06-09-2014, 08:59 AM #1
How to rebuild Mikuni SBN 38 Triple Carbs
This thread will describe how to rebuild the Mikuni SBN 38 Triple carbs found on all Polaris Fuji Engines. Note that the 650, 750, and 780 versions are all the same, with a few minor variations I will point out.
Carb kits can be obtained from many different sources. Ensure that only Genuine Mikuni parts are used. For this thread, the carb kit was obtained from John Zigler at Watcon.com. At the time of this post, the kit was $150 USD plus shipping.
The parts included in this kit are 3 ea o rings for the high and low speed adjusters, 3 ea needles and seats (size 2.0), 3 ea springs (size 80 gram), 3 ea clear check valves, 3 ea filters, and 3 ea diaphragms.
Here is a layout of typical tools and supplies needed for the rebuild:
Carb cleaner, multipurpose spray lubricant, small and large phillips, small and large flat heads, scraper, 2 stroke oil, and paper towels. I also used various small pics and brushes as you will see throughout the photos.
Last edited by BlueFishCrisis; 06-09-2014 at 11:08 AM.
06-09-2014, 09:02 AM #2
06-09-2014, 09:05 AM #3
Next, remove the fuel inlet cover. Pay attention to which cover comes off of each of the various locations ( MAG, CEN, PTO). The covers are different for each location, and may vary based on year and motor size. All, however, are interchangeable and will work on any version.
Remove the fuel filter, and discard.
Remove the black rubber gasket. Keep this as long as it is in good condition. The kit does not come with a replacement.
06-09-2014, 09:08 AM #4
Before removing the adjuster needles, you can count how many turns it takes to screw each of them in so they are fully seated. Record this measurement for each carb, each screw. When it its time to Re-assemble, you now have documentation on where they were. Or, you can reset to factory settings.
Next remove the low speed adjuster. Note the o ring. If the adjuster comes out without one attached, you will need to reach in with a small pick and retrieve it. Often the washer stays in place covering the o ring as it is painted after it is installed.
Remove the blue cap on the high speed adjuster with a pair of needle nose pliers. I choose to discard these and not re-install after the rebuild.
Remove the high speed adjuster, keeping an eye out for the o ring.
Last edited by BlueFishCrisis; 08-18-2014 at 10:55 AM.
06-09-2014, 09:14 AM #5
06-09-2014, 09:18 AM #6
Next, remove the screw holding the lever arm pin. This may be corroded and tough to remove. Use lots of downward pressure when removing. You can also use an impact screwdriver to assist in removal of any of the screws in the carb. It is essential to remove the fuel inlet cover first, so the carb will lay flat on the bench when trying to remove these screws.
Next, remove the lever arm, pin, and needle.
Note the spring that remains when the arm is removed. This spring will need to be retained for 780 carbs, as the replacement provided is for the 650 and 750 models. If you are rebuilding a 650 or 750 set, discard the springs.
06-09-2014, 09:21 AM #7
Here we will remove the seat retaining screw. This compresses a small plate the holds the seat firmly in place.
With those removed, use a pair of needle nose pliers to grip and remove the seat. Pull straight up with a decent amount of force. The more corroded your carbs, the more difficult it will be to remove. PB Blaster or similar may help in removal.
06-09-2014, 09:24 AM #8
06-09-2014, 09:28 AM #9
Remove the low speed jet using the small flat head screwdriver. Find a screw driver that just fits inside the hole for the jet. Remember the jets are brass and therefore a softer metal. The larger the blade you use, the better chance you will NOT cause damage to the jet.
Remove the high speed jet.
Retain the jets for re-installation. The size of the jets are imprinted on top of the jet next to the screwdriver slot for the high speed, and on the side of the jet for the lows. Ensure you have the proper jets for your ski, especially if you bought the carbs separate from the ski. Reference your owners manual for the correct sizing.
06-09-2014, 09:30 AM #10
Now that the old carb is completely disassembled, it is time to clean it. Be sure to use spray carb cleaner and compressed air to clean it out. Others prefer a full carb bath and small gauge wire to clean out the passages. Ensure every nook and cranny is clean and corrosion free, including the jets themselves.
You may need to use a wire brush and or picks to clean out corrosion.
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
By screamindemon in forum Kawasaki PWC Performance (2-stroke)Replies: 16Last Post: 08-03-2011, 09:44 PM
By ctct2118 in forum Kawasaki ClassifiedsReplies: 14Last Post: 07-15-2010, 05:04 PM
By ctct2118 in forum Yamaha ClassifiedsReplies: 24Last Post: 07-15-2010, 05:01 PM
By vomitspot in forum Yamaha ClassifiedsReplies: 39Last Post: 09-02-2008, 06:40 PM
By TomToro in forum 2-Stroke PerformanceReplies: 4Last Post: 07-27-2008, 06:51 PM