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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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Default Does it need one ? (Accelerator Pump)

Quick question for future reference. Does the 2004 Sportster need that squirty jet thing that fires extra fuel down the gob of the carb? Is there a list of carbs and makes on here that have been fitted to our bikes with success? Thanks
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Originally Posted by 93trident View Post
Quick question for future reference. Does the 2004 Sportster need that squirty jet thing that fires extra fuel down the gob of the carb? Is there a list of carbs and makes on here that have been fitted to our bikes with success? Thanks
You mean the "accelerator pump nozzle?"

Pre-1989 or so, I believe the carbs did not have one, but used the jet needle to add fuel off idle. I'm sure someone with other brand carbs can add more. I know Mikuni HSR series, S&S, and even Lectron, are common upgrades.

John
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The usefulness of a pump depends in part on how how violent the transition between successive circuits is from above idle to part throttle. These factors include throttle size vs. venturi size, throttle area vs. engine size, even static CR (small chamber volume increases vacuum).
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Default done that...

Yes, it is needed. Without it or even reducing the shot will affect the rideability in a negative way.

Opening the transfer port in the float bowl a bit will reduce the shot... Trouble is the float bowl is not sold separately. When you realize it was a mistake you will be purchasing another carb.
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Originally Posted by John Harper View Post
You mean the "accelerator pump nozzle?"

Pre-1989 or so, I believe the carbs did not have one, but used the jet needle to add fuel off idle. I'm sure someone with other brand carbs can add more. I know Mikuni HSR series, S&S, and even Lectron, are common upgrades.

John
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Mikuni VM series and SU carbs have also been used on Sportsters neither of which have accelerator pumps.
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the VM was really designed for 2 cycle and has a diff dynamics in intake than 4 cycle.
the accel pump is need as it states, to accel!
when you trounce the throttle, venturi goes atmospheric and no fuel can be drawn up the nozzle so the squirt of fuel kicks the engine in the butt so flow and be established with rpm. that is why you get a bog out when the pump does not work. yes, it will still work with minor throttle movements.
also, the 4 cycle usually has transfer ports to aid in a smooth transition of rpm changes. the VM has none as the pilot and main/needle/nozzle acts as such. if you trounce the throttle, there is a brief high vacuum pull that pulls a large amount of fuel out the main nozzle. the beauty of the VM is the cold start, a hands off procedure.
can it be fitted on a evo, why sure but i would opt for a 40mm min as the 38mm would be borderline.
i have nearly 200k miles on one.
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