Small Fox "Burp?" / Cold temp?

Stuka Stunt Main Forum · 7 of 7 known posts recovered

captcurt · Nov 27, 2000 04:49 PM

I had the opportunity to fly the Akromaster and Fox .15 aluminum/ Slant plug over the weekend. The temperature was about 40 deg. I am still running 10% /25%castor fuel. The engine was a bit hard starting but seemed to run well after it was first started.

I did notice however, a new behavior--a very pronounced cut-out during hard pull-ups. I tried several things to make it quit but it never went away. THis is a very brief shut-off of the engine. Not even a sputter--perhaps .5-.75 second--then it just keeps on like nothing was wrong.

Am I seeing the famous Fox "Burp"? Is my seeing this more in the lower temperature day consistent for this phenonomena?

Would a hotter plug and or 15% fuel help this out any?

I think its time to start using the 15% fuel just to get the thing running. If it was any colder, I'm not sure It would have gone.

Will a heat gun help any? to preheat the engine?

Just wonderin'

Curt

Kelvin · Nov 27, 2000 07:49 PM

#1 source

Sounds like it is going lean. The burp, as I understand it, is mostly found in the Stunt 35, and on outside corners. One thought about the cold weather is that the density of the air is higher at low temps (lower density altitude for you full size plane fliers). Perhaps it needs a touch more fuel to balance the denser air.

Kelvin · Nov 27, 2000 07:52 PM

#2 source

I would add that the smaller motors tend to like more nitro because they need the added heat to keep running. Witness Cox Tee-Dees that run fine on 35% but will hardly burp on 10%. I would try the 15% as well.

Currell · Nov 29, 2000 02:12 AM

#3 source

Up here in Michigan, we need at least 15% nitro in a .15 during typical Fall weather. (By the way, I understand that there is something called the "sun"; do you know anything about it)?
Also, use the hottest short plug you can find. A Fox should work OK.

This may help, but you may not completely eliminate the burp.

Currell

mrwhizkers · Nov 29, 2000 02:32 AM

#4 source

Why would a short plug be better than a long plug? Also, I've never been able to get a Fox plug to work in warm weather so how can you expect it to work in cold weather? 15% fuel sounds good though. We've been having good luck with Fox 15/12/12.

Currell · Nov 30, 2000 02:07 AM

#5 source

Because the engine is designed around the short plug. Certain longer ones, especially the RC types, might create an interference. But check this first, because you may be able to get away with a long in some cases. I have done this with more than one plug wsher, for example, on smaller engines.

I am at a complete loss re your Fox plug comment. For me, they have worked well in all sorts of weather. Could you be more specific? What kind of engine, fuel, etc?

Currell

gcb · Nov 30, 2000 07:22 AM

#6 source

LAST EDITED ON Nov-30-00 AT 12:50 PM (EST)

Try several types of hot plugs until you get one that works best with your conditions. Changing heat range of plugs and nitro content of fuels is equivalent to adjusting the timing on a spark engine. Duke Fox used to recommend Missile Mist fuel for the Fox .15.
If you remove the head on your Fox .15 you will see that a short plug should be used because a long plug protrudes into the combustion chamber. Heads are designed to have the plug flush with the surface. Generally, a .15 and smaller should use a short plug.
There are always exceptions. I find that my Norvel .15's can use long or short plugs. I generally use short ones.
Good luck,
George