Major surgery for an acute breathing problem with Bugatti T30

A while ago, a customer contacted me as he was always having problems with the (presumably) original carbs fitted to his '25 Bugatti T30. Things couldn't carry on as they were, so I suggested he send them to me for inspection as no fault could be seen on the photos he mailed to me.

As they arrived, the problem was immediately detected: two different types of carb, one a 35HR and the other a 35MOHR. Very similar to each other, but tickover drillings and main-jet holder were different. They were two extremely rare bronze-cast bodies, well patinad and even with the original type-plates rivetted on from the supplier, -Händler and Co., Berlin-, in those days main-dealer and manufacturer for the french mother company.

You can clearly see (Pic 1) that the main-jet bosses are at different heights - there were also two different types of main-jet holder and main-jets. The 35HR had jets from carbs that are not available anymore - the 35MOHR "modern" types that are still on the market. Probably the car was modernised from a single to a twin carb set-up and one just took the 35MOHR as it looked so similar. Somebody forgot to check it properly and it had been running all these years with te incorrect jetting. But still, old bangers tend to fart and cough...

The question is: how? The 35HR had to be modified to the same specification as the 35MOHR. The bronze-cast bodies were ideally suited for modification by silver-soldering. This would not have been possible with the later tye of die-cast zinc. Firstly a new brass main-jet boss was produced from a solid billet (Pic 2) and shaped to suit the victim. The old boss was removed (Pic 3) and the new one silver-soldering. (lower melting-point than normal braze) into place. Finally it was filed to original size, fine emery-clothed and polished (Pic 4). The tickover drillings were drilled and plugged.

Δ Back to Top

Standard repairs were still caried out: the bodies were bored out to 36mm (Pic 5) as they were badly warped. Therefore new butterfly discs (at correct angle) were turned and the badly worn spindles were replaced (Pic 6), which had suffered considerably in 80 years of breathing. Some mundane parts also had to be replaced (Pic 7) and, of course, as in a general overhaul, the float-valves and jets were re-newed.

You can see the results of the work (Pic 8&9) and notice that they are now virtually identical, also when running. This was a very satisfying and challenging job. Obiously a vehicle like this won't run perfectly on the spot, so I supplied the customer with a selection of various sizes of jet for tuning purposes. After fine tuning the car runs well now (Pic 10&11).