seeking opinions on "matched" dellortos

[dgym]

My car has two different Dellortos fitted. A 40 and a 40E.
these two carbs have a different number of progression holes, this is a problem.

I spoke to my local carb guy who suggested that If I can find another 40 or 40E body I could swap over most of the internals and have a pair the same.

I did some of my own research and kept coming across "matched pairs"..apparently each carb has a numbered tag, and If you have two carbs fitted to a car you want them in sequence. This is because as the tooling at the factory wears down, the holes inside change size. so carb number 1 from the factory will have wider internal diameters than carb number 30.

so, is it being anal or just correct to seek out a matched pair?

cheers!
-Jim

[rgh0]

Hi Jim

I don't believe there is any need for a "matched pair" of carbs. The various jet settings are what determines the carbs performance and they are all changeable to match provided you have the same basic body and the same progression holes drilled in that body. The minor differences in some of the other drillings you may find due to tool variation do not matter I believe as these do not control the carbs calibration.

However you do need to check all the changeable components and not just the main and idle jets and ensure they are set the same. Things like pump jets and pump stroke and floats and float valves and butterfly angles all affect performance

Any 40 DHLA body of the same era should be perfectly suitable provided all the other parts match.

"Matching Pairs" is just another part of the whole "Matching Numbers" thing that people carry on about these days for some reason. Its a piece of machinery to enjoy driving not a museum collection item I hope and machinery parts needs replacing from time to time if your using them to the fullest which you should be.

cheers
Rohan

[bill308]

Thanks Rohan and hi Jim.

Fuel, air, and emulsified fuel/air passages drilled in the body casting, are relatively large compared to the precision machined, metering orifices. This means the drilled passages have little effect on flow and the jets, AC's, emulsion tubes, and progression are most important. If you were designing a new carb, this would be one of your design goals.

Drilling long, precision passages, is a difficult thing to do. So, make them more than big enough and meter them with replaceable and tunable restrictions.

Bill