Just a little shared learning here although most may know this...…


It seems common sense but sometimes overlooked when buying new parts but since I rebuilt my 650 lump it never has run right and always had to have a little choke on. So this weekend I finally bit the bullet and stripped the carb off for examination. I had previously 'flatted' off the bottom of the carb but as the bakolight spacer was new I never gave it a second thought to check it, however after putting a steel rule across it I was stunned at how warped it actually was on both sides!!…….so after a little flatting off it's now nice and flat.....


I rebuilt the carb also but didn't check the main spindle as the kit I bought had the oversize shaft in it and at the time I didn't have enough time to ream out the carb body so I didn't even check it, big mistake!!!!…….the bushes are non existent and the shaft is heavily worn on the throttle lever side, luckily the carb body has virtually no wear on it (measures 6.05mm max) so I have purchased a new standard size spindle.


In my other world of VW's I know how detrimental this shaft being correct can be and I'm quite (extremely) peeved off with myself that I didn't sort all this out at day 1!!!!!!!!!!…….my fault for rushing I suppose...…


I'll drop a note back here on how the car reacts once it's been rebuilt.


On a side note the bushes for the main spindle are plastic, has anyone ever machined and fitted brass ones? I used to do them with the VW's ok (in fact I had all the lads asking me to machine them and made little tools for fitting them)……..I might do this on the Fiat carb?....


Cheers


Rob

The Whitakers said:

...........
On a side note the bushes for the main spindle are plastic, has anyone ever machined and fitted brass ones? I used to do them with the VW's ok (in fact I had all the lads asking me to machine them and made little tools for fitting them)……..I might do this on the Fiat carb?....

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I once worked in a College where they had an engineering shop... many a lunchtime was spent making and fitting bushes to various things ...
I would make them out of oilite bronze (they just happened to have it there..)
I have looked a a couple of carbs from my spares box and noticed the wear and wondered about bronze bushes...

And I have just been advised that the 6.0mm standard spindles are obsolete now and the smallest available is 6.2mm (VDL)...……...

The Whitakers said:

And I have just been advised that the 6.0mm standard spindles are obsolete now and the smallest available is 6.2mm (VDL)...……...

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And this again is an example of how the "collective" knowledge on here needs to be put in some sort of library rather than lost in threads...

Bigvtwin996 said:

I have looked a a couple of carbs from my spares box and noticed the wear and wondered about bronze bushes...

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I don't suppose one of them is a 28IMB that is in a serviceable condition have you that you would sell to me?


I would like to strip one down and do a 'full' soda blast refurb on it and machine some bronze bushes etc...….

The Whitakers said:

I don't suppose one of them is a 28IMB that is in a serviceable condition have you that you would sell to me?......

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sorry my stuff is mostly old "Prototypi"..
you need the Hoarders - Peter and Tom (they always seem to have a spare or two of everything..., I believe Peter has a shed full of engines so he probably has loads of carbs ....

Bigvtwin996 said:

sorry my stuff is mostly old "Prototypi"..
you need the Hoarders - Peter and Tom (they always seem to have a spare or two of everything..., I believe Peter has a shed full of engines so he probably has loads of carbs ....

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I'll await them to jump on this thread then with their meagre offerings of rusty

The Whitakers said:

I don't suppose one of them is a 28IMB that is in a serviceable condition have you that you would sell to me?...….

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I have still got one brand new late model Weber 28IMB carb. Genuine and not one of the dodgy reproduction ones that are on the market. I had two but have just delivered one to a satisfied customer in New Zealand while I was down there [emoji3]

Toshi 975 said:

I have still got one brand new late model Weber 28IMB carb. Genuine and not one of the dodgy reproduction ones that are on the market. I had two but have just delivered one to a satisfied customer in New Zealand while I was down there [emoji3]

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Hi Dave, good trip and festive break?


Are you actually saying that you would sell this carb or are you just showing off? (chuckling as I type this) I know how you like to keep your NOS shiny bits, I bet its next the shiny new Panda 30 head ……..Speaking of heads the one I got from you is still in the box you sent it in, damn the house move for spoiling fun things...……..


PM/text or email me a price if you want to sell it, I'll ensure I'm sat down when I read your message......or quite happy to take one for rebuild if you have one?


Regards


Rob

The Whitakers said:

Hi Dave, good trip and festive break?


Are you actually saying that you would sell this carb or are you just showing off? (chuckling as I type this)

I know how you like to keep your NOS shiny bits, I bet its next the shiny new Panda 30 head

……..Speaking of heads the one I got from you is still in the box you sent it in, damn the house move for spoiling fun things...……..


PM/text or email me a price if you want to sell it, I'll ensure I'm sat down when I read your message......or quite happy to take one for rebuild if you have one?


Regards


Rob

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Hi Rob
Yes happy to sell the carb. I will just do what I usually do. Think of a good price then double it [emoji15][emoji3]
Will be in touch.

By the way of an update...…..apologies for the ramblings...


So when a spindle is advertised at 6.2mm it isn't actually 6.2mm!.....the initial measurement was 6.28mm but once I had 'buffed' the black coating off it reduced slightly but only to 6.25mm...….


Through my 'assumptions' of the shaft advertised as a 6.2mm shaft a purchased a 6.2mm long taper reamer to run through the carb assuming the shaft would fit a 6.2mm hole....this naturally was leagues away!!!...….as I wanted to rebuild the carb last night the new spindle was bobbed in the lathe and meticulously polished down until a snug but free moving spindle was fitted......it measured between 6.17 to 6.19. At this point I do have to state that the larger dimension was where the butterfly disc was which for all intense and purpose once the spindle is fitted makes no difference to its operation. The spindle had no play and full assembly commenced.....


