Carburretor Refurbishment. A step into the dark...

Hi Martin,
Yes, I did note some play in these linkages (all but one) and I could see the sense in that.
Too early? I'm just pulling bits off and noting where they came from! So far I'm quite confident that I won't end up with bits left over afterwards.

Just spent a happy 20 minutes with a metal coat hanger fishing out a crows foot spanner from between the cambelt and the crankshaft pulley. It's not something you want to leave to do another day!

Heading back to the car now - for another hour I guess, updates and questions as & when they occur

 

Righto! I will leave the manifold in situ.

Obviously, that's about the only spanner type I don't have... FFS

 

The rear most pair are now sitting on my workbench.
They are covered in engine degreasant - I want to get the worst off them before I strip them down and stick the bits in my shiny, new ultrasonic cleaner.

3 bolts are holding the front pair in. I will tackle them tomorrow.

Thanks everyone for your help. The quick responses saved a wasted evening. Without them, a few hours work can end up being spread over days or weeks!


Here's the first one:
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One done. Three to go!

As I suspected, the outside was filthy but inside everything was good. No jets were blocked, no residue anywhere.
derekw - I should have listened to you!

I totally dismantled it down to the last nut and bolt. Everything went in the Ultrasonic Cleaner at maximum temperature, with some degreaser stuff for 30 minutes.
I did remove the butterfly spindle and the bearings. I regreased the bearings and put them back, they had small inserts/discs that sealed them off (I've seen posts where these aren't present, allowing air to ingress - the solution is to pack with grease? No such problems for me)

I've been putting this job off for years but it's really enjoyable. Sitting in front of the TV with some basic hand tools. No need for breaker bars, angle grinders and heat (unless #2, #3 and #4 cut up rough?)
The diagrams look really complicated but there are multiple small constructions put together to form the carburettor. Individually they are really straightforward and nicely engineered. I made copious notes and took cartloads of photos and it was really easy.

I think it's fairly obvious that I prefer functional over concours or coffee table art!


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Mine weren't sealed bearings as such but there were round covers, like washers, that would appear to seal the bearing off.
Considering these haven't been touched in my ownership (20 years) and there is nothing in the car's history to suggest they were maintained prior to my ownership - these Weber carbs have thrived on almost 40 years of neglect!


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I totally agree with you.
I did this some years back - Martin and Adrian still bear the mental scars. Mine uses the SM805A dizzy with the magnetic pulse, my ignorance was total at the beginning. I now tour the UK providing lectures on the Hall Effect

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I've ordered the sealed bearings. They should reach me by the weekend.

I will take this as an opportunity to get the spindles re-anodised. When I removed the first one, I had to file away some burr to get it out - exposing some bare metal in the process...



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Not yet Derek. But I will definitely heed your advice! I will peer down those holes once I get the last 2 carbs off the car. I only picked up my half moon spanner yesterday - I will be 'customising' that tool today!

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Carbs cleaned, rebuilt and reinstalled!
I will be refilling the car with fuel later this evening, with the intention of setting the carbs up tonight/tomorrow.

New fuel hoses and oil hoses installed.
The balls on linkages were all spherical.
The linkages have been tightened to allow some rotational movement.
I inspected the inlet manifolds, they were all spotless with no sign of leaked/dried coolant around the joint to the block.
All the lead/welch plugs appeared to be firmly in place.

I only removed the butterfly's and spindle on one carb. It was such a pain in the neck that I cleaned the other 3 with the spindle and butterflies in place.
Removing the spindle involves de-burring the damage caused when the staked bolts (that secure the butterflies) are removed. The spindle then has to be re-plated/anodised.
When replacing the spindle and butterfly, the nuts have to be staked. This is a pain.
The spindles and butterflies on the other 3 carbs cleaned up just fine in situ. I really don't see the point of pulling them unless there is an obvious problem.

I left the original bearings in place and simply repacked the grease. I did buy new sealed bearings but I wanted to get this job done and I couldn't be asked to build a mini puller to get the old ones out.
I get that the grease will be washed out over time but my mileage is minimal and I suspect that this won't be an issue for many years. I would happily rebuild the carbs again in a few years and do a more cosmetic job, getting everything re-plated. I would allow more time to allow me to use the sealed bearings.

The bypass screws were all set to 5 or 6 turns out, which seems quite a lot.
The standard starting position when tuning these carbs appears to be 3 turns out, so that's where I will start. I've got one of those flow meters.

