C-150 starting problem

[crazynut52]

I have a Cessna 150 with the 0-200. Lately it hasnt been starting well. It will kinda studder for a while, but won't "catch" and take off. Once in a while it will start right up with no problem. My mechanic can't seem to think of what the problem is. Maybe someone can give us an idea....

we took all the plugs out, cleaned them and checked their spark. We rotated the prop by hand to make sure they were are getting spark. We checked the timing, it is set at 28 degrees which is because of the superior cylinders. It has a brand new carb, and fuel does not seem to be the problem. He thinks possibly it could be the impulse coupling, but wasnt sure, because it sparks when turning it over by hand.

Any ideas, please let me know
I appreciate the help.

 

[Gofish]

I am assuming you give it a shot or two of primer?...That always worked for mine. Either that or firewall the throttle a couple of times to get some fuel into the cylinders.

Hope that helps.

 

[NW_Pilot]

What's the temp out side? I lean mine about an inch when starting on hot days and she pops off every time.

 

[erj-145mech]

The impulse coupling should be snapping around TDC. With the switch to both, the bottom leads off, the top leads on the removed top plugs, and the plugs on the cyklinder fins, and a prop degree wheel on the prop/spinner, as he pulls the prop thru by hand, with a thumb on the top spark plug hole to check for piston position. But he should already know that, basic recip knowledge.

 

[crazynut52]

Hey guys, we're sure its not my starting procedures. I have started this plane and thousands of times. The problem actually started when the mechanic had the mag off when working on the plane. I think he had one mag off when changing the generator. He said the previous mechanic had it timed to 32 degrees, and said it had to be turned back to 28. I do not know if this caused the problem, but it was around this time it began to start hard. He went throught he procedure of checking the plugs and spark etc... and all checked out fine. As far as we can tell, both mags have impluse couplings, which makes me wonder how they could both go bad... and if they were both bad, then we wouldnt have a spark when turning the engine over by hand, right?? I sure hope it's not a cam... the engine has 350 hours on it.

 

[bocefus]

Like erj said, check to make sure the impulse coupling is catching, winding and snapping. A lot of times when a mag is removed and re-timed, the angle gets changed. This can cause the impulse coupling pawls to miss the striker pin and cause it do not wind up.

 

[GravityHater]

impluse couplings, which makes me wonder how they could both go bad... and if they were both bad, then we wouldnt have a spark when turning the engine over by hand, right??

this is wrong, not right. A mag will still spark even though the IC is weak. Ive had this problem in a Lyc., where the IC spring is weak and will not make the spark hot enough.
It may also appear that they both went bad when in fact one has been bad for a long long time and you were starting on only the other one....which recently went bad.

BTW, in your posts I did not see where the compression (do it cold if the problem is when starting only) was checked* or the points visually examined.

 

[crazynut52]

The mechanic said he visually did check the points, and it seems to do it whether cold or warm.... but he did check the compressions and all were high 70's

 

[Gryphon]

Hey guys, we're sure its not my starting procedures. I have started this plane and thousands of times. The problem actually started when the mechanic had the mag off when working on the plane. I think he had one mag off when changing the generator. He said the previous mechanic had it timed to 32 degrees, and said it had to be turned back to 28. I do not know if this caused the problem, but it was around this time it began to start hard. He went throught he procedure of checking the plugs and spark etc... and all checked out fine. As far as we can tell, both mags have impluse couplings, which makes me wonder how they could both go bad... and if they were both bad, then we wouldnt have a spark when turning the engine over by hand, right?? I sure hope it's not a cam... the engine has 350 hours on it.

Basic common sense... he took the mag out, put it back, and changed the timing and now you have a hard start problem.. what about putting the timing back to where it was and see if that changes anything? Obviously thats where the problem started, go back to the beginning and start over. There may have been a reason it was set at 32 and not 28.. good luck.

