Polaris Fuji engine (blue painted engine)

URL web link for this page ==> Polaris Fuji (blue) engine

Click here for information specific to the Fuji blue engined Polaris PWC models (1992-1997), other than the engine itself

What you need to know about Polaris 650 750 780 and Pro 785's

Xlint89's list of maintenance and upgrade items for Fuji engines

Common problems and fixes for your Fuji engined Polaris
River Rat's excellent Polaris Fuji engine article (temporarily offline)

My Fuji engine is hard to get started. Should I just add a primer kit?
(and I have not rebuilt the carburetors or done the other recommended fuel system servicing)
"Knowing what i know about the Polaris Fuji motors ( which is what you have) they are KNOWN for fuel related issues. The fuel pumps are weak, fuel lines go bad, the fuel select valves go bad, and your carburetors are 15+ years old, and probably have never been rebuilt.

I would strongly suggest doing some routine maintenance to your ski. rebuild the carburetors, update your fuel system to a triple outlet fuel pump, replace lines, etc. I think you will then find it will start and run properly.

If you DO NOT do this, you will run the risk of running lean, and ultimately engine failure."

Friscoboater's Fuji threads and Youtube channel (scroll down to find the Polaris related clips)

Why the plastic battery cover is important
If the metal shell of the electrical box touches the battery positive post it will burn up the Black stator ground wire

Improve the battery ground connection to the Fuji engine
The stock connection for the heavy black battery cable to the engine is actually a small bolt on the engine bed plate, not the engine itself.

If the bolts connecting the bed plate into the bottom of the engine became corroded or loose it will create a poor electrical connection between bed plate and engine, which will cause electrical problems (poor engine ground back to the battery). One symptom of a poor battery ground is that the thin black wire to the battery gets warm when the engine is cranking.

Cranking may or may not be noticeably slower with a poor battery ground, but it will be better with a good solid ground from battery to engine.

Since it is impossible to see those engine bed plate bolts underneath the bed plate, they are easy to ignore. Move the engine end of the heavy black battery cable to one of the intake manifold studs at the PTO cylinder. That ensures the negative cable really does have a solid, zero ohm electrical connection to the engine itself, not just to the bed plate. Makes sure both ends of both battery cables are clean and provide solid metal-to-metal contact.

Note: If moving the battery negative cable solves the electrical problem you must check the bolts that hold the bed plate to the engine bottom. If they are loose you must tighten them.

Start by checking compression and crank index
Simple method for checking Crank Index

How to test CDI, Magneto stator coils & Ignition coils on Fuji engines
Polaris PWC wiring colors - what each wire color is used for, Fuji and domestic
How to check for spark, and trim spark plug wires

How to replace the magneto stator on a Fuji engine

Common causes of piston damage (burn down) in Fuji engines

Hole melted right through the piston top and/or damaged piston outer edges
You need to read Fuji engine Burndown Basics

How to do a leak down test
Leaky crank shaft seals and/or leaky intake gaskets can allow excess air flow into the engine, which can cause lean burn piston damage. A static (engine not running) leak down test can detect whether there are air leaks into your engine, and where.

Notes: Always use air pressures below 10 PSI to prevent over-stressing the crank seals.
You can only use soapy water to check for leaks (bubbles) if you are using air pressure, not vacuum.

Carburetor Rebuild

Mikuni Super BN (SBN) carburetor manual
Mikuni Super BN (SBN) carburetor rebuild guide
Alternate file download source for Mikuni SBN rebuild guide
Note: Always use genuine Mikuni Super BN (SBN) carburetor rebuild kits for 38mm carburetors, not aftermarket brand rebuild kits.
Needles and seats are 2.0 push-in type
Carburetor pop-off testing tip; Retest the pop-off after putting the carbs back together

Tip: It is easier to get the carbs off if you use a 12mm stubby ratcheting combo wrench and reach over the ski from the port side.

If you don't have a stubby 12mm wrench, consider cutting the handle shorter on one you do have.

