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BF135 surge problem

flaterps

New member
Gents,

My BF135 is giving me problems and I can't find anyone having a similar issue on this forum. She starts and idles great. Once I push up the throttles all fun begins. The engine will surge slightly as its accelerating. Once I get it to WOT it runs ok for 20 seconds or so and then the rpm will cut back to 4000 rpm. One one test run she cut back to 2500 and even after multiple restarts wouldn't correct.

What at kind of rpm should I expect out of this engine (ballpark)? I have had it for about a year now and haven't seen better than 5200.

thanks in advance for any help you guys can provide.

blair
 
You have a number of high and low pressure fuel filters, water separator and a vapour separator (and possible racor) to check and clean to ensure fuel delivery is good. I have seen a surging issue before that only presents itself at certain revs below WOT that was caused by a loose earth wire that would cause intermittent disconnections caused by vibration at lower revs. Check all wires for good connection. Check your coils for good/equal resistances, sometimes coils only present issues at higher revs so a swap out with a known good coil can help diagnose this. Make sure your battery charging circuit is functioning correctly and your battery is charged and in good condition. Your WOT specification is between 5000 and 6000 so you are within spec but on the lower side of it, when your engine is running correctly you can drop a few inches of pitch on your prop (a new prop) and it will increase your WOT rpm and improve holeshot but otherwise not really of great concern.
 
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