Forget push-up bras, keg cans, iPods and 52-inch flat screens…for my money, outboard jets have to be one of the best inventions of all time. I mean, anything that allows me to blaze 30 mph through 2-inch shallows is definitely on the short list of cool stuff to own.
But on the other hand, there are days when I want unbolt my outboard and use it as an anchor. Talk about an inefficient way to propel one’s self upriver! Outboard jets are about 30 percent less efficient than their prop-driven cousins…and that’s when the stinking thing is brand spankin’ new. After some good use, the output goes down even more.
Luckily, there are some things you can do to help make your outboard jet run like new again.
With an outboard jet, most of your bottom strikes are going to occur right on the grates on the underside of the shoe. Once good “thunk” on the bottom can bend several of your grates. And it’s pretty simple – the more bent up those things are, the more the motor has to suck to get water up inside. Luckily, it’s not to big of a job to tap out the two pins that hold the grates in place and then either replace them with new ones or pound them straight again.
Regardless of whether you straighten out the old grates or buy new ones, a cool trick is to sharpen the edges of each one. With a bench grinder, sharpen the leading edges of each one to a triangular point.
You’ll also loose plenty of power if your wear ring (sleeve) is worn or grooved. An outboard jet works best when the outside edges of the impeller blades are as close to the inside edge of the wear ring as possible without rubbing.
When you’ve got grooves in the sleeve, water gets sucked around the outside of the blades instead of over them and that will cost you a noticeable amount of horsepower.
Probably the best way to ensure that you maintain your highest level of propulsion is to purchase and install a new wear ring (about $50).
If you use your boat at all, you’re going to eventually suck up sand or gravel. Hard, rocky material running over the blades of your impeller will result in dings, divots and a general dulling of the leading edges.
Kinda like a dull steak knife, worm impeller blades have a tough time cutting through the water. And like seemingly everything else in this game, little imperfections can cause big decreases in performance.
With impellers costing several hundred bucks, you’re probably not going to be replacing them very often, so the next best thing is to sharpen up the blades. It’s a pretty simple affair, but it does take a little concentration.
Take a file to the bevel side of each blade and work inside out with light strokes. You don’t want to take too much material off or you will be ordering a new impeller. The real trick to this game is to take the same amount of metal off each blade. To do this, count your strokes with the file and use the same amount on each of the blades.
Jim genaw says
115 merchant 4 jet on 18 fish rite..excessive spray..can trim some.. Pain..
Jim genaw says
115 merc4 stroke on 18 fish rite..spray in excess..can trim most of it out but still a pain.
I just bought a 2020 blazer SS 17/52 with brand new 60/40 Merc 4 stroke. It runs real well, but I was wondering on trim while running the boat. I have buddies telling me to trim up slightly once planned out, but reading the owner’s manual says not to do this, because jet is not like running a prop, which makes sense considering it needs to be pumping lots of water through. With that being said, should you start and ride the whole time with the motor trimmed all the way down? Or maybe slightly trimmed up, but not past vertical.
Tyler, I generally run fully trimmed down…unless things get real skinny and then I may til her up a bit.
When your on plane wide open trim it up just a little and you will find the sweat spot with rom up a little and you can feel the boat speed up and if you go too high it will suck air . The seat spot will gain you 2-5 mph. Just have to play with it just like a prop, you will feel it break Lise and speed up . Choppy water you will have to keep down .
Daniel Douthitt says
This is a true statement for myself i bought a 25 factory jet and was haunted by people saying I won’t like it……. Going from a 2 stroke prop to efi 4 stroke jet I didn’t loose but 1 or 2 mph with speeds up to about 26mph!!!!!! With trim all the way down about 21mph (With just myself @185lbs.)and you can hear that sweet spot he’s speaking of and not to mention the fuel savings and able to troll without fowling plugs. It’s a 1448M side console Lowe I absolutely love it.
Good info here JD. I’m about ready for a new liner. With regard to trim, I’ve been running a jet now for about 11 years. I start trimmed all the way down to get on plane and trim up once I’m at speed. Makes a huge difference on my sled hull. You’ll find your boat’s sweet spot. If you trim too high your engine will let you know. You’ll hear the rpms increase and your speed will decrease. Kind of like what happens when a clutch slips.
Yeah, Keith, jets certainly don’t like cavitation! Like you said, if your motor is revving up high you need to trim in back down.
Annie Kennedy says
What would be some reasons we can’t get our 16’ aluminium boat on plane with a 90 horse Yamaha outboard jet?
Well, could be that your impeller blades are worn down. Could also be that your wear ring has lots of grooves in it and needs to be shimmed or replaced. Also, look at your intake grates…are they straight or bent?
David Cummings says
My boat mechanic took out my sled with an extra tank of fuel he could not get it to plane. He used his tank and the boat planned right out for him. He replaced the old fuel line in my sled and the problem was solved. I felt so awesome to take out the sled last weekend and get the boat to plane. check your hose for separation, fuel filter plupging up.
THOMAS J ELLIOTT says
I tested a boat that would barley get on plane. The jet shoe was on backwards. It would run and do about 14 mph. Turned the shoe around 180 and now do 28mph
Gareth Smith says
Looking at a 2015 Lowe with a 2015 115/80 mercury jet drive that has 200 hours. Is tat a lot of hours for this engine and what are some things to look out for?
That is very low for hours. Should be about brand new! Take a look at the lower end of the pump housing (“the shoe”) and see if it’s been beat up by rocks. Also look at the grates on the underside of the pump…bent or straight? Then, peer up inside and check out the impeller. If any of this stuff is really trashed you can bet the seller was rough on his equipment.
Sutton Turner says
I never knew that with an outboard jet, most of your bottom strikes are going to occur right on the grates on the underside of the shoe. We are going out on our boat this weekend. Thanks for the tips to improve outboard jet performance.
Des Finlay says
What RPM should a 115etecget at full throttle should get Mine is new,but it only gets 4,800RPM full throttle is there a logical reason for this?thanks
Oh wow. Not sure that’s above my pay grade. ?
Kirk Bonanny says
You’re only achieving 4800 peak RPM with a jet drive? This is quite rare indeed, but will give you likely places to start looking.
IF this was an issue on a propeller equipped outboard, changing the prop to one with less pitch and possibly diameter would be the solution. With a jet outboard, there is nothing preventing the engine from achieving peak RPM UNLESS the bearings in the jet pump are totally FUBAR’d….at which point I’d like to think the owner of the boat would have been hearing a lot of noise LONG BEFORE a bearing can become this bad!
WHAT YOU NEED: spark plug socket, extension, ratchet…. can of fogging oil, preferably the factory SERVICE & PARTS manual.
OPTIONAL: a “jumper” wire or hand held solenoid switch to engage the starter motor while you’re at the back of the boat to make this a one man job.
OPTIONAL: brand new properly gapped OE spark plugs, tube of dielectric grease
The 1st test should be the base test on ANY engine, which is compression. I’d run the first test in all cylinders “dry”, and then spray 3-4 seconds of a quality fogging oil into each cylinder, through the spark plug hole, and run the compression test again. This is a “wet” compression test. Do make certain to disable the ignition by pulling your lanyard off of your gear shift lever as this will cut power to the ignition coils. Failure to disabled the ignition “CAN” result in burnt coils. You also want to make sure the throttle is wide open in order to get the most accurate readings possible. Once you have a compression gauge inserted into cylinder #1, have someone (or do yourself) crank the outboard so that you can hear 5 pulses. On a 4 stroke, these are easily heard while on a a stroke this can be a little tricky, but if you’re not sure, add a pulse or two to your cranking time. Write down the reading from your compression gauge for cyl #1, cyl #2 etc etc, with the 1st set of numbers being from the “dry” compression test and the second set from running a “wet” compression test. The reason to run a dry & a wet test is to get an idea of how much piston ring wear there may be inside each cylinder. If your wet readings are more than 4 to 8% higher than the dry numbers, that’s indicative of ring wear or scored cylinder walls. Your cylinder should be within 5-8 PSI of each other as well. IF you have 3 cylinders reading 145 psi compression and 1 cylinder only reading 130, you have imminent failure approaching and in the interest of not making a bad situation worse you don’t want to be running this engine until the issue causing the lower than normal compression on a cylinder is resolved, which requires “major surgery”. Running it like this can lead to a destroyed block and/or other issues that are only going to radically add to the cost of repair.