Triple outlet fuel pump upgrade

What is a triple outlet fuel pump?
Why do I need one for my Fuji 650 or 750 engine?
Mikuni Round Triple Outlet fuel pump DF52-92 (35 liters per hour flow rating)

Fuel hose routing for triple fuel pump upgrade (1/4" size hose)
Alternate carburetor fuel hose routing
Triple pump hose connections
Use Mercedes diesel engine injector return line plugs to cap off the unused fuel return fittings on the carburetors

Be sure the hose you use for the pulse line is stiff enough not to collapse under suction
Also applies to the fuel lines from tank to fuel pump, which are also under suction

Mikuni Pentagon Triple Outlet fuel pump (65 liters per hour rated) was stock on 1996-1997 Fuji 780 models - Polaris Part# 3240291

Remove the auto-cock device from all 1993-1994 Fuji engines; SL650, SL750, SLT750

Remove the Auto Cock Automatic Fuel shutoff device, if it is still installed
(applies to all 1993-1994 Polaris PWC)
Why should the auto-cock be deleted - what was it for, anyways?

What is a fuel line restrictor, and where is it supposed to be located?

Some 650 and 750 Fuji engine models have a small metal flow restrictor (Polaris part number 5020773) inserted inside the return fuel line, about one inch from the last carburetor. It looks like a brass plug in the return fuel line, and it has a tiny hole driller through the center. The restrictor is used to boost fuel pressure inside the carburetors, and is in addition to the internal flow restriction in the Mikuni SBN carburetor.

The restrictor was present in 1994 and 1995 SL650, SL650 STD, SL750, and SLT models.
May have also been used in some 1993 650 or 750 engines. It was not used on the Fuji 780 or 785 engines.

If the fuel lines are replaced and the restrictor is accidentally discarded with the old fuel hose then the carburetors will not have enough fuel pressure to run the engine properly at high throttle levels, and lean burn piston damage can occur.

Apparently it doesn't hurt to add the flow restrictor to the 1993 return fuel line even if the original fuel system did not have one.

How to make a replacement flow restrictor using 1/4" hose barb and Mukuni main jet

Consider upgrading the pre-1995 fuel tank venting to the 1995 specification

Tip: If opening the gas cap releases a very strong whoosh of air pressure, check or replace the tank venting check valves. Sticking check valves are difficult to properly clean, so just replace the old valves.

On any model with two check valves, make sure the existing check valves really do open and flow air under mild pressure (max 2PSI) in one direction, and seal under mild air pressure in the other direction. Bad check valves can cause excess air pressure or excess vacuum inside the fuel tank. Neither is good.

Replace the old fuel lines inside the fuel tank (1992-1994, some 1995 models)

Polaris used flexible fuel lines inside the fuel tanks on all 1992-1994 models and on some 1995 models (1995 SLT and 1995 SL650 STD have hoses inside the fuel tank). Later in 1995 production switched to one-piece metal pickup assembly inside the fuel tank.

Note: There should be a metal mesh intake filter (called a clunk intake) on the end of each fuel intake hose inside the fuel tank. Polaris part number 7052037, 7052081 (item 6 in this diagram) and aftermarket from Jetski Solutions.
If you have two intake hoses inside the tank, the 'Reserve' intake reaches to the bottom of the fuel tank and the 'Main' hose is about 2 inches shorter.

Be sure to use quality replacement fuel hose which is rated for continuous submersion in gasoline and is rated for ethanol blended fuel. A fuel leak, even a small one, is very dangerous inside an enclosed PWC hull.

Replace old fuel lines
On any model/year inspect all fuel lines, even those little sections between the carburetors.
Replace all your fuel lines if any appear degraded, brittle, hard, or have surface cracking.

Replace gray Tempo brand fuel lines
The Tempo fuel hose degrades internally and can gum up the carbs with greenish goo
From about 1994-2002, the factory installed gray Tempo brand fuel hose chemically reacts where it connects to metal fittings, creating a greenish or bluish goo inside the hose that clogs the fuel system and carburetors, causing lean fuel delivery and burned pistons. The outside of the Tempo fuel line can look and feel just fine despite the internal degradation.
Often associated with SeaDoo PWC, the same gray Tempo hoses were also used on Polaris and Yamaha PWC.

Where can I get replacement fuel and oil hose?
Depending on the model you have you will need 20 feet of fuel line, maybe a bit more.
What grade fuel line should I be using?

Where can I get a replacement fuel selector valve (On-Off-Reserve)?

