Just got back from a very pleasant overnight at a localish campsite, made better by getting home just before a thunderstorm hit. However, we weren't running great on the way back. Started up this morning, no problem, idling around 900 rpm, all good. After about ten minutes we came to a fairly steep hill, I'd have expected to have gone up in third no problem, however, the motor got really 'lumpy', and we clearly lost some power, felt like we were maybe firing on only three cylinders? Got to the top and all was fine when the road levelled out. Felt a bit 'lumpy' again on the next hill, but didn't seem to loose much power that time. Anyway, got home with no further incident, but when I stopped, the motor was idling at just under 2000 rpm, much higher than normal, and there was also a strong smell of petrol. Seemed to be OK until the chokes warmed up? Anyway, I was looking at the carbs wondering if maybe some dirt was in one of them, or sticky valve, when I noticed that on the left one there was a short rubber pipe, blocked with a screw, that was missing on the right hand one. I'm guessing this is the vacuum pipe that goes to the distributor? I've got a 123ignition distributor, that would take a vacuum pipe, if it wasn't sealed off. I don't think there ever was a similar tube on the right hand one, but one may have fallen off? Would that have caused the issue? Or could the high idle and lumpy running under power be due to the carbs not being balanced, or maybe a problem with one of the chokes? The arrow in the image below is pointing to the bit missing on the right hand carb. I'm not sure exactly what type of carbs these are, but its a 1776. Nice clean fuel filter, so I don't think there is much dirt going through the system.
Don't know what they are either. Solex? Clones? I think you're right that spur is for the vacuum advance so connect it up? I think you are correct carbs unbalanced. Check all the lock nuts on the linkage, that's obvious. It also might be possible that it one choke fails it can hold both open at fast idle via that bar dropping down from the RHS of the choke in your picture. Also the lock nuts on those coming loose can cause the same. But you think the carbs would be in balance with your foot down a bit and run ok-ish, so I'd guess a choke or it's 12V supply because that would also cause over fuelling. Just thinking out loud.
Thanks for the feedback. The carbs look remarkably like the Solex carb kits I can find images of. The PO, but one, made lists of everything he did, or had done, unfortunately it just says, new carbs... that was ca. eight years back. Checked the linkages, all seem solid with locknuts locked. Engine running I have just over 12 V on both chokes. But just letting it idle, it goes from a nice 900ish rpm to 2000 in about three minutes, with the increase starting after a about a minute, so does seem to be related to the chokes doing their thing. I'll try to sort out the idling and 'lumpiness' first, but if I were to connect the vacuum from the carb to the distributor, could I take the vacuum from either? Or would it somehow have to come from both?
Just the one is fine and normal - it's why the other doesn't have the fitting. Another thought - if you've been setting the timing recently, did you tighten the clamp?
The only recent change I've made, was fitting a tachometer. I ran a wire to the negative terminal on the coil. Tacho works fine. I think the chokes take their +'ve from the +'ve on coil, could that have any impact?
No, was thinking more like a wire fell off one. Next time it's idling at 2,000rpm, look at the throttle stops to see the carbs being held open? Have a fiddle about, it may be obvious which carb is (also) holding the other open. It looks like the fast idle stepped mechanism is inside the chokes and those also do break and could potentially hold the throttle open. You'll just have to try and follow the chain of evidence.
Had a look inside the chokes, couldn't see anything obviously broken, all the levers seemed to move freely and spring back in place. On starting the motor, the chokes warm up nicely, in sync with the idle increasing. When it was warmed up, and now idling at ca. 2000 rpm, I adjusted the throttle stop screws (?), red arrow below, on both sides until they were both just touching the arm, and idle was just under 1000. If I took it any lower it started to sound very lumpy. As our company lawyer would say, for the avoidance of doubt, and before I touch anything else, the screw with the yellow arrow is the one that will adjust the mixture? I was half expecting to see two screws to adjust. From the smell, and colour of the exhaust fumes when revved, I think it's running rich. The last carburettor I had in bits was from a Morris 1000, I recently found a 'rich needle' I'd been toying with at the time in a box of old bits, been sitting there for 25 years...
If your revs is “suddenly” changing from ~ 900rpm to over 2,000 I would suspect an air leak. I am guessing you have aluminium manifolds? I have seen them split. When cold - all is ok. When hot - crack opens and revs go up might not be a crack - but could be loose nuts. This would throw the balance out and also cause the change in revs screws don’t “move” so I wouldn’t have gone and changed settings. If it was good for 8 years it is something broken or loose
What Barry said. Something broke or became loose and covering the symptoms with adjustments is not wise. Smelling of fuel when revved won't be mixture adjustment, which only effects idle. The hexagonal brass jet near the top in you photo with the ball bearing pressed in will be the idle jet. I know when a single solex won't idle unscrewing that a tad (just to see) sometimes works because it lets petrol past the jet. So... worth checking yours are both tight I reckon. If I think of anything else I'll post. The other thing that will increase idle speed is of course timing advance. So, if ANYTHING (air leak or whatever) causes the revs to rise enough (1300rpm I think for 123) the mech advance kicks in causing the revs to rise even further.
Thanks for the feedback, sounds like it might not be a quick fix. One thing I did notice, probably not relevant, but just in case. There is a screw missing from the plate just above the red arrow head in the above image. I think this is covering the choke vacuum diaphragm? I can't see how this would leak air in, but if the plate wasn't sealed properly, might prevent the vacuum and cause the choke to not work correctly?
I know nothing of vacuum chokes, are you sure you even have one? Put your finger on the hole - do the revs drop?
Shows how little I really know. "Rob and Dave" have at least wondered about it! http://www.vw-resource.com/automatic_choke.html#vacuum Seems like it uses the increasing manifold vacuum as your throttle plate closes to close the choke flap more at the same time, so if it failed you'd think the symptoms would be opposite to yours, but I guess if it "worked too well" for some reason... But I think it's a red herring.
Just thinking allowed, I'll have a look when I get home. If the membrane is moved by a vacuum from the manifold, and the membrane was leaking, loose, or broken, the vacuum would be sucking air into the manifold, rather than moving the little notched rod. Would that be sufficient to account for the apparent air leak? Or have I connected the wrong parts together in my head?
I doubt it would be enough to double the revs, it's going to be a small hole to prevent it causing the engine to pulse.
