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Did I Break It?

todehnal

Well Known Member
Well, I guess if it ain't broke, I should leave it alone.
At the last inspection I noted that one of the floats was at 4.2. The others were at 3.1, 3.2, and 3.3. Total engine time was 315 hrs.

I had planned to install the new torsion throttle springs anyway, so I bought a full set of new floats and installed them at the same time. By the way, each new float weighted in at 3.2. I fired it up, warmed it up, and performed the carb balance. Everything was great and it ran terrific (smooth as glass). The next morning I was off for a breakfast fly-in, or so I thought. After warm up I did the normal ignition check and found Ignition A was faltering badly. I shut down and did the simple thing first. I swapped all of the plugs top to bottom and bottom to top. Sure enough, the problem moved to ignition B. I don't mess with iffy plugs, and even though this set only had 115 hours on them, I installed a new set. All was well, smooth as glass again and run up was great.

That brings me to this morning when I was planning a nice morning flight. Having just been through some issues, I was very attentive at startup, which seemed good with everything running smooth. After warm up I did the ignition test and all was good. I powered up for takeoff and noticed some stuttering, and promptly aborted the take-off. Additional ground run testing revealed that it is running very rough at almost any rpm, and ignition check shows no difference using A or B. So, I shut down and pulled it back into the hangar. A finger swipe in tail pipe revealed extremely heavy soot. I pulled the top plugs and found #1 and #3 totally black whereas #2 and #4 looked pretty good. Obviously the right carb is running way too rich. ***THIS WAS AN ERROR*** Actually it was spark plugs #1 And #2 that were sooty. #3 and #4 were the ones that looked pretty good. So it ain't the carbs!!! So, my last paragraph here doesn't hold up, but I left it for clarification.........

I think that I have identified the fact the the right carb is running rich. The problem is knowing why, and what happened? I'm not much of a believer in coincidence, so I am trying to figure out how I could have possibly caused this, or where do I go from here.? Any help will be greatly appreciated..... Tom
 
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Sounds like you might have gotten some crud under the needle while changing floats.

Or, possibly damaged the needle/seat?

Good luck with the sleuthing.
 
Are carb bowl gaskets properly seated? Did you blow air through the orifice in the lower corner of the carb bowl to clean out any debris (I believe that orifice is part of the start/idle circuit but it wouldn't hurt to make sure it is free of debris)? Check that the right-side starting carb ("choke") is properly configured (i.e., spring, cable, etc.).
 
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Okay. I guess I am a little upset here, and I made a mistake in identifying the black spark plugs. Actually it is number 1 & 2 plugs that are all sooty. Now that is starting to look like an ignition unit. What I am having trouble with now is that the poorest ignition test comes when grounding A. According to the schematic, #1 & #2 are connected to ignition A, but that is where it ran the best

I did go ahead and pull and check the floats. They all look good and still weigh in at 3.2. There is no fuel on the drip trays, and the needles and seats appear to be functioning correctly. I really think that I may be looking at a bad ignition, but I'm not sure how to proceed from here.

I think that I will put it back together with clean plugs, do a run up, and shut it down from a high RPM, then re-examine the plugs. What stumps me is that both upper and lower #1, and #2 cyclinder plugs look sooty, while all #3 and #4 plugs look pretty good. Sorry for the confusion...........Tom
 
Similar problem today

Watching this thread for ideas.

This is a older Rv-12 that had been sitting a few years but only has 70 hours. My friend bought and we did all upgrades, paint and service bulletins. Ground ran a few times on newly overhauled carbs with new floats. Ready to fly but waited due to defective fuel pressure sender and motor would only turn about 4800 static. Replaced sender and repitched coarse prop to Vans pitch. Motor was running rough, pulled carbs and flushed. Tried to run up but appears to both miss fire and run rich. Number 1&2 top black and wet (both appear to go to same coil). A ignition runs smooth but could only get about 3200, B very rough but could get about 4000 with or without A. My plane smooth as silk on either for one ignition over 4900. Thinking ignition but not sure where to start to trouble shoot.
 
Are carb bowl gaskets properly seated? Did you blow air through the orifice in the lower corner of the carb bowl to clean out any debris (I believe that orifice is part of the start/idle circuit but it wouldn't hurt to make sure it is free of debris)? Check that the right-side starting carb ("choke") is properly configured (i.e., spring, cable, etc.).

I very much appreciate the suggestions. I pulled the carbs again, weighed the floats, blew out the orifices, and verified all of the linkage. I think that I mis-identified the sooty plugs, and have now verified that they were #1 and #2. Sorry for my stupidity. It's just that I have totally enjoyed my 315 hours of superb performance, and now I am faced with a difficult problem, but I guarantee that someones suggestion will nail this thing, and I will be back at enjoying the fruits of my efforts. I need all of the help that I can get.
Thanks.......Tom
 
I wouldn't worry about rich appearance on #1 and 2.
That is pretty common if the engine has been run at idle or low power for a while before shut down (different mixture to front cyl because of intake man. shape).
 
