CAPT John

My Feedback: (15)

I'm new to gas engines and am out of airspeed, altitude, and ideas with my Fox 3.2 engine. The engine is new with about 3 gallons of gas run through it. My problem is even with the throttle fully closed I cannot get the engine to idle below about 2300 RPM and once it heats up, it won’t idle below about 4000 rpm. The engine idled well for the first 1 ½ gallons of gas before the problem started. I have reset the needles to 1 ½ turns from closed and I have tried increasingly richening the low end until the needle is up to 4 turns out and I can’t detect a significant change in the idle or transition. The engine has a good transition and WOT is about 5900 rpm with a 22 X 10 Xoar prop. (The high end needle is leaned to about ¾ of a turn from closed to get the top end set).

When the engine is cold it seems to do better, although it still cannot be shut off by closing the throttle (thank goodness for the ignition kill switch). With the idle rpm increasing as the engine heats up, I thought the high end might be too lean but it is set to slightly rich of max rpm. I have gone through the fuel system looking for an air leak, but can find nothing.

Thanks for any help you might offer.
John

Carlos G

Hi ONF,

Just guessing I would say you have an air leak between the carburetor and the rest of the engine. You need to look for leaks around the carb and its mounting and or the mounting or insulation block and cylinder. Failing to find any leaks there, then you need to check the rest of the engine for leaks at seals, seams, and gasket areas. Also check for loose attachment screws or pressure taps.

Good luck and I hope this helps

Carlos G.

Bass1

Check the carb butterfly and make sure it is still round and not loose. I've seen the little screw that secures the butterfly to the shaft that's supposed to be swagged so it can't back out in fact does loosen and back out a bit. Then the butterfly bangs around inside the carb throat and becomes distorted and doesn't seal/seat properly causing a big air leak. Happened to me with a Brison 3.2 which is similar to your engine. Thank goodness I had an alternate transmitter activated ignition kill switch as it happened in the air and the engine was turning at about 3000rpm with the throttle pulled all the way back. Took me awhile to figure that one out.

STUKA BARRY

Starting fluid is great for finding leaks.

earlwb

It sure sounds like there is a air leak there someplace. The base of the carb where the carb bolts onto the engine is likely the culprit. If you remove the carb you should replace the gasket, just in case. Is there a idle speed or stop screw on your engine? You might check to see if it moved on you or not.

You can see the idle stop screw in this pic, it is used to adjust the idle speed for the engine.

STUKA BARRY

If the idle stop screw is still installed, get rid of it and use the servo throttle trim to adjust your idle and engine cut off.

CAPT John

My Feedback: (15)

Thanks everyone for the great suggestions. I had removed the idle screw, so that's not the problem. I'll check the butterfly valve and screw. I had removed the carb for a re-build, so maybe I pinched the gasket. I'll try the starting fluid technique to see if I can find the air leak. Thanks again for the help. I'll post the results.

All Day Dan

My Feedback: (5)

Get in touch with Chris at Fox (479)646-1656. Dan.

CAPT John

My Feedback: (15)

I’m back for more help. I still cannot get my Fox 3.2 engine to idle below 4000 rpm. I found that the carb butterfly was binding and not closing completely, so I thought that was the problem with the idle not going below 3500 rpm. The bad news is that I broke the butterfly assembly while trying to fix the problem so I ordered a new carb nd gaskets from Fox Mfg. I installed the new carb and gaskets and went through the fuel lines and could not find an apparent problem. I reset the high and low needles to the 1 1/8 turns setting Chris from Fox recommended.

The good news is I can now shut down the engine with the throttle. The bad news is the engine now won’t idle below about 4000 rpm without dying. As I bring the throttle down near closed, the rpm gets unsteady and seems to gradually load up and die.

At one point I had a good transition and top end, but nothing I did would get the idle below 3700 rpm before the engine died. The mid range rpm also seemed high at around about 5500 rpm with a WOT peak at about 6300 rpm (with a 22 X 8 prop).

I changed out the spark plug – no help. The engine is also hard to start, requires choking each time, and will only start with the throttle open more than half.

I can’t find an air leak. My best guess is there’s a fuel flow problem, but I can’t find the source. I’m out of ideas, so I will probably send the engine back to Fox and ask Chris to check it out.

I would appreciate any ideas or recommendations you might offer.

All Day Dan

My Feedback: (5)

My recommendation is to copy this post, as you have written it, and send it with your engine to Chris at Fox. He has done wonders with all the engines I have sent him. Dan.

CAPT John

My Feedback: (15)

I spoke with Chris at Fox and will be sending him the engine to check it out. If it runs good on his bench, I'll know the problem is with my fuel system.

Tony Hallo

It's hard to image the fuel system minus the carb causing the engine to run at 4000 rpm and not idle below 4000 rpm. AIr leak, missing gasket, loose case, crack carb insulator is where I would look.

Carlos G

Hi ONF

One other item to check is to verify that the throttle plate isn't positioned incorrectly. It could be flipped around 180 degrees so that the edge of the throttle plate isnt passing by the idle fuel ports in the throat of the carburetor. I ve seen where someone has worked on their engine and inadvertantly flipped the throttle plate over to get a better angle for the throttle servo linkage to work. This usually happens during the build of a new plane. If the edge of the throttle plate doesn't pass the idle fuel ports the engine will not idle at all.

Hope this helps

Carlos G.

overbuild

I would suggest you ck inside the fuel tank the feed tube and clunk. Too stiff tygon can cause clunk to bind and not float free in tank. Also fuel line to carb. if routed in a tight bend may restrict fuel flow. I had the problem of no idle and hard starting it turned out to be the tygon fuel line I was useing had too thin a outer wall and had collapsed at a tight bend in line to carb. I have found that tygon is made with the  same id but you will find the outer wall to be thinner and less collapse resistance on some tubeing.

CAPT John

My Feedback: (15)

Thanks everyone. I have sent the engine to Chris at Fox to determine if the problem is in the engine/carb. I had checked the fuel lines inside the tank, but while the engine is being checked out I'll pull the tank and check the lines from the clunk to the carb again. I'll post the results.
Thanks again.
John

CAPT John

My Feedback: (15)

My engine problem has been fixed and as they say, "we have met the enemy and he is us." The problem began as a loose/binding carb butterfly that was not allowing the throttle to close enough to get a low idle. While I was attempting to repair the butterfly, I broke the bar. No problem, I had a spare and replaced it. The bad news is I rotated the replacement butterfly 180 degrees when I installed it. My first clue should have been the need to reverse the throttle travel on my transmitter to get the correct direction. This basically made the low end inoperative and explains why I could not throttle below about 4,000 rpm without the engine dying.

I didn't figure out my self inflicted wound until I sent the engine back to Fox for Chris to check it out. Of course the engine ran great when Chris put it on the bench. He gave it a thorough check up and tweak and sent it back to me the same day. As I was re-connecting the throttle I realized my dumb *** mistake. The engine now runs great. The silver lining of this frustrating user error is that I learned a lot along the way.

I appreciate everyone's help and advice.

All Day Dan

My Feedback: (5)

Thanks for posting the cause of your problem. Let me assure you that you are not alone. Dan.