O-200-A fuel primer

[Hercfix]

Hi,

Is it normal when priming a o-200-A in a C150 to have fuel run out of the airbox on the carby?

[146fixer]

Yes if you over prime it.

[NutLoose]

As above and be careful, its not unknown when you get that for it to flash back and set fire to the air filter carb etc when you attempt to start it with the resulting damage.

If you do get that crank away, better in the eng burning than outside trying to get in, if you know what I mean...

[Hercfix]

This issue is with just one pump on the primer there is fuel dribling out of the airbox housing on the bottom of the carby, this doesn't seem normal?

[SNS3Guppy]

Are you using the primer, or pumping the throttle? If you're pumping the throttle, you're using the accelerator pump, and that's not the primer.

[Hercfix]

Ahhhh noo, definatly the PRIMER

[Hercfix]

Does anybody else have any info on this problem?

[barit1]

How many "shots" are you using on the primer, and what air temperature? Fuel dripping out the airbox certainly tells you that it's overprimed - I seem to recall an O-200 doesn't usually need much prime, especially on a warm day.

In fact on some engines it may be best not to prime at all except while cranking.

[Hercfix]

One shot on the primer is enought to have it run out

[On-MarkBob]

As I remember it the 0-200 (continental engine) has a carburettor mounted on a manifold above it with the Airbox below it. Some only had one priming line that went to the manifold just above the carburettor and not individually to manifold at the cylinders. If this is the case it is perfectly normal that you will see un-vaporised fuel dripping from the airbox, since gravity is at work here. It is particularly apparent when the weather is cold, since less of the fuel is able to vaporise. The fuel is dripping back down the carb and out the bottom. This could be a good thing since the excess fuel is escaping and should be less of a fire hazard than it might be if it did not. Once the engine starts the rest of the fuel will be quickly consumed by the engine.
These engines do not have a 'Choke' so the engine will be more difficult to start in cold conditions if you use ecessive throttle openings. Setting the throttle 1/4 open for example could be too much. Shut the throttle completely, prime the engine and start the motor with the throttle closed. The throttle butterfly will act as a valve and stop some of the fuel draining away, also it will act as a 'choke'. When the engine fires, that is the time to open the throttle to the 1/4 open position and it will quickly suck up the remaining fuel.

[First_Principal]

I've got to check my 150 for its annual shortly so will look more closely at the priming mechanism then. However I only ever give it one pump on the primer and about 1/2" of throttle and it starts first time, every time, with no fuel leakage.

The Cub I fly mind you, same engine (RR 0-200), is generally started without primer and a pump on the throttle (also no fuel leakage). It's the owners preference and I guess he should know given his experience.

[Sandy Hutton]

Yes, it's normal for the fuel to run back down into the airbox. The primer sprays directly into the X junction at the base of the induction pipes just above the carb, not to the rear of the valves as in a lycoming..best to do a start as soon as you have primed and this will reduce any fire risk too.:ok: