Boyesen Accelerator Pump Cover?

[Plusdome]

As for the P-38 I will say that I took my 426 out for the first time today and saw NO bogging down low. Even though it was my first time out on it and have'nt ridden the stock carb I imagine the low end bog was pretty noticeable without as I have seen many posts about it. The only other mod on the bike is a full White Bros. exhaust and my carb is set to 1 1/2 turns out so you guys make the call.

[YZ426FROCKS]

Try the Factory R&D plate, from what I understand, it is built for a specific bike. Boyesen's is the same for all FCR carbs. I installed one and it did what it said it would do, it got rid of the sputter when I tweeked the throttle as fast as I could. Don't do it no more!

[Guest]

So has anyone tried the 40 LJ with the Boyesen pump cover?

[ncmountainman]

i'm putting it on today with the 40 lj ?

[Guest]

Right on let us know how it works

[Ga426owner]

i'm putting it on today with the 40 lj ?

NC I assume #40 with the Boyesen correct? I am interested in this akso...ket us know how it works...

[ncmountainman]

here's the deal folks. you need to get the boyesen AP cover and install the #40lj if you don't have it already. i had the 40 lj and it helped alot but there was still room for improvement. this thing combined w/the 40 is totally awesome,that problem i had at low rpm tight stuff on/off the throttle....GONE!! i had learned to finesse the throttle in these situations to avoid stalling. after install i could NOT make it stall, i was whacking the throttle in the same areas and the bike responded with wraaap,wraaap,wraaap right off idle !!! as many times as i wanted,it never ran out and died like before. its also way better at speed when traversing obstackles,instant loft! i guess jd never tried it with the 40 lj because its night and day compared to just the lj change. the only physical difference i could see was the fill hole was about a 1/8" higher(allowing the squirt bowl to fill completely) my jetting right now is 48pj 120paj 170mj 40lj 70sj STOCK 04wr needle 4th clip (after it gets in the 80's i go to 45pj 165mj still 4th clip) this is run with a power bomb,powercore4,powernow(no plus),and a yz airbox w/twinair filter. this is now the best running bike i've ever owned. i gotta say though there was a install problem. there is a tab that had to be filed off for the holes to line up(it was hitting the bowl) no biggie but still a person shouldn't have to do that. i'm gonna call boyesen monday and alert them to the problem(it may have just been a casting tab that accidently got through QC?) other than that HELL YAAA ?

[Ga426owner]

here's the deal folks. you need to get the boyesen AP cover and install the #40lj if you don't have it already. i had the 40 lj and it helped alot but there was still room for improvement. this thing combined w/the 40 is totally awesome,that problem i had at low rpm tight stuff on/off the throttle....GONE!! i had learned to finesse the throttle in these situations to avoid stalling. after install i could NOT make it stall, i was whacking the throttle in the same areas and the bike responded with wraaap,wraaap,wraaap right off idle !!! as many times as i wanted,it never ran out and died like before. its also way better at speed when traversing obstackles,instant loft! i guess jd never tried it with the 40 lj because its night and day compared to just the lj change. the only physical difference i could see was the fill hole was about a 1/8" higher(allowing the squirt bowl to fill completely) my jetting right now is 48pj 120paj 170mj 40lj 70sj STOCK 04wr needle 4th clip (after it gets in the 80's i go to 45pj 165mj still 4th clip) this is run with a power bomb,powercore4,powernow(no plus),and a yz airbox w/twinair filter. this is now the best running bike i've ever owned. i gotta say though there was a install problem. there is a tab that had to be filed off for the holes to line up(it was hitting the bowl) no biggie but still a person shouldn't have to do that. i'm gonna call boyesen monday and alert them to the problem(it may have just been a casting tab that accidently got through QC?) other than that HELL YAAA ?

