fisher.garrett
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I am in need of some serious help with fuel/carb problems on my C-85 J-3. In 50 years of Cub rebuilding, my grandfather has never seen an airplane that is so difficult.
Here is the story of the airplane and what we have done:
1941 J-3 with C-85 134 SMOH (done in 1994) and Stromberg carburetor
The airplane had some wind damage while tied down in 2001. It sat in a warehouse from 2001 to 2010 WITH AUTO FUEL IN THE TANK. Yes I know thats your problem.
We did the following to clean it out:
Soaked tank bottom and flushed repeatedly with isopropyl alcohol until the alcohol stopped discoloring. Replaced copper fuel line. Replaced gascolator. Flushed line from gasc to carb with alcohol until clean (visually inspected to be clean). Had carburetor rebuilt by my A&P/IA (replaced all gaskets using kit from Univair). Installed new airbox.
She wouldnt start. Would run on ether (I know stupid idea we dont do that anymore) but only until the ether quit. Would run at full throttle on ether no ignition issues just fuel delivery problems.
So we rebuilt carburetor again. No change. There was some dirt in it that wasnt there after the last rebuild. No change. After 50 cranks, I got it to sputter once, that is it.
Checked timing. Checked all spark plugs (literally took them out and confirmed spark). Replaced all outer and inner intake seals. Replaced intake gaskets. No change. I also removed the quick drain as it was leaking, and a rather clean pile of dirt fell out. I cleaned the drain and quick drain mount and reattached.
Installed primer. With 3 pumps (in 45 deg weather), she would start and run albeit somewhat poorly. While tied down, she would run pretty good and then start belching black smoke and RPM would start dropping. Pumping carb ice would resurrect. I then would taxi it and the rpm would hunt all over the place and the engine would quit when I was making 90 degree taxiing turns with any small bit of speed. Couldnt bring rpm under 1000 or she would quit. I could get up to rpm and she would fly 10 feet above the ground (before I pulled back NO WAY I was going up with it acting like this).
We figured the carburetor was hosed, so replaced needles with Fresno Air Parts steel needle kit and tried to get in some of the orifices better to clean it. Also soaked carb again in more cleaner (A&P confessed to having inadequate tool to get in there properly to ensure certain parts were clean). At this point, the engine required the primer to stay open (cracked) for the engine to run. This meant that the engine is sucking needed fuel via the primer system to stay alive still too much fuel as it belched some black smoke.
So I had the carburetor rebuilt by a highly recommended Ray Stillwell in SC. He advised the float was leaking and replaced that, the inlet metering jet and the idle jet something. Put it on the airplane. NO CHANGE. Still needed primer to run.
I had been putting 2 3 gallons in the tank for all this testing, so I added it to get to 6 gallons. No primer needed! So I tried the good old run-up to full throttle. It would get to 2400 (46 deg prop installed) for 2-5 seconds and then the engine cut out. I could save it from quitting by taking the throttle and going back to idle. Further testing determined that whenever I was above 1800 rpm and hit bumps, lifted the tail or did intentional S turns, she would cut out.
So I suspected a dirt problem. Replaced fuel strainer as it was dirty. In the process, had to remove quick drain. Another pile of clean dirt fell out. No change.
I suspected vapor lock as I had a mildly unacceptable kink in the copper line (even though I could drain fuel at 30GPH through carb hose into a gas can). Installed Univair stainless steel line. No change.
I suspected dirt still (at the behest of a suggestion). Removed quick drain again to see if another pile materialized. None. I used a broomstick and a scouring pad to buff the tank down to aluminum shininess turning some adhered sediment into dust. Vacuumed with shop vac. Rinsed with fuel through a napkin. Napkin was dusty no particles. Removed gascolator screen and rinsed some very small particles off. Then replaced fuel line from gasc to carb just in case.
Ran engine. Basically same problem. Engine cuts out after a few sec at full throttle. Runs all day sitting still at 1800 rpm.
Read in Cub Club about necking on fuel cap (ie, cap works but you have the same situation I do despite having replaced the entire fuel system) but the air vent is reduced. Removed cap and tried run up while taxiing. No change.
Now that fuel level is down a bit from 6 gallons, she is starting to skip and run worse.
Called my carb guy (who now has some medical issues and cant do further work). He supposes that the float might need to be adjusted again though its a low confidence assumption.
I have gotten advice that there are occasions when a carburetor can be rebuilt 3 to 4 times and the engine will just not run right and a new carburetor fixes the problem. I am not so sure I want to take this rather expensive step. Here are some facts that I am stuck with:
1. There was dirt in the carburetor each time the A&P had rebuilt it. There was dirt in the tank.
2. I have run fuel in the J-3 tank, drained into a gas can and put it in my PA-11 (O-200 with Marvel carb) and flown just fine. Repeatedly. So if there is evil Satanic dust clogging my carburetor, it doesnt do that to the other airplane.
3. I have 30GPH flow rate through the carb hose into a tank.
4. There is no dirt in the tank now.
The only thing I can think to do at this point is drain the fuel, check the tank thoroughly and scrub the most minor of remaining imperfections, vacuum, rinse and confirm with a napkin filter remaining white as snow and also remove the carb, flush it and put the whole thing back together again though my gut says nothing will change. I am not in the mood to gamble on a new carburetor and I also want a working airplane too!
