av8tor1977

My Feedback: (6)

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

w8ye

My Feedback: (16)

A copy of this was placed in the newbe sticky at the top of the gas forum.

av8tor1977

My Feedback: (6)

Thanks W8YE.

AV8TOR

captinjohn

I was going to suggest this years ago...but most guys would not take the time to set a primmer bulb up and even try one. They sure are good to get the fuel up quick....so you do not waste time and your arm, proping the engine over several times to get the fuel where it should be. Good idea AV8TOR....it will be of help to some for sure. Capt,n

ggraham500

My Feedback: (4)

So can we add a primer to our existing gas engines and how?

av8tor1977

My Feedback: (6)

It depends on the carb. If it was a carb that originally had an external primer bulb, it should have two fuel fittings on the carb, one of which was blocked to run it on an airplane. Unblock that fitting and run a fuel line from there to the suction side of an external primer bulb. The other connection on the primer bulb just uses a line that goes into the top of the fuel tank much as a common vent line does. The external primer bulb could be mounted somewhere inconspicuous like on the bottom of the cowl, etc.

If the carb was for an application that never used a primer bulb, it gets a little more tricky. You would have to create a fuel line connection that goes into the regulator chamber below the regulator diaphragm.

AV8TOR

Truckracer

My Feedback: (19)

In many cases the primer bulb would be a great idea. But in other cases, there is no access to the carb when the engine is fully cowled so the bulb would be worthless for the most part. I say go for it if your applications allow for its use. It sure is handy on lawn equipment and I've had more than one chainsaw that I wish had one!!

av8tor1977

My Feedback: (6)

You are speaking of the types of carbs that have the primer bulb mounted on top. My thoughts were of the remote mounted primer bulbs as shown in the picture.

AV8TOR

MetallicaJunkie

now thats a good idea!.... a remote primer

captinjohn

You can find the remote primers on string trimmers....ect. Best to buy a new one as they tend to get brittle and crack. Most any good small engine repair shop should have them.

Capt,n

captinjohn

One last Idea. Place the primer in line from fuel tank to fuel inlet on carb. Drill & tap the carb for a nipple & install a short piece of fuel line on it. Now when you prime the carb direct the excess fuel into carb throat. This will give the engine a shot of fuel to start. Choke may not be needed. Plug end of short line with a fuel dot before starting. Worth a try. Capt,n

ADDED more in the engine conversion thread.

karolh

What is the basic difference in operation from the type shown here versus the rubber plunger type as fitted on mowers etc.

Karol

av8tor1977

My Feedback: (6)

The carbs on four stroke lawn mowers are a completely different "animal", but the idea of the primer is basically the same; get fuel to the carb.

On two stroke yard equipment, sometimes the primer bulb is mounted on top of the carb, sometimes it is remote as shown in the post with the pic. Operation is exactly the same.

AV8TOR

karolh

On one of my gas models once the engine is shut down in between flights, if the model stands for say 30 minutes before it is started again, the fuel in the feed line drains back into the tank. I have always thought that this is caused by an air getting into the system, but the engine runs great everytime. What are your thoughts on this.

Karol

av8tor1977

My Feedback: (6)

Sounds like the carb needs a rebuild. Both the inlet needle in the carb, and the flapper check valve in the fuel pump should prevent the back flow.

AV8TOR

av8tor1977

My Feedback: (6)

For anyone interested, Google "remote primer bulb" and you'll find them. They are common on Ryobi string trimmers and many Poulan chain saws among many others.

AV8TOR

2walla

My Feedback: (10)

I ran converted mcculloch weedie motors for years and used the stock primer bulb mounted remotely on several diffent motors.. Worked fine.. Just as easy to put a blob of solder on the hole of the choke butterfly and to flip it thru a few times..

karolh

Will replace the inlet needle as I have already fitted a new flapper diaphram and see if that cures the back flow.

Karol

captinjohn

Some primers have a black rubber disc inside. It needs to be in good shape for the primer to function right.

Best Regards, Capt,n

ira d

Foe rc use what would be a good idea is a primer pump that is worked by the throttle linkage, After you fuel up you run the throttle up and down
a couple of times and the carb is primed.

1QwkSport2.5r

They call that an accelerator pump. I believe some Webra Carburetors for glow engines had a type of accelerator pump feature. Novel idea, but at an added complexity and cost.

av8tor1977

My Feedback: (6)

Some Walbro carbs have accelerator pumps as well...

As the original primer system for Walbro and Zama carbs is designed, you cannot flood the engine. The more you pump the primer, the more you are just circulating the fuel through the entire fuel system and back into the fuel tank. You are not ever injecting fuel into the engine, so you can't flood it. It's what we call "idiot proof". Other than the Walbro factory accelerator pumps as equipped on some carbs, I wouldn't want a primer system that actually pumped fuel into the engine. It would be really easy to flood the engine that way....

AV8TOR

ForcesR

The Evolution's new engine EVO62cc GXI EFI is said to be equipped with a "Primer Bulb".

Roger

av8tor1977

My Feedback: (6)

I would love to play with an EFI system for our little engines. Going to have to wait for the price to filter "down to the masses" though... (In my case that means REALLY cheap.) I wish I had the time and wherewithall to make up a simple fuel injection system that one could tune on your computer. Along with today's readily available telemetry, that would be a fun tuning exercise.

AV8TOR

ForcesR

Horrizon has the EVO62cc GXI EFI listed for $579.99. That is a decent price for a EFI 62cc engine, compared to other makes without EFI in the 60+cc range.