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mark.bitterlich(at)navy.m
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 Posted: Wed Sep 28, 2016 10:12 am Post subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl |
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I assume you know that if you leave the primer handle in the "Prime" position, I.E. "Not in the middle"..... that fuel will come in through the primer circuit and make the engine run overly rich, which is most especially noticed at idle. These hand pumps can develop internal leaks that then causes the engine to run rich.
My logic is this: It would be very unusual for a carb to just go "adjusting itself". So then why is the engine running so rich? Well, it is getting excess fuel from SOMEPLACE apparently. If we take that as a given, then it most logically would be through the primer circuit or from something wrong within the carb itself.
Neither one can really be cured by starting to make adjustments on the carb. At best you would be robbing Peter to pay Paul. So I would not run in where angels fear to tread, at least not right away. You need to make sure that primer is not the cause. I believe there are better guys out there that can come up with ideas better than mine, but I would locate the hose on the firewall that feeds the primer nozzle. It is way far away from the prop and would be easy to just take off with the engine running and put your finger on the end of it. I have never done this by the way. I hope Dennis or George can come up with a better idea.
Another thing that can cause the engine to run poorly at idle is if you have a drain kit installed on the bottom cylinders and there is a big leak in that system. Hose or pipe damaged, valve shot, etc. Also take a very close look at the intake tubes, for signs of anything loose or leaking.
If you decide to go straight to the carb and start making adjustments, take pictures, make marks, do whatever possible to make sure you can put things back the way they were.
Mark
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ggtyler
Joined: 05 Mar 2016
Posts: 29
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| Posted: Wed Sep 28, 2016 11:04 am Post subject: Re: [Non-DoD Source] Re: M14P running very rich at idle, st |
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Mark,
Yes, primer handle is in the upright position. The carb was reasonably recently fully rebuilt by M14P.com
The stumble is not excessive, but it's there and on the ground seems to run rich. The airplane was previously located in Indiana with a much colder environment than out here in California, so it may actually be jetted rich for the colder climate.
All your points are valid and I'll take a look at all of that, thank you for the suggestions.
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dsavarese0812(at)bellsout
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| Posted: Wed Sep 28, 2016 11:41 am Post subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl |
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As Mark pointed out, check the intake tubes on both ends and the intake drain kit. One of the bug-a-boos was the intake drain mechanism. They are very brittle and they have cracked before. I have seen them crack around the round collection cannister where the tubes empty into the Curtis drain valve.
Do you know how old the primer hose is under the cowling? They can easily deteriorate and crack over the years which would cause an air leak regardless of what position the primer pump is in. The hose connects to a firewall fitting just inside of the top cowling brace and runs over to the left side to a stand-off clamp mounted on the #2 intake tube. One way to check it for leaks is to raise the top cowl. With the engine off, pump the primer (Primer turned to the right) and have someone observe the hose for leaks while you're pumping the primer.
If you suspect an intake leak, remove both cowls. Start the engine. Then using a spray can of ether, spray around the intake tubes at both ends; spray around the intake drain kit and anywhere. Spray around the primer hose and fittings. If there is a leak, the engine RPM will increase when the ether is sprayed on the intake leak.
The idle speed adjustment is on the right (cockpit right) side of the carburetor under a knurled cover which is usually safety wired. If you have the carburetor heat ducts in place, you won't be able to easily see it because the heat duct on the right side will be covering the knurled cover. The knurled cover is on an angle pointing to the rear of the carburetor. You'll have to remove the heat duct to gain access to it. Under the knurled cover is the adjustment screw. It's a click adjusting screw. About 8 clicks from one stop to the other if I remember correctly. You'll need a long, thin, straight blade screwdriver to adjust the screw one click at a time without burning yourself on the exhaust stack. Adjust for peak RPM, then adjust the idle stop screw on the other side to bring the idle RPM to approximately 26% or around 750 RPM.
Dennis
From: ggtyler <ggtyler(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Wednesday, September 28, 2016 3:04 PM
Subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl
--> Yak-List message posted by: "ggtyler" <ggtyler(at)gmail.com (ggtyler(at)gmail.com)>
Mark,
Yes, primer handle is in the upright position. The carb was reasonably recently fully rebuilt by M14P.com
The stumble is not excessive, but it's there and on the ground seems to run rich. The airplane was previously located in Indiana with a much colder environment than out here in California, so it may actually be jetted rich for the colder climate.
All your points are valid and I'll take a look at all of that, thank you for the suggestions.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=460801#460801http://www.matronics.com/Navigator?Yak-Listhttp://forums.mat - NEW MATRONICS LIST WIKI -
_ http://wiki.matro -Mats.com/contribution" target="_blank">http://www.matronics.com/contribution==============
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mark.bitterlich(at)navy.m
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| Posted: Wed Sep 28, 2016 12:19 pm Post subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl |
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| Quote: | Yes, primer handle is in the upright position.
