Zenith 30 VM carb query

[PaulRM]

Micro drills also available through watch repair dealers. Search eBay under watchmaking supplies.

[Forumadmin]

I have not used these but they would be useful for cleaning.
https://www.ebay.co.uk/itm/402920712531
These are the drills I have.
https://www.ebay.co.uk/itm/193037574754

[PaulRM]

The cleaning brushes I don't have. Getting some of those. Thanks.

[Nick Webster]

By way of a bit of a follow up from this thread. After the last posting I did buy some of the cheapo Chinese microdrills. Generally speaking they are reasonably accurate in size, although according to my measurements, two are actually the same size, which must have been a packing fault. I dare not get two out of the packet at the same time for fear of mixing them up and having to check all the sizes again! I should say at this point that until recently I have never felt the need to drill jets and indeed had heeded the dire warnings in workshop manuals against attempting such a thing.

I have a car where the previous owner had (as I understand it by an email trail) experienced a variety of problems including a dreadful flat spot. The engine had been rebuilt before I bought it but had never really run well. The carburettors had been rebuilt with reconditioned spindles and new throttle discs. It came to me still with the awful flat spot.

I tried swapping float bowls complete with jets but the fault persisted. The engine did not tick over slowly enough for my liking either, so I eventually abandoned the carbs and used another pair with new spindles and old discs which were definitely a better fit. And still the flat spot persisted (I don't have much hair but would have started pulling it out at this point if I did). Eventually I tried fitting 65 /95 main and compensator jets from a slightly hot engine. That cured it at the expense of the car being rather thirsty.

Having obtained the pack of micro drills, I intended making standard jets slightly larger, but not as large as the last ones fitted, which were rather over doing it for a standard build engine. I was surprised to find that several of my spare standard jets were in fact under size. This (as I think Keith has already suggested) I attribute to dirt build up in the jet hole. The under size jets included the spare ones I had previously fitted and failed to cure the engine flat spot.

I don't know how long the drills are supposed to last and I was pleased from the point of accuracy that I was only going through an existing hole which in theory was the same size as the drill already. Anyway, I eventually got through the holes in the main and compensator jets. I wasn't expecting significant change in performance but to my immense relief the flat spot had gone and the engine picked up as required. Before I had to floor the throttle and drive on through!

I've made a bit of a tale of this, but the bottom line is that I would certainly endorse the purchase of microdrills to check jet sizes.

Nick