Mark, I need to make a point about safety. I agree that running an engine briefly for test without an air cleaner in a clean area will not suck enough dirt into the intake to cause any problems, but there is a safety issue here.
Particularly with an engine that has or may have problems, you have to consider the possibility that the engine will produce a "spit", a symptom of lean mixture which causes a puff, or a blast, of partly vaporised, possibly burning, fuel to be spat out from the intake. Aside from the (probably small) risk of a general fire, when we are working on engines we are often standing close to them. A blast of burning petrol onto a person, especially the person's face and eyes, can have horrific effects.
I confess I sometimes do start an engine without the air cleaner, usually to see if it is the air cleaner that is causing the problem I'm investigating. I shouldn't do this: the way to check for a filter problem is to remove the filter element then put the air cleaner housing back together. However if I do take this rather hazardous short-cut I always do it with the possibility of a spit at the front of my mind. I have seen a lot of spits over the years, and seen a few small fires, some of which badly damaged the bonnet of a car. The ejected fuel often bounces off the hood and ignites the carburetor generally. The fuel in the float bowl will vaporise, causing a steady emission of fuel into the venturi. Sometimes the under-hood insulation burns as well, in which case the whole car will probably be destroyed. Do not perform such tests in close proximity to anything that might be damaged by a blast of burning petrol - especially yourself. And don't ever use an engine, especially a car engine, routinely without at least a flame arrestor over the carburetor. I can recall a greatly-prized Bolwell which was driven to the local shops by the owner's wife, who then stood there saying "Oh dear" while the fibreglass bonnet was burned to uselessness, after the engine spat during startup.