NC thanks for the findings - I will try it with the #40 - w/ JD Jet kit -

[Unibomber]

I rode a hare scramble yesterday with the accelerator pump cover, it was awesome , it made a noticable difference. Cut my up hill rock climb stalling by 80%. IT WORKS !!!

Im ordering my 40lj jet today just to nip it in thu bud. ?

[Ga426owner]

Does anyone have a Yamaha part # for a diaphram for a 03 YZF450?

thanks

[ncmountainman]

Does anyone have a Yamaha part # for a diaphram for a 03 YZF450?

thanks

5JG-14940-17-00 yamaha has a online parts catalog for future reference

[Ga426owner]

5JG-14940-17-00 yamaha has a online parts catalog for future reference

Thanks again NC

David

[Ga426owner]

if your talkin' to me i never told anyone to change their leak jet,i'm referring to how the new ap cover would work with a 40 lj . obviously if the 426 has none;hence "maybe the 00 has none" if the conversation we were having here didn't apply to speeddemon i was trying to help him where to look for it as i was not sure if it had one or not. anything i'm saying is directly related to the 03-05 as that is what i have. NOT a crf go spew crap on the honda forum

I have news for you all, the 2003 YZF450 has no leak jet in the floatbowl - I have mine completely apart and the place that the leak jet is on a WR450 is not even casted in on the YZF.... I was suspicious of this because there is no leakjet diagramed in the YZF450 manuel.....or the YZF450 parts list from Yamaha. I ordered a 4JT-1494F-03-00 leakkjet per NCMountain that is now for sale to any WR450 owner

There is however Starterjets #3TJ-1494F-13-00 -- 3TJ-1494F-19-00 These look identical to the leakjets that NCMountain is referring to. Has anyone tested different starterjets?

So why would WR's have this and YZF's do not?

Oh well at least my carb got a good cleaning today

[ncmountainman]

i use a 70 starter jet,sorry about misundrestanding i was under the impression they all had leak jets yep,apparantly none of the yzf4-- ever had leak jets to start with! it only applies to WR's, sorry for the confusion

[Ga426owner]

i use a 70 starter jet,sorry about misundrestanding i was under the impression they all had leak jets yep,apparantly none of the yzf4-- ever had leak jets to start with! it only applies to WR's, sorry for the confusion

No problem NC - It gave me a chance to fully dissassemble my entire carb - I installed the Boyesen cover as well as new diaphram, orings, spring and will test it tomorrow - if it dries up down here a little.....

If anyone needs this little leakjetfor their WR just PM me.

[YamahaRacer]

OK, now I am thoroughly confused! So my 03 YZ450 does NOT have a leak jet? So then what should be changed in conjunction with the Boyesen Cover? What's the difference between a leak jet and a starter jet? Thanks in advance!

-Chris

[Unibomber]

Ah Ha , you are correct the YZ does not have a leak jet, yet I just recieved one also, ummmmmmmmmm.

Well I was so eager to try it out anyhow, I was thinking of ordering the WR float bowl, but I dont think you can, I have looked at the parts schematic several times and it doesnt have its own part number, o well not a big deal, I am however very very hapy with the boyesen pump cover.

[biznet1]

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

Dang it! A little too late, but thanks anyway James. You still da man!

[Ga426owner]

Ah Ha , you are correct the YZ does not have a leak jet, yet I just recieved one also, ummmmmmmmmm.

Well I was so eager to try it out anyhow, I was thinking of ordering the WR float bowl, but I dont think you can, I have looked at the parts schematic several times and it doesnt have its own part number, o well not a big deal, I am however very very hapy with the boyesen pump cover.

I would not try that bowl idea - too much complexity- I will test with different diaphrams to see if the results are different - I have all 3 now

This does however negate James Deans results as the YZF has no leak jet - the results he found were solely on the WR

I do not know yet the benefits of the different starter jets

[ncmountainman]

i've seen somewhere in another post that the 05 yzf 450 is the first year for leak jets on a yzf,is this true ?