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Articles / Standup / Pump Nozzles - To BORE or NOT to BORE

Pump Nozzles - To BORE or NOT to BORE

17 September 2018
Article Pump Nozzles - To BORE or NOT to BORE
The question was asked "I googled and found I should bore my nozzle on my 550 what do you think?" OK -- first hint -- " I googled it ??? uhhh what does Google know about 550 jet skis ( that have not been made for over 20 years ??? ) - next hint - he is just going to bore his nozzle - no word about any other mods - if any - just bore that damn nozzle out - . SO - realizing that we have a newbie here ( at least to JS skis ) I said - no - don't do that - because - his bilge pump won't work anymore cause google will not tell him to replace the ridge in the nozzle - and - he WILL lose considerable top end with the STOCK prop and likely lose bottom end also - with the STOCK prop. Got it guys ???

A whole slew of people responded with - " I bored mine and it works and I love it " - sure you do - cause you do NOT run a STOCK prop.  :) :) :)

IF - you have a 440 pump with a stainless overlapping prop - that prop and pump will NEVER perform to its potential without a bored nozzle. A bulkhead support brace is an absolute must do here. The nozzle should end up paper thin and the hole for the bilge pump should have an 1/8th inch copper pipe epoxied into the hole so the bilge works again. You WILL love it. Do NOT bore the nozzle with a stock alloy - non-overlapping prop.
IF you have a 550 pump - and you are looking for all around performance - with THIS pump - AND - you have a stainless impeller installed - boring the nozzle will help low end performance and cut top end speed - almost in equal amounts - in MOST applications. Some guys - running 650 motors and such run entirely different props and pumps because of the torque of a 650 motor ( that a 550 PP will NEVER have ) and - some ( not many ) have an aftermarket reed hooked up to a 550 pump and they NEED a bored nozzle desperately. Apples and apples guys - not - apples and oranges :) Finally - if you have a stock 550 prop - do NOT bore the nozzle - unless you do not care about top end at all.

The single most important part of Jet Ski "tuning" is getting the pump and the motor to work as one. Having a motor that comes onto the pipe at 5000 RPM's and a pump that will not allow 5000 RPM's no matter how much HP you have is not gonna be a good thing. Having a pump that allows the motor to come onto the pipe at 3000 RPM's and a motor that comes onto the pipe at 3000 RPM's is a total success story. Generally speaking - note the word “generally” here boys and girls - a 550 pump will not allow a piston port motor to come onto the pipe until that ski has travelled a long ways. Where’as a 440 pump ( generally ) will allow the motor to come onto the pipe almost instantly. Allowing a 2 stroke motor to reach it's "working" RPM's is half the battle - getting the pump to USE those RPM's and NOT waste them is the other half.

There is no question that the 440 pump is superior when used with a piston port motor - BUT - the design flaw of pushing the boat through the water with the bulkhead - when the bulkhead is SO weak - is tough to get by for most rec riders.

SO - spend your time - equally - "tuning" the pump along with tuning the motor - get them to like each other and YOU will like it too :)

By Cliff Jones


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