7gcaa mixture travel

S

staticbags

New member
just bought a new to me 74 gcaa. LOVE it. I am surprised and little worried about the mixture travel and distance it travels before engine dies.
when i pull out the mixture to lean, it goes dead after only pulling it out about 1 inch. It starts running rough just below the 1" out mark. So i really don't have much room to lean it.
Now the engine runs great. idles great, cranks great. It seems to have full power.
Does anyone else out there with a citabria or similar have one that does this?
Ok,i did check the travel and the mixture arm on the carb is traveling full distance from stop to stop and cable is straight. On outside of the carb, it seems to be working properly.
If anyone know of another doing this, please let me know. IF not, i'll have to pull carb and send off.
you can reply with post or email me direct at jeff@hightechpackaging.com
Jeff H
austin tx
 
Have you checked the idle mixture? Also check the intake system for leaks, it sounds as if you engine may be running a little on the lean side. At this time I wouldn't pull the carb until you have ruled out some of the less expensive items.
 
i have not checked the "idle mixture" don't really know what that is. It dies with 1" mixture pulled out at all rpm settings. idle, mid rpms, and wide open.

ON Intake leak:
I know when i was checking to make sure mixtue cable was going from stop to stop on the carb, i did notice the rear clamp (at the carb) is not on the rubber from air filter to carb. It looks like there could be some leakage there but at worse, i think it may get some unfiltered air from inside cowl. but the rubber "boot" connecting airfilter to carb fits pretty nice but there is a clamp off. So if you think that is why, its an easy fix and i will go get it back on correctly.
jh
 
In order to check your idle mixture, you need to have the engine warmed up to normal operating temps. When you have the throttle at idle, slowly pull the mixture to the cut off position. As you are pulling the mixture control back watch the tachometer closely, you are looking for a 25-50 RPM mixture rise before the RPM starts to drop off. As far as the boot off of the filter/carb housing, that isn't what I'm refering to when I mentioned the intake leak. By intake leak, I am refering to the portion of the intake system from the throttle butterfly to the engine cylinders. One way that you can check for intake leaks is to take the exhaust air from a vacuum ( make sure that only clean filtered air is coming out of the vacuum) and hook it to the aibox on the carb.(Make sure the throttle is opened). Essentially you are pressurizing the intake system. Now take a soapy water solution and spray down the intake system from the oil sump to the cylinder bases. Look around the rubber couplings at the oil sump and the flanges at the cylinders. Also look for signs of blue dye from the fuel. If you have an intake leak it usally only shows up at low power settings as the maniflod pressure in the intake system is fairly low compared to the ambient pressure. If you don't feel comfortable doing this procedure it is something that your mechanic will be able to do.
 
i did notice the rear clamp (at the carb) is not on the rubber from air filter to carb. It looks like there could be some leakage there but at worse, i think it may get some unfiltered air from inside cowl. but the rubber "boot" connecting airfilter to carb fits pretty nice but there is a clamp off. So if you think that is why, its an easy fix and i will go get it back on correctly.
Click to expand...

JH----There is only supposed to be one clamp on the rubber "boot". It just slips on at the carb end.

Bill
 
Deere 345; thanks for explaining and now i understand what you meant. I"ll go that route (pressure check carb)down road if i need to. First another friend also suggested checking to see if mixture was too lean just as you did. I think i have tried that and there seemed to be no or hardly no noticable increase in RPM, but i will check that again and be more precise on the test. That might show me my problem? So if i don't get the RPM increase, does that mean my idle mixture is off? and easy to have my mechanic set correct?

bill: Thanks for the intake carb rubber explaination. that does make sense to what i was seeing. But i think i saw two clamps; one up keeping rubber boot connected to filter exit and one on the carb but not over bubber boot at that location.

thanks for help. weather is crap today so i'll try to warm up and run tue and give an answer to the rpm increase or not.

jeff h
 
deere 345 or anyone else with experience here:
ok from above post, today i warmed up and flew the plane for a bit then landed, went to idle and slowly pulled out mixture. I got NO increase in RPM. If there was one, i could not see it. So i think i need to follow on your assumption of a too lean idle mixture. Would you agree?
This mixure pull is the same at idle 500rpm, 1000rpm, and at2100 rpm or 2500 rpm. it acts same at all rpm.. pull mixture knob aprox 1" and engine dies. no noticable increase in rpm before it dies.

jeff h
 
Staticbags,
I would check your induction system for leaks, before you adjust the mixture on the carb. (Remember induction air leaks are more pronounced at idle due the greater pressure differential between ambient and the induction system). One other note, at higher power settings the idle mixture has nothing to due with the idle mixture settings. At around 1200-1400 RPM the main fuel nozzle is what is suppling fuel to the engine. The amount of fuel that is supplied to the engine is directly porportional to the amount of air the is being pulled thru the venturi. The float level in the carb. also plays an important role, if the float level in the carb is set to high the engine will tend to run rich and visa versa if the float level is set to low the engine will tend to run on the leaner side. Sorry no definite answer to your problem, but maybe a couple of areas that you can look at.
Deere_345
 
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