Another observation was the plastic bushes, these are not bushes at all they are dust guards and in this case were a really poorly manufactured!!


From my inspection of the carb body a could not ascertain if any form of bush actually exists or the spindle bore is actually just a hole machined through the alloy carb body?! answers on a post card please if you have witnessed anything different.....


I fitted the carb and started the set up, got it running and fired up the timing light and little by little adjusted both the timing and carb settings.....


I finally got it to run and tick over and a brief spin around the courtyard it seemed to run and drive ok in first and briefly second gear however the tick over screw is wound right in!!! I'm not sure im happy with that to be honest!...….Also I noted the butterfly has no hole in it like other carbs (I think I've read on here about this so will research it)


Another thing I noted was that the ignition timing was jumpy, not massively but I'm running an Accuspark (yes I bit the bullet after all my negative prior dealings) and wasted spark coil so I would expect it to be pretty rock solid. I tried putting the HT pick up on both leads and it was the same.....Ill inspect that further.....


So for me after all this rebuild with new gaskets etc and setting up I got my can of parts cleaner and gave it a good squirt at the base of the carb to ensure my rebuild was good and no air was being sucked in...……..the car stopped dead!...…..


I turned the lights out and locked the garage...…...

So I grabbed a brew and headed for the garage last night...…..


The car pretty much fire up first time with full choke and idled smoothly.....


I let the car warm up for a couple of minutes and reduced the choke to half, still ok and reversed the car out...…


Reduced the choke to roughly a quarter and went for a drive around the block, it ran great!!!....pick up ok and accelerated smoothly.....


Pulled back in front of the garage and slowly pushed the choke off and the engine slowed and slowed until it stopped...…


I'll have another play with the idle adjustment screw over the weekend....


Oh and my brew went cold before I got to drink it...…

I have come across a couple of carbs where the idle mixture screw seems to have no effect. Being the only easily accessible adjustment on the carb they may get over tightened when people try to sort running problems. A bit like the bolts on the front exhaust elbows that get stripped in the head as it is too easy to get a nice big wrench on it.
I have also rebushed a number of carb bodies by using a piece of 8mm diameter dural which is a far superior material to the original casting. I found a suitable drill that gives a press fit for the bushes which have already been drilled just under 6mm then running a suitable reamer through when installed.

I'm interested on where this goes as I have a very similar issue, my 650 starts and sometimes runs nicely but weirdly its developed a tick over issue. Sometimes it ticks over and others not. I've had the carb changed... then a new carb kit (just in case something inside was damaged). New HT leads, distributer cap, plugs, voltage regulator, condenser, just about everything I can think of. If you do come up with a solution with your issue I'd love to hear about it. Cheer db

Hi to The Whitakers,

Let me preface this by saying it's not directed at The Whitakers, as he/they? have shown that they probably know what they're doing - anyone who can use a lathe and take accurate measurements is not an amateur, in my book.

My take on reaming out/boring out the butterfly spindle to fit either an oversize spindle or bushes and a standard spindle is that it's oh-so-easy to get it wrong and ruin a carb.

The butterfly valve needs to be capable of completely closing off the bore in the carb with the throttle stop screw fully backed-off.
Below this closed off butterfly valve or perhaps with it just cracked-open a tiny amount, the idle mixture hole will be uncovered and exposed to engine vacuum, thus drawing in sufficient fuel and air (drawn in around the tiny gap around the butterfly valve/disc when the idle speed screw is turned in) to allow the engine to idle.
As the throttle is opened further, other tiny holes, called progression holes are exposed at the appropriate time in relation to the increasing amount of air passing around the butterfly valve, allowing extra fuel to be drawn from the emulsion tube circuit.

The problem with using a reamer, is that the holes, in which runs the butterfly spindle, may have worn approx. oval shaped. To allow the reamer to centre itself on a hole/bore worn oval is possibly going to result in slight misalignment of the butterfly valve when closed. Same if drilling into a worn oval shaped hole in order to fit bushes. Even slight misalignment of the new spindle, can upset the position of the butterfly valve (I know there's a small amount of adjustment available before the screws are tightened). If this valve isn't capable of closing off all airflow, then it may prove almost impossible to set the idle mixture and speed correctly.

I've seen some carbs ruined by ham-fisted attempts to fit bushes and a new standard spindle. I'd prefer to centre any reamer or drill on the centreline of the carb bore, just to avoid any possible misalignment of this butterfly valve.
The height of the centreline of the spindle should also remain the same as before to maintain the same relative position of the butterfly valve with the idle mixture and progression holes. So some careful measuring/setting up is required - it's not a case of just sticking a drill bit in a drill and going at it, as some have done.

Re:- Ignition timing moving around when checked against the timing marks?
(also sometimes referred to as 'timing scatter'?).
Usual reason is a worn timing chain/sprockets.
Can also be due to wear in the drive gears operating the distributor, also any keyed/dowelled/splined joints/connections in the distributor drive system. Also check out the mechanical ignition advance unit in the distributor for wear or faulty springs .
Note:- some mech. advance units use 2 different springs, a light one to work from idle speed and another that only becomes operational at higher engine speeds - this 2nd spring may be loose on it's mounting post, it's designed to be, don't tighten this!. 2 springs are used to give a advance 'curve' instead of a straight-line advance.

The only way I know of to avoid any variation/wander in ignition timing is to go full electronic and trigger the spark from a crank position sensor, as on modern vehicles.

Hth,

Al.