FX91 mixture problem
01-25-2004 | 01:23 PM
#1
FX91 mixture problem
Hi Bax,
I have just broken in a new FX91. I am running stock muffler, 13x6 prop, std. fuel tubing, OS#8 glow plug, 15% nitro/18% oil.
From half throttle to full throttle the engine runs well. The engine also idles well with good transition to full throttle. However, loud knocking is observed in low to half-throttle range. Based on what you advised I thought this might be normal. However, while in level flight at 1/4 throttle the engine itermittently goes from running smooth with a good smoke trail to knocking/no power with no smoke. This may cycyle 4 or 5 times in just 1 pass of the field. I have tried to simulate on the ground and have had limited success. My experiments on the ground suggest the low speed mixture might be too rich. During this knocking phase if I pinch the fuel line the engine seems to gain rpm and recover from the knocking phase. However, I am concerned I might already be too lean. My mid-range to full and my idle is great. Zero hesitation on the low end with great idle. Does this sound like a rich running engine? Does this sound consistent with an engine needing a pump? Any information you can provide would be really helpful.
Thank you
Matt
I have just broken in a new FX91. I am running stock muffler, 13x6 prop, std. fuel tubing, OS#8 glow plug, 15% nitro/18% oil.
From half throttle to full throttle the engine runs well. The engine also idles well with good transition to full throttle. However, loud knocking is observed in low to half-throttle range. Based on what you advised I thought this might be normal. However, while in level flight at 1/4 throttle the engine itermittently goes from running smooth with a good smoke trail to knocking/no power with no smoke. This may cycyle 4 or 5 times in just 1 pass of the field. I have tried to simulate on the ground and have had limited success. My experiments on the ground suggest the low speed mixture might be too rich. During this knocking phase if I pinch the fuel line the engine seems to gain rpm and recover from the knocking phase. However, I am concerned I might already be too lean. My mid-range to full and my idle is great. Zero hesitation on the low end with great idle. Does this sound like a rich running engine? Does this sound consistent with an engine needing a pump? Any information you can provide would be really helpful.
Thank you
Matt
01-26-2004 | 10:48 AM
#2
My Feedback: (11)
RE: FX91 mixture problem
Some clatter is normal in larger engines. We've heard this on engines of all types .90 and larger. We've never found any evidence of internal damage on these, and have concluded it's an exhaust note, probably caused by imperfect firing at mid- to low-throttle settings.
If the high-speed needle and idle mixture are set correctly, you just have to let the midrange and low-midrange take care of themselves. If you have doubts, increase the idle RPM slightly and richen the idle mixture a hair. This should help richen the midrange a bit.
If the high-speed needle and idle mixture are set correctly, you just have to let the midrange and low-midrange take care of themselves. If you have doubts, increase the idle RPM slightly and richen the idle mixture a hair. This should help richen the midrange a bit.
