Mid range burble
 

BME 102 engine has good idle and ripping 26X10 prop at full throttle, when first started it has to warm up a bit before it will take throttle so I think low end is lean enough. The engine still has a mid-range burble that that I would like to reduce, I may be able to go a little bit leaner on the high end needle but I don't think very much leaner, wondering if there is anything else I can do to reduce the burble.

Have you had that engine a long time? I ask to base current performance to the past. Has the engine always had the same burble? Have you always run similar sized props? What kind of RPM does it turn the 26 -10? My guess is quite fast if it is ripping. A 26 inch prop is small by 100 twin standards.The fix (or reduction of the problem) might be had just by going to a slightly larger prop to increase the prop load. The carb might be an issue and a change or rebuild might be in order. Playing with the pop off pressure might help but at the expense of time spent that may not pay off with any improvements. Lastly, that might just be a normal characteristic of that particular engine and exhaust system.

Keep in mind that burble is just the engine running a bit rich at a particular throttle setting with a given load. Usually when the engine is burbling in level flight, just raising the nose will reduce the burbling w/o touching the throttle. A larger prop size has the same effect.

Yes the engine has always had a burble but it has not been flown long and I rebuilt the carb before flying the plane as it sat for quite a while before it was recently started for the first time. I am going to go to a larger prop in fact I just ordered one a couple of days ago, since the engine is just broken in I wanted to use the 26x10 to keep the load down for break in as recommended. I am not new to large gas engines but this one seems to run a bit richer in the mid-range than some others.

I bet the larger prop load will help quite a bit! Let us know how it works out.

If the big prop does not help....I have another Idea.

captinjohn, you have my curiosity up wonder what you have in mind?

Also how much prop is normally used on 100 size engines, I thought 27x10

I cured that mid range being too rich by cutting the "moon" on the throttle plate a few thousands larger. If you cut too much out....the engine will continues to run with throttle closed. Best to research it to see how it is done. All it take is a slight touch....

Yes I have heard of that and will research it, also prop size you think is "normal' for 100 size engine?

On a DLE 30, the mid-range burble was lessened by gapping the plug to 25 thousandths. Might be worth a try.

Update on my Burble reduction progress, went to a larger prop and leaned the high end a little bit, this made the situation measurably better, will not make anymore changes till the engine is completely broken-in, but things are
headed in the right direction.

WRK That sounds good. Let us know more later Thanks