O-360 rough between 1000-1300 RPM

simtech

simtech

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Simtech
I had a prebuy done today on a PA28-180. Everything went good and while the mechanic didn't seem concerned about this I did. He said the engine balked between 1k-1300rpm. I asked what does that mean and he just said it was rough. He said it likely needs new plugs since there are 500 hours on them. I flew this plane back in July and it was sooth, and the seller just today said he doesn't feel anything either but he admits he is not a mechanic. He is having his mechanic look at it tomorrow.

My question is what can cause this other plugs? Induction leak, carb??? Is this a cause for concern. The seller still flies it and the mechanic didn't seem real concerned:dunno:
 
If you're worried, just make fixing it a requirement as part of your offer for the airplane.
 
Probably a minor problem,make it a condition on the sale. Wouldn't let that be the terming factor.
 
simtech said:
I had a prebuy done today on a PA28-180. Everything went good and while the mechanic didn't seem concerned about this I did. He said the engine balked between 1k-1300rpm. I asked what does that mean and he just said it was rough. He said it likely needs new plugs since there are 500 hours on them. I flew this plane back in July and it was sooth, and the seller just today said he doesn't feel anything either but he admits he is not a mechanic. He is having his mechanic look at it tomorrow.

My question is what can cause this other plugs? Induction leak, carb??? Is this a cause for concern. The seller still flies it and the mechanic didn't seem real concerned:dunno:
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Might also be a weak accelerator pump in the carb, not a big deal.
 
Only other real issue was a leaky strut that was disclosed before prebuy which the seller is going to fix anyway. The pre buy mechanic said it was a solid plane. I can see his mechanic saying its fine when maybe its not?? I don't live in the same state as the plane. He will address it so we shall see.

I'm actually not too worried about it honestly. Comps were in the upper 70's so its not valve related. More than likely will be plugs. We will see soon. Just trying to pole if other issues can cause it.
 
simtech said:
Only other real issue was a leaky strut that was disclosed before prebuy which the seller is going to fix anyway. The pre buy mechanic said it was a solid plane. I can see his mechanic saying its fine when maybe its not?? I don't live in the same state as the plane. He will address it so we shall see.

I'm actually not too worried about it honestly. Comps were in the upper 70's so its not valve related. More than likely will be plugs. We will see soon. Just trying to pole if other issues can cause it.
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If he says he'll fix it, it's not your worry. It's not going to be a big issue, likely be able to fix it with a screw driver and a wrench with a couple of adjustments.
 
Henning said:
If he says he'll fix it, it's not your worry. It's not going to be a big issue, likely be able to fix it with a screw driver and a wrench with a couple of adjustments.
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I agree, Next time I see it, ill own it!
 
My guess is carburetor. 1,000 to 1,300 is the transition point from idle to main circuit.
 
Can ordinary A&P's and IA's work on carburetors? I've had them tell me they can't open them up. They have to be sent off, or replaced. Dont replace it, its easy to fix btw. Just that a lot carbs get replaced because a mechanic CAN do that. Correct me if Im wrong, its been a while.
 
Silvaire said:
My guess is carburetor. 1,000 to 1,300 is the transition point from idle to main circuit.
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Agreed. It might even be able to be cured with a simple idle mixture screw adjustment.
 
coloradobluesky said:
Can ordinary A&P's and IA's work on carburetors? I've had them tell me they can't open them up. They have to be sent off, or replaced. Dont replace it, its easy to fix btw. Just that a lot carbs get replaced because a mechanic CAN do that. Correct me if Im wrong, its been a while.
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They can but it's tricky because of all of the ownership changes that Marvel Schebler has gone through. I think they belong to Kelley Aerospace now, unless that has changed recently so getting parts or any sort of technical support for a shade tree overhaul is probably like pulling hen's teeth. When you factor in the cost of an overhaul kit along with the hassles it becomes economically unsound for a mechanic to undertake. They may be fairly simple devices but they are finicky and if there's any sort of a hitch the mechanic can end up sinking a lot of time into it. There's no way he's going to beat the prices offered by the dedicated overhaul shops that do nothing but carbs.

Not to say there aren't people out there who can fix the thing, you just have to find them.
 
Any A&P can legally work on float carburetors to include taking them apart and overhauling them, but pressure carburetors are a different animal. I know you don't have a pressure carb but I just wanted to clarify that not all carbs can be overhauled by an A&P.
 
Silvaire said:
They can but it's tricky because of all of the ownership changes that Marvel Schebler has gone through. I think they belong to Kelley Aerospace now, unless that has changed recently so getting parts or any sort of technical support for a shade tree overhaul is probably like pulling hen's teeth. When you factor in the cost of an overhaul kit along with the hassles it becomes economically unsound for a mechanic to undertake. They may be fairly simple devices but they are finicky and if there's any sort of a hitch the mechanic can end up sinking a lot of time into it. There's no way he's going to beat the prices offered by the dedicated overhaul shops that do nothing but carbs.

Not to say there aren't people out there who can fix the thing, you just have to find them.
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Actually, Kelly has been more than helpfull to us, with procedures, parts, and specs.
As to being finicky, they are no more so than any other carb, and way less so than most.
 
bluerooster said:
Actually, Kelly has been more than helpfull to us, with procedures, parts, and specs.
As to being finicky, they are no more so than any other carb, and way less so than most.
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Well that's good to hear then.

All I meant by "finicky" is that if you overhaul it then install it and it runs rough between 1000 and 1300 rpm then you have to pull it off and take it apart again and try find the issue.....

If you get it from an overhaul shop you just pull it off and send it back for another one.
 
Mine does that occasionally....usually on a hot day. If you lean on taxi and just slightly while boring holes in the sky it seems to subside.
 
Silvaire said:
Well that's good to hear then.

All I meant by "finicky" is that if you overhaul it then install it and it runs rough between 1000 and 1300 rpm then you have to pull it off and take it apart again and try find the issue.....

If you get it from an overhaul shop you just pull it off and send it back for another one.
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Yeah, same with any other overhauled part. ;)
 
bluerooster said:
Actually, Kelly has been more than helpfull to us, with procedures, parts, and specs.
As to being finicky, they are no more so than any other carb, and way less so than most.
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Yeah, MS carbs are as simple as they come. Want finicky start playing with multiple SUs on an MG. Setting up 6 Webers on a V-12 is interesting too.
 
simtech said:
Only other real issue was a leaky strut that was disclosed before prebuy which the seller is going to fix anyway. The pre buy mechanic said it was a solid plane. I can see his mechanic saying its fine when maybe its not?? I don't live in the same state as the plane. He will address it so we shall see.

I'm actually not too worried about it honestly. Comps were in the upper 70's so its not valve related. More than likely will be plugs. We will see soon. Just trying to pole if other issues can cause it.
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Did I read that right? The owners mechanic is doing the prebuy, not your mechanic?

Just asking......
 
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Henning said:
Quick question, how many people believe that the mechanic would give a dishonest evaluation?
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The larger problem isn't really that the existing mechanic would give a dishonest evaluation as much as each mechanic out there tends to "focus" on certain things and is picky about certain things. Therefore what is acceptable to one as airworthy won't always be acceptable to yours when annual time goes.

Ideally you would have the mechanic that does your annuals do the prebuy but that's quite often not practical to arrange.

Of course, one could say, money aside it's not a bad thing to have different eyes look at it. But pilots are some of the cheapest people out there :)
 
jesse said:
The larger problem isn't really that the existing mechanic would give a dishonest evaluation as much as each mechanic out there tends to "focus" on certain things and is picky about certain things. Therefore what is acceptable to one as airworthy won't always be acceptable to yours when annual time goes.

Ideally you would have the mechanic that does your annuals do the prebuy but that's quite often not practical to arrange.

Of course, one could say, money aside it's not a bad thing to have different eyes look at it. But pilots are some of the cheapest people out there :)
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Oh, I understand that aspect of the issue and agree, my question is limited to seeking people's opinion on the honesty of the mechanic not disclosing something to further the sale.
 
