Primer bulb???
 

I've been contemplating lately how much help the use of a primer bulb on our planes could be, and how many problems it could solve, especially for newbies. I know, I don't really want one on my plane(s) either, but it does have some logic. When someone says "firing up your (weedeater, leaf blower, chainsaw)??" when you are using one on your plane, just tell them "Hey, at least my plane always runs!"

Here's the "argument". Most people don't have a clue about how a primer bulb system works, but it is pretty ingenious actually. It does not "push" fuel to the carb, and it does not "inject" fuel into the engine. What it does is draw fuel from the tank all the way into the regulator fuel chamber. It creates a suction that moves the regulator diaphragm open, which opens the inlet needle valve, which allows fuel to be drawn from the tank, through any filter you might have in the tank, through the inlet fuel tubing, through the fuel pump, through the inlet screen in the carb, past the regulator needle valve, and finally into the fuel chamber. The excess is then expelled through the other line in the primer bulb system, and dumped back into the tank.

So think of what all this accomplishes:

1. Flushes old fuel out of the carb and replaces it with fresh drawn from the tank.
2. Proves that the filter in your fuel tank is flowing.
3. Proves that there is probably no kink nor obstruction in your fuel feed line to the engine.
4. Proves that fuel can flow through the fuel pump, indicating that the check valves in the fuel pump are wet and probably functioning. (At least the inlet flapper valve is not stuck.)
5. Proves that the inlet screen in the carb itself can flow fuel.
6. Proves that the inlet needle is not stuck shut. (I have had this happen.)
7. Proves that the regulator diaphragm is not stuck in the closed position. (It still could be too stiff to operate correctly but at least it is opening the needle valve.)
8. Proves that there probably not an air leak at the fuel pump nor diaphragm cover gaskets.
9. Prevents the "dry carb won't draw fuel" syndrome.

Interesting heh?? I fix a lot of yard equipment, and the first thing I do after checking compression and spark is to put fresh fuel in and pump that primer bulb. If it doesn't pump fuel and fill up, the very first trouble shooting step is to find out why not.

AV8TOR

RE: Primer bulb???
 

I've been running one on my Mac 32 for a couple years because the G230 (Car engine) carb I used (it was handy and a good match) had one, it is handy as heck! Like you said, flushes the carb, pushes out air for the first start if it's been a while since the last time you had it out. If you run a 3 line fuel system, tee the fill line into the return line from the bulb and even if there is an air leak in that line it doesn't matter at all.

If it wasn't physically on the carb I don't know if I would put one on, but I've thought about doing it, and I think if a plane I put together has a carb that's set up for it I might try to incorporate one... Might just be another one of those conversation starters like explaining to someone that your engine used to cut weeds or wood :)

One down side on the carb mounted bulbs I've ran into, if there's no fuel in the bulb they don't seem to want to draw fuel if you forget to prime the system, I think it might be from the membrane or whatever is in it's valve assembly.

RE: Primer bulb???
 

There is a tiny rubber one way valve that needs to be wet. Sometimes the primer bulb may need to be replaced with a new one. Good insurance anyway. Capt,n

RE: Primer bulb???
 

That's basically what I figured

Primer bulb kits are available at Home Depot and Lowes for under $10, there's one kit with a walbro bulb, zama bulb and a remote bulb in the same package... The other kit comes with some fuel line, a filter clunk (the ceramic one I think), and a remote primer bulb labeled to fix a Ryobi.

RE: Primer bulb???
 

Yeah, because of the carb orientation and accessabliity on the Ryobi trimmers, most of them had remote primer bulbs. A lot of Poulan chain saws do as well.

AV8TOR

RE: Primer bulb???
 

Primer bulbs (several different configurations) are available on ebay. Check it out. I just bought 6 for $10.00. I do a lot of weed whip and chainsaw work as well as engine conversions. FLATHEAD

RE: Primer bulb???
 

Gotta say I'm giving this some serious thought. My gassers so far have been exposed and If there's ever any starting issues when the choke alone won't get it done (mostly only after not running for extended periods of time) I've kept a little eyedropper thingy I made handy to shoot a little fuel directly into the carb and away it goes. The next model I'll beputting together has a full cowl with no way to easily access the carburetor. I'm thinking most tuning will be done with the cowl off or I might have to make some kind of small access hole to allow access to the needles. To facillitate easy starting in all circumstances I do believe a primer bulb is just what the doctor ordered. All my carbs are set up for it anyway. If I can manage to locate it somewhere that'sfairly inconspicuous I may just do it...

RE: Primer bulb???
 

Well, think of it this way. If it wasn't really super useful, the manufacturers certainly wouldn't spend the bucks to include them on yard equipment.....

AV8TOR