01 7GCBC rough only at 1200 rpm

T

tkearns

New member
She runs beautifully with this one exception...

When slowly advancing throttle, at 1200 rpm it drops back to 1100 and runs a bit rough...the slightest throttle nudge takes it right to 1400 rpm. When it's running rough at 1100, changing mixture does nothing which indicates it may be lean. Perfect timing, clean pugs, no induction leaks.

I have a friend who had the exact same problem on his carberuated citabria. He chased the problem for quite some time, replaced the carb and never did get resolution.

Before I throw money at it, any thoughts???
 
Try looking at the accelerator pump in the carb. A hesitation or lag in acceleration can often be traced to a worn out accelerator pump.
 
If it happens when "slowly" advacing the throttle I don't think it could be the accelerator pump.
BB
 
It stays rough at that rpm range if you approach it by either reducing or applying power. For this reason we doubt it's the accelerator pump.
 
Is this a new plane? model year? I have had problems with mine only when I pull power back while landing then need just a little more power. I found out on hot days with 100LL it does that. (runs rough) I have an auto gas STC and it never does this with auto gas. If you don't have a Auto gas STC, just try it with some car gas to see what it does. B
 
Few things could be involved. Check your intake seals and gaskets. If they are cracked or worn down can cause an induction leak which indicates more on lower RPM's (1500 rpm's and lower). Also the idle mixture screw on the carb can cause a burp in the lower rpm. Check with your engine at idle and see if you have a rise in rpm when you pull the mixture off. Should indicate 50 to 75 rpm rise for correct idle mixture. If there is no rise, it is set to lean, if a high rise , 100 rpm or more its to rich. Good luck
 
Thanks scout...new gaskets and it does rise at cut off. Not sure what it might be...may just invest in a new carb.
 
TK

Pull your carb heat when its at the 1100 RPM range and see what happens.

Also what happens when you run it through that range on just one Mag?
 
Have you checked the plug wires with a tester? They can cause some strange things on these engines. The first thing we always think of is the plugs and it usually turns out to be the wires. I was helping my son finish an annual on a 152 a month are so back. We cowled it up, pushed it outside to wash it and I told my son to see how it was running before we did, sounded terrible, was running perfect when it arrived. After recleaning the plugs and retesting, we checked the ignition leads all showed good. Let it cool down , restarted for just a few seconds and check for a cooler cylinder and it was there, checked those two plugs again, even changed from another cylinder, no change, had to be one of the leads, tested again, must be nice to have good eyesite, Joel saw a small arc in the braiding on the wire, repaired and it was fine. If you have access to a good infared therometer, check each cylinder when you first start it up and see what the temps are doing.

Woodie
 
Did you ever figure out your rough engine condition? Check out link on carb condition. http://www.sacskyranch.com/eng55.htm
 
You must log in or register to reply here.
Back
Top