To chime in:
Yes, An A&P can repair the carb and sign the work off
Yes, I agree it is likely the carb
(other possibilities, but carb needs to be ruled out first)
Yes, you can get a repair kit/parts
Yes, the MA4 and it's cousins are stone simple and reliable
My thought is that you have worn throttle shaft bushings and it is sucking air around the shaft at a certain position/rpm
(likely sucking all the time but only upsets the fuel flow enough to be noticed at certain positions)
Besides putting a rebuild kit on it have your mechanic install a new set of throttle shaft bushings.
You will be impressed at how smoothly your engine runs after that.
 
Henning said:
Oh, I understand that aspect of the issue and agree, my question is limited to seeking people's opinion on the honesty of the mechanic not disclosing something to further the sale.
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Intentional dishonesty? Can't say for certain but I've encountered some things on pre-buys that have set off alarm bells. Could simply be sloppy work, but I've found planes signed off as airworthy that have cost IA's their ticket. One was a Piper Arrow with flush countersunk rivets in the wings. That one was outright fraud. It was represented as a NDH plane that had previously been a victim of a gear up. No mention of the repairs in the logs.
I did not feel the least bit guilty about calling in the feds.
 
GMascelli said:
Did I read that right? The owners mechanic is doing the prebuy, not your mechanic?

Just asking......
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No a mechanic neither of us knew did the pre buy. I got recommendations for a pre buy mechanic and used him. The seller or the mechanic have never met before. I'm in another state than the plane so I chose that route.

I then discussed the issues found with my mechanics and we both feel confident in the plane as well as the pre buy mechanic who has never seen the plane before.
 
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Henning said:
Quick question, how many people believe that the mechanic would give a dishonest evaluation?
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Probably the same A&P / IA that does an annual on a retract and forgets to check the gear up horn...:rolleyes:......:redface:........:mad2:
 
bluerooster said:
Actually, Kelly has been more than helpfull to us, with procedures, parts, and specs.
As to being finicky, they are no more so than any other carb, and way less so than most.
Click to expand...


Not finicky. Just inconsistent. When I was looking after flight school airplanes I bought Lycoming factory overhauls. They came with MS (Precision Airmotive) carbs. No two carbs behaved the same, and some were downright dangerous. One was missing the accelerator check valve ball spring and would suck extra fuel on climbout and ran rough. Another had really poor atomization and pulling the throttle back in the climbout let the fuel hit the throttle plate and get atomized better, and would gain 40 or 50 RPM doing that. An HA-6 carb on the R182 dribbled fuel so badly that the cylinders fed off the bottom of the intake manifold would not run at idle; they just flooded. That was an O-540-J3C5D, which has that sidedraft carb that feeds into the back of the engine. Lyc sent us another one, and that one encountered AD issues regarding the mixture control valve internal stuff coming loose.

Yeah, they're simple, but somehow the manufacturers think they're so simple that they don't have to pay attention to quality. The 68-year-old Stromberg on my A-65 is ten times better than an MS carb and runs as smooth as silk.

Dan
 
Dan Thomas said:
Not finicky. Just inconsistent. When I was looking after flight school airplanes I bought Lycoming factory overhauls. They came with MS (Precision Airmotive) carbs. No two carbs behaved the same, and some were downright dangerous. One was missing the accelerator check valve ball spring and would suck extra fuel on climbout and ran rough. Another had really poor atomization and pulling the throttle back in the climbout let the fuel hit the throttle plate and get atomized better, and would gain 40 or 50 RPM doing that. An HA-6 carb on the R182 dribbled fuel so badly that the cylinders fed off the bottom of the intake manifold would not run at idle; they just flooded. That was an O-540-J3C5D, which has that sidedraft carb that feeds into the back of the engine. Lyc sent us another one, and that one encountered AD issues regarding the mixture control valve internal stuff coming loose.

Yeah, they're simple, but somehow the manufacturers think they're so simple that they don't have to pay attention to quality. The 68-year-old Stromberg on my A-65 is ten times better than an MS carb and runs as smooth as silk.

Dan
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If Exp Non Commercial ever comes about I'd be either rigging TPI or a pair of Weber updrafts.
 
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