Not sure if you have tried this...but I would get a “new” set of plugs....also check plug wires (go for the easy stuff first). Put vacuum gauges on and check for leaks. Normally, it is something simple.

Also, check choke operation is right..
 
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I wouldn't worry about rich appearance on #1 and 2.
That is pretty common if the engine has been run at idle or low power for a while before shut down (different mixture to front cyl because of intake man. shape).

Instead of shuttling down after a long idle, I ran It up to about 3500 rpm, let it run for about a full minute, then did a quick shut down. When I pulled the plugs #1 and #2 were still sooty. Also, the cough and sputter was really bad when I grounded the A ignition by turning it off with it ition switch. Is a trigger coil a possibility?
 
Here are a few more thoughts: Are the two carbs fully seated in their respective rubber sockets? Spark plug wires properly routed to plugs? Were you careful when removing / replacing the spark plug wires / connectors so as not to damage the connectors' internal components? See connector cross-section at:

http://content.invisioncic.com/r130500/monthly_08_2016/post-3-0-34948900-1470288710.jpg

Sure sounds like a carb issue as opposed to ignition modules.
 
Yeah the carbs seat well. In fact, I removed both carbs, drop the bowls, re-weighed the floats, checked the float level, via the needle valve double arm height, Blew out the small jet in the corner of the bowl, even though both bowls were pristine, re-examined all of the controls and stops, cleaned the plugs again (these are new as of 2 days ago) carefully installed them and the plug wire caps. I started it and again it runs nice at idle all through warm up. I do notice that the egt temp on the left seems to stay 40 to 50 degrees cooler than the right. but even doing the ignition check at idle, around 1850 rpm it sounds great. At soon as it gets warm and I do a run up to 3500 or so the EGts get closer (within 10 degrees or so) but when I run the ignition test at this higher rpm, it will begin that very rough running on B, while A runs smooth. I even tried shutting the fuel of to lower the float bowl level, and it continued to run rough until it was about to die of fuel starvation. I'm totally baffled at this point, so I closed the hangar and decided that it was time for a break. Frustrating to say the least. If I didn't know any better, I would swear that it was a defective new spark plug. I guess I can't rule that out, but I've never heard of that......Tom
 
We have done about the same and are having the same issue but for us A is smooth as silk but you can not get RPM up. B extremely rough but you can get RPM up a lot higher. Like you thinking ignition. Perhaps the coil that fires 1 & 2 top plugs or something with the ignition modules. Am hearing a rattling sound too. Now thinking it could possibly be ignition firing out of sync on a plug causing some pre-ignition?
 
Hey Scott, sorry to hear that I have company with this rough running Rotax problem. From everything that I have read, it sure looks like the likely suspect is that I have a carb problem. I ordered the small kit that Lockwood offers for about $50, and it does both carbs. As soon as it gets here, I will go through them. It doesn't look too complex and I think that it will be the best next step. I'll post the results as soon as I can. Hope you solve your issue, and will post your solution as well..........Tom
 
Talked to Lockwood today after doing a lot of ignition related research myself. Check White wire from the A & B boxes for corrosion, connectivity and intermittent grounding. Frequent problem from component shaking. Reference Maintenance Manual 74-00-00 page 29 ignition system for a good ignition system schematic. Hope this is the problem for us both. They did not suspect carb since just rebuilt by them, worked fine last run and no evidence of any blockage or fuel contamination.
 
Easy/Simple things first

I'd buy a complete set of new plugs and install them. Save the current set as this may not be the problem. I have experienced one new plug that was no good. Maybe you too? Best of skill to you in solving this problem.
 
Todehnal - I posted about our RV12 engine running rough above 3500 to 4000 RPM. You asked me to let you know if we solved it. We did today, hopefully.

Gascolator screen was clean so we removed the carbs, Found a very small piece of black debris in the pass side carb. Small, but still big enough to block fuel jet. Cleaned carb and plane ran great today. We will keep an eye on it.

Bob1393
 
Thanks Bob1393. I pulled the carbs and am ready for the tear down. I have ordered the carb kits from Lockwood. Should be here today. I will just feel better if I have a few replacement item on hand before taking them apart. I have a little hard time understanding how a clogged jet can cause these way over rich conditions, hut I am hopeful. I'll post my findings as well......Tom
 
We may have fixed our problem too. Disconnected all black box connectors, inspected all wiring, cleaned up grounds and reassembled and it works. Smooth pulling over 5100 static. Flying it another day with heavy gusty cross winds today.
 
Well, I'm pretty sure that I have found my problem as well. First, a few more details.

After reading everything that i could find on the subject, all things pointed to the cards, and that included suggestions from Rotax gurus. I ordered the small carb kits from Lockwood, and when they arrived, I went to work. By the way, like many things, the scary part of the job was the unknown. After watching a few videos, and reading up on the process, I set up a very clean area with lots of light an a magnifying glass. It was really pretty straight forward, and to be honest, I didn't find the smoking gun. There was a little black residue hear and there which cleaned off nicely. Oh, I guess the choke works a bit smoother now.