Thanks everyone for you help and advice.
If anyone is considering this job, do it! It's a really pleasant job and very straight forward. As ever, the diagrams (and many write ups) make these jobs look difficult but they really aren't. A bit of commonsense and a little patience is all you need.


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Hi Derek,
I'm sure you are absolutely correct. The bearings had no visible signs of grease as far as I can recall.
But... I am 99.9% confident that this is the first time the carbs have been off the car (i.e. 40 years and 50,000 miles), so I think my work will be good for at least 5 years and a few thousand miles!
I would have no hesitation in doing this job again. And having done it once, I would attend to matters such as this, the next time.

I prodded every plug with a screwdriver and they all felt solid, so fingers crossed I'm OK. The ultrasonic cleaner did a good job but I still needed to use Gunk and a toothbrush for a few nooks & crannies. In hindsight, I think dropping the carbs in a tank of Gunk and manually cleaning the carbs with a brush wouldn't be the end of the world.

The car has petrol in it, the battery should now be fully charged. It's 9.30pm on a Saturday night, I'm heading out to the garage to start her up and see if it works!

 

Help!

The car is running. The linkages are all in place and the 8 pots are all pulling equal amounts of air.

Here are my questions/observations.

1. The general consensus across the various tutorials/books is that at idle, the air flow should be around 4 or 5kg/hour. I'm pulling about twice that at 1200rpm, even at lower revs it is still way above the suggested volume. I haven't been too concerned by this as each choke is pulling equally but it may be relevant for the next questions.

2. Ignoring the idle mixture number of turns in/out for the moment, what are the following symptons of:
- If the throttle is blipped (say up to 3000rpm) the engine doesn't drop/return to idle promptly
- If the throttle is blipped, the engine speeds up beyond where you would expect it to (i.e. it races a bit)
- Even with the mixture leaned right off, if I rev the engine to 3000 rpm, it doesn't drop straight back but hops/fluctuates around at 3000 rpm for a second or two then drops back.

3. The actual exhaust note sounds OK but the carbs intakes spit now & then. Is this an indication of too lean or too rich?

I am expecting the answer to be air leak. But please don't blame the butterfly spindles, they have been packed with grease, so I think this early on they are innocent.

Happy to provide more information.
Before you ask I've had the idle mixture screws set at anything between 1 turn out to 3 1/2 turns out and got these sorts of results across the board - another pointer at an air leak?
Thanks in advance!

 

Hi Martin,
I've focused on Mike Pierce's instructions (https://www.piercemanifolds.com/category_s/313.htm) for the tuning part of the operation. The balancing part I used Birdman's tutorial.

I didn't touch the air bypass screws when I dismantled and cleaned the carbs. I didn't realise the significance of them at the time and they were quite tight so I left them alone.
But the balance between the throat pairs is pretty much spot on, so I haven't been overly concerned. (I have assumed that at least one is fully shut but I guess there would be a problem if both were wound out? - i.e. contra to the correct set up)

I balanced the pair of carbs at the rear of the car first. Then the pair of carbs by the firewall.
I then adjusted the linkage to balance the front pair and the rear pair.
This seems to be OK, they pull equally whatever weird idle I've got going.

I didn't set the the idle speed screws, I backed them off and used the throttle cable adjuster to adjust the idle, when balancing the carbs.
I have some theories but I won't muddy the waters by putting them out there.

 

Thanks Martin.
I am reasonably confident that the linkages are returning to the stops OK - I can understand the problems this would cause.

My plan is to
1. check the linkages as above
2. check the air bypass screws and make sure that at least one of each pair is fully wound in
3. check that each carb is properly seated to the intake manifold.
4. check that the butterflies are fully closing at idle and that the progression holes aren't being exposed.

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I did the above last night and fired the engine up this evening.
The return to idle (after blipping the throttle) is much better but still not right.

I started with the idle mixture screws turned out just 1 turn, the engine was running OK-ish but the carbs were spitting away.
I wound out the idle mixture screws a little (maybe between half a turn and one and half turns), trying to find the spot where the engine started to run less well and then turn the screw back in a little.
The spitting reduced but I was getting a load of muted pops and bangs in the exhaust.

I really need to understand what is going on here...
My immediate thoughts are that the spitting in the carb chokes is because the mixture was too lean.
And my instinct tells me that the noise in the exhaust is because of unburnt fuel - i.e. the mixture is too rich. But I suspect I am wrong and that this is another sign that the mixture is still too lean.
Also, my guess is that if I can get the mixture correct, the return to idle will be better too.