If your fuel selector valve is leaking air into the fuel system, you will have problems and risk engine damage (lean burn). Refurbish the selector valve internal seals, or replace the valve.
The ON-OFF-Reserve Polaris fuel selector valve 7052063 is no longer available, but the 1995 Yamaha Wave Blaster Fuel Selector valve may be a good replacement (PN 6K8-24500-02-00)

Why you want to actually turn your fuel valve off when not riding
Avoid gasoline flooding of the engine, and possible engine damage, fire, or hull explosion.

Oil pump, oil injection system
There are check valves in the intake manifold oil feeds

Flame Arrestor upgrade for 650 and 750 engines
The stock 650 and 750 air intake flame arrestor is restrictive, and reduces engine power somewhat. Some owners remove the rubber elbow from the intake.
If you retain the rubber intake elbow on the flame arrestor, be sure the rubber intake opening faces down, not upwards.
If you remove the elbow, the high speed adjusting screws on all three carburetors may need to be opened up (turn anti-clockwise) a little.

You can upgrade to the OEM flame arrestor versions used on the 780 and 785 engines, but the carburetors may need adjusting for correct fuel mixture.
See the 'Piston Wash' notes.

Aftermarket Flame Arrestor Comparison

Exhaust water injection - Check and clean the mesh filter screen and orifice
The location varies with the engine model, but every Polaris PWC engine has exhaust water injection, and it must not be clogged

Checking the exhaust water injection orifice and mesh filter screen

How to figure out which cylinder is running poorly
By testing the cylinders one at a time, you can narrow down which cylinder is dead or weak. Ground the ignition wires for all but one cylinder, and see if it will start (you may need to squeeze the throttle to get it to run). If it does, ground that plug wire, and test the next cylinder. Each single cylinder should run the engine about the same.

The 'one cylinder at a time' test will reveal a cylinder that is not producing power due to mechanical problems (low compression, broken reeds, out of phase/index crank shaft),  fuel problems (carburetor, fuel delivery), or something wrong with the spark (coil, wire, plug).

This video shows the process in action.
In this example, there were two problems. Incorrect spark plug firing order (wrong sequence of spark plug wires) and the PTO carb was missing a part!

How to figure out which cylinder is dead or weak

Note: Normal/stock Fuji 650/750/780 engines do not have sequential spark. This particular tweaked Fuji engine in the video happens to have an aftermarket ignition system which has sequential spark, similar to the Pro 785 engines.

Carburetor sizes used in Polaris PWC

What are reed spacers, and how do I install them on my Fuji 650 or 750 engine?

Polaris PWC Spark Plug Application Chart 1992-2002

Detonation - what is is, how to avoid it

Reading 'piston wash'

Interchangeability of 650, 750, 780 crank shafts and crank cases

LR voltage regulator and Start/Stop modules
Substituting different LR voltage regulator versions (LR-23, LR-31, etc)
Connections, functions

Magneto stator rewinding services
Jet Ski Solutions is in Georgia, USA
RM Stator is in Canada

Engine Removal and Installation - Fuji 650, 750, 780cc

How to loosen PTO coupler using 'rope trick' inside the cylinder (works for flywheels too)

Engine rebuilding - gaskets
For the engine assembly (cylinder, cylinder head, intake, exhaust) you can use either genuine Polaris OEM gaskets or Cometic brand gasket sets

Cometic gasket kits are available from DennisKirk for both Fuji and red domestic engines

Polaris crank bearing replacement sources
6207 and 6307 bearings are used in many Polaris watercraft 2-stroke engines are somewhat unique. In the case of the Fuji engine, the 6207 is pinned and the 6307 is pinned and also has a snap ring. The pin is used to keep the outer race from spinning in the case.
You can use the unpinned bearing. Use Loctite 680 Green on the outer race to secure them.

6207 Bearing

6307 Bearing
Loctite Green 680 bearing retainer

How to remove the flywheel and magneto stator

How to properly flush your 1992 or 1993 Polaris PWC
The 1992 SL 650 and 1993 SL 650 engines have an unusual cooling system that can be tricky to properly flush. These engines tend to accumulate sand in the water jacket, causing reduced water cooling and potential engine damage.

Technical Articles and Explanations (How Stuff Works)

Combustion and Ignition basics

How to install a Pro 785 CDI into a Fuji 650/750/780 electrical box

Homemade piston pin puller