine at the specified idle speed". There's also a mention earlier where it says "...the pushrod extends to place the throttle plate in the hot idle position". So, it would appear that "just touching" isn't true, it should push the screw to open the throttle plate. This also makes sense when you turn off the engine - the pushrod retracts, closing the throttle plate. Has anyone turned the idling control valve? Is this how it changes the idle - by extending the pushrod, thus opening the throttle plate? When I turn off my engine, the pushrod stays in much the same position. I'm guessing there's a spring inside the 3/4 unit which is knackered in mine. It means I don't get the burst of revs on starting the engine.
So: at cold start, before any ignition key action, the 3-point unit's (3PU) pushrod should be about 15mm extended (by a strong spring inside the unit, as you say), and definitely touching the screw that pokes through the right angle plate. During the first few seconds after turning the key (from cold), it should stay fully extended like this, to give that initial burst of revs. The number of seconds it stays extended depends on the ambient temperature, or more precisely, the temperature of the ThermoTime Valve (TTV). The colder the TTV, the more seconds it will stay extended. Then, once the pushrod withdraws from fully extended, the waxstat and associated components on the other side of the carb will hold the throttle open without any help from the 3PU. This is a variable thing, the amount of throttle opening decreasing as the waxstat heats up from the circulating coolant. At a certain point after a few minutes, the waxstat will have pushed the 'warm-up cam' far enough round clockwise that it no longer touches a pin/stop protruding from the throttle mechanism on the UK passenger side of the carb. At this time the throttle will close as far as it can until the plate with the screw through it meets the pushrod of the 3PU. Nothing else (unless you have your foot on the accelerator) is holding the throttle open at this point, so the full force of the return spring of the throttle is leaning on the pushrod of the 3PU. It is at this point that the 13mm adjuster on the rear of the 3PU can be tweaked to adjust the fully warmed up idle speed, so: Yes, that is the only correct way to adjust the fully warmed up idle speed. It should not be used to attempt to adjust the idling at any time before fully warmed up. It will not affect the fully extended cold-start position of the pushrod, only the middle position. The 3rd 'point' of the 3PU's operation is the fully retracted position, which happens at shut-down (via the action of the overrun-cutoff valve), and this allows the throttle to close off all airflow through the carb, leading to a nice, controlled engine shutdown. If the waxstat should be defective, and is holding the throttle open even when the engine is warm, the result will be that the engine does not have its air supply cut off. As carbs supply fuel in proportion to the air passing through, this means that fuel will still be supplied, and the only missing ingredient will be spark. Carbon build-up in the combustion chamber may be hot enough to ignite mixture for some seconds after ignition off, causing run-on. This third (full retraction) point may also be used on some cars as a fuel saving mechanism during overrun - say when approaching a junction - by means of an additional control unit in the fusebox which can cause the overrun/cutoff valve to be depowered above a certain rpm point, around 1200 I understand. Haynes makes a big deal of this process, but few cars seem to have the control unit fitted. I don't know whether they were dropped from a certain date, or certain models did & didn't get it. My 91 1.6 Driver never did. Clear as mud? Might add some piccies over the weekend...
Here are a couple of pics and a diagram that may help visualise what's described above. The first is the fully extended pushrod of the 3PU holding the throttle quite wide open for the initial burst of revs. This image was taken 3 secs after a first start on a fairly cold morning (6.5C). Just after that pic, the 3PU retracted to its mid position. Apologies for blurriness, my camera's too cheap to focus that close. The next is a photo of a diagram of the waxstat together with the parts it moves as the pin extends. Unfortunately, it's almost impossible to see this complete mechanism with the carb on the engine, as it's obscured by other bits, so can't be photographed really, except on a stripped down carb. The thing labelled 'stop' is what prevents the throttle closing when it is resting on the thing labelled 'cam' which is rotated in the direction of the red arrow as the coolant melts/expands the wax in the waxstat and extrudes the pin. Due to the shape of the cam, the angle of the throttle is gradually reduced as the cam rotates, so the revs drop accordingly. Once the waxstat pin extends to rotate the cam far enough for the 'stop' to miss the left-hand edge (labelled 'recess'), the waxstat has no further influence on the throttle. The pic below shows the phase where the waxstat and mechanism is holding the revs, leaving the 3PU pushing on fresh air. Until that cam/stop stuff releases the throttle mechanism on the other side, the gap between the 3PU pushrod and the screw will gradually reduce. This pic was taken 15 secs after start-up, so quite a big gap at this point.
can you explain for bimetal spring in the part of carb 2e2, there is participation bimetal spring in the cold start? and how?