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Yes, I am sure it is. What I was trying to say was that even with it in the upright position, it can still leak INTERNALLY. You should eliminate that as a possibility.
| Quote: | The carb was reasonably recently fully rebuilt by M14P.com
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Did this start after the carb was rebuilt or before? If after.... well, that is a totally new story.
| Quote: | The stumble is not excessive, but it's there and on the ground seems to run rich. The airplane was previously located in Indiana with a much colder environment than out here in California, so it may actually be jetted rich for the colder climate.
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A word to the wise. Don't think of this instrument like you would a Holley carb in your car. A lot of the jets in this carb meter air and not fuel. It's a complicated beast.
| Quote: | All your points are valid and I'll take a look at all of that, thank you for the suggestions.
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Pay more attention to better engine mechs than myself. I'm pretty much just a hack with a little bit of experience.
Mark
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mark.bitterlich(at)navy.m
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| Posted: Wed Sep 28, 2016 12:24 pm Post subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl |
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As a further comment ... I have flown my YAK-50 to Pennsylvania in the winter and to Florida in the summer. Never once had to mess with the carb to overcome issues like you describe. In fact, I have never had to touch the thing at all for performance issues. I did richen up the main circuit to bring down engine temperatures, but that is a totally different topic.
Just be sure you've eliminated all other possibilities before messing with carb adjustments.
Mark
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cjpilot710(at)aol.com
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| Posted: Wed Sep 28, 2016 1:46 pm Post subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl |
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Hell! I'm going to print out this and put it in my manual! Very good Dennis!
Pappy
In a message dated 9/28/2016 3:42:20 P.M. Eastern Daylight Time, dsavarese0812(at)bellsouth.net writes:
| Quote: | As Mark pointed out, check the intake tubes on both ends and the intake drain kit. One of the bug-a-boos was the intake drain mechanism. They are very brittle and they have cracked before. I have seen them crack around the round collection cannister where the tubes empty into the Curtis drain valve.
Do you know how old the primer hose is under the cowling? They can easily deteriorate and crack over the years which would cause an air leak regardless of what position the primer pump is in. The hose connects to a firewall fitting just inside of the top cowling brace and runs over to the left side to a stand-off clamp mounted on the #2 intake tube. One way to check it for leaks is to raise the top cowl. With the engine off, pump the primer (Primer turned to the right) and have someone observe the hose for leaks while you're pumping the primer.
If you suspect an intake leak, remove both cowls. Start the engine. Then using a spray can of ether, spray around the intake tubes at both ends; spray around the intake drain kit and anywhere. Spray around the primer hose and fittings. If there is a leak, the engine RPM will increase when the ether is sprayed on the intake leak.
The idle speed adjustment is on the right (cockpit right) side of the carburetor under a knurled cover which is usually safety wired. If you have the carburetor heat ducts in place, you won't be able to easily see it because the heat duct on the right side will be covering the knurled cover. The knurled cover is on an angle pointing to the rear of the carburetor. You'll have to remove the heat duct to gain access to it. Under the knurled cover is the adjustment screw. It's a click adjusting screw. About 8 clicks from one stop to the other if I remember correctly. You'll need a long, thin, straight blade screwdriver to adjust the screw one click at a time without burning yourself on the exhaust stack. Adjust for peak RPM, then adjust the idle stop screw on the other side to bring the idle RPM to approximately 26% or around 750 RPM.
Dennis
From: ggtyler <ggtyler(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Wednesday, September 28, 2016 3:04 PM
Subject: [Non-DoD Source] Re: M14P running very rich at idle, stumbl
--> Yak-List message posted by: "ggtyler" <ggtyler(at)gmail.com (ggtyler(at)gmail.com)>
Mark,
Yes, primer handle is in the upright position. The carb was reasonably recently fully rebuilt by M14P.com
The stumble is not excessive, but it's there and on the ground seems to run rich. The airplane was previously located in Indiana with a much colder environment than out here in California, so it may actually be jetted rich for the colder climate.
All your points are valid and I'll take a look at all of that, thank you for the suggestions.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=460801#460801http://www.matronics.com/Navigator?Yak-Listhttp://forums.mat - NEW MATRONICS LIST WIKI -
_ http://wiki.matro -Mats.com/contribution" target="_blank">http://www.matronics.com/contribution==============
|
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http://www.matronics.com/Navigator?Yak-List |
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Rob Rowe
Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK
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| Posted: Thu Sep 29, 2016 4:50 am Post subject: Re: [Non-DoD Source] Re: M14P running very rich at idle, st |
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You might also want to check the idle air filter to see if this is obstructed too.
Located as per image ...
Rob R
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