IF your compression numbers are where they’re supposed to be ***EVERY ENGINE WILL HAVE MANUFACTURER’S SPECIFICATIONS*** and within a few PSI of each other, the next are to look at will be fuel. Now, unless you’re a highly trained technician, you have the OEM factory service & parts manual, proper tools & training etc etc you’re likely not going to be able to handle fueling or ignition issues. Both require an intimate understanding of each system, how it works, what could have failed etc etc etc.
Now, being that “Mr. ETHANOL” has been dumped into our laps by overzealous lobbyists, eco-nuts and crooked politicians (as they’re bought & paid for) most issues I’ve seen in the past decade plus are directly related to a fueling issue. This is CRITICAL on both 2 & 4 stroke engines, but more so on a 2 stroke due to the fact that a lean mixture not only causes increased cylinder temperatures (leads directly to melted pistons!) it also means your lean on the oil mixture as well unless you have oil injection separate from the fuel. IF you pre mix your gasoline, a lean running cylinder(s) is quite possibly lead to rod & crankshaft bearing damage, which can lead to crankshaft damage etc etc. Ethanol gasoline should NEVER be used in your 2 stroke/cycle outboard, PERIOD! I’d keep it away from 4 stroke outboards also simply due to the super corrosive nature of this fuel and the fact that all alcohol is HYGROSCOPIC, meaning it literally absorbs moisture/water out of the atmosphere, and a boat lives on water. It is a mix made in hell!
The majority of issues I’ve dealt with required carburetor rebuilds, which is disassembling each carburetor, allowing all parts to soak in a carburetor acid bucket for at least 45 minutes, then washing everything off to neutralize the acid, blow out every orifice with air pressure as well as using tiny carburetor cleaning rods to clean every single jet, fixed orifice in the carb body etc etc. & then reassembling the carburetors with new needle & seats, gaskets etc (at the bare minimum) and reinstalling them onto the outboard. BEFORE trying to run the outboard, it is highly advisable to get rid of the old gas in the tank, making certain the tank is CLEAN inside, flushing or outright replacing the fuel hose & primer bulb and then running the outboard.
On an EFI (fuel injected) outboard, there’s nothing much you can do without training & equipment. DO NOT attempt to clean injectors if you don’t know exactly what you’re doing as you’re likely going to cause a great deal more problems if you don’t know exactly what you’re doing.
The next area is ignition, and again, outside of replacing spark plugs with whatever the OEM (original equipment manufacturer) recommends, then inspecting the spark plug wires/testing the resistance with an Ohmmeter….there is not much the average person can possibly do.
The above are the 1st three items to check, in order. Always start with compression unless a visual inspection reveals something plain as day standing out on the power head.
Jd , on my 2003 Mercury 60/40 factory jet I was looking at the nut on the end the propeller shaft and it seems to be tight but I noticed a little washer seem to be a little bit loose? Does this make sense what do I need to do
Would there be any advantage to having the liner anodized?
Hmmm…never thought of that but I don’t think so. It’s still going to groove out.
I have a 1448 tracker with a efi 25 tilt trim have hard time getting it on plane it misses when under a hard load like the prop is slipping but sometimes it don’t and suggestions
Hmm, so this is a prop not a jet, right? How does the prop look? Beat up? Dented? Bent? If not, it may be the wrong pitch for that boat.
Lynda White says
Hi I love your tips this help me to gain more knowledge about fishing as a newbie.
I never forget this kind of help thanks for wonderful blog with 406 page best effort.
Hi I just got a new ranger 1760 mpv with the Mercury 60/40 and I’m only getting 15.5 mph the motor is still new maybe 5 hours tops.. But I’ve been told hot weather can hurt the overall performance of the engine 95 deg days and water temps in the high 80…
Mark, I haven’t noticed much of a problem with heat. Have you checked that the impeller is seated very close to the inside of the sleeve?
Dana Mesaros says
How about those Outboard Jet Whales tail do they work well for shallow water or not at all?
Dana, I’m not sure…never tried one. Sorry!