New waxstat fitted. And as I would guess from comments earlier, the revs dropped to 500 and lower so I switched it off as soon as I was home. I will try the screw/bolt on the back of the 3 point unit to raise the revs when warm. Too busy now though! Heynes shows 2 screws in the diagram, but mine has just one in the centre that I can turn by hand. Is this the one? Looks like it. There was steam/smoke flowing out the throttle plate when I whipped the airbox off. Is this normal?
The bimetallic coil spring inside the autochoke housing directly opens the choke flap as it heats up and 'unwinds' via the electrical heater right beside it (for the first minute or two from cold) and also by the effect of the warming coolant circulating through the water housing right on the end.
The 3-point version only has one 13mm adjuster on the back, the 4-point unit (fitted to some, not all automatic transmission cars) has two adjusters. Sounds like yours needs winding in a bit; try to get the fully-warmed-up idle revs to around 900-950. The fact that there are these two versions is why Haynes and everyone refer to it as the 3/4 point unit. Not sure about your steam/smoke, was it coming up through the carb, or just from the general area of the carb (in which case I'd guess that one of your coolant hoses to the waxstat is leaking onto hot manifolds and making steam??).
It was like a grandad's pipe smoking from the choke flap, just quickly googled it and sounds like fuel vaporisation. The was a pool of petrol in the... Whatever the round hole behind the choke flap is called?! Might have been due to me holding the revs with my foot then almost stalling but not quite whilst I parked up... About 5-10 seconds of spluttering as I live on a hill and have to use my brake as I roll back into my park space so can't keep the revs up. I'll not worry unless I see it again. Might get it checked by someone in the know soon once I've done what I can. ......... One thing I keep meaning to ask. There is a problem with the fuel tank breather hose. When I replaced the corroded filler neck a few years back, I noticed that the breather hose ran from the valve thing above the filler, down behind the wheel but then stopped! It should go to the tank, which I assume was just plugged (think it is a new tank at some point iirc). This causes nightmares when filling with petrol as it just keeps cutting of due to build up in the neck...... Anyway, could a lack of breather cause issues with fuelling?
Just warmed her up and set the revs to just under 1000. Drove fine for 10 -15 mins but then started spluttering again Temp went up to 3 quarters (best check the fan at some point) and once it cools down to half way the revs rise to 1200. The engine is also making a horrible metallic noise when idling so I'm giving in and taking it to a garage. I could replace the plugs, air filter, clean the idle jet only for it to be the same again, and that noise is embarrassing!
Thanks Pete. That kind of confirms what I thought should happen. With a dodgy carb and some misleading words from the Haynes manual, it's difficult to know exactly what pierburg intended. Isn't this the 'switchover' valve? My carb has a square box on the back that gets a similar connecting plug to the TTV. I'll try and get a pic. I think this is the valve you mention. My pushrod doesn't extend far enough to effect the screw when cold, so the waxstat is the only item holding the throttle open when cold. When it fires it withdraws slightly, but obviously doesn't make any difference to idle speed. When the waxstat fully extends, after about 20 mins, the pushrod is touching the screw and the revs are around 500. When the engine is turned off, the pushrod doesn't withdraw, but stays much the same. All a bit weird really. I'll try and measure the extension of my pushrod at the various stages.
That's the one. Number 12 in this image from RJ's FAQ thread: All 2e2s have this solenoid air-valve, but not all cars have the control unit in the fusebox to do the fuel saving thing. Number 13 is the 13mm adjuster for the fully-warmed-up idle speed, as discussed earlier in the thread.
Ah, I see. I might put a meter on the plug and see if it changes at 1200 revs then. I'd just expected it to work if I had the square box.
Well, After confusing myself thinking the timing might be out, which wasn't, I gave up and took it to a garage (a better one than the first one who failed to fix it - those posts have gone missing). They opened up the carb and cleaned it and apparently is all good now, pick it up Monday. So, I remember EZ Pete mentioning this could be the case some time ago from moving my carb around, so ten out of ten for that. I however, wasn't brave enough to split it, should have guessed when I cleaned a blocked idle jet 2 or 3 times Anyway, they didn't charge much, and hopefully she's good to go. Just wanted to close the thread and say thanks to all who helped.
