0-300A Running problem on a rebuilt engine.

cfiatzph · Post by **cfiatzph** » Thu Feb 22, 2007 9:52 pm

I have a 0-300A on my C172 (yea I know its a c170 board but its a engine the 170 uses!). This engine was rebuilt 2 years ago and sat. Upon trying to start the engine it would not make full power and would not shut off with the mixture control even with the carb adjusted full lean. I called the engine shop and they said pull the carb off and send it back to where it got rebuilt. I sent it in and the shop said they would take it apart and fix it free of charge and that the needle had stuck on me. I got it back installed it and same thing running rich not making full power idle is set highest it will go and it idles too low like at 300 rpm (if that) will not shut off with the mixture control. Even at full power (2100 rpm) if I pull the mixture all the way out it only loses 50 rpm and does'nt even run rough. I am still assuming carb problems, like a jetting problem? Is it possible the wrong cam was installed at rebuild or cylinders or cylinder valve springs etc etc. I did'nt think it was possible? (GO-300 cam?) I don't know. Any ideas? I am leaning towards a misjetted carb. It has a MA-3SPA on the tag now which is the correct carb.

Thanks

bradbrady · Post by **bradbrady** » Fri Feb 23, 2007 12:21 am

I have seen cams misstimed and not produce power, but usualy shut down with full lean. The carb is a MA-3SPA but what is the part number? is Ok'ed for your engine? Just a couple quick ideas!
brad

doakes · Post by **doakes** » Fri Feb 23, 2007 12:22 am

Send the carb to some one else?

If the engine won't stop with the mixture pulled, either the mixture control is not adjusted properly or fuel is not severed inside the carb.
Fuel is getting to the engine someway.

Post by **GAHorn** » Fri Feb 23, 2007 3:34 am

The carburetor is still your problem. While there were several different part numbers for MA3-SPA carbs, the original Marvel Schebler one for our installation was PN10-4439 (TCM628945). It's unlikely that a simple sub-part no. is the problem tho'.
Did the engine rebuilder supply that carb to you? Or did you have it overhauled independently? If the engine rebuilder supplied it, then you should let them determine how to make it work correctly. (Either fix it or exhcange it for a different carb.)
But you should first make certain that it is installed correctly and with the controls properly connected before blaming the carb. (Getting full idle cutoff? Getting full throttle-plate application?)

blueldr · Post by **blueldr** » Fri Feb 23, 2007 3:35 am

When re-assembling the carburetor, it is very easy to inadvertantly allow the rotating mixture control to go down in the bowl rather into the mixture control well in the bowl half of the carburetor. This will cause a full rich mixture at all times and will preclude idle cut off. I've had it happen!

Pull the carburetor and very carefully raise the top off the bowl while watching the location of the flexible rotating mixture control rod. I'll bet you find it out of the well.

Remember that the idle mixture adjustment sontrols mixture and idle speed is controlled by the adjusting screw on the throttle shaft.

KMac · Post by **KMac** » Fri Feb 23, 2007 4:21 am

Blueldr knows what he is writing. I had that exact thing happen to me with my newly rebuilt carb! If the mixture control is in the correct place (well) inside the carb, and your linkage is working (like George indicated), there should be nearly no way for the engine to get fuel when the mixture is full lean (idle cut-off).
Kevin

Post by **GAHorn** » Fri Feb 23, 2007 2:58 pm

All good words...and for most guys not challenged by common hand-tools, it's a simple matter to look for this last suggestion by blu elder.
Keep in mind tho'... that if the carb rebuilder made that error, then it raises some other questions.
Also, if you disassemble that carb, and if it was a CRS that had rebuilt it, then you will likely void any warranty on the carb when the identifying security-seal or torque-seal is broken. Subsequent or continued problems with that carb might not be covered by the carb rebuilder.
I'm still curious as to who actually supplied the rebuilt carb.... the engine rebuilder? Or the owner? THAT is the person who should hold the carb rebuilder's feet to the fire (after being absolutely certain the carb is properly installed and the engine controls are correctly adjusted.)

cfiatzph · Post by **cfiatzph** » Sat Feb 24, 2007 7:19 am

It is tricky because this engine was rebuilt about 2-3 years ago before my father got sick and died. The aircraft went through a MAJOR overhaul. Tanks, wiring, instruments, interior etc. Think about it, it happen on this A/c except for paint. Just now gettting to running the engine. The people that rebuilt the carb are more than willing to swap it out for different carb (yellow tag etc) I explained to the tech what was happening and he said I'll send another one (even thou it was rebuilt 2-3 years ago). Have'nt been able to get ahold of the engine guy but the first time he indicated carb problems even the repair station admits carb problems. AND all the other mechs. I think I have the prob solved with minimum money. What a PITA though I got alot of time removing sending off reinstalling ETC. Overall I am pleased by the repair stations customer service, I have seen this happen with other repair stations at least 2-3 times and it really is annoying and makes you wonder.

