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Mikuni BSR36 Jet Types - Photos!

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Hey if you have problems with the images just copy and paste the urls.

Don't you get pissed off at how tough it is to find

basic technical info on the web? So do I. So here

it is, served up on a plate for you.

What main jets and pilot jet types are used in the

Mikuni BSR36 on 2003 KLX400SR and DRZ400S USA (and

EU and UK)?

Here it is for you pictorially, including my own

'stage 1' mods based on seat-of-part performance and

plug color of my individual KLX400SR.

http://i162.photobucket.com/albums/t279/tehlos/100326MikuniBRS36BottomJets_.jpg

The BSR uses the small round jets for main and

starter jets. I had the next richer 147.5 only in

the large round style. I found zero difference

between the large round and small round Mikuni main

jets except head diameter, which goes from 6 to 8mm.

Everything else is exactly the same. I checked out

flow clearance around the jet head with respect to

the bowl and found it huge, so no clearance issues.

Jet sizes, by the way, are no big mystery. On

Mikuni they are just metric diameters with the

decimal moved right two digits. So a 142.5 main jet

is in fact 1,425mm diameter or .056". Amazing,

hugh?

Stage 2 on the main jet will be the large round

152.5 I have, but plug color on the 8 heat range

plug was not particulalry light with the stock

142.5. Maybe 7 on the heat range (plug insulator

conductivity) plus the 152.5? We shall see.

Now I would have preferred a 25.0 versus the stock

22.5 pilot jet for stage 1 had I had one. But

again, I had to get in there to confirm jet type.

The bike ran lean on bottom, with excessive engine

braking throttle off, then lurching forward when the

throttle is cracked open. The lean pilot circuit

was also confirmed by the fuel screw - once

liberated from the infernal EPA nanny cap - to be

turned 3.3 turns out. That's a lot. I'd rather

have a 25.0 pilot jet and, say, 2.5 turns out with

enrichening.

But jetting varies with individual bikes, and we

shall see how my other mods affect the bike before

going to my budget 'stage 2', changing pilot jets

for example.

http://i162.photobucket.com/albums/t279/tehlos/100326MikuniBRS36TopJet_.jpg

Now this top jet is the air jet for the pilot jet.

It breathes through the air space under the carb

diaphragm, which is roughly the same as it being on

the airbox side of the slide in the venturi. The

jet for EU and UK is larger by 0,3mm for some

reason.

http://i162.photobucket.com/albums/t279/tehlos/100326MikuniBRS36JetNeedle_.jpg

The jet needle I found to be the exact same as the

EU and UK adjustible needle. Here I typically just

raise the needle to enrich the midrange response a

little, in this case with 1,27mm or .050" shims.

That llows loading the bike more, such as gearing up

to 39/16 as I am about to, without the midrange

going all soft.

We shall see.

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manuals says that i should have 5dh36, but i have 5dh39 needle.

whole internet know nothing about this thing 👍

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lol,you guys are killing me.

there is nothing that you have posted that hasnt been discussed here in depth hundreds of times.

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lol,you guys are killing me.

there is nothing that you have posted that hasnt been discussed here in depth hundreds of times.

👍

You are right of course, but the problem is getting at that information efficiently. Got a PM asking to use the photos in an FAQ, so it must've been useful to someone.

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:jawdrop:

:applause:

You are right of course, but the problem is getting at that information efficiently. Got a PM asking to use the photos in an FAQ, so it must've been useful to someone.

Easy now 👍 ,, he did not say it was not useful info,, he said it has been discussed a million times on the forum and he is correct.

The search works great, it's just that most people are unwilling to use it as designed.

Folks should try these next time they want to use the search (though so many would prefer to just post a question and let others do the work for them)

Searching Forums and Threads

And this one

How to use advanced boolean searching

The same folks who are not willing to read the FAQ,, and then post up about this "New" DRZ issue that ruined there motor... melted there stator, broke the case, etc etc, only to have a user here link them to the thread in the FAQ that describes that exact issue and the preventive fix 🙂:banghead:

Same thing happens with other common questions, and folks post up a simple search string in seconds that nets the user the answers he was seaking... For the most part, The DRZ sub forum likes to help those willing to help them selfs, an rewards that self action with all the Q&A they can stand.

Often those who are too lazy or otherwise unwilling to even try and find the answer them selfs are ignored. It's not the lack of understanding or asking of a often answered question that is frowned upon, it's the lack of self help.

I asked if i could use the pictures in a future write up.. Not that I would be sitting down today and writing it because it was new, and otherwise unavailable info.. :cheers: I make that same request about 5 times a week and when I get a reply like yours I copy and store the info and reference data for later use.🤣

Thanks for the yes.. not sure if or when I'll write that article

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The search works great, it's just that most people are unwilling to use it as designed.

if that's a rock into my garden - i did use search and use it constantly🤣

and i think there is no such thing as new topics - just new people 🙂

p.s. Eddie really surprises me - he just seems not getting tired saying same things to different people. 👍

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🤣

Easy now 👍 ,, he did not say it was not useful info,, he said it has been discussed a million times on the forum and he is correct.

....Thanks for the yes.. not sure if or when I'll write that article

Yeah, I can understand the new versus old people thing. Thanks for the search tips. That'll help. Forums - especially this one - can be overwhelming in shear volume!

BTW. I've done my test rides and found my original assumptions were correct. Pilet jet 25 would have been a smidge more ideal than 22.5, but I can open up the fuel screw to 4 turns out and get by.

The 147.5 versus 142.5 main results in very strong top-end performance, even geared up 44/16 and 39/16. I don't think on this individual bike going larger will add anything to power. It seems stoichiometric as is. The raising of the jet needle also seems about right. No dyno of course, just seat-of-pants comparison, pegged to pressure-temperature.

I have, and will keep, the stock pipe unaltered. The airbox hole was opened up not to 3X3 but simply extending the radiused hole left 1-1/2". It breathes quite well and has a pleasing intake roar feedback.

Other than the appaling 5-speed gearbox, I'm finding this bike to be quite sweet and fun for road work. For dualsporting with offroad, I vastly prefer my KLX330S.

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just fyi stoich is not where you want to be.

a drz will not even rev properly at 14.7 to 1.

if you really want to see what the a/f ratio is you need a wide band a/f meter.

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just fyi stoich is not where you want to be.

a drz will not even rev properly at 14.7 to 1.

if you really want to see what the a/f ratio is you need a wide band a/f meter.

I thought stoichiometric was not necessarily a specific number (though 14.7 is close) but that AFR in which the engine was making the most efficient use of of available oxygen, a wide number of variables considered. I assume you are saying we should be on the rich side of Stochiometric?

I don't have a wide band AFR meter, only years of experience and seat-of-pants meter. I can say this thing pleasingly runs like a scalded dog, even with the new 39/16 gearing, which is a dream on the highway.

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i will let you use the search function to learn more about it,but just for example at wide open throttle maximum power is produced at 12.8-13.2 to 1.

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