912uls runs rough at 2600 rpm

by gabriel dellaventura in 912 / 914 Technical Questions 10 years ago

Dear Sir. Received my carbs. Back from Lockwood Aviation for a 5 year service. Installed and syncronized them. At idle and high rpm all is fine. At 2600 rpm runs rough. Pulled spark plugs and found #1 cylinder shows signs of carbon build up. Never had this problem before. All cylinders burned clean and engine always ran smooth at all rpm. Could it be the new service bulletin concerning carb. Floats absorbing fuel making them heavy. Your input is very much appreciated. Gabe.-*

Re: 912uls runs rough at 2600 rpm

by Roger Lee » 10 years ago

Roger Lee

126 5.14k 4.58k

Hi Gabriel,

A dry sooty plug can be very normal after running in those low rpms like idle. Try and sync your carbs at your bottom idle setting (i.e. 1700 +/-) and at 3500 rpm. Don't worry about 2500 rpm. You don't idle there and you don't fly at those low rpms. I know we don't fly at 3500 either, but it is a better representation of the higher rpm range and makes sure you are completely out of the idle circuit. If they sync up well at these rpms then you're most likely ready to go. You won't have the dry black soot after running at higher rpms (i.e.4K) or above for a minute or two. All that burns away. The black sooty plug can move from one plug to another at times or even be more than one plug.

p.s.
I'm sure Lockwood set the mixture screw on the bottom of the carb at 1.5 turns out.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: gabriel dellaventura

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Re: 912uls runs rough at 2600 rpm

by Kevin Stewart » 10 years ago

Kevin Stewart

3 389 1.16k

Hi Gabe,

Problem sounds very similar to my motor. Did you read my rough running thread?

I do not have any more investigations I can make, I think I tested every component. My next action is to take motor apart and inspect. This is very expensive and I am not happy.

Good luck with your problem.

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912uls runs rough at 2600 rpm

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