The second batch arrived today. I'm much happier with the revised choke part. Despite making the spindle hole as small as I dared there's still a tiny bit of lash that isn't there with the original part. But it's tight enough to stay on the spindle under gravity (just).
I tweaked the geometry a fraction too, as the original part had the end stop a few degrees out. This one is much better.
If I ever do a third batch there's room for a couple of further tweaks, but I'd say the parts from this batch are good to go.
The throttle part seems ok too. The spindle hole is spot on for a nice loose fit round the brass spacer and the geometry seems pretty good too. In these photos I've fitted it without any washers and I've found that a 3.2x12 wide flange rivet works fine. There's room for a washer on top under the rivet head but then you'd need a 3.2x16 rivet. And with that longer rivet there'd also be room for a washer on the underside where the rivet squashes, just in case you make a mess of drilling out the old part, say. I'll put both rivet sizes in with each kit, as well as a couple of washers.
The only bit I'm not 100% happy with is the geometry where the part meets the cam on the primary throttle spindle. It seems to sit about 1mm further south. I'm not really sure why this is - my prototypes seemed fine. Logically you'd think this would affect the point at which the secondary flap would start to open but as near as I can tell by calibrated eyeball it seems about the same as an OEM part in that respect. I think this is because the face of the part starts to ride around the heel of the cam before it gets to that bottom corner. But again, if ever I do another batch there's room for a tweak there I think. It would be interesting to see photos of other installations if anyone else fits this part.
"I'm a man of means, by no means....King of the Road!"
I built up my spare carb and used both of these new parts. Had an early start this morning and fitted this carb in my van, ready for a trip out today. Wish me luck. I may be gone some time.
"I'm a man of means, by no means....King of the Road!"
I always too get that apprehensive feeling driving the van, after I have done some work.
In this case, I am sure it will be fine.
You have done some good work here.
I have a spare carb here too now - with the choke flap - and it seems to work on a `cog` or `staged step` mechanism, which is at least more than the one on the van now. When I get some time, I will swap them over.
So if possible, I would like to have one of each of your spares.
I am planning on stripping the old carb down and using a refurb on it.
At the very least I will then understand how they work more clearly...!!
'89 1.9 DG
“It's Easier to Fool People Than It Is to Convince Them That They Have Been Fooled.” ~ Mark Twain.
At the very least I will then understand how they work more clearly...!!
Don't bet on it I have been tinkering with them for years and I still only know the half of it.
Well when all else fails - I have the Itchy-Carb-Wizard to ask
As soon as I swap them over and start taking the other apart, I will give you a `heads up` on another thread so you can see my errors, fails, successes and attempts
'89 1.9 DG
“It's Easier to Fool People Than It Is to Convince Them That They Have Been Fooled.” ~ Mark Twain.
OK, I'm fairly sure the two parts work ok, and they haven't broken after a 35 mile round trip. The choke is obviously working as it starts OK from cold and I can feel it slowly coming off as the engine warms. And the throttle part seems to work OK, as the engine pulls just as strongly at full throttle as it did before.
But....
I'm reluctant to give the all clear because there's an issue with this carb, and while I don't think it's related to these parts I can't be certain. The issue is that if I try to pull away from rest with my 'normal' pedal action it will stall. I have to give it more revs than I'd like in order to pull away smoothly. It idles fine, and pulls well under full throttle, but when pulling away there's a very marked weakness, and it feels a bit weak under a light throttle at low revs too. This characteristic seems less marked when cold, i.e. when the choke is operating.
I'm hoping a carb expert can say "ah yes, that's the such-and-such, and it's nothing to do with the choke flap or the secondary throttle". My feeling is that it may be the idle mixture screw. This is a carb that I've never run on the van before, although it's been stripped and cleaned, and had a carb service kit fitted. I'm pretty sure there are no air leaks. My worry is that one of the new parts might be the cause. Could the very slight lash in the choke flap be the issue? I doubt that. Could an error in the geometry of the secondary throttle part cause that to open too much or too little under a light throttle? Again, I think it unlikely, because that part seems to do the same job as the original part, and anyway, I don't think the secondary venturi flap does anything under a light throttle. But should it perhaps open a little bit more than it does under an initial vacuum?
I'm pretty sure this sounds like the 'Pierburg cough', but I'd appreciate pointers as to what causes it, so that I can fix it and then be a little more confident that these new parts aren't to blame.
"I'm a man of means, by no means....King of the Road!"
Does the choke pull down work as it should when you operate the accelerator?
ie does it open slowly and smoothly, and not snap open.
Does the transfer jet deposit a healthy squirt of fuel in the throat as you depress the accelerator?
I have this same issue.. I just cannot pin it down
Thanks Kev - I'll look at those issues. I've not had a look under the engine lid since getting back. I do know that the constrictor in the choke pull down hose is present though - I checked that while I was assembling it. And I'm pretty sure it was a new pull down unit that I fitted when I first serviced the carb.
"I'm a man of means, by no means....King of the Road!"
Interesting post here from Pionte. I think he's referring to this cam, which controls when the accelerator jet operates. Something else to investigate.
"I'm a man of means, by no means....King of the Road!"
