Engine stumble at High RPM

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   On the lake today trying out a spare prop I’ve had for a while.  Trying to find top speed/rpm. It’s a older 3 blade OJ 14 x 16. Plus the 422 was singing so I decided to give it a try. 

Flat lake, 5000’ elevation.  I’m running the RPMs up and up.  When I get to about 5700, it stumbles and I back off the throttle.  It felt like an electronic cut out only because it was quick and sharp.  Either the stern came up a bit or the nose dropped slightly. 48 mph on the GPS. I just confirmed the tach reading with a cheap laser. 

Any ideas?  I always thought the end of the power band would just stop accelerating.  Was it a prop issue? 
It was pretty rough running.  
I’m going to put the 422 back on tomorrow and see what the numbers are. 

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AlfaDon Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: September-18-2011 Location: San Leandro, Ca Status: Offline Points: 407	Post Options Post Reply Quote AlfaDon Report Post Thanks(0) Quote Reply Topic: Engine stumble at High RPM Posted: September-18-2020 at 1:38am
	On the lake today trying out a spare prop I’ve had for a while. Trying to find top speed/rpm. It’s a older 3 blade OJ 14 x 16. Plus the 422 was singing so I decided to give it a try. Flat lake, 5000’ elevation. I’m running the RPMs up and up. When I get to about 5700, it stumbles and I back off the throttle. It felt like an electronic cut out only because it was quick and sharp. Either the stern came up a bit or the nose dropped slightly. 48 mph on the GPS. I just confirmed the tach reading with a cheap laser. Any ideas? I always thought the end of the power band would just stop accelerating. Was it a prop issue? It was pretty rough running. I’m going to put the 422 back on tomorrow and see what the numbers are.

GottaSki Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: April-21-2005 Location: NE CT Status: Offline Points: 3363	Post Options Post Reply Quote GottaSki Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 5:53am
	5700, it's Valve float likely
	"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11118	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 6:56am
	Maybe a little bit of info on the engine and what's inside it and bolted onto it would be helpful

AlfaDon Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: September-18-2011 Location: San Leandro, Ca Status: Offline Points: 407	Post Options Post Reply Quote AlfaDon Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 10:39am
	Thanks. I should add this to my diary Stock crank and rods. New pistons, Ported Aluminum heads w/ 2.02/160 valves running 10.5/1 compression, Hyd roller cam and lifters .550 lift, about 230 duration both I & E. New Comp springs to match. Edelbrock Performer Intake manifold 650 CFM Quickfuel Carb, DUI Dizzy

TRBenj Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-29-2005 Location: NWCT Status: Online Points: 21186	Post Options Post Reply Quote TRBenj Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 11:02am
	5700rpm and 48mph with that prop don’t make any sense... some of your numbers are wrong or your prop should’ve been retired a long time ago.

AlfaDon Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: September-18-2011 Location: San Leandro, Ca Status: Offline Points: 407	Post Options Post Reply Quote AlfaDon Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 11:11am
	Yep. It’s a prop I got cheap as a backup. It’s officially been determined that it’s junk. I now have a Nibral candle holder or wall ornament.

GottaSki Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: April-21-2005 Location: NE CT Status: Offline Points: 3363	Post Options Post Reply Quote GottaSki Report Post Thanks(0) Quote Reply Posted: September-18-2020 at 11:21am
	heh, hot motor..forgot that
	"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole

Engine stumble at High RPM

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