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Jetting Question...

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I took the slide out of the carb earlier and discovered that the needle has 5 clip points (it was on the 2nd from the top)

I dont know if its the stock needle, DJ needle or JD needle (I dont know the difference in looks between them)

Well I took the clip off and fitted it on the 4th from the top and re-assembled it all...

What a difference it has made :ride:

It will loft the wheel under power in 1st (I still need to adjust the fuel screw though)

The only downside, is the top end 😏

It used to get to around 85mph (private road) and then run out of puff (big rider plus low gearing)

Since doing the 3x3 mod it wont get past 75 and anything past 70 is slow.

So I know its running lean....

Now, I know that every engine is a little different and that you should tune to your engine uniquely...but I just want to change the main jet once and then ride it 😏

Now I remember reading that a dynojet kit with stock airbox, with performance end can, that the 142.5 stock main is runs about right with the needle on the 2nd clip from the top (which mine was), so I have reason to believe that the main will be a stock...

What would get the power back and run a tad rich?



If its already on a 150 main, what about a 160?

All I can say is that once the top end jetting is sorted, its going to be a very different beast🤣

Definitely need to start saving for an FCR and different header pipe :cheers:

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Yes, its in my first post :cheers:

I'm not worried if the tuning isnt perfect, as long as its a little rich 😏

I was reckoning adding 10 to the jet size

e.g. 142.5 so fit a 152.5

or 150 so fit a 160


I have been searching for pics of a dynojet needle for the DRZ and its definitely a dynojet I have...

All I need to do is sort the main jetting 😏

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For some reason my sig isnt showing :S

Just to recap

2002 DRZ400S K2

DEP End Can (free flowing)

3x3 Air box mod

Dynojet kit (that was fitted before I had bike, so have no other main jets)

Thats why I am just trying to get a rough idea of how much bigger I am going to need....


The damn sig is showing now :S

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I know thats the easiest way to work out what size is in it, but its a bit of a pain to get to take the float bowl bottom off...

So, if its running on a 142.5, what do you reckon I need to put in instead?

And if its running on a 150, what?

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Yes, stock header (as far as I know)

But the DEP can does add some extra flow to the system...

I know the stock header is restrictive, but I cant afford to fit an E header or other header at the moment...

The header is the bigger restriction.

I'm thinking you need around a 145 main jet.

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That doesnt seem a lot bigger than a 142.5 considering the amount of air has increased so much...

Its increased from a 1" x 2" hole (roughly) to a 3" x 3"

Thats an area increase of 4.5 times...

So an increase of a main jet from 142.5 (if thats whats fitted) to a 145 :S

Thats why I was thinking around a 150 mikuni if its got the stock mikuni 142.5

It seems like I might have to buy some different jets 😏

Or just stick a 160 in an have done...

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One thing I have thought of, is what octane fuel do you get in the US (and what do you use)

The minimum I can even get in a petrol station is 95 octane...

Which I use (I am not spending out an extra 10 pence a litre for 98 octane)

95 octane is already expensive enough at £122.9 per litre 😏

I will get a 155 main, stick it in and see how it goes, and do a plug chop (if I can..I dont want to push the bike 1/4 of a mile...)

And from what I can read with most of the kits, they are designed for a stock airbox with stock pipe (or modified)...

My end can increases the flow a lot compared to even a modified stock pipe, and with the 3x3 mod, I still reckon a 155 might be needed...

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Yes, because I wasnt sure whether I would need to remove the float bowl to get to the main jet when I realised I have a dynojet needle...

And as soon as the main jet circuit comes into play, the bike just runs out of power very quickly...

Which, unless my knowledge of tuning in general is completely wrong, means its not getting anywhere near enough fuel....

If it was just a bit lean, then it would still have power just not as much...

The rest of the jetting seems about right, and has a lot of power and torque...

Thats why I thought that I need a major increase in main jet size (around 10 so 142.5 to 152.5)

So I think the best option I have got is get a 155 main jet...

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For some reason my gut tells that with your Dynojet setup the 155 main is going to be too rich. But give it a shot, it may be what you need. But you really should check all the jets and see whats in there now before coming to any conclusions.

Was the jetting way off before you cut the 3"x3"? I ask because I cut mine before jetting and while it definitely ran on the lean side it didn't lose anywhere near 10 mpg off the top end.

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