 

[TrafficInSight]

Basic common sense... he took the mag out, put it back, and changed the timing and now you have a hard start problem.. what about putting the timing back to where it was and see if that changes anything? Obviously thats where the problem started, go back to the beginning and start over. There may have been a reason it was set at 32 and not 28.. good luck.

I can't imagine any good reason for the timing to be wrong.

 

[Gatorman]

Have you tried pushing in the clutch and pumping the gas peddal a couple times?

No really, I would put the timeing back to 32 like it was and see if things get better.

Then again, you could have a bad mechanic and have to replace it with a new one.

 

[Gryphon]

Have you tried pushing in the clutch and pumping the gas peddal a couple times?

No really, I would put the timeing back to 32 like it was and see if things get better.

Then again, you could have a bad mechanic and have to replace it with a new one.

lmao !

 

[avbug]

If you've checked spark and you have spark, then it's probably time to start looking elsewhere for your troubles. Go back to basics. If spark exists, then timing is important. If it was firing before you changed the timing, then put it back.

If timing is right and you've got spark, then you have only fuel and air to consider. If you're getting fuel, it may not be mixed properly or metered properly, or you may have an air blockage. Carb air door for example.

Your mags aren't stabbed one eighty out, by chance, are they?

 

[Geronimo4497]

Well, you did mention that it has a brand new carb. Did your problems start showing up around this time also? Will it start nicely on a cold start (first of the day) but not so well on a 'hot' start?

Hmmm, won't start, so we better replace that starter. Hmmm, that did'nt work, let's replace the carb. Hmmm, that did'nt work, let's start messing with the mags............................Tinckeritis at its best! :laugh:

 

[avbug]

Used to be that mechanics fixed things, troubleshot, and their work was their signature.

Now mechanics replace things, replace more things, and their signature is their signature.

What went wrong?

 

[LearLove]

Used to be that mechanics fixed things, troubleshot, and their work was their signature.

Now mechanics replace things, replace more things, and their signature is their signature.

What went wrong?

While I'm not an airplane mechanic (although I wish I was) I did work as a bicycle mechanic for many years back in HS and college. After about a 12 year leave from the bike (and doing bike mx) I reciently got back into the sport and I see the same stuff avbug talks about above.

It used to be when a bottom bracket needed service you took it apart, looked at the bearings, races, cups and shaft then determined what needs repair or replacement and put it back together for another 1500-3000 miles. Now days the mechanic pulls out the whole BB cartridge tosses it away and replaces it with a new sealed one. The same thing with headsets and hubs. Nobody trouble shoots and fixes.

 

[avbug]

In all that component changing, the real problem, aside from the loss of craftsmanship, is that nobody actually finds out what's really wrong. Just keep changing parts and either could-not-duplicate it,or assume it's fixed because it doesn't reoccur after some particular component change or another...and send it back into the air.

I ran into a group of individuals wearing white lab coats bearing patches from various aircraft manufacturers, all working on a Cessna 210 at a Northwest airport some time ago. They were parked next to me, and for the better part the day, ran that contraption at full bore while fiddling with this or that. I sat on the flight deck for hour after hour trying to study, and at the end of the day finally approached them to ask them if they could be helped.

Aside from the fact that their smocks were from several different aircraft manufacturers, or the fact that I've never seen line mechanics wearing white lab coats, or the fact that they were all wearing concealed sidearms, or the fact tha they didn't have a clue what they were doing...the nose was giving me a splitting headache and the curiosity was killing me.

They asked if I knew anything about the airplane, and the described their problem. They'd made seven forced landings over the past two days, with engine problems and failure. Kept screwing around and then flying again. They'd replaced certain components repeatedly...the same components, all with no change in the condition. I suggested that possibly they might stop guessing and changing components, and then isolated their problem to a ruptured diaphram in the fuel flow divider. Problem solved.

(Turns out they were pilots for a federal agency performing aerial surveillance, and truly didn't have a clue what they were doing...another story). So, when a problem develops, just keep changing components (eventhe same one, over and over) until it goes away...

