engine stutter upon advancing throttle

[N74DV]

ever since my annual was completed I've noticed a more pronounced stutter when advancing throttle from idle to full.

My mechanic informed me that when he checked the timing during the annual he found that it was 2 gear teeth retarded on each mag. He says the stutter is more pronounced now because the engine is producing more power and is probably more lean during the transition from idle to full. He suggests richening the mixture.

Is there an idle circuit mixture adjustment on the Stromberg and if so is this what I would enrichen? and how would one go about doing this and how much would one adjust?

[VictorBravo]

Re: engine stutter upon advancing throttle

First, tell that !(#*% mechanic that the airplane is supposed to operate better and more reliably after he puts you through a ten thousand dollar ordeal like that. Tell HIM to get off his ass and fix the problem, and you've already paid him a very large sum for the airplane to be safe so he better make it safe.

Remind him that paperwork does not make an airplane safe to fly, and what's he gonna say if your heirs' lawyer puts him on the stand and asks him if he was so !($*% concerned with the paperwork why wasn't he just as concerned about mechanical reliability.

After you make him sweat a little, and feel FREE to tell him I said for you to do it, then let him know that the big knurled thumbscrew on the upper back side of the carburetor is the idle mixture. Sounds like it has to be richened up a little.

[Forrest Barber]

Re: engine stutter upon advancing throttle

Now really shock him and let him know which way to turn it to richen.....

Bill , big snow coming AGAIN. Yes on the other thread that could have been carb ice; recall it is instant at 59 F & high humitity ; sure it cannot happen at full throttle, but you had been landing, taxiing, idling , etc... Wish I had been there wearing my brown shorts so no one would have noticied. Keep at it cautiously!

[tawadc95]

Re: engine stutter upon advancing throttle

my ia rides with me after he is done and goes down his after annual checklist and my dad does the same thing with his customers..........just to look for things such as that.
make him get in with you.
this annual finished last week it payed off in a small way .during run up 1 mag was missing on a cylinder and he had not put 1 plug wire back in the mag.
i would have figured it out myself but it is nice to know he cares!

What does the engine do when you advance the throttle rapidly from ilde to full? if it misses a few beats as you say or backfires I would check the idle bleed holes for being plugged or for a loose fit where the throttle valve shaft goes throught he carb body, either one of the above will make for an instant and short lived stumble from leaning during throttle advancement

[crispy critter]

Re: engine stutter upon advancing throttle

[QUOTE=Forrest Barber;38614]Now really shock him and let him know which way to turn it to richen.....

Turn in to lean and out to rich. Clockwise is to lean and counter clockwise will make it richer.

[Forrest Barber]

Re: engine stutter upon advancing throttle

Any other ideas, remember this is the Stromberg and that is the "air bleed" ...

[astjp2]

Re: engine stutter upon advancing throttle

Try to push in the carb heat after advancing the throttle, its not the same as the Marvel procedure. Think of this, Carb heat on, throttle out, land/t&g, throttle in, carb heat off. I have had to dead stick it a lot before I changed my procedure. Tim

[VictorBravo]

Re: engine stutter upon advancing throttle

Any other ideas, remember this is the Stromberg and that is the "air bleed" ...

I didn't know the idle mixture was for air bleed. In that case closing the bleed clockwise would reduce the amount of air and thus richen the mixture.

Can't we just get a Bosch direct fuel injection system for these things ?

[astjp2]

Re: engine stutter upon advancing throttle

If we do the direct injection, how about coil on plug technology!

http://www.aempower.com/ViewCategory.aspx?CategoryID=123

[flyguy]

Re: engine stutter upon advancing throttle

Bet that would fix my radio noise.
DC

[Forrest Barber]

Re: engine stutter upon advancing throttle

It needs to be done, these designs we fly around are about 75 years old!! More on this Sunday, I will be away. the new folks that acquired Precision presented at my IA renewal the newest ignition system they are coming out with right now.

[N74DV]

Re: engine stutter upon advancing throttle

ok so... which is it? clockwise to richen (air metered) or counter clockwise to richen (fuel metered) ?????

[Guest]

Re: engine stutter upon advancing throttle

Hi DJ,

The actual Stromberg manual has a 2 page color fold out cross section of this carb.

Woo hoo, look out Heffner!

That fold out has color codes for the state of the fuel and air at each port and jet.

The idle screw clearly regulates metered fuel (pink), therefore CCW is rich and CW is lean.

The idle air bleed is clearly a different port.

That is info directly from the Stromberg manual.

Dave

[robbie]

Re: engine stutter upon advancing throttle

reach down the right side of the engine, might have to loosen the top two zuse fasteners and turn the big screw 1/4 turn out or ccw, try it, if no better try another 1/4 turn, should not have to go more than a 1'2 turn.

[flyguy]

Re: engine stutter upon advancing throttle

Drude and Robbie have it right.
BUT the air bleed is involved. It mixes a little air, as bubbles, with the fuel coming through to make it easier to break into particulate when it is sucked out throught the idle discharge nozzles. Still you are controlling the amount of idle FUEL being supplied with the idle adjust screw. CCW (screw out) to get more fuel.

Oh, yeah, in case no one said it, or you don't know, shut down the engine to do the adjust. (sounds obvious, doesn't it) but you can do it with the engine running, not going into that here. Don't try it.
DC