O-360 idle cutoff not cutting off

Garage Guy · #1 09-01-2008, 10:49 PM

O-360-A1A in a RV-6 with about 470 hours, 10-3878 (MA-4-5) carb.

Lately, when shutting down, pulling mixture full back to ICO does not reliably stop the engine... it just makes it idle slow and rough. It's worst doing this with the throttle all the way back; with 1/4" or 1/2" of throttle, ICO does seem to work a bit better but still not great.

This is with the engine warmed to operating temperature. With engine cold (for example I've just started it and idled it for a minute) ICO works fine.

I've pulled the cowls to get a good look at the carb, and the mixture lever is getting full travel, stop to stop. It looks like the mixture control shaft has a bit of play in the carburetor housing.

What do you all think? Get an overhauled carb ($795 from Aircraft Spruce)? Get a rebuild kit ($460) and do it myself? Or is there some known trick to try at this point?...

--Paul

mahlon_r · #2 09-02-2008, 05:14 AM

If you have an engine primer, make sure you disconnect it first before overhauling the carb, and see if things improve. You could be sucking fuel through it when trying to shut down.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

pierre smith · #3 09-02-2008, 05:20 AM

.....advancing the throttle leans the mixture more during ICO,

Regards,

Geico266 · #4 09-02-2008, 06:34 AM

Time for a new carb. Same thing happened to me on my 0-235. It was something leaking inside the card. A new carb / rebuilt and all was good.

osxuser · #5 09-02-2008, 09:36 AM

Sounds like a leaking mixture control OR a leaking primer (as mahlon said). Easiest solution is the overhauled carb, for $800 is hard to go wrong with that plan. We bought a new one for $1200 two years ago, but no telling how much new ones are now.

If you are comfortable doing the work yourself, the overhaul kit would be an option, but make sure you have someone handy that has done it before, AND the manual for the carb.

Garage Guy · #6 09-02-2008, 09:47 AM

Quote:

Originally Posted by mahlon_r

If you have an engine primer, make sure you disconnect it first before overhauling the carb, and see if things improve. You could be sucking fuel through it when trying to shut down.

No primer, unless there is some vestigial primer system in there that I didn't notice? There certainly is no primer control making its way to the cockpit.

--Paul

Ken · #7 09-02-2008, 01:07 PM

Like Pierre says open the throttle. I did this on my Grumman for years. Just be sure there are no other issues. If you do overhaul, Lycoming has a mandatory service bulletin No. 582 which deals with floats on various carburetors.

Ken

gmpaul · #8 09-02-2008, 08:04 PM

I had the same problem with my 0-320. The fix was fairly simple once I found out what was wrong. Take the carb off and split the case (just four screws). Look at the way the half-round cut-off or lean mixture valve stem is oriented. I taped a tongue depressor to the flat side of the valve. This gives you a better view of the cut-off position (the orifice hole in the side of the carb). To my suprise the half flat part can be rotated on the spring stem. Rotate till rounded side covers the fuel inlet orifice on the side of the carb. This is hard for me to describe since you can't see my hand gesters. Give me a call if you can't understand my jiberish. 1-979-345-3274

GP

Brantel · #9 09-03-2008, 06:21 AM

I can offer you some advice as I just went thru the process of obtaining a carb without a core.

Most (all 15 or so of them that I talked to) of the people that advertise rebuilt carbs don't actually have one in stock right now to swap you for your core. They will offer to send yours in for rebuild and that will take some down time for you.

The prices for a full rebuild are somewhat variable between $700 and a $1000 so one has to wander how these rebuilds differ. I understand that there are several companies that these people use to perform the rebuilds so I assume that some are better than others or some do more than others.

Good luck finding a new one or a rebuilt one without core from normal sources. Even if they are advertised, most if not all do not have them in stock.

I have the rebuild manual and exploded parts diagram on PDF if you want them.

After reading the rebuild manual, I would say that a full rebuild is outside of the reach of what a normal homebuilder is willing to do. There are several special tools that are needed that either must be purchased or fabricated. The hardest parts will be the throttle shaft bushings (pressing and reaming required) and related stuff and messing with the economizer settings.

One thing is that the full rebuild kits for these things cost almost as much as the lower end of a factory exchange/rebuild so for me it would not be worth the hassle and the risk.

Garage Guy · #10 09-03-2008, 11:18 AM

Quote:

Originally Posted by Brantel

After reading the rebuild manual, I would say that a full rebuild is outside of the reach of what a normal homebuilder is willing to do.

I see what you mean... here's the sectional view of the thing. Not a simple old tractor carburetor after all:

And I had a chat with the maintenance director of the shop next to our hangar... he said they had to overhaul these carbs in A&P school but he hasn't done it since and wouldn't want to.

--Paul