"...left at Bandaid ...?"

That would have to be the indominable Truman Sparks from the movie Fandango, as he flies under a bridge to rescue the blushing bride.

Where the hell is my laundry?

 

[Gatorman]

Used to be that mechanics fixed things, troubleshot, and their work was their signature.

Now mechanics replace things, replace more things, and their signature is their signature.

What went wrong?

I can answer that.....glad you asked

When it becomes more economical for the mechanic to get paid their hourly rate verses shot-gunning a part, then it will go back to their work being their signature.

Also, when the mechanic has the time to fix something rather rushing through a job to meet a schedule.

 

[avbug]

I don't rush to meet anybodies schedule. When I pick up a wrench, the job will take as long as it takes. Speed kills.

I've seen that happen first hand, time and time again.

Shotgunning problems by throwing parts instead of troubleshooting and fixing, has always been false economy. Gee, we've replaced that generator five times now, and the problem still exists. We keep having to cancel flights or charter...it's costing us a fortune. We better get another generator in here to throw on that engine. I hope this one works...

False economy.

 

[mcjohn]

Glad I read this thread. Really makes me want to learn more about engines. I might get my chance this summer (most likely only airframes, but that's a start!) Glad to see you posting on propilot avbug. I'll be there as soon as I get my lazy arse to sign up. Nothing wrong with FI but I'll like the balance.

Well, crazynut52, how's the 150 doing? Can't wait to hear what the problem was.

 

[IFollowRoads]

Used to be that mechanics fixed things, troubleshot, and their work was their signature.

Now mechanics replace things, replace more things, and their signature is their signature.

What went wrong?

Ask your favorite lawyer.

 

[crazynut52]

well, as some of you had suggested, it took another mechanic to fix the problem. Turns out it was the capacitor inside of the magneto. Apparently the mag wasnt producing enough of a spark at low rpm (starting) but once running it ran fine. So it starts great now...and I have a new capacitor ordered for the other mag too.

 

[avbug]

I thought you said spark had been verified...

we took all the plugs out, cleaned them and checked their spark. We rotated the prop by hand to make sure they were are getting spark...He thinks possibly it could be the impulse coupling, but wasnt sure, because it sparks when turning it over by hand.

Ask your favorite lawyer.

What would my favorite lawyer tell me about mechanics who don't troubleshoot or fix, but who keep changing components until something eventually works? Poor craftsmanship equates to reduced liability?

I don't think so. Try again.

 

[IFollowRoads]

Try again.

No thanks. I have to go swap some fuel pressure sensors from right to left on a Cessna Conquest I. The engines are running fine, the gauge pressure reads normal, but the pilot reports that at altitude he's getting a "LOW FUEL PRESSURE" warning light. After looking at the fuel system schematics I think it's a bad sensor. If the problem swaps sides I'll know for sure and I'll order a new one. Will cost the guy 1 hour shop time and the cost of the sensor.

 

[RoundMotor]

Are you priming the engine? or are you pumping the throttle? If you prime the fuel goes into the cylnder if you pump the fuel goes into the intake manifold,if the engine is turning, If it isnt turning it pools in the carb.
I would check the inpulse coupling first if its and older aiplane, square tail, it might have a booster coil in which case that would be your problem.

 

[avbug]

No thanks. I have to go swap some fuel pressure sensors from right to left on a Cessna Conquest I. The engines are running fine, the gauge pressure reads normal, but the pilot reports that at altitude he's getting a "LOW FUEL PRESSURE" warning light. After looking at the fuel system schematics I think it's a bad sensor. If the problem swaps sides I'll know for sure and I'll order a new one. Will cost the guy 1 hour shop time and the cost of the sensor.

That would be troubleshooting, and irrelevant in respect to my point...which is valid.

If you had merely decided to start replacing fuel sensors, that would be another matter.