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Carbon Cub Rough Running Engine

Neat thread. I hadn’t read all of it before. Just goes to show what a sticking open(or clinker under it) intake valve will do to you. You don’t just loose that cylinders output power, you loose at least the next cylinders fuel charge and power too, since intake system is pressurized at that point instead of vacuuming


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….He also said the old school method of leaning until the engine stumbles and then enriching a bit does not work with electronic ignition. The electronic ignition has a hot enough spark to run smooth with a lean mixture which is how the owner had been leaning it....

Reminds me of a guy I used to know.
He said he switched to one mag, leaned until just barely rough, then switched back to both and called it good.
I wonder if that would work with the dual electronic ignition?
 
We just put the 4-5 carb on the 0-340 we installed on my supercub. Can not go full rich, full throttle on take off without it running very rough. (acts like its getting way to much gas) We have to lean about 3/4" travel on the mixture. My fuel flow gauge shows this to be about 13-14gph. At no time have I ever been able to get the 15-16gph fuel burn without the engine running rough and stumbling. My CHT are around 325-375 but the #2 cylinder EGT is high. I have to work at it to keep it below 1400. The others in cruise are around 1200. After reading this thread I may be leaning it to much my self. I am running a Vetterman exhaust which I think was designed for the 150hp engine and wondered if that was a factor. At 30 hours and working out the bugs. (with a smile)
 
We just put the 4-5 carb on the 0-340 we installed on my supercub. Can not go full rich, full throttle on take off without it running very rough. (acts like its getting way to much gas) We have to lean about 3/4" travel on the mixture. My fuel flow gauge shows this to be about 13-14gph. At no time have I ever been able to get the 15-16gph fuel burn without the engine running rough and stumbling. My CHT are around 325-375 but the #2 cylinder EGT is high. I have to work at it to keep it below 1400. The others in cruise are around 1200. After reading this thread I may be leaning it to much my self. I am running a Vetterman exhaust which I think was designed for the 150hp engine and wondered if that was a factor. At 30 hours and working out the bugs. (with a smile)
Joe with the Super Legend might can help. He changed his carburetor and has now gone to fuel injection.
 
J5Mike, the exhaust systems for 320s and 360s are basically the same. The 360 is 1.8 inches wider than the 360. I designed most popular system which was the 360 crossover and placed a cutoff mark on pipes 1 and 2 if it was going on a 320. Vetterman
 
Steve had one local with some EXTREME fouled plugs. Assume you checked this but it solved our issue locally.
 
Intake valve journey

Steve Pierce -

Does this picture look familiar? We went on quite the journey before discovering the burnt intake valve. It's an 0-340 on a CarbonCub EX. It began with a quick miss, maybe 1 second in duration, and then back to normal. I began trouble shooting fuel flow issues with no luck. I grounded the plane after a few of these occurrences and my mechanic buddy and I began looking at the ignition. We started at the plugs and worked back to the ignition boxes. We had several ah-ha moments only to find no improvement. We contacted Klaus and went through his checklist, and when that was completed, he sent us a loaner ignition box. No luck. You might think it was about time to look somewhere besides the ignition but in our case the miss only occurred on the RIGHT ignition. We were able to get the engine to cut out consistently at about 1800 rpm but only on the right ignition. It sounded like the engine in your video. Ran smooth when we switched to the left. The plane was flown about 150 miles to my mechanic's shop on the "good" left ignition. He changed out both ignition systems with no improvement. The plane was flown to CubCrafters in Yakima for about 500 miles on the left ignition. The engine stumbled briefly on take-off about 100 miles from Yakima for the first time on the left ignition. CubCrafters spent a few days trouble shooting the ignition system and in the process was able to get it to miss once on the left ignition during a ground run. They eventually got a low compression reading on the #1 cylinder, pulled it, and the result is in the picture below. They had never seen this before. I sent them the picture of your burnt valve. I now have about 10 hours on the new cylinder and life is good again.

- Mike Macon

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Looks like a JPI EDM 350

8b2179a63b3f224fa65581b84a976cb2.jpg
 
Were you ever able to find out the drill size for the 10-3678-32 i have that carb. on a RV6 and have high CHT temps on take off?
Thanks
EV
 
Were you ever able to find out the drill size for the 10-3678-32 i have that carb. on a RV6 and have high CHT temps on take off?
Thanks
EV
Are you absolutely 100% certain that your full power, low airspeed, high CHTs are caused by a lean mixture? Have you done tests to confirm that this is the case? Have you leaned the mixture at full power and noted an EGT rise or does the EGT drop immediately as soon as the mixture is pulled back? You may just have an engine cooling baffle error.
 
I had a very minor miss in flight, leaned the engine and determined which cylinder head temp would not come up then traced plug wire to proper coil and found a small spade connector loose, crimped it and solved the problem. Again it was minor.

Had same exact prob. same fix. all good from there.
 
