done bk mod, guidance required with jets

hey there thumpertalkers,

I have spent heaps of time reading jetting threads in the archives but most seem to relate to bikes without stock pipes or yz timing.

I have a 2000 wr 400, wr timed, lid off, stock jetting for australia- 165 main, 42 pliot,2.5 turns and a DRQ needle in 4th clip pos.

We dont have a grey wire over here.

I have just done the bk mod and set the squirt for about .5 sec, down from about 5 seconds stock. It's just missing the slide as recommended and the bike seemed to go pretty well during a quick 5 minute blast around the block in the dark at 10.00pm last night.(rego. is good) The plug does look a little bit whiteish but I didn,t do a proper plug chop after the ride so this probably isn,t that accurate.

Could one of you jetting gurus such as TAFFY or JD give me a rough idea on which way to go with the jetting. Should I richen up the main and needle clip to compensate for the lack of the AP dribbling for 5 seconds previous to the BK mod? Are my main and needle going to be close enough to ride with until I whack on a new pipe/header, and YZ time it?

Any advice I can get would be much appreciated,

I,ve got a huge easter ride planned and wont be able to get a hold of another needle before then but I have heaps of main and pilot jets on hand to play with.

love this site, tons of info and ideas on free mods.

love it

what PAJ do you get with that 42PJ?

the needle is horrible. it's the Q bit that kills it. get a DMM needle drop the MJ to a 160 and put the DMM at clip 2 or 1. that 42 PJ should be with a 75MAJ ideally.

if you want to go further and gain a little top speed and 3/4 sharpness try 160MAJ, 155MJ needle on either clip 2 or 3. you should add 5 to the MJ when jetting for a D needle as opposed to a E needle. so my EMM @ 150 should be your DMM @ 155

good luck.



thanks very much for replying so quickly, this place is a wealth of knowledge and infinite wisdom to me.

I have a #75 PAJ to go with the 42pilot standard and a #200 MAJ, sorry I didn,t mention these in my first post.

I have swapped to a 160MJ as you reccommended, but havent taken it for a ride yet.

I cant get a hold of another needle before my next ride so will have to use the DRQ for the time being. I have it set at pos 4 at the moment(unchanged since BK mod). Will this be close? rich? lean?

Should I have it in another clip position or take it for a blast with the smaller 160MJ first and see what kind of a difference that makes

Any more advice would help me enormously as I am only about a month into owning my first WR. I am learning very quickly though, thanks to the awesome amount of knowledge contributed to this site by straight talking gurus like yourself.

It really helps to have someone who knows whats going on in these carbs when it comes to tuning. The dealers over here in australia havent really got a clue when it comes to jetting or tuning these weapons properly.

Thanks in advance for any more advice you or any others can offer me. The weather is perfect and the rainforest I,m going riding in over easter is a total blast, cant wait to try your recommendations out in the tacky red mud.

dropping the MJ will have the equivelant effect of dropping the needle 1/2 a clip. so if your 3/4 throttle is improved=do try actually dropping the needle to see if more is good.

likewise if the midrange is **** then try lifting the needle.


need help with bk mod. put "bk mod" in search and came up with alot of info but no real help or pics on how to do it.


I found some really good pictures by searching the archives for 'bk mod'. I think the post you are looking for is even called 'bk mod pictures' or somthing similar, other than that try to find a link to motoman's website, the pictures really make the mod self explanatory and simplify things a lot.


I took it for another strap around the block and there is no poping or backfiring or anything like that to speak of, still starts first kick and idles ok.

The power didn,t seem to really be any more responsive than before I did the bk mod though. I expected her to pull some easy mono,s at a reasonably high speed but to tell you the truth it felt a little bit doughy. I don,t know whether I was expecting too much from this mod and really need a new pipe to appreciate the difference, or maybe my jetting is still all thats holding her back. Coming off a kdx 200 tweaked up to the max,

I really cant complain about the amount of power that I am getting from this WR cosidering it is still trying to breath through the standard exhaust and is basically a stock motor, but I feel it should be a bit more crisp and snappy.

In your reply you said to adjust the needle if the midrange is "****". what do these for stars stand for? good? crap? flat? rich? or lean?.

I assume you meant bad, but an assumption makes an ASS of U and ME, so I wont do that.

Could you please clarify this for me mate, and then hopefully I can stop bugging you.

That is until I get a staintune exhaust and YZ timing and do the whole jetting thing again,

thanks in advance again

Michaeltrundle I read that you are intending to put a staintune exhaust on your bike.A mate of mine got sponsorship from staintune which included the full system. The bike would not run properly.Staintune could not help with any information so the bike was put on a dyno to help jet it but no matter what was done the bike never ran right. The FREE staintune exhaust system was sent back to the factory. A FMF muffler was purchased [$549.00] & the bike now runs perfect. I would not recomend staintune.


if i'd said nice it would have printed it!

sheet is what i said.


If you'd said bad it would have printed it too! :)

Taffy :)


thanks for the guidance, after doing the bk mod and dropping the main jet to a 160 the bike seems to be going really well, starts first kick hot or cold, the plug looks nice and grey, and most of all the fuel economy is imnproved out of sight. I was previously only able to milk about 100 kilometers max. out of the 8 litre yz tank that we get in australia, inluding reserve, but now she manages 150km easily. This isn,t while &%$#@! footing around either.

I think I will ride it like it is for now, until I decide on which exhaust to fit and then I,ll do it all over again.


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