Never mounted or run McCoy series 21 .35
While this engine is new the box is not collector-quality
$50.00 plus shipping

TD .049 $50.00
Cox 020 $50.00
Plus 10.95 priority mail

Joseph .... interesting you mentioned the inboard mount for a Fox 35 ..... I did that .... the interesting thing is that the 'burp' now occurs on the hard inside maneuver.

I don't think that the phenomenon is a hard influx of richening gasses.  I think its the opposite, at the time of the acceleration, the bypass gases are pushed back into the bypass, resulting in a momentary starved condition.  (but I may be wrong)

Frank

with the overly large bypass, the gas velocity isn't strong enough the overcome the acceleration
the reduced bypass area helps create a higher velocity to help the gases get into the combustion chamber

I am no expert on the subject but I think that you are right and it is an issue of gas velocity or more like gas velocity at a given RPM. A tuned pipe might be giving you a form of adjustable gas velocity. There is probably an ideal formula for RPM/gas velocity that creates a stable run with power at a given RPM. Art Adamissin used to block off a port on the OS FPS to increase gas velocity but I think he did this to get a stable run at lower RPMs than the engine was designed for.

A point I would like to add. Klean Strip lacquer thinner flashes of fairly quick. This means that with any kind of humidity, you can experience blushing. A splash of retarder will take care of this problem.

Been using Klean Strip for years. Works great!! I don’t find the blushing to be a big deal as I use auto clear. As soon as the clear goes over the blushing, it disappears

Sand is called SAND because it's between SEA and LAND 

I'll show myself out.

Cheers,
-Andrey