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boyesen ap cover w/40lj

By ncmountainman,
in WR400F/426F/450F

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Grand Master

Dan_Lorenze

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Well, I went down to my local shop where they take great care of me to pick up my #40 leak jet that's been sitting there for a couple of weeks after ordering it. My dealer had no problems looking up the part and ordering it from Yamaha, he says that leak jets have been popular with the 250f guys but had no problem ordering me one for the 450. While I was there I asked if he had the Boyesen AP covers in stock, he told me he didn't but could order one and have it to me in just a couple of days. Then he handed me another brand of AP cover, it was the "Factory R&D" brand, they call it the "Lightning" :D Whatever... It looked like a nice little piece, the dealer said it had been out for a while and guys were very happy with it so I told him to ring it up. I mounted it up last night with no problems, the machining is top notch and used all the stock bolts and oring. I bought the little cover for $55.00, much cheaper than the Boyesen so it was easier to swallow the price of the purchase.

Here are some photos I took:

Here's the Factory R&D cover next to the OEM

Leak jet replacement and location

Here's a shot with the cover installed

On the bike...

Part number for the #40 leak jet from Yamaha

Contrary to what I've read, the stock Yamaha leak jet for my bike is a #50, it's what was in there and the manual states it as well.

I've yet to test my upgrades to my carb. Sometime this morning I'll go out and fire her up when all my neighbors go to work but I'm not going riding until next weekend so I won't have any true testing done until then.

Now that I've looked at both covers side by side it looks like the only difference is the fuel passages in and out of the pump cover, certainly we could come up with a "free" mod for this. The volume of the covers seem to be identical. It would be cool to see what drilling out the fuel passages would do instead of spending any money for an aftermarket part.. :naughty:

Dan :naughty:

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Rising Star

Jackazz

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Interesting, DL... thanks for the info. :naughty: I thought that one of the "features" of the boysen cover was supposed to be additional capacity, but I might just be imagining that. Hopefully NCMM can comment about the Boysen cover when he sees your post.

I'm interested to know the difference with the Boysen, I just did a quick check on the Zanotti website & they sell the OEM AP cover for $18.61 + S&H, so it might be worth gettin out the drill bits. :naughty:

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Grand Master

ncmountainman

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the boyesen does not seem to have more volume (if it does its not noticable) the difference between the p-38 and the boyesen (now that ive seen the p-38) is the two fill holes are higher(on the boyesen),right at the top as far up as they can there is also a third hole down where the stock one was. looking at them both it seems as though the boyesen would fill the highest. (thats the problem that is trying to be corrected,elimination of the airspace) the p-38 definately has more "BLING" factor though!! as far as function i'd say the boyesen was an improvement on the p-38 design :naughty: i really don't think you could modify one. i'll go look at the stocker but somehow it doesn't seem possible and i'm a rigger from way back :naughty:

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Grand Master

Dan_Lorenze

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as far as function i'd say the boyesen was an improvement on the p-38 design

I dunno.... Too early to tell, I haven't tested both of them to make a call yet.. I do know that my bike already ran flawlessly without it, I'm just hunting for more... :naughty: Too early to make a call about which one's better, I know I paid a lot less... :naughty:

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tgodwin

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I too have installed the Factory R&D P-38 "Lightening" AP cover. I haven't been able to truely test it out, going riding on Sunday. I rode around my neighborhood and noticed a significant decrease in the off-idle bog, much more responsive. There is still a little bog there though. I have a #45 leak jet in there now and will likely go to a #40 is the bog persists. I also installed the zip-ty fuel screw and haven't quite got it dialed in, so I want to take sometime getting it set up before I report on the P-38. Is the pilot jet the same as the leak jet? Is this why the dealers are confused?

Cheers,

Tim

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Grand Master

ncmountainman

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I too have installed the Factory R&D P-38 "Lightening" AP cover. I haven't been able to truely test it out, going riding on Sunday. I rode around my neighborhood and noticed a significant decrease in the off-idle bog, much more responsive. There is still a little bog there though. I have a #45 leak jet in there now and will likely go to a #40 is the bog persists. I also installed the zip-ty fuel screw and haven't quite got it dialed in, so I want to take sometime getting it set up before I report on the P-38. Is the pilot jet the same as the leak jet? Is this why the dealers are confused?

Cheers,

Tim

pilot and leak two different animules. pilots up in the carb body, leak is in the bowl. there's some pictures earlier on. :naughty:

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Proficient

Seabass

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I rode last weekend with the Factory R&D P-38 Ap cover and my bike never once cut out on me like it had the last couple of times I rode. Now that I've got the parts number for the leak jet I'll be trying that as well.

And I feel like a total puss asking about how difficult it is to replace the leak jet, it looks like one of the easiest mods to do.

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Rising Star

Jackazz

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...Contrary to what I've read, the stock Yamaha leak jet for my bike is a #50, it's what was in there and the manual states it as well...

Hey DL, care to do a little scanning & share w/ us? I can't find ANY mention of the leak jet (accelerator pump jet) in my '04's manual... :naughty:

EDIT:

OK, I just checked the Yamaha online microfiche & noticed the jet, it shows up just below the main jet in the exploded diagram. I checked the part #'s for the accelerator pump diaphram, rod, & cover & they're the same for '04 & '05. I was curious if they were different, as the '04 has a #60 leak jet standard, & they switched to a #50 for '05... :naughty: Maybe they were finally listening & trying to cure the dreaded "Yamabog".

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Experienced

mtrablue

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Hey DL, care to do a little scanning & share w/ us? I can't find ANY mention of the leak jet (accelerator pump jet) in my '04's manual... :naughty:

hey scott, check the 2nd chapter, "maintenance specifications". there's a listing of all your jets. '03 USA wr's came with a 70 leak jet. what do ya know, the EURO model came with a 50.

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Jackazz

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Hey scott, check the 2nd chapter, "maintenance specifications". there's a listing of all your jets. '03 USA wr's came with a 70 leak jet. what do ya know, the EURO model came with a 50.

Sonofa... I guess it does pay to RTFM! :naughty:

Thanks Alan.

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jayled

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I just got off the phone with the man that designed the Boyesen quickshot.

I had questions about the AP short stroke modification (BK) I did to my 2002 FCR 39mm carb on my drz400 and what this product would do for me.

I got my answer and a LOT more! The bottom line is control. This product will give precise throttle control where others will not.

Good luck getting one. I'm waiting on a 3 week back order.

Oh I just remembered he said 50 max on the leak jet.

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Grand Master

ncmountainman

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The bottom line is control. This product will give precise throttle control where others will not.

Oh I just remembered he said 50 max on the leak jet.

it works dang good with the 40, when i talked to boyesen they said they never tried it with a different lj and were aiming for it to work with the stock 50 (05 model) but i don't see it working any better than it does with the 40! ya the more i ride it since install i really notice the throttle control especially on technical uphills. the leak jet from what i gather limits the amount of flow for the ap and the smaller it is the fuller the bowl stays? if thats wrong i'm sure someone will correct me :naughty:

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