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nzjetboating.com Forums => Tech Library => Topic started by: lobsterman44 on October 14, 2015, 00:52:32 AM

Title: loss of speed
Post by: lobsterman44 on October 14, 2015, 00:52:32 AM
I have a 36'leblanc with a qsc 8.3 cummins 490 hp on a hamilton 292 speed is down  to half rpms are up changed out impellar and wear ring ,cutless bearing,same thing.
checked aftercooler, turbo,transmission,filters all good.
what else on the jet could be making this happen?
Title: Re: loss of speed
Post by: Jeff B on October 14, 2015, 06:14:15 AM
Obstruction/turbulence in grill?
Sucking air into unit?
Hull overloaded?
Hull obstructions?
Partially in neutral/reverse?
Title: Re: loss of speed
Post by: Matthewf/Norbert/TuiDog on October 14, 2015, 16:25:30 PM
 Mech seal leaking air into unit
Something in grill
Impeller OD worn
Title: Re: loss of speed
Post by: kym on October 14, 2015, 16:36:56 PM
ensure inspection hatch is tight[ check oring and grease ] , mechanical seal broken, ceramic face  damaged water will leak into boat at rest [ will draw air through the inpection hatch, broken mechanical seal and will cause cavitation , intake grill not installed correctly,protuding below hull, large diameter oring around Tailpipe Spigot not installed and allowing air to be drawn between intake and tailpipe housing , has the impeller been changed or rebuilt or pitch changed, or accidently been dropped and damaged the blade  . rgs
Title: Re: loss of speed
Post by: Matthewf/Norbert/TuiDog on October 14, 2015, 20:27:48 PM
Welcome back kym : )

All knowing advice, kym is "the" man in the know for this issue
Title: Re: loss of speed
Post by: mohawk on October 14, 2015, 20:39:10 PM
Welcome back kym : )

All knowing advice, kym is "the" man in the know for this issue
Agree Matt  b> . I was worried all the little boats might have scared him off .
Title: Re: loss of speed
Post by: mohawk on October 14, 2015, 20:40:58 PM
Reverse bucket might be hanging abit low  or something disturbing flow under the hull .