After re-installing the carbs and doing a run up, the roughness was still there on Ignition A, and with all of the black plugs, I was still unable to identify the bad cylinder. So much for carbs being the problem. Everything that I read stated that ignition component failure is very rare, but I thoroughly did a physical inspection again of all ignition connections. I tugged on every connector, seated every plug, and verified that there were no broken or chafed parts.

So, I ran it up again and had the same roughness but this time I kept it up at about 3600 rpm, putting up with the roughness for a couple of minutes and the did a radical shutdown. This time I could detect that cylinder 1 plugs were worse. .On a whim, and really not expecting anything good to come of it, I dig out the old plugs, picked the best looking two and put them in cylinder 1.

Wow! It was like magic! So I did the carb balance and everything looks good. Bottom line, I guess I had replaced a bad spark plug with a fresh out of the box bad spark plug. Thanks for everyone's help. ..........Tom
 
So it was ignition after all. Glad you sorted that out. We will do some plug swapping ourselves just to make sure.

I kind of high jacked your thread with our issue. Today flew the plane. Mag drop only 50 with A off but about 200 with B off at initial run up. Flew for about 45 minutes. Engine smooth and strong. Next run up with B off drop was about 350 with noted roughness but it did fly and run strong and smooth. Still thinking perhaps the 1T, 2T coil may be bad and missfiring. It is very compact and inaccessible under the black boxes. Is there an easy way to check coils still on the engine?
 
Scott,
Swap the coils by plugging them into the opposite ignition module. See if trouble stays or follows the swap. That should tell you if its the coil pack or the ignition module.
Alex
 
Hey Scott. Coils and ignition modules are pretty solid devices. In fact my search did not truly identify any failures, although I am sure there have been some. For less than $3 each, and the most simple swap, spark plugs are a definite go to item. I know that I sure have learned my lesson. Good luck with your fix.....Tom
 
For hard to find issues like this a good 1,2,3,4 step diagnostics makes things easier and usually cheaper because most issues aren't some exotic problem. Jumping around usually takes much longer to find an issue. There are usually simple solutions and common causes to learn from others. Replacing plugs is a good start for a larger than normal mag drop. Then trimming back the spark plug wire ends by 3/8" that go into the threaded prong plug cap. Poor grounds or wire wire rubbed through that goes under something on top of the engine is another good place to check. If you drop on plug then that is around 300 rpm mag drop. To be an ignition module that would be 800-1000 drop and it may just stop the engine. Ignition CDI modules rarely go bad for the 26 degree BTDC normal running phase. Where they do go bad at times is on the start circuit at either 4 degrees BTDC older modules or the soft start at 3 degrees ATDC. The soft start module seem to be holding pretty well. The failures seem to be more of the older CDI modules.
 
For hard to find issues like this a good 1,2,3,4 step diagnostics makes things easier and usually cheaper because most issues aren't some exotic problem. Jumping around usually takes much longer to find an issue. There are usually simple solutions and common causes to learn from others. Replacing plugs is a good start for a larger than normal mag drop. Then trimming back the spark plug wire ends by 3/8" that go into the threaded prong plug cap. Poor grounds or wire wire rubbed through that goes under something on top of the engine is another good place to check. If you drop on plug then that is around 300 rpm mag drop. To be an ignition module that would be 800-1000 drop and it may just stop the engine. Ignition CDI modules rarely go bad for the 26 degree BTDC normal running phase. Where they do go bad at times is on the start circuit at either 4 degrees BTDC older modules or the soft start at 3 degrees ATDC. The soft start module seem to be holding pretty well. The failures seem to be more of the older CDI modules.

Thanks Jolly. All good stuff. I almost called you during my late frustration period. It just seemed like nothing that I did helped. Traditional diagnostic strategies just don't seem to work on Rotax, such as reading spark plugs. By the time you get to them, they are all black, at least cylinders 1 and 2. I think that doing the radical shutdown gave me a little more insight, but maybe I just got lucky. I will keep the mag drop numbers that you posted. Like I said Good Stuff. I have the add-on soft start module. Not sure how they fail, when they do. My guess is that it will either kill an ignition, or fail to retard. Not sure and it is good to know that they are pretty stable devices. Thanks a bunch. ......Tom
 
Hey Jolly!!

Any experience with trigger coil, or ignition coil failures. Such as reliability of them, and perhaps mag drop clues like you did with the spark plug and ignition module clues.

Thanks..Tom
 
All ignition problems fixed. The last problem with excess mag drop was a "bad" new out of the box spark plug. Makes you wonder about the supply of new NGK Rotax plugs with two cases at the same time. Just swapped back in two of the old 70 hour plugs to 1 and 2 top and all now works like it should. There were other issues earlier like corroded ground connections that caused the earlier serious ignition loss.
 
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