Common issue with the connectors on the coils. The wires are not properly supported across the bottom of the engine. Most of the ones I have had come loose were furtest from the wire supports. Put a dab of silicone at each connector to coil and add the supports. Most of the time when the re is a coil issue it takes out the plug as well.
 
Were you ever able to find out the drill size for the 10-3678-32 i have that carb. on a RV6 and have high CHT temps on take off?
Thanks
EV
I will look but that was for that carb on an O-340 with the peppered nozzle, the sleeve in the induction. Not sure we are talking apples to apples here.
 
I will look but that was for that carb on an O-340 with the peppered nozzle, the sleeve in the induction. Not sure we are talking apples to apples here.
Steve, can you elaborate on the induction insert and nozzle change?

I've been flying a friend's CCK-1865 that will run rough at about 3/4 throttle and is smooth on either side but has a large EGT disparity in cruise. I understand they had a nozzle change for the Marvel carbs but this has an Avstar.

Thanks,
 
Steve, can you elaborate on the induction insert and nozzle change?

I've been flying a friend's CCK-1865 that will run rough at about 3/4 throttle and is smooth on either side but has a large EGT disparity in cruise. I understand they had a nozzle change for the Marvel carbs but this has an Avstar.

Thanks,

Research the service bulletins, instructions and memos on Cub Crafters website. Verify they are current per your serial number. If they are not then I would strongly advice you do so. They were implimented because there were issues. As I have posted before this engine was designed to use a bigger carburetor but that carb would not fit the Carbon Cub cowl. The early Carbon Cubs prior to late 2012 have a Sport Cub cowl that does not cool properly. The ground adjustable cowl flaps, the insert into the intake throat and the peppered nozzle in the carburetor were all attempts to make these engines run correctly and cool in the Carbon Cub Airframes. There is also a 22 degree flywheel timing ring that many have installed to combat the cooling issues.
 
It appears to have the insert installed. This airplane was a kit that was finished in 2014.

It still has the old induction couplers so I will order the kit for that and see what happens.
Thanks!
 
The induction hose kit is just to eliminate the issues with using heat shrink as an induction hose especially when you have a backfire on a little island and all you have for tools is a Leatherman. ;)
A little weight from real hose and hose clamps is a good compromise in my opinion.
 
Burnt intake valve

Steve -

I posted a picture of my intake valve on 4/12/20 that came from my #1 cylinder at 600 hrs. This weekend a experienced the same symptoms and now have another burnt intake on #4 at 650 hrs. You may want to pass this on to your client. The fun may not be over.
 
Steve -

I posted a picture of my intake valve on 4/12/20 that came from my #1 cylinder at 600 hrs. This weekend a experienced the same symptoms and now have another burnt intake on #4 at 650 hrs. You may want to pass this on to your client. The fun may not be over.

What are the particulars on carb, throat insert, nozzle, cowl model, timing ring and engine gauges? That airplane was sold and went to Montana and replaced with an EX2 with 65 hours on it. Had some major baffle problems that I post about recently.
 
It’s an EX with the kits purchased from 2013 to 2015 and completed in 2016. Cowl has cowl flaps and I have an EI 30P. No work has been done on the carb. I have done some research on the internet and have only found one other case of a burnt intake besides yours. I would think that if this was not just an isolated manufacturing problem there would be a lot more cases out there. Between RVs and CarbonCubs alone there are a few of these engines out there.
 
I did not realize there were O-340 in RVs. Does SB22 or SI0031 apply? What does the data from the CGR show? The local dealer only uses the 22 degree timing ring vs the 25 and have seen now other issues.
 
Hearsay only on my part. One cc appeared to have ignition problems. Turned out to be a broken inner valve spring Another cc had every ignition part replaced down to switch electronic ignition modules and even battery. Problem continued. CC looked at it on site with no luck. Took the aircraft back to Yakima on one mag. I don’t know what they did to solve it. CC is aware of some issues that appear to be ignition related. To the best of my knowledge (hearsay only) that was not ignition either.
 
The only ignition issue i have had was a bad crank sensor. Klaus with Lightspeed didn't believe me until I proved to him I ha troubleshot the whole system. he said he very rarely sees a crank trigger go bad. From all of my experience it has been pretty trouble free except when a coil wire gets disconnected and it takes out the plugs.
 
Is there any merit to people over leaning with the electronic ignition? Too hot and poof there goes a valve. I have seen it a few times now.


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An electronic ignition will burn a lean mixture where a conventional magneto will start to stumble. The old way of leaning till it stumbles and enrichen a bit does not work on electronic ignition, you will burn something.
 
An electronic ignition will burn a lean mixture where a conventional magneto will start to stumble. The old way of leaning till it stumbles and enrichen a bit does not work on electronic ignition, you will burn something.


Doesn't that depend on the power setting? Lots has been written on the subject, some of it supported by data from well instrumented engine test stands. My current belief is that I can't damage anything at any lean mixture setting as long as power is less than 60%. If there is data that disproves that I'd appreciate a link.
 
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