Gotta love the snarl of twin-carbs with no air filters. When it gets to about 6000 RPM it snarls. Wow!

I put the twin carbs on my A14 engine. It started right up, but after a minute or so the idle started rising and would approach 4,000 RPM then I would shut it off. It had a strange whistling rising note at the same time. Kinda scary.1

I checked the throttle linkage, it was not sticking. Everything looked OK.

Figuring it was a leaking intake gasket, I got ready to take it off when I noticed the Mikuni-Solex 'starters' were on. I had forgotten to turn them off! They are used for cold starts, just like a choke on other carburetors. I didn't know they would cause the engine to run so high. But now it drives fine.

Mikuni PHH choke: A most interesting feature of the PHH is that instead of a choke butterfly valve for cold-start enrichment, it using an enriching circuit called a "starter" which rotates to open the starter jet. Yellow circles in photo, connect choke cable to these.

It is good practice the set and fix the starters back, or just fit a customised choke cable. The starter discs can 'creep' to the on position, or partially there and completely ruin your fuel economy and driving experience ( along with other more serious long term effects).

They are a great feature, a similar concept is used on the dellorto and weber carburettor.