Engine runs "Rich"

[supercub]

I have a PA-18-150 and it runs rich. Have to lean for takeoff at sea level. Had a rebuilt carb that ran rich and had a flat spot aroudn 2300 rpms.........sent it out to be bench checked and everthing checked out ok........reintalled and still did the same thing.....finally purchased a new carb........and it still ran rich.......only difference was the flat spot moved from about 2300 rpm to about 1400 rpm. I wrok for a shop and the AI who has rebuilt many cubs over the years and overhauled many carbs can't figure out the problem either. We even tried a two piece venturi........anyone have any ideas...HELP..thanks for the input.........Happy and Safe Flying. "Brian"

 

[Lawn Dart]

The problem seems to be utterly hopeless. I recommend that you give the plane to me, thus ridding yourself of this misery. Hey, I?m only trying to help!

Okay, seriously, I don?t claim to know squat about Cubs but I do know a little something about motors, and I certainly don?t want to send you chasing your tail around in circles but?I?m curious, do we know for certain, and I mean certain, that the intake and exhaust tracks are unobstructed and in good order? does it exhibit the same problems with and without carb heat? and has the problem recently developed or always been there?
An intake problem that develops only under high flow or vacuum or a muffler that folds-up (internally) only in the presents of high flow/pressure could exhibit these same characteristics. I assume that the other motor components are in good tune, valve lash, timing, etc.

One carb before and after the shop, an entirely new carb (3 carbs) and no resolve? Time to look elsewhere.

Talk to us MD, Crash, etc.

 

[SuperCub MD]

Double check that the carb is correct. A 150 should have a MA-4SPA part #10-3678-12.

 

[cubdrvr]

............and that the intake hoses are not cracked.

 

[SuperCub MD]

A quick check on the intake system is to wipe grease on the hoses, gaskets, and connections, turn the motor over with the throttle at idle, if the grease disappears, you found a leak.

Also do a cold cylinder check after running, spit on each exhaust, it should sizzle right off, if not you have found a problem. (Also known as the farm boy EGT, or these days, the graphic engine analizer).

 

[T.J.]

delete

 

[SuperCub MD]

-12 for a 150

-32 for a 160

 

[T.J.]

delete

 

[SuperCub MD]

I stand corrected, it is possible to have a straight bore riser 150 hp on a Cub, most 150's you see usually have the standard sump and take the -12.

 

[T.J.]

delete

 

[Lawn Dart]

Brian

Have you had any luck solving your problem?
Let us know.

 

[supercub]

Engine Runs Rich

I pulled the carb the other day and sent it off to Consolidated. They are going to bench check it............nice people on the phone. I just installed a used carb while mine is out being checked....and engine runs fine..flat spot and richness went away. I should hear back from Consolidated in a few days..will be interesting to see what they have to say.

 

[supercub]

Engine Runs Rich

Ok.........first off............thanks to everyone for their input. So far.still having problems..........Got the carb back from consolidated and it's somewhat better......but still not right.........won't idle well at all.......still has a minor flat spot......better..but still there........and still runs rich. Anyway............we're going to try some different carbs........a overhaul shop has 3 or 4 carbs.........and are going to let us try them.......to see if we can find one that works.......the carb I have is a -32...........as far as the sump...........we're going to look at that very closely when I pull the carb.......again thanks for the input..........as far as intake leaks........it's my understanding that would cause it to run lean........but I have check the intake system and it's fine.....hoses are only a couple years old....and look great. I also called Precision and talked to them.....no real answers........called Stan at Cub Crafters.....The AI I work for who has 40 plus years of experience and myself ........are determined to get this fixed.......I only like things when they're right.....and this isn't. Happy Flying

 

[gdafoe]

Some of us are interested in how your carb testing is going. I'm real interested in this. Mine runs rich all the time. I have to lean for t/o as others do. It sure would be nice to find the solution to the problem, is it going back to a two piece venturi? Or the new design that is being developed? Any more info from your research let us know. Mine blows a fair amount of black smoke if I don't lean it, but it nothing like the black smoke I see in your avitar. :roll:

 

[supercub]

Gerald........I tried everything.....even the two piece venturi. My original overhauled carb, I sent out and had it benched checked again, didn't fix the problem, so I then bought a rebuilt carb from consolidated.......still had problems. sent it back to them for bench checking. While it was out, I tried another carb, same problem. Got the carb back from Consolidated and still ran rich. After talking to eveyone I could, including folks on this site, I decided there wasn't anything left to try. Yes, I've been over the entire induction system several times. The IA I work for has too. Anyway, I ended up buying a New Precision Carb. It has worked fine. I really won't be able to tell for sure, until the hot weather sets in this summer. That will tell the real story as far as richness. but from all indications........it seems to be better. The flat spot I had around 1300rpms went away, The larger mag drop I had on the LH mag went away too. I know.....how can the carb effect just one mag........don't ask me, but let me tell you, it did. I even changed that mag one time. I probably tried a 1/2 dozen different carbs, 3 of them fresh from overhaul shops. Was a frustrating problem and one that I hope has been fixed.
Brian

 

[FlipFlop]

I really won't be able to tell for sure, until the hot weather sets in this summer. That will tell the real story as far as richness. Brian

Actually Brian, your richness shouldn't be a problem after April 15th...

Sorry, I couldn't resist!... :lol:

 

[supercub]

Dave........you're Right......glad to see you're hanging in there.
:lol:
Brian

 

[gdafoe]

Ok thanks Brian, I for one will be very interested to see what happens over the next few months with your New Precision Carb. How it stays fixed. What did that set you back?