Fox 4.2 runs erratic
 

I have a Fox 4.2 that runs very erratic since the day I bought it. Just a day ago though I found some posts about the DLE-30 running very erratic as well and it was due to the spark plug. From what it sounds like, I am having the same problem. The midrange will barely tune and the high end, when tune properly will not run very consistantly. The engine had tons of power but I just don't trust it at all. The spark plug that is in it is a NGK BPMR6F. Would anybody know of a better plug then this or a different plug that I can use? At this point I am going to try process of elimination. So, anything is up for grabs.

Chris

RE: Fox 4.2 runs erratic
 

That is the correct plug...The ignition could be faulty, try another...Be sure the carb diaphragms are good and in the correct order in the carb....

RE: Fox 4.2 runs erratic
 

Chris, Double check the position of the diaphragms and gaskets in the carburetor. There has been a mix up at Fox on occasion. Go to this website and enter your carb number. Make sure yours has been assembled right. When all else fails you can call Chris at Fox. 479-646-1656. Dan

http://wem.walbro.com/walbro/family2.asp

RE: Fox 4.2 runs erratic
 

I thought it was a bad ignition when I bought the engine initially. I actually sent the ignition in to find out it was the sensor for the ignition was never gapped at the factory and the prop hub was ripping the tip of it off. So, when I replaced the sensor I thought my problems would be over. It solved the issue of really bad running and constant dead sticks but now I cannot tune the midrange at all. If I leaned out the midrange at all it would give the characteristic that it was too lean and on throttling up it would cut. Dan, I never knew that there was a mix on occasion with the carbs. The number on the carb said WJ71, and right underneath it with the numbers 805. I am going to check that out and see if that could be the case.

RE: Fox 4.2 runs erratic
 

Guys, one other thing I just noticed while taking the carb apart. For like the 3rd or 4th time I have found crap in the carb screen. That would definitly contribute to my problems as well.

RE: Fox 4.2 runs erratic
 

dingo, the mix up was the location of item 29 , it should be against the cover, and item 62, it was distorted because the metering diaphragm assemby was too close to it. I have attached an image of a Walbro tool that shows that the meter lever postion should be 3/32 inch below the level of the body of the carb. Dan.
http://wem.walbro.com/walbro/product...um=WJ%2D71%2D1

RE: Fox 4.2 runs erratic
 

Dan, I just spoke to Fox and he turned and basically said that it is leading to the carb and not the engine. Just what I expected, because the engine has tones of power. I told charlie everything that the engine was doing and be began to think that the carb was assebled incorrectly like you were saying. I know somebody at the field that has been working with small engine carberators for around 35 years so I am going to allow him to look at it with you diagram in mind. Thanks for the help with that one. I am inexperianced with gas engines so I have no problem admitting it and I always have people willing to help at the field.

RE: Fox 4.2 runs erratic
 

Thanks for the thanks. Dan.

RE: Fox 4.2 runs erratic
 

I just had somebody look at the carb. They are all saying a combination of things, but all are leading to air leaks and the carb like usual. I cleaned out the fuel port of the diaphram and cleaned out the filter in the carb. I also found out something else; the plastic extention between the engine and the carb, if it is tightened too much it will actually buckle and let some air in. So I put a really fine layer of sealent around it to help reduce that problem. I was also told that the carb's metering valve may need to be opened a very very small amount to let more fuel in. Hence, why the engine must have a rich low end because its not getting enough fuel. Dan, you were saying something like that. How do I know how much to open it if I need to do this?

RE: Fox 4.2 runs erratic
 

Dingo, the position of the metering needle lever needs to be 3/32 of an inch below the body of the carb in accordance with that Walbro tool I sent you an image of. That assumes that the metering diaphragm assembly is in the correct position and that is against the cover and not the carb. Your best bet is to get a rebuild kit and change the four diaphragms and gaskets, metering needle and its lever. Don't tighten the four screws over the metering diaphragm because you can easily crush the gasket, moving the diaphragm closer to the lever, and distort the cover. That plastic isolator between the carb and engine can be cracked if the bolts are tightened too much. Dan