26VA interchangeability

[Andy Bennett]

I have a 26VA carb on my 33 RP.
After an enforced layup I had problems with running on anything other than full choke. 
I replaced fuel, slight improvement, but still poor running.
I then blew through the jets with compressed air, again slightly better but still poor.
I couldn't get the jets out so tried poking a very fine needle through jets. Met some resistance, again slightly better, now running half choke but no better.

So, in accepting that the problem likely lay somewhere in the jets, I dug out a spare carb I had purchased as refurbished by Holmesdale Sevens. 
So, here is the crux of my question.
I recall some information a while ago about some subtle differences in 26VA carbs and reasons not to mix bowls. 
The bowl on the carb on my car is subtly different to that on the spare carb, in that the jets are in slightly different positions and the resulting moulding on the base is different. From what I can tell the rest is identical, the emulsion block and all connections look to be the same. I therefore bolted it on and the car sprung into life and ran as sweet as could be, revved if anything better than it has in a long time. Problem apparently solved.


I appreciate that the immediate comment might be: it fits, it doesn't leak and it runs well, enjoy. Also some might say well just replace the whole carb. 

But, I don't want to break the banjo joint or the manifold joint if I don't have to. But, there is the niggling comment in my mind that there is a reason not to mix different bowls on different carbs.

Any of this making sense?
       

[Ian Wegg]

Andy, I had a very similar situation to you which I posted in this thread: Zenith 26VA differences 

In my case, the differences weren't so subtle. One float bowl has a completely flat bottom. Also, as on yours, one set of attaching bolts is hexagonal and the other square.

I was pointed to the answer, quite likely the one you remember, here: Carburettor problems.

However, here's the nub of the matter, the combination that works best for me is a mismatched one! When I attach the bowl that is supposed to fit the idling cannot be lowered to a sensible speed but with the "wrong" bowl it runs sweetly - the exact opposite of expectation.  I have been running that way for a few weeks and all seems well.

[John Cornforth]

Hi Andy

I can't answer your question directly, but here is an observation. Many of these carbs have spent some point in their lives laid up with some water in the bottom of the float bowl. This causes flaky corrosion of the Mazak, which you can clean off to some extent. However, I have a suspicion that similar corrosion occurs within the fine drillings and passages. The resulting deposits are extremely difficult to remove. I had one example which had been given the full treatment of soaking in solvent, blasting with a high pressure air line and cleaning with Arklone in an industrial ultrasonic bath. Despite all this it never really ran satisfactorily and the idling mixture adjustment did little or nothing.

[Andy Bennett]

Thank you both.
John, there is some obvious roughness at the bottom of the bowl so there might be something in that as I have never found the mixture screw to make any difference.
Ian: at least I know I am not going mad, that was the one I was thinking about but for some reason couldn't find.
So, been back in the garage to check.

Strangely what I have on the car (as purchased 15 years ago) is a mismatch from R's photos. I have a single tube top and 2 uneven length tubes underneath (my picture above right), whereas it seems this top should have a 'bowl' style under the bowl.
The spare carb from Holmesdale is unsurprisingly right in every aspect. It has 2 tubes top and 2 even length tubes under (as per R's picture).

I think I shall bite the bullet and swap the whole thing over. Need to get some high temp silicon sealant first for the banjo.

Andy

[Andy Bennett]

Carburettor swapped and car going like a train, better than I can remember, which is useful since I have just moved her 300 miles to a land of hills, more to come in 'what have you done today'

[Ian Wegg]

Great news Andy!

[Dennis Nicholas]

Just thinking to myself while sitting here in hospital.  All passageways must have got there somehow.....I think usually by drillings.  Where corrosion build up suspected....nay almost certain......try work out where a drill could have been inserted.  Even drill a new opening down into passageway.  Nothing to loose if all other cleaning methods used and bits unusable anyway.  Part fill passageways with fine sharp sand and carry part around in your cars......never know, may just "sand blast" clean enough. 

[jpsmit]

Just thinking to myself while sitting here in hospital. 

that sort of slipped in. I hope all is well. (or will be)

[Dennis Nicholas]

Thanks, engineering works on my accelerator leg fluidics.......Propylene tubes should last till next Centenary celebrations.