I can attest to that. I only use the boost pump for priming before starting and for hot starts. If you leave it on, you WILL flood the engine.My IO-346owner's manual tells me not to leave it on.

----- Original Message ----
From: Bob Steward <n76lima@mindspring.com>
To: musketeermail@yahoogroups.com
Sent: Tuesday, April 22, 2008 10:15:24 AM
Subject: Re: [musketeermail] IO 346 Fuel Injection

>When he quickly advanced the throttle the engine quit. Some quick work by
>the instructor got the windmilling engine restarted. They came back over
>the airport and duplicated the problem, left tank, right tank, boost
>pump on... Back to the hangar and it did it on the ground.

The IO-346A injection system is substantially unique among aircraft
injection systems. Why Beech/Continental didn't go with the industry
standard Bendix RSA style injection can only be speculated as a cost issue.

Because of the differences in the injection from all other aircraft, you
have a really small number of Beech Musketeer injection experienced
mechanics to work with. And you may spend a lot of time (and money)
educating your mechanic of choice. (As Braden pointed out, it took them 8
months to find his problem.)

One common issue is the "boost pump", which is NOT a boost pump on the
IO-346A injection, it is an emergency replacement for the engine driven pump.

Flipping on the "boost pump" will kill the engine in many situations. It
just floods it out. You use it to start the engine and prime the
cylinders, and in the event that the mechanical pump quits. Running both
will flood the engine.

So if your "problem" with advancing the throttle is that it dies, and you
had the "boost pump" on for safety because of low altitude or unusual
attitudes, then you are causing the problem by not following the factory
checklists and procedures.

Pilots not properly trained on the A23 or A23A will flip on the boost pump
like you do on a Cherokee -- before T/O and on downwind, when changing
tanks, etc. Some of them are so lax, that they fly on for HOURS without
bothering to shut it down, because they don't notice a difference (there is

The IO-346A engine driven pump provides the required FLOW based on RPM with
about a 10% excess through a positive displacement pump, and the
throttle/mixture block leaks the excess back to the tank, based on the
control positions. Turning on the "boost pump" increases the flow
dramatically, and the "leak" in the throttle control can't drain away
enough to run properly.

Going full throttle, as you suggest is the time it dies, floods out the
engine from the excess fuel.

Other injection systems are PRESSURE systems that depend on a steady fuel
pressure. The Continental IO-346A system varies the pressure as a function
of RPM, which changes the FLOW.

You can get the Continental Fuel Injection manual that covers the IO-346A
from www.TCMLink. com, the Continental web site.

Bob Steward, A&P IA
Birmingham, AL