Jeff Engle says
Whale tails for jets are a waste of money, if they really gave any advantage, OBJ would put them on every new unit
From my experience on whale tail hole shot is better , slides are more accurate, when you let off the throttle slightly the tail keeps you up on plane as the back end raises up instead of dropping down allowing you to run on plane at half throttle or less through the shallows. (Who the hell runs half throttle )… but It works great when coming up on a group of kayaks or tubes and you can’t back off due to a shallow sandbar or obstacle. Ran without mine for one day after always running with one and could not wait to put it back on I will never run without a whale tail again just my personal experience.
Ooh thanks for that! I just looked those up. Gonna order one. Good tip!
If your jet outboard is pulling/turning to one side/direction there are two tabs inside the jet/water output, located one on top of and one on the bottom of the exhaust tube (inside the water output) IF you bend them both slightly to the right (or left depending) they will direct the output flow of water slightly one direction. these are there to counter act the force that is turning your jet outboard one direction. You will have to try bending them one direction and/or the other to find out if you bent them the right direction to counter act your pull or push.
Connor Brady says
I have a 2001 Yamaha 90 jet drive. My wear ring is worn out, do you know Of any websites to order a new one? Mine looks identical to the one you have pictured above.
Connor, I always buy mine at http://www.bucksoutboard.com
I need a part number to order a stainless steel 4 blade impeller for my mercury jet20.its a 1996 model
Jeff Engle says
There is a stamped # on the jet pump housing ,located on the boss that the reverse bucket pivots, use that # when ordering , OBJ sells to bucks outboards or River Marine in Medford or call Ken at Bob’s Marine in Modesto Ca -just an FYI, unless you are constantly getting into rocks and gravel and it eats you aluminum impeller, a SS impeller wont give a Jet20 much benefit and at $300+ bucks for a SS, you can buy 3-4 aluminums in fact with low HP motors ,the ONLY advantage with SS is durability as Stainless impellers only help performance on motors above 60hp and really over 115+
Anyone know how and where to drill a flush hole on an older 60/40 mercery?
Scott Balko says
I have the same motor and I also need a flush hole.
Jeff Engle says
I sure do, but I have to show you where, impossible to explain in a reply box
Jeff Engle says
You have to remove the jet pump, and pull off the seawater pump housing,rubber impeller and SS plate also make sure you have the proper tools to drill and tap the flush hole AND a plug to keep in said hole! You will need a 5/16 drill bit and a 3/8 NC tap along with a mercury or Evinrude gearcase fill plug to cork the hole when not flushing, and a screw in hose adapter (available from mercury Marine) ,then FORWARD of the grease tube (appx the same height) look where you can drill and hit the water passage in the seawater pump BASE also a seal must be installed between the plastic base and the aluminum jet pump housing so it doesn’t suck air (a proper sized ,glued in, rubberized cork gasket will work and easily replaced)
Check you motor height. this is the most inportant part of outboard jet setup.
We just purchased a 13 foot Jon boat (Wide) with a 30/25 Mercury EFI Jet. It seems way underpowered. However, before we made our purchase, everyone said it would be more than enough power, if not too much. We need a little help!! The boat has a max HP rating of 20HP. It barely gets up on plane. HELP!!!
I bought a 60/40 merc a few years ago and love the thing its on the river every weekend , my problem was that the marina set it up WRONG . after I looked into it i found that the height was an inch to low. after I adjusted it where it should be I gained almost 5mph it incressed to top speed of 27 mph upstream then added pods and a splash sheald l gained another 3 mph . now the guys are doing the same thing to theres cause they cant keep up with the trim set and adjusted correctly the thing scoots
What are the pods you added?
beavertail pods is what i used
Likely you have too much weight at back of boat. You have a 30hp, weighing what ever a 30hp weighs, but only putting out roughly 20hp. Do what I have done and get as much weight out of the ass end of the boat. Gas cans, batteries, gear should be moved as far to the front of boat as possible. This includes gear, humans when you are under way, anchor, steering console if you have one. Also center these things, from left to right for good balance.
