B

bill price

Member
i landed my rv-4 last night and it quit half way down the runway. i has plenty of power but runs eratic and dies easily at low rpm's. Has anyone experienced this and know what the problem is. It has a marvel carburetor on a Lyc. 0-320. Help.



Bill.
 
One cause can be a float that is leaking and has started to sink. It will make the engine run rich. The engine can manage the extra fuel at higher power but at or near idle it is much more sensitive to the amount of fuel it is getting.

Try pulling the mixture back a bunch at idle (on the ground) and see if it runs better.
 
?

Try looking for induction leaks!!!! spray some wd-40 is it? around the induction and the rpm will change if you have a leak.. somebody help me out here... Also.. when you pull your mixture back from 800-1000rpm depending on if you have FI or carb.. you should get 20-50 rpm rise.... please let me know what you get.
Best
Brian Wallis
404-405-1315
:)
 
Carburetor Loose?

I'm not an engine guy but from my own experience you may want to include in your search for the answer checking the bolts holding your carburetor on. When I was a student pilot many years ago on my long solo cross country I pulled the power on final and the engine conked out. What a fun experience as a solo student. To this day I am always careful about pulling the power until over the threshold. The engine would start up and run fine in anything higher than idle. The A&P from my home airport flew up to look at the plane and found the problem very quickly. He tightened up the bolts and the engine ran fine after that. As he explained, when you run at low rpm the loose bolts caused the engine to suck in air which over richened the mixture.

Let us know what you find.
 
Be careful..

...please. Milt Concannon had a great writeup yesterday about his engine failure on final with a torn up airplane. You just have to correct this. BTW, a loose carb will lean the mixture, not richen it, because of the extra air. For this reason, I like to leave some power on while on final.

Regards,
 
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Wood prop or metal? What is normal idle speed? Mine used to quit like that if I let it. (wood prop, idle too low, so it chuged a bit)
I'd like to know what you find on this one.
DM


bill price said:
i landed my rv-4 last night and it quit half way down the runway. i has plenty of power but runs eratic and dies easily at low rpm's. Has anyone experienced this and know what the problem is. It has a marvel carburetor on a Lyc. 0-320. Help.



Bill.
Click to expand...
 
I had the same problem with my -4 when I bought it. (Low time FN O-320 D1A w/ MA4 and Catto 3 Blade) I upped the RPM to about 820, checked induction (no leaks) adjusted the idle mixture (it was way too lean, no rise on shutdown) and cleaned the plugs, (bottom ones had some lead but none were fouled). Idled great after all that. Since I did all this at once it's hard to say what it was, but I suspect the prop RPM more than anything -- those lightweight, low diameter props don't have a lot of inertia.

Carb ice is always a possibility too, (for quitting on rollout) if you had just done a low power or idle descent without carb ht -- even on a beautiful day -- that's when it sneaks up on you!

Hope you get it squared away quickly and please report back to the group what fixed it for you.

- Brett
 
RV-4 dying at idle

Last night I pulled the carburetor.

I have checked the induction nuts and carb. bolts and nuts and they are all tight. This plane has 500 hrs. TT and a wood prop with a MA-4 carb. It has run flawlessly for 18 months. The idle mixture screw is tight and was 1/2 turn from bottoming in the seat. I taught auto mechanics for 24 years and the symptons to me suggest a plugged idle port in the carb throat below the throttle plate. Leaning and enrichening made no difference. I did not think to try the left and right mag seperately though. It has always given me a rise on lean out shut down but it was running so rough this time that it was impossible to tell if this was.

It tried both tanks and leaning it did not help it. It idles at 750 rpm but now it takes about 1000 just to keep it from quitting.

I have ordered a gasket set for the carb and I have it split in two. It was Very clean inside. Blowing air through the idle port and the transfer ports (the 2 holes above the idle port) revealed clear passages.

This spooks me as I am at 2O3 (Angwin) CA and we are up in the mountains with trees on both ends of the runway. I am also Chief Flight instructor here at the college with 32 flights students in our program so safety is utmost in my priorities.

I am baffled. The gaskets will be here Wed. and I will reassemble and test run it. I have used the WD 40 trick also with autos and ether works great also.

Thanks so much for all the response. You guys are just the best.

I'll keep you posted.

Bill.
 
CARB ICE

The weather is changing. I first learned about carb ice with a 51 Ford that would die at idle in the fall season.

From http://www.sacskyranch.com/crbice.htm "The heat loss from evaporation of gasoline at the stoichiometric ratio creates a theoretical temperature drop of 40 degrees F. The adiabatic expansion of gas across the carburetor's venturi also lowers the temperature. Thus, you could drop the carburetor temperature to freezing and form carburetor ice at an ambient temperature of 72 degrees or higher. Stoichiometric is the leanest possible mixture. At richer mixtures the ambient temperature at which carburetor ice forms is even higher - Lycoming publishes a temperature range of twenty to 90 degrees F. for carburetor ice. "

In older cars the windshield wipers were vacuum operated off of the intake manifold. The greater the vacuum the greater the speed of the wipers. The increase in vacuum was graphically evident with this set up. They always worked best at idle (when you least needed them) and would slow to almost stopped when you accelerated (when you needed them most). They ran like crazy going down a hill with your foot off of the gas!

Bottom line is that your rich mixture, low power setting and probabaly a different weather condition than last month set you up for carb ice.
 
rv-4 dying at idle

Thanks for all the advise guys. I got new gaskets and went thrughthe carburetor. It was totally clean. The mixture screw was 1/2 turn from closed and this seems to tight to me based on all the carburetors I have ever seen. I opened theidle mixture screw 1 and 1/2 turns and reinstalled the carburetor. It ran too rich at this setting so I closed it 1/2 turn and that was better. I closed it 1/4 turn more leaving it at 3/4 turn open and that seems to be just right. It runs great now. When I lean it out I get a 50 RPM rise before it starts to quit so that is just right.
I drilled a 1/16" hole in the flange of the mixture screw knob and safety wired it to the body of the carburetor as I think what happed was it crept closed and it seems to be very critical as to where it should be set.


Thanks a lot.



Bill.
 
rv-4 dying at idle

I got the problem solved and fixed it. I posted the fix on the wrong post. It is under carb icing in the general forum. I don't know my wat around these forum sites too well.
Bill.
 
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