tom clark
Line Up and Wait
- Joined
- Apr 12, 2005
- Messages
- 609
- Location
- St. Petersburg, Florida
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Display name:
Tom Clark
Hi all. I had posted an idle problem on another board, got some helpful suggestions and now that my plane is running well again, i wanted to post what i learned so maybe it will help some of you. FWIW. tc
Some of you may recall, I posted on here a few months ago asking what may be the cause of my rough idle below 1500rpm. The first thought was an induction leak, and my mechanic used wd40 on the system while the engine ran (looking for an rpm surge--sounds dangerous!) and came away with nothing. He then pulled a few plugs, just kind of looked over a few things and announced there was nothing obvious and it would require further investigation if I wanted it fixed. To tell you the truth, it became on of those things I'll do tomorrow. The plane ran beautifully above 1500 and I just went on flying it, with no sign of improvement or deterioration.
A few months went by, and this week when I was in for an oil change, i told them i wanted this fixed. Once again, my mechanic pulled a few plugs, eye-balled a few things and announced I needed a new carb. Well, I've seen a man armed with the "parts shotgun" before and have never been happy with the results, so I set out to get a second opinion.
I called another mechanic (same shop) I've known for years (his name is Lindberg, good aviation name!) and told him the problem. He rattled off numerous things that should be checked before we start replacing carbs. Here's what he found when he tore into the project. Gotta love this guy, he works on a plane like it's his own.
He did the wobble test on the valves because I'd thought I might have morning sickness---results negative (wooohooo!).
He plugged the primer to make sure it wasn't flooding the engine, he disconnected the standby vac to check for a manifold leak and he checked the vac lines. all results negative.
He pulled the carb idle jet. It was partially clogged--bingo!
He checked the carb idle mixture setting---too lean. another bingo!
He checked the mag timing. One on 25 degs, the other on 28. He corrected it but it didn't effect the idle.
All this improved the idle considerably, but he said it still wasn't as smooth as it should be, and he didn't think I'd be happy with it. We talked money (i like that), and I told him to proceed. He checked the cylinder temps. One was cooler than the rest. He checked the plugs and found a bad connector that was occasionally arching and causing a miss. He also noted all my plugs were on their last legs. They looked like footballs. They'd probably pass, but never make it another 100hrs before my next annual. So we changed them all (misewell theory at work).
After all this, it still wasn't quite right. Every action made it better, but it still wasn't purring, so back to the induction system he went. And guess what? He found two old cracked or torn intake gaskets. So much for the wd40 test. He replaced those and now she runs like a champ again.
Lessons learned:
If its busted fix it. it won't heal itself and you're just postponing the inevitable. i actually thought i knew that, but i guess i forgot.
I need to pay more attention to my maintenance. I got in the habit of just sending it in and assuming the work was being properly done. There were way too many little things wrong with my plane to make that assumption anymore. And my baby was trying to tell me something, i just wasn't willing to listen.
Never hesitate to get a second opinion. The proposed new carb may have "fixed" the problem, but for the same money, or less, I got a laundry list of problems fixed.
Have fun! I know I will!
tc
Some of you may recall, I posted on here a few months ago asking what may be the cause of my rough idle below 1500rpm. The first thought was an induction leak, and my mechanic used wd40 on the system while the engine ran (looking for an rpm surge--sounds dangerous!) and came away with nothing. He then pulled a few plugs, just kind of looked over a few things and announced there was nothing obvious and it would require further investigation if I wanted it fixed. To tell you the truth, it became on of those things I'll do tomorrow. The plane ran beautifully above 1500 and I just went on flying it, with no sign of improvement or deterioration.
A few months went by, and this week when I was in for an oil change, i told them i wanted this fixed. Once again, my mechanic pulled a few plugs, eye-balled a few things and announced I needed a new carb. Well, I've seen a man armed with the "parts shotgun" before and have never been happy with the results, so I set out to get a second opinion.
I called another mechanic (same shop) I've known for years (his name is Lindberg, good aviation name!) and told him the problem. He rattled off numerous things that should be checked before we start replacing carbs. Here's what he found when he tore into the project. Gotta love this guy, he works on a plane like it's his own.
He did the wobble test on the valves because I'd thought I might have morning sickness---results negative (wooohooo!).
He plugged the primer to make sure it wasn't flooding the engine, he disconnected the standby vac to check for a manifold leak and he checked the vac lines. all results negative.
He pulled the carb idle jet. It was partially clogged--bingo!
He checked the carb idle mixture setting---too lean. another bingo!
He checked the mag timing. One on 25 degs, the other on 28. He corrected it but it didn't effect the idle.
All this improved the idle considerably, but he said it still wasn't as smooth as it should be, and he didn't think I'd be happy with it. We talked money (i like that), and I told him to proceed. He checked the cylinder temps. One was cooler than the rest. He checked the plugs and found a bad connector that was occasionally arching and causing a miss. He also noted all my plugs were on their last legs. They looked like footballs. They'd probably pass, but never make it another 100hrs before my next annual. So we changed them all (misewell theory at work).
After all this, it still wasn't quite right. Every action made it better, but it still wasn't purring, so back to the induction system he went. And guess what? He found two old cracked or torn intake gaskets. So much for the wd40 test. He replaced those and now she runs like a champ again.
Lessons learned:
If its busted fix it. it won't heal itself and you're just postponing the inevitable. i actually thought i knew that, but i guess i forgot.
I need to pay more attention to my maintenance. I got in the habit of just sending it in and assuming the work was being properly done. There were way too many little things wrong with my plane to make that assumption anymore. And my baby was trying to tell me something, i just wasn't willing to listen.
Never hesitate to get a second opinion. The proposed new carb may have "fixed" the problem, but for the same money, or less, I got a laundry list of problems fixed.
Have fun! I know I will!