I predict this will solve your problem. Joe
Make sure your getting proper rpm out of motor and its running properly. Next check reverse gate is not interfering with pump output, check impeller and liner for wear and improper gap at impelled to liner
Dan B. says
On my first pump I had, the exhaust tube was rusted out, not completely but it was missing about 1/3 of the tube, that allowed the water to expand prematurely inside the pump unit. Kind of like hooking a 3 inch hose up to a 2 inch pump, the volume is still there but the pressure will decrease. after replacing the exhaust tube, it over doubled the power and propulsion. Might be something to check into.
Good tip. Thanks!
I just bought a 17 valco with a johnson 65/45 jet. i have driven jets before but this is my first one. It really pulls the handle to the left. What can I adjust to correct this. Boats I have driven in the past did not pull at all.
You probably have a rock stuck in the nozzle…
No rock, I just looked. Was told by another to bend the fins on the tube the other way?? what do you think?
Yea, that really is the only other thing that would make a jet pull like that. Just be careful…you don’t want to break the fin!!
mark wasielewski says
where did u guys find the ss impeller tryin to find one for my yamaha 70/50 two stroker its an 03
I got mine at http://www.bucksoutboard.com
Barry Simpson says
Glad to see some results on the SS impeller. What size engine do you run with it. I have a 115/80 Merc on a Wooldridge boat. It’s a great rig.
I have a 2008 mercury 90/65, where could I buy a stainless steel impeller? I read the article called enhancing outboard jet performance by Chris Gorsuch, he had good thoughts on how to get more out of the jet and how to set it up properly, but he wrote that a dozen years ago. I called my local dealer and he says there are no other impellers available for my motor.
Jeff Engle says
Not available from mercury but they are available from Outboard Jets (they build mercurys and all others jet pumps for them) Try River Marine in Medford they will need your Pump # (located on the boss at the rev bucket pivot (stamped 5-6 digit #)
Andy Martin says
Saw this in Salmon Trout Steelheader quite a while ago. Glad I was able to find it on your site. Easy to understand tips on getting the jet to run top notch. Thanks.
Bruce Jentink says
JD, never mind on the reverse gate question, I was looking at the exaust tube, like I said, I’m new to this.
I did the other things recomended, looking forward to trying it out.
Bruce Jentink says
JD, Thanks for the tips, I just bought a Alumacraft 16′ AW Jon boat with a 60/45 hp. merc jet, we are going thru the jet for the first time and I notice the reverse gate when in full forward position is a hair smaller at the leading edge than the output tube, does it do any good to polish and remove a little aluminum to fit it closer to the output tube size? And what about polishing it on the inside, the casting looks rough. Any performance gains here???
And how about those funky intake fins you can put on the foot, do those really improve the handling and the speed of the boat ?
You know, Kevin, I’ve never tried the fins…but have heard they do boost your output…
Patrick V. says
Yes, they do help. 1. Better turning response–they act as rudders. They assist in funneling more water into the shoe, and minimize cavitation.
Jeff Engle says
but they add drag and drag slows you down , they do give a slight improvement in turning, but top end suffers
James Hinton says
ON the phone to Outboard Jet to get me a shiny new STAINLESS STEEL impeller
James Hinton says
I’ve got a question for you, What do you think about stainless steel impeller vs. the standard aluminum one ? And how about those funky intake fins you can put on the foot, do those really improve the handling and the speed of the boat ?
Funny thing…I just took my 3-blade aluminum impeller off a few days ago and put my old stainless 4 blader back on. I had tried the alum to see if it, being lighter, would give me a better hole shot. Nope…the stainless out-performs the alum hands down. My sled jumps outta the water now, turns lower RPMs and has a better top end.
I have a 25 mercury four stroke on a 1448 tracker sometimes it will plane out and sometimes it needs more throttle to plane out being wide open all rdy any suggestions??
Jeff Engle says
weight and its distribution is a huge factor also Impeller/liner clearance along with wear factor and proper trim angle/ motor height Proper clearance for aluminum Impeller is .018 at tightest point and .015 for SS,, weight should be 60/40 FORWARD of center ie; fuel, batteries, people, height should be front edge of scoop flush with bottom of hull, trim should be ALL the way down
Thanks for the input, Jeff!
Jim Long says
Exactly what I needed to know! Thank you!