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05-31-2009, 11:32 AM #1
How I remove tamper evident caps on GPR carbs
Yamaha enginered the GPR motor to meet emission requirements, in doing so they gave us a few litlle challenges to modifying the motor. One of those was the "tamper evident" or "tamper proof" caps on the carburetor. These caps are pressed in brass plugs that cover the high and low speed adjuster screws. The carbs are painted which makes these difficult to identify, I have had a few members contact me who drilled into the carb in the wrong location and basically ruined them.
This is a pretty simple mod to do and there are several different ways to do it, I will show how I do it. I will also show where these are located and the size of them so you can see how deep to drill. My method insures that I do not remove anything other then the plug. Some people drill the enire plug out and end up drilling into the aluminum housing.
- Drill with drill bit for tap of choice, I use a #19 bit
- Tap, I use 5mm x 0.8 tap
- Screw, I use a 5mm screw
- Prybar or vise grips.
05-31-2009, 12:07 PM #2
I start on the high speed adjuster which is the top of the carbs as they sit in the ski. Note the letter H in the casting of the carb body just below the cap. The fuel lines will have to be removed to access the caps on #1 and #2, The accelerator pump should be removed from #3 for access.
05-31-2009, 12:25 PM #3
Now drill a hole in the center of the brass plug. Be careful not to force the drill through the cap as it breaks through, this can cause the drill bit to hit the adjuster screw and cause damage. I use a little wd-40 to lube the drill when doing this. The brass plug is 5mm (.197")thick.
05-31-2009, 08:51 PM #4
Next tap a thread through the plug
05-31-2009, 08:55 PM #5
Next install screw then use prybar or vise grips to remove. I like the prybar method it makes it really quick and easy. If you use vise grips clamp the screw well and rock it back and forth while pulling it works well too. Result is you have a nice clean hole when finished.
05-31-2009, 08:59 PM #6
Follow the same sequence for the lows. The lows have L in the casting next to them. look in the photo and in the center just right of the brass plug and left of the throttle shaft is the letter L
05-31-2009, 09:02 PM #7
For reference here is a pic of the top of the carbs as you would see them looking in the ski showing the high speed adjusters with t-handles installed. I cut the hoses longer and route them as shown for easier access to the high speed adjusters. Also take note of the grease around the shaft of the t-handle, this is critical to keep water from sitting in the pocket and seizing the adjuster. If you use the oem adjusters fill the cavity with grease where the plug used to be.
05-31-2009, 09:08 PM #8
Pic of the bottom side of the carbs showing low speed adjusters with T-handles installed.
05-31-2009, 09:23 PM #9
- Join Date
- Jul 2007
- Pontoon Beach Illinois
Fantastic! you could be a technical writer.....
05-31-2009, 09:28 PM #10
Killer post Bill! Thank you for all your help on the carbs! You are the man and the carb man of the Hulk. Cudos to Bill
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