cfiatzph · Post by **cfiatzph** » Sat Feb 24, 2007 7:24 am

Another WIERD Thing was upon putting 10 gals each tank (same tanks as 170) it would trickle, would not flow sat over night and it just gushed out. What is this all about? It worries me. Is this air? Its sorta wierd if you ask me?

Post by **GAHorn** » Sat Feb 24, 2007 12:04 pm

cfiatzph wrote:Another WIERD Thing was upon putting 10 gals each tank (same tanks as 170) it would trickle, would not flow sat over night and it just gushed out. What is this all about? It worries me. Is this air? Its sorta wierd if you ask me?

Now you've asked a question that cannot be given a simple answer over the internet. If the airplane has fuel system issues, then you've got work to do.
How did you determine it was just a "trickle"? Was this at a fuel drain? Or was this from the fuel supply line with it disconnected from the carb?
If it's the latter, then it helps explain why you weren't getting full power from the engine.
The low fuel flow can be due to obstructed supply lines and/or screens, collapsed/kinked hose, failure of system to vent, etc.

bradbrady · Post by **bradbrady** » Sat Feb 24, 2007 10:43 pm

If fuel lines were left open for two years, the problem could be spider webs! Had this happen to a friend. Compressed air went through with no problem, but didn't blow the webs out! Left tank run with no problem, but when he went over to right, (the tank with the web in the line), the engine would actualy die!

The only way to get webs out I know of is some type of "snake"

Hope you find your problem!!!!!!
brad

Post by **GAHorn** » Sun Feb 25, 2007 1:49 am

A reasonably good way to clear out lines that have no 90-degree turns is to drill a hole thru a wood plug and thread a strong nylon string thru it, knotted on the other side of the plug. Thread the string thru a small hole drilled into the side of a rubber nozzle in the nose of the blowgun. Using compressed air, blow the plug thru the line. The string will unwind as the plug progresses thru the line. The string is also used to retrieve it should it run into an obstruction or fitting that will not clear.

cfiatzph · Post by **cfiatzph** » Sun Feb 25, 2007 4:26 am

gahorn wrote:
cfiatzph wrote:Another WIERD Thing was upon putting 10 gals each tank (same tanks as 170) it would trickle, would not flow sat over night and it just gushed out. What is this all about? It worries me. Is this air? Its sorta wierd if you ask me?
Now you've asked a question that cannot be given a simple answer over the internet. If the airplane has fuel system issues, then you've got work to do.
How did you determine it was just a "trickle"? Was this at a fuel drain? Or was this from the fuel supply line with it disconnected from the carb?
If it's the latter, then it helps explain why you weren't getting full power from the engine.
The low fuel flow can be due to obstructed supply lines and/or screens, collapsed/kinked hose, failure of system to vent, etc.

After it sat over night like I said it was GUSHING out so what ever the obstruction was it cleared. Is this air? I am confused a spider web mud daber dirt, wasp etc would get caught up somewhere and would not clear up over night and would eventually end up in the gascolator.

Post by **GAHorn** » Sun Feb 25, 2007 4:43 am

Like I said previously, I have no idea what it is if you don't. You're on the scene. You'll have to check that out yourself, but I wouldn't take it up until I was satisfied it wouldn't happen again.
I once had a situation in a Baron where an engine would not make full power unless the elect. boost pumps were ON. Engine-driven pumps were healthy but the engine would not make full power. (On takeoff the engine would sputter and act fuel-starved.)
Replaced the flexible fuel lines between the firewall and the fuel injector pump and all was fine. Turned out the flexible fuel lines inner-liner had become loose and was collapsing under suction from the engine pump but would inflate under pressure from the elect. boost pump.
Of course, the 170 (in original configuration) is a gravity feed system and it's unlikely that such could happen. But the example illustrates how the unexpected can occur.
I'd certainly be cautious about flying that thing until a cause was found/corrected for the previous failure to properly deliver fuel.

bradbrady · Post by **bradbrady** » Sun Feb 25, 2007 9:56 pm

A spider web will alow fuel thru. And it will gush for a time after sitting. Untill head preasure is restricted by said web. I like Georges idea for a compreser aided cleaner!
brad