Thread: ACC Pump whys?
03-30-2007, 12:55 PM #1
- Join Date
- Nov 2006
- Brookfield, wisconsin
ACC Pump whys?
So im sitting wiht my carbs all re jetted and can not figure out why i should remove the ACC Pump. is there a valid reason ? i honesly dont feel like putting on a primer, and getting rid of the choke.. i was told the acc pumps perpose was for out of the hole an exta shot of fuel.. im not premixing. so why not leave it on ?
03-30-2007, 01:03 PM #2
From what I understand the acc. pump causes a lean rid range condition. I still have not figured out why Yamaha only ran it to the #1 and #3 cylinders only. I guess it might be because of the extra heat on !1 cylinder and the lean condition in #3. This is just my assumption. I would disable the pump and rejet accordingly. The accel. pumps have been known to freeze up on occasion too.
03-30-2007, 08:31 PM #3
by disabling the accel pump you can use a larger pilot jet - this will provide a bit more fuel in the lean spot (approx 6700 rpm)
if you keep the accel pump a good idea is to add a fitting so it also feeds #2
if you disable it you can leave it mounted and use it as a primer
03-30-2007, 08:48 PM #4
yup. I used it as a primer when I first built my GPR back in 2003.
If you Remove the accelerator pump, rejet to 110p,120 mains, 1.5 N/s 95 gram spring.
Per FERCHO's original recommendation years ago on testing he did.
Old Threads over this topic
Here are some good thread from back in the day
* The lean spot has been known to exist in the 5000-6000 RPM range also, depending on the the ski.
READ this old thread FERCHO posted to
GROUP K quote:Accelerator-Pump Carbs - Many late model pwcs are coming, from the factory, with accelerator-pump carbs. These carbs have an injector nozzle (fed from the float chamber) that delivers a small spray of raw fuel into the carb throat(s) when the throttle is applied quickly. When the throttle is applied slowly, this system injects little or no fuel. The advantages of this system are many. First and foremost, it allows for a big improvement of low range throttle response on engines that have relatively mild compression ratios. Another big advantage is the reduced sensitivity to slight lean conditions throughout the low speed ranges. The low speed adjustment screws on these accelerator-pump carbs can be set at a slightly leaner setting that permits for very clean and smooth "5 mph zone" operation. Settings this lean (on a non accelerator-pump carb) would likely exhibit a bottom end hesitation when the throttle was applied quickly from idle. When adjusting the low speed screw on these accelerator-pump carbs, we recommend to avoid settings that offer even the slightest rich condition during idling rpms.
Last edited by RX951; 03-30-2007 at 09:00 PM.
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