My grandfather told me many stories of shockingly dirty fuel tanks and no issues flying, so I dont know what to say.
Any help is appreciated!
Here is the story of the airplane and what we have done:
1941 J-3 with C-85 134 SMOH (done in 1994) and Stromberg carburetor
The airplane had some wind damage while tied down in 2001. It sat in a warehouse from 2001 to 2010 WITH AUTO FUEL IN THE TANK. Yes I know thats your problem.
We did the following to clean it out:
Soaked tank bottom and flushed repeatedly with isopropyl alcohol until the alcohol stopped discoloring. Replaced copper fuel line. Replaced gascolator. Flushed line from gasc to carb with alcohol until clean (visually inspected to be clean). Had carburetor rebuilt by my A&P/IA (replaced all gaskets using kit from Univair). Installed new airbox.
She wouldnt start. Would run on ether (I know stupid idea we dont do that anymore) but only until the ether quit. Would run at full throttle on ether no ignition issues just fuel delivery problems.
So we rebuilt carburetor again. No change. There was some dirt in it that wasnt there after the last rebuild. No change. After 50 cranks, I got it to sputter once, that is it.
Checked timing. Checked all spark plugs (literally took them out and confirmed spark). Replaced all outer and inner intake seals. Replaced intake gaskets. No change. I also removed the quick drain as it was leaking, and a rather clean pile of dirt fell out. I cleaned the drain and quick drain mount and reattached.
Installed primer. With 3 pumps (in 45 deg weather), she would start and run albeit somewhat poorly. While tied down, she would run pretty good and then start belching black smoke and RPM would start dropping. Pumping carb ice would resurrect. I then would taxi it and the rpm would hunt all over the place and the engine would quit when I was making 90 degree taxiing turns with any small bit of speed. Couldnt bring rpm under 1000 or she would quit. I could get up to rpm and she would fly 10 feet above the ground (before I pulled back NO WAY I was going up with it acting like this).
We figured the carburetor was hosed, so replaced needles with Fresno Air Parts steel needle kit and tried to get in some of the orifices better to clean it. Also soaked carb again in more cleaner (A&P confessed to having inadequate tool to get in there properly to ensure certain parts were clean). At this point, the engine required the primer to stay open (cracked) for the engine to run. This meant that the engine is sucking needed fuel via the primer system to stay alive still too much fuel as it belched some black smoke.
So I had the carburetor rebuilt by a highly recommended Ray Stillwell in SC. He advised the float was leaking and replaced that, the inlet metering jet and the idle jet something. Put it on the airplane. NO CHANGE. Still needed primer to run.
I had been putting 2 3 gallons in the tank for all this testing, so I added it to get to 6 gallons. No primer needed! So I tried the good old run-up to full throttle. It would get to 2400 (46 deg prop installed) for 2-5 seconds and then the engine cut out. I could save it from quitting by taking the throttle and going back to idle. Further testing determined that whenever I was above 1800 rpm and hit bumps, lifted the tail or did intentional S turns, she would cut out.
So I suspected a dirt problem. Replaced fuel strainer as it was dirty. In the process, had to remove quick drain. Another pile of clean dirt fell out. No change.
I suspected vapor lock as I had a mildly unacceptable kink in the copper line (even though I could drain fuel at 30GPH through carb hose into a gas can). Installed Univair stainless steel line. No change.
I suspected dirt still (at the behest of a suggestion). Removed quick drain again to see if another pile materialized. None. I used a broomstick and a scouring pad to buff the tank down to aluminum shininess turning some adhered sediment into dust. Vacuumed with shop vac. Rinsed with fuel through a napkin. Napkin was dusty no particles. Removed gascolator screen and rinsed some very small particles off. Then replaced fuel line from gasc to carb just in case.
Ran engine. Basically same problem. Engine cuts out after a few sec at full throttle. Runs all day sitting still at 1800 rpm.
Read in Cub Club about necking on fuel cap (ie, cap works but you have the same situation I do despite having replaced the entire fuel system) but the air vent is reduced. Removed cap and tried run up while taxiing. No change.
Now that fuel level is down a bit from 6 gallons, she is starting to skip and run worse.
Called my carb guy (who now has some medical issues and cant do further work). He supposes that the float might need to be adjusted again though its a low confidence assumption.
I have gotten advice that there are occasions when a carburetor can be rebuilt 3 to 4 times and the engine will just not run right and a new carburetor fixes the problem. I am not so sure I want to take this rather expensive step. Here are some facts that I am stuck with:
1. There was dirt in the carburetor each time the A&P had rebuilt it. There was dirt in the tank.
2. I have run fuel in the J-3 tank, drained into a gas can and put it in my PA-11 (O-200 with Marvel carb) and flown just fine. Repeatedly. So if there is evil Satanic dust clogging my carburetor, it doesnt do that to the other airplane.
3. I have 30GPH flow rate through the carb hose into a tank.
4. There is no dirt in the tank now.
The only thing I can think to do at this point is drain the fuel, check the tank thoroughly and scrub the most minor of remaining imperfections, vacuum, rinse and confirm with a napkin filter remaining white as snow and also remove the carb, flush it and put the whole thing back together again though my gut says nothing will change. I am not in the mood to gamble on a new carburetor and I also want a working airplane too!
My grandfather told me many stories of shockingly dirty fuel tanks and no issues flying, so I dont know what to say.
Any help is appreciated!
