Kennethyfz450
03-07-2005, 04:26 PM
James dean review over the Boyesen Accelerator Pump Cover//
I purchased the $89.95 pump cover (plus $8 shipping = $98) to make an evaluation of your exact question.
The answer is yes, a smaller leak jet will do the same thing. (The instructions also say to turn the fuel screw out 1/4 turn more and set the accelerator pump timing screw to stock.)
The pump cover is designed to refill the cavity with 2 ports flowing fuel upwards toward the diaphram, lifting the diaphram to add more fuel (only slightly). This might add 10% more fuel to the cavity which actually does seem to push more out the nozzle. I made some tests, and checked the duration and distance fuel squirted with an FCR carb and throttle off of the bike. The Boyesen cover change was compared to lowering the leak jet by #10 and #20 (#70LJ with Boyesen -vs- #60LJ and #50LJ with stock pump cover).
The leak jet lowered by #20 (#50LJ with stock cover) was pushing far more fuel than the Boyesen cover with #70. Both the duration and distance of squirt was greater with the #50LJ,
The stock cover with leak jet lowered by #10 (#60LJ) was nearly identical to the Boyesen cover with #70. The amount and distance the fuel squirted was nearly the same after repeatedly snapping the throttle open, both fast and with a brief delay between snaps.
If you want to get the same effect, just lower the leak jet by #10. Remove the float bowl and it's the little jet in the bottom.
Yamaha leak jet part numbers are-
#70- 4JT-1494F-15-00
#60- 4JT-1494F-11-00
#50- 4JT-1494F-07-00
#40- 4JT-1494F-03-00
#35- 4JT-1494F-01-00
(cost is ~$12 for these)
Honda leak jet part-
#55- 99108-MEB-0550 (cost is ~$8 for this)
Sorry to those of you who may have already purchased one. I spent the money on the cover and full range of leak jets too.
I hope this helps,
James
__________________
I purchased the $89.95 pump cover (plus $8 shipping = $98) to make an evaluation of your exact question.
The answer is yes, a smaller leak jet will do the same thing. (The instructions also say to turn the fuel screw out 1/4 turn more and set the accelerator pump timing screw to stock.)
The pump cover is designed to refill the cavity with 2 ports flowing fuel upwards toward the diaphram, lifting the diaphram to add more fuel (only slightly). This might add 10% more fuel to the cavity which actually does seem to push more out the nozzle. I made some tests, and checked the duration and distance fuel squirted with an FCR carb and throttle off of the bike. The Boyesen cover change was compared to lowering the leak jet by #10 and #20 (#70LJ with Boyesen -vs- #60LJ and #50LJ with stock pump cover).
The leak jet lowered by #20 (#50LJ with stock cover) was pushing far more fuel than the Boyesen cover with #70. Both the duration and distance of squirt was greater with the #50LJ,
The stock cover with leak jet lowered by #10 (#60LJ) was nearly identical to the Boyesen cover with #70. The amount and distance the fuel squirted was nearly the same after repeatedly snapping the throttle open, both fast and with a brief delay between snaps.
If you want to get the same effect, just lower the leak jet by #10. Remove the float bowl and it's the little jet in the bottom.
Yamaha leak jet part numbers are-
#70- 4JT-1494F-15-00
#60- 4JT-1494F-11-00
#50- 4JT-1494F-07-00
#40- 4JT-1494F-03-00
#35- 4JT-1494F-01-00
(cost is ~$12 for these)
Honda leak jet part-
#55- 99108-MEB-0550 (cost is ~$8 for this)
Sorry to those of you who may have already purchased one. I spent the money on the cover and full range of leak jets too.
I hope this helps,
James
__________________