Petrol Bike jetting...

[IgorVigor]

I know, I still have a petrol bike, but its a case of having to as cant afford much at the moment...

The bike in question is a Suzuki DRZ400S
Mikuni CV Carb (Cant afford the Keihin FCR)
DEP End can.

I have done an airbox mod commonly refered to as the 3x3.
Which basically entails removing the snorkel (which is roughly 1" by 2") from the airbox and then cutting the hole to 3" x 3"...

I have done that, and have lifted the needle to the 4th clip and its running brilliantly...

Apart from 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 to mod it wont get past 75 and anything past 70 is slow.

So I know its running lean....

Across the rest of the range its brilliant as I said, so its only when the main jet is in play...

Now, I know that every engine is a little different and that you should tune to your engine...

BUT, I