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Looking for first thoughts - Brain Storm - Loopy Idle

ELEDSALL

Member
http://youtu.be/9_r40NSSX1c

Particulars:

Dual Lightspeed
New plugs - 5 hours
New Avstar Carb - 3 hours
Superior O-360 - 40 hours new
Fuel Pressure - new sender not sure if accurate
Fuel Flow - not accurate - new red box needs to be relocated.
Cleaned gascolator
Checked timing
Never misses at fuel throttle

All "new" items were made after from slight miss in flight and occasional hard to restart condition both after more than 30 minutes flight time.

Problem occurred with electric pump and without, right tank and left.
 
Last edited:
A few questions to clarify some things....

Did the new parts (carb. and plugs) you installed fix the original problems.

Did the new problem first show up after changing the carb.?
Will it not idle any slower than shown in the video?
Have you made an attempt to check and adjust the idle mixture?
 
Q&A

Did the new parts (carb. and plugs) you installed fix the original problems.

No, they were changed in an attempt to fix the original problem. The carb had an AD on the floats and I could not find anybody that wanted to work on it. It was cheaper to buy the Avstar and take a rebate on the old core. I was hoping the old floats were leaking and causing the engine to flood. This might account for the miss and would account for the hard start on a hot engine after flight - engine just free wheels without any sign of ignition then after resting the starter and increasing the throttle it catches, sputters, then runs well after a few seconds.

Did the new problem first show up after changing the carb.?

See above.

Will it not idle any slower than shown in the video?

Yes, it will idle down smoothly to 550 or 600 rpm. This loopy behavior began after landing, taxing to the hangar. I shot some video thinking that somebody would have seen this before.

Have you made an attempt to check and adjust the idle mixture?


Yes, I set the idle mix and speed after the carb install.
 
It looks like your CHT's are really high for taxiing after landing. Perhaps the fuel is boiling and causing the rpm stutter.
Have you fine tuned your baffles?
 
I note that your RPMs are cycling right in the band where the carb transitions from the idle circuit to the main circuit (1,000 - 1,400 RPM). Does the cycling behavior occur when you have the throttle set above 1,400 or below 1,000 RPMs? Does leaning out the mixture help?
 
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