- Location
- Texas
First, absolutely need to start with an Engine that has good Compression and no Air Leaks. The Carbs also need to be in good working order with a recent rebuild. Check for worn Throttle Plates and Shafts. Replace as needed. Ensure the Throttle Plates are synchronized and the Throttle Cable has the proper Adjustment throw/slack on the Throttle Cam/Wheel, full open and close.
This is the Keihin Carb Tuning Method. In my opinion, It's the easiest way to tune PWC Carbs as a good Tachometer does not lie. No screwing around with Spark Plug Color, Exhaust Sound Pitch or tying the Ski to the Dock. No guessing here.
So leave the Ski strapped to the Trailer, back it into the Water, start and warm up the Engine, USING A TACHOMETER set the Idle to about 1500 rpm. Then find the highest Idle rpm reading by tweaking the Low Speed Adjusters, not the Idle Set Screw. When you find this maximum, be aware that this will be TOO LEAN to ride with and will hesitate or "fall on its face" when you open the throttle because the Engine needs more fuel underway with the Rider Weight and Water Drag on the Hull. So now, OPEN THE LOW SPEED ADJUSTERS 1/4 TURN MORE to get the right amount of fuel into the Low Speed Circuit (Idle to Half Throttle). This will be close to perfect. To test, idle out into the water while on your Knees, then snap the Throttle open, if it jumps out of the Water and snaps your Head back, then it's spot on. If a delay in response, it's Lean, If it sputters, sounds rough and gurgles, it's rich. Adjust the Low Speed Screws accordingly. But the Tachometer On-the-Trailer Idle Max + 1/4 Turn should be almost perfect, if the Engine has no Air Leaks. Now reset the Idle back to about 1500 rpm using the Idle Set Screw only.
Next, assuming you have the right size Main Jet, with the Tachometer velcro'd to your Dash, make a couple of WOT flat water passes no longer than 100 ft each. Note the highest rpm reading, then try opening the High Speed Screws by +1/4 Turn and test again. If the rpms go up, then open another 1/4 turn and repeat until the rpms go down. Go back to where the highest rpms were reached. Then fine tune with 1/8 turns. You have three turns out maximum available on the Screws.
If the rpms go down when the high speed screws are opened, then it's too rich, so turn the Screws in 1/4 turn at a time and retest. Pete and Repete till the best rpm is reached.
Many richen the High Speed Circuit by opening 1/8 of a Turn for a safety margin.
This is the Keihin Carb Tuning Method. In my opinion, It's the easiest way to tune PWC Carbs as a good Tachometer does not lie. No screwing around with Spark Plug Color, Exhaust Sound Pitch or tying the Ski to the Dock. No guessing here.
So leave the Ski strapped to the Trailer, back it into the Water, start and warm up the Engine, USING A TACHOMETER set the Idle to about 1500 rpm. Then find the highest Idle rpm reading by tweaking the Low Speed Adjusters, not the Idle Set Screw. When you find this maximum, be aware that this will be TOO LEAN to ride with and will hesitate or "fall on its face" when you open the throttle because the Engine needs more fuel underway with the Rider Weight and Water Drag on the Hull. So now, OPEN THE LOW SPEED ADJUSTERS 1/4 TURN MORE to get the right amount of fuel into the Low Speed Circuit (Idle to Half Throttle). This will be close to perfect. To test, idle out into the water while on your Knees, then snap the Throttle open, if it jumps out of the Water and snaps your Head back, then it's spot on. If a delay in response, it's Lean, If it sputters, sounds rough and gurgles, it's rich. Adjust the Low Speed Screws accordingly. But the Tachometer On-the-Trailer Idle Max + 1/4 Turn should be almost perfect, if the Engine has no Air Leaks. Now reset the Idle back to about 1500 rpm using the Idle Set Screw only.
Next, assuming you have the right size Main Jet, with the Tachometer velcro'd to your Dash, make a couple of WOT flat water passes no longer than 100 ft each. Note the highest rpm reading, then try opening the High Speed Screws by +1/4 Turn and test again. If the rpms go up, then open another 1/4 turn and repeat until the rpms go down. Go back to where the highest rpms were reached. Then fine tune with 1/8 turns. You have three turns out maximum available on the Screws.
If the rpms go down when the high speed screws are opened, then it's too rich, so turn the Screws in 1/4 turn at a time and retest. Pete and Repete till the best rpm is reached.
Many richen the High Speed Circuit by opening 1/8 of a Turn for a safety margin.