Mercury Jet Drive Pump Adjustments

[wildchildc1]

I have a 1988 115 Mercury outboard with a jet. I cannot find any manuals on the jetpump or much info on the maintenance and adjustments. Does anyone know where I can find a manual or information on its maintenance or impeller adjustments? Thank you

 

[CharlieB]

Re: Mercury Jet Drive Pump Adjustments

You'll need a set of long feeler guages.

The impeller clearance is generally set to .020 from the outer edge of the impeller to the replacable liner.

This is done by moving shims from one side of the impeller to the other, increasing shims behind the impeller close the clearance to the liner, moving shims from the backside to under the retaining nut increases clearance.

Watch WOT RPM, you can 'fine tune' impeller clearance to match engine performance/power output, increase clearance to raise WOT RPM, and decrease clearance to lower RPM.

Merc pumps are a carbon copy of (insert brain fade here)
I'll have to repost tomorrow from work with their name and number, you can order a parts and service manual identical to your pump.

 

[shawn00]

Re: Mercury Jet Drive Pump Adjustments

i have a 1997 regal jet boat it has a 4 cylender 130hp mercury the moter runs fine but its not fast as it shuold be it sounds like the inpeller is sliping????should go about 45-55 mph only does about 25-30 wide open i have called lots of places but no one around here will touch it.can any one tell me what mite be wrong with it

 

[mikesjet]

Re: Mercury Jet Drive Pump Adjustments

This will help you with some of the preventive maintenance of your jet. I have a merc 60/45 and just got done doing all of this to it. This file will show how to sharpen the leading edges of the impeller, this will make it more effecient.
Also, with your speed problem you have to realize that there is a 30% powerloss from powerhead to the jet because of the design of it.

All outboard jet motors have the same manufacturer of the jet itself that they are Outboard Jets.

Go to outboardjets.com and look for "IMPELLERSHARPENING pdf"

 

[shawn00]

Re: Mercury Jet Drive Pump Adjustments

thanks but the boat has a inboard motor....dont know if that make a diff.but i talked to a friend that has a jet boat and he said the inpeller mite need to be replaced but i looked at the inpller and it looks new?????i dont want to replace it if that wont fix it.is there any thing i can check that mite make a diff.

 

[CharlieB]

Re: Mercury Jet Drive Pump Adjustments

First ? that should be asked is what RPM are you running WOT?

Has it changed?

Gone up?

Or gone down?

As pump clearances wear engine RPM will rise due to the UN-loading of the motor due to increased pump slip.

If RPM has fallen the you need to start checking your motor, compression test, spark test, clean carbs, rebuild fuel pump.

 

[shawn00]

Re: Mercury Jet Drive Pump Adjustments

the rpms are up..dont sound like bogging down i replaced all spark plugs and checked carbs.it has lots of power just no top end speed from 0-25 very fast top seed about 30-35 this boat went 55+ at one time.but trim plate is lose.. does is it need to have some play or could that be a problem.that is the only thing i could fine wrong

 

[CharlieB]

Re: Mercury Jet Drive Pump Adjustments

Worn impeller and/or sleeve.

Need correct service manual to be sure of the shimming and factory clearance.

Inboard mounted OB with a jet are now of the snail shell design used on most Outboards, but more like the Berkley. Simple shaft with impeller inside a box containing a throat. They still have shims before and after the impeller, used to move the impeller forward or back to adjust the clearance.

Correct 'filing' of the leading edge will make a noticeable difference also, AFTER shimming.

Watch WOT RPM to 'fine tune' shimming.