Carb balancing

by Neil Cooper in 912 / 914 Technical Questions 8 years ago

I have balanced my carbs mechanically and have a carb mate for balancing pneumatically however I found that while the engine runs smooth, the carb mate says that it is slightly ou at idle. As I increase rpm the carb mate says the balance is better until I get to normal rpm operating ng range where the carbs are balance (according the carb mate)
What I'm wondering is should I leave this as is (balanced at operating rpm and slightly out pneumatically at low rpm? Does something change at high rpm that gives this result?

Re: Carb balancing

by Roger Lee » 8 years ago

Roger Lee

128 5.28k 4.98k

Hi Neil,

You'll find it easier to balance carbs and be able to diagnose issues much easier with a set of gauges. You can't diagnose with an electronic device. Gauge's tell you so much more info with just a glance.
You should have no problem having the carbs balanced at the higher rpm like 3300-3400 and at idle. I much prefer this higher balance rpm over the 2500 in the book. Sync the high rpm first then do the idle. You must use a sync device because the human ear is not capable of discerning slightly out of sync carbs. Most set the idle balanced rpm around 1650-1750. This is somewhat of a personal preference, but you shouldn't just sit there and idle at those low rpms for any time. The UL engine can handle lower rpms better than the ULS due to the compression difference.

Once you understand what you're being told with the gauges and how it relates to the info you see carb syncs are very easy. It usually takes me 10 min. to maybe a tougher one 20-30 min. The longer ones is usually because of a poor throttle and cable system in the plane that doesn't return to the same place each time you move the throttle.

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

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Carb balancing

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