Fox .40 Again
 

Thanks to all that replied to my original message concerning how to make a Fox .40 run from idle to full rpm's. The address to the Fox website was particularly helpful. I used information from the web to try to make the engine perform properly; unfortunately, to no avail. Comments at the website lead me to conclude that the single-needle valve carburator also has problems. However, a re-engineered two-needle valve carburator by Fox may be in the works. I'll just be patient and wait for it to be released.

Again, thanks very much.

Louis A.

Fox .40 Again
 

Although it's been a while since we've ordered any, we have been able to obtain the new style TN carb. for the .40 by contacting Fox directly and asking for it. It is part #2600. It is the carb. for larger engines that is not yet available. Why they continue to supply the often troublesome EZ series with new .40 engines when the new carb. is available is another Fox marketing mystery.

Besides possible carburetor problems, there are other areas that can contribute to the problems you have been experiencing. In particular, the head button version and vacuum slot in the crankcase.

Assuming the engine is otherwise in good mechanical condition, there are three factors that determine the reliability and throttle response of the Fox .40. These are the head button version, the EZ series carburetor, and more recently, the addition of the vacuum slot in the crankcase. These problem areas can work in combination to cause you all kinds of grief. On earlier engines, with the MKX series TN carb., the problem was primarily the head button, although the carburetor usually got blamed. With the newer style head button however, the MKX carb. should work well enough to satisfy the needs of most flyers. The EZ series carb. , in our opinion, is not an improvement. The fixed "midrange" metering system has, to us, proven to be inconsistent from one carb. to the next, and with no provision for adjustment, does not always work well in all installations. The addition of the crankcase vacuum slot often compounds the problems. Earlier bearing equipped engines incorporated a spiral groove machined in the crankshaft just behind the front bearing. The purpose was to draw fuel away from the bearing to prevent leakage when the engine was running. Later, the spiral groove was deleted and instead a thin slot was machined inside the crankcase casting between the carb mount and front bearing. The intent was for the intake vacuum to draw the fuel away from the bearing. This may have been a cost saving measure, but unfortunately, in many cases, too much air is drawn in through the slot upsetting carburetor operation. Basically, it's an air leak. In some cases we have resorted to filling the vacuum slot with JB weld to obtain decent carburetor operation.

We would recommend sending the engine back to Fox for examination. If the head button needs updating, or some other mechanical problem is found, they will likely fix it for free. You could also request the new TN carb. be installed and the engine test run with this. Although they may charge you for the carb. is is not that expensive anyway, and really is preferable over the EZ series. Once it is in proper running form you will really enjoy the Fox .40. It is small, light, powerful and reliable. We only wish Fox would seriously address some of the small remaining problems so that more people could enjoy the full, and considerable, potential of this engine without the fuss.

Best regards from,
FliteLine Solutions
www3.telus.net/fliteline

Fox .40 Again
 

Louis, read the post below.

The Fox .40 BB (I prefer the lapped piston variety) is a WHOMPING engine. When they're running good...they're running GOOD! This is a superb engine...I just wish Fox would quit D_icking with carbs and move on.

MKX, TN, EZ.....gadzooks!

Spend the time to get it right....you won't be sorry.

Fox fan for life.

(currently have a little Fox .15BB in a plane....it's a sweetie...and strong!)