sidsel.svein(at)oslo.onli
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 Posted: Thu Jul 12, 2012 9:17 am Post subject: SV: 912ULS - Rough start & Rough on one magnet |
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Thank you very much for all suggestions received on how to solve the problems I experienced.
The “rough on one magnet” is now resolved, and the rough start of cold engine almost gone (maybe I have become paranoid and forgotten that 912ULS always starts a little “hard”).
I replaced the battery with identical one – Leoch 28 Ah. The first cold start (with choke) was a little rough. I let the engine run some 20 seconds and stopped it. Restarted again with choke – now much less roughness.
I did several stops and restarts. When the oil temp reached the mid-30s, smooth starts.
Carb sync solved the second problem – some roughness on one magnet at 4 000 rpm, smooth on the other, rpm diff some 50 rpm: At 4 000 rpm the carbs where out of sync by 1.5 cm HG ( a good ˝ inch). Carb sync at this rpm made the roughness on one magnet go away. Rpm drop on either magnet abt 180 rpm, rpm diff + - 0.
Before I started the engine, I pressure checked that the float valves closed, and I inspected the carb bowls (clean). With engine on idle, I bent, pushed and pulled on the wires to and from the electronic modules on top of the engine. No indication of broken or intermittent contact.
The positive effect of new battery was to be expected. The carb sync was suggested by the Scandinavian Rotax agent, but I must admit that I was a little skeptical. He explained it by pointing to how the spark plugs are connected to the magnets on 912: Magnet A: cyl 1-2 top, cyl 3-4 bottom. Magnet B: cyl 1-2 bottom, cyl 3-4 top (#1 is right forward, 2 left forward, 3 right aft, 4 left aft). ) 914 has all 4 tops on one magnet, all 4 bottoms on the other. I still cannot explain why carb sync should matter during mag check, but it certainly does.
Regards,
Svein
LN-SKJ
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