A delay in power input

RyanB

RyanB

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Yesterday I was out doing some solo flight. I was doing some touch and goes and on one of the T&G's I put flaps up, carb heat cold and went to give it full power as normal. However when I went to give it power it seemed to have a 1-2 second delay, meaning when i gave it power that time it had a slight delay, it did not respond to the throttle input right away like it normally would. Any reason why it did this? BTW this was in a C152
 
Hmmm.. spool up time? Is this a turbine C152?

But in all seriousness, was your application of power smooth, or more of a quick jam?
 
Ryanb said:
Yesterday I was out doing some solo flight. I was doing some touch and goes and on one of the T&G's I put flaps up, carb heat cold and went to give it full power as normal. However when I went to give it power it seemed to have a 1-2 second delay, meaning when i gave it power that time it had a slight delay, it did not respond to the throttle input right away like it normally would. Any reason why it did this? BTW this was in a C152
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IIRC many 152s don't have an accelerator pump so if you jam the throttle open you'll get a lag before the fuel flow catches up with the need. If it is equipped with an accelerator pump, it is likely bad.
 
Was it too rich? It has been cooler out recently at least in the midwest. When running really rich, I have noticed a bit of a hiccup when applying throttle.
 
Hmm, can't remember giving it the go any quicker than normal, but I definitely could have.
 
Two seconds is long for a rich miss.

It's possible, but I'd be concerned about other things, especially weak spark (fouling?) or carb ice. Something got out of its sweet spot.
 
I would look at carb ice since you took it off before passing throttle in.
 
Ryanb said:
...on one of the T&G's I put flaps up, carb heat cold and went to give it full power as normal.
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Several possibilities, starting with a bit of carb ice (which is why I teach people to advance the throttle and catch the carb heat with their thumb as the throttle passes about halfway rather than pushing carb heat in and then advancing the throttle), as well as jamming the throttle faster than the engine could respond -- you really can choke even a normally aspirated, carbureted engine that way. Beyond that, I'd need more information, and probably to see/hear it happen, to try to get a handle on the cause.
 
Ron Levy said:
jamming the throttle faster than the engine could respond -- you really can choke even a normally aspirated, carbureted engine that way.
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That is was I was taught to go to full power on a nice smooth 3 second count...one one thousand....two one thousand...three one thousand...at full power.

Gives the engine a chance to catch up with the fuel and speed up the fuel pump adding yet more fuel rather then just dumping the throttle open full and waiting for it all to catch up.

...now was that your problem?...could be a possibility.
 
Shawn said:
That is was I was taught to go to full power on a nice smooth 3 second count...one one thousand....two one thousand...three one thousand...at full power.

Gives the engine a chance to catch up with the fuel and speed up the fuel pump adding yet more fuel rather then just dumping the throttle open full and waiting for it all to catch up.

...now was that your problem?...could be a possibility.
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Ugg, unless you have a fuel injected engine, there is no engine driven pump that directly relates to the fuel going to the engine. With a carburetor there is more than enough fuel in the bowl available to cover not only acceleration but even to get you off the ground before it runs out of fuel if you have the fuel selector turned off.

Carburetors use the vacuum created by the venturi effect to suck fuel into the engine. When you open the throttle plate, the vacuum drops off momentarily until the engine speed increases, that is why most carburetors are affixed with an accelerator pump to squirt extra fuel into the airstream until the vacuum comes back up and can once again suck the fuel out of the float bowl through the main jet. Opening the throttle slowly decreases the vacuum drop so the the fuel still gets sucked out through the main jet. If there is no accelerator pump or if it is defective, quickly opening the throttle will create an excessively lean condition that the power produced will drop off. If the engine is already running well and load is low, typically it will rebuild vacuum in a few moments and start producing power again; if the engine is barely running or under high load, it will die.
 
Shawn said:
That is was I was taught to go to full power on a nice smooth 3 second count...one one thousand....two one thousand...three one thousand...at full power.

Gives the engine a chance to catch up with the fuel and speed up the fuel pump adding yet more fuel rather then just dumping the throttle open full and waiting for it all to catch up.

...now was that your problem?...could be a possibility.
Click to expand...

Ugg, unless you have a fuel injected engine, there is no engine driven pump that directly relates to the fuel going to the engine. With a carburetor there is more than enough fuel in the bowl available to cover not only acceleration but even to get you off the ground before it runs out of fuel if you have the fuel selector turned off.

Carburetors use the vacuum created by the venturi effect to suck fuel into the engine. When you open the throttle plate, the vacuum drops off momentarily until the engine speed increases, that is why most carburetors are affixed with an accelerator pump to squirt extra fuel into the airstream until the vacuum comes back up and can once again suck the fuel out of the float bowl through the main jet. Opening the throttle slowly decreases the vacuum drop so the the fuel still gets sucked out through the main jet. If there is no accelerator pump or if it is defective, quickly opening the throttle will create an excessively lean condition that the power produced will drop off. If the engine is already running well and load is low, typically it will rebuild vacuum in a few moments and start producing power again; if the engine is barely running or under high load, it will die.

All a fuel pump on a carbureted engine does is refills the float bowl want il the float rises and drives the needle into the seat cutting off the fuel flow.
 
Well, I was trained in a fuel injected plane, so there is that...

Think we are both pretty much saying the same thing though...slammed throttle can = hesitation...regardless of the mechanics behind it.
 
If it's running a bit rich, at idle, after a few touch n gos, is when you may notice the delay caused by idling at full rich.
Also, in ideal carb ice conditions, apply power before removing carb heat.
Recent temperature changes could be the reason for this new experience to you.
 
dtuuri said:
If it was warmer recently it could account for a rich mixture. Might want to rethink that.

dtuuri
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I don't know if this is an issue for the carbs and conditions at hand, but some intake systems will evaporate fuel poorly with at idle with cool temperatures, especially air-cooled. While this isn't really a rich mixture, its symptoms are similar -- fouling and missing with unburned fuel. The solution, however, is more fuel, not less. That's why you need more priming to start an engine in cold weather.
 
frfly172 said:
I would look at carb ice since you took it off before passing throttle in.
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It takes longer than that for carb ice to form. That said, the engine will accelerate better in cold weather when the carb heat is still on, since the heat helps vaporize the fuel spray. Liquid fuel going into the cylinder does nobody any good.

Pushing the throttle in too fast can also trigger brief detonation, especially in larger engines. Detonation is more likely at high MP, lean mixtures and low RPM, the exact conditions created when the throttle is shoved in too quickly. Do that often enough and the engine's life gets shorter.

Dan
 
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