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gliderx5
Joined: 30 Jun 2008
Posts: 203
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 Posted: Tue Oct 20, 2009 3:42 pm Post subject: Rotax 503 Running Rough |
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I am looking for some help figuring out whats wrong with my SCSI 503. A couple of weeks ago I noticed a miss at higher RPMs (5000 and above), It quickly got worse and then began missing at lower RPMs as well. I changed plugs (resistor type), even though the ones that I was running only had 6 hours on them. Same results. I tried non-resistor plugs, same results. I tried raising and lowering the carburetor needle which only made things worse. I readjusted the timing from 0.072 to 0.086 inches BTDC. Same results. I removed the shielding around the sparkplug wires. Same results. I changed points and condensers, and may have goofed up the timing, because now it runs terrible! I'm not sure what I'm chasing here! Another thing that puzzles me, and might be a clue, has to due with the kill switch and behavior of the points. Let me explain. When setting the points on the right, the continuity light connected across the points dims noticably as the points open, regardless of kill switch position. The points on the left only dim when the kill switch is in the run position. With the switch on the off position there is barely a perceptable flicker as the points open and close. I'm wondering why the behavoir of the points would be different.
The engine was running fine all year long and I've logged several multi-hour flights over the summer without a problem. It has less than 2 years and 60 hours on new plug wires and suppression caps. Have any of you guys been down this road? Any thoughts?
Malcolm Morrison
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WhiskeyVictor36(at)aol.co
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| Posted: Tue Oct 20, 2009 6:23 pm Post subject: Rotax 503 Running Rough |
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In a message dated 10/20/2009 7:43:07 P.M. Eastern Daylight Time, gliderx5(at)comcast.net writes:
| Quote: | I changed points and condensers, and may have goofed up the timing, because now it runs terrible!
Malcolm,
This may not be the answer, but something to look at on your new points.
My buddy, Alan, had a Rotax 377 with points ignition. After installing new points, we had a hard time getting the (Yamaha) point checker (Ohms meter) to indicate properly. Discovered that the new points were dirty, either oil or some other kind of preservative coating on the face of the points. Point cleaning chemical spray would not get them clean. Had to resort to very fine grit sand paper to get them clean. And as a final cleaning step, an old timer once told me to slide a clean business card between the closed points to remove any lasting residual dirt after cleaning them.
Bill Varnes
Original Kolb FireStar
Audubon NJ
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h20maule(at)hotmail.com
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| Posted: Tue Oct 20, 2009 6:54 pm Post subject: Rotax 503 Running Rough |
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could it be a coil?
Daniel
From: WhiskeyVictor36(at)aol.com
Date: Tue C 20 Oct 2009 22:22:38 -0400
Subject: Re: Rotax 503 Running Rough
To: kolb-list(at)matronics.com
In a message dated 10/20/2009 7:43:07 P.M. Eastern Daylight Time C gliderx5(at)comcast.net writes:
| Quote: | I changed points and condensers C and may have goofed up the timing C because now it runs terrible!
Malcolm C
This may not be the answer C but something to look at on your new points.
My buddy C Alan C had a Rotax 377 with points ignition. After installing new points C we had a hard time getting the (Yamaha) point checker (Ohms meter) to indicate properly. Discovered that the new points were dirty C either oil or some other kind of preservative coating on the face of the points. Point cleaning chemical spray would not get them clean. Had to resort to very fine grit sand paper to get them clean. And as a final cleaning step C an old timer once told me to slide a clean business card between the closed points to remove any lasting residual dirt after cleaning them.
Bill Varnes
Original Kolb FireStar
Audubon NJ
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Hotmail: Trusted email with powerf/01/' target='_new'>Sign up now. [quote][b]
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gliderx5
Joined: 30 Jun 2008
Posts: 203
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| Posted: Fri Oct 23, 2009 11:43 am Post subject: Rotax 503 Running Rough |
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Update on the 503. I took everything apart again, tweaked the timing, put in 2 new resistor plugs, and it runs like new. I'm not sure what the issue was, but I suspect it may have been a condenser. I now have good timing, new points, condensers, and plugs. I did reseat the wires on the coils, which could have been an issue also. Now, I just need some nice flying weather. I did a quick flight today just to check out the engine, but it was windy and bumpy.
Malcolm Morrison
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slowaero
Joined: 28 Nov 2009
Posts: 17
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| Posted: Sat Feb 13, 2010 10:30 am Post subject: Re: Rotax 503 Running Rough |
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Dear Malcolm,
I have a 377 which had similar intermittent problems resulting in two forced landings. (FireStars don't stay up long running on one cylinder.) The first landing was in the trees. Fortunately a friend with a Hui was near and had me back on land with-in an hour. I never unbuckled my seat belt. Praise-be to cell phones and Helis. The second time I was trying to find the problem by holding full throttle for several minutes while over the airstrip. Happy landing on that one. The culprit = coils were breaking down.
Good luck,
Dave
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Mon Feb 15, 2010 5:36 am Post subject: Re: Rotax 503 Running Rough |
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| gliderx5 wrote: | Update on the 503. I took everything apart again, tweaked the timing, put in 2 new resistor plugs, and it runs like new. I'm not sure what the issue was, but I suspect it may have been a condenser. I now have good timing, new points, condensers, and plugs. I did reseat the wires on the coils, which could have been an issue also. Now, I just need some nice flying weather. I did a quick flight today just to check out the engine, but it was windy and bumpy.
Malcolm Morrison
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Well, as you've discovered by now,  , the older points 503's are a little bit like our old cars used to be regarding the points. Pretty much the same maintenance/trouble-shooting steps hold there that used to hold on our old Fords etc....
A couple things to keep in mind on the points motors. With new points, be aware that the cam lobe on the points will wear a little quickly when they're new (this is of course reduced if you lube the cam when you install the new points). So expect the dwell angle to increase and the timing to retard a little bit at first. Once they wear in, tho, they'll stay put. I didn't have to adjust the timing on my points 503 at all after the points wore in.
Another possible trouble spot is overtightening the fan belt. There's a caution against this in the manual for the points motors. this can actually pull the crank out of position slightly which can goof up the timing. I never ran into this on my points 503 as I couldn't detect any side play in the mag end of the crank. All the same I used a tensioning measurer when I set my fan belt tension to make sure it was what was spelled out in the manual (i.e. the correct deflection at 5lbs, can't remember exactly what it was). Anyway, keep this in mind when adjusting your fan belt tension....
Otherwise, the points 503's are remarkably reliable, unlike our old cars' points which we were kind of always fiddling with. Once worn in and set, the motor should run a long time with no maintenance to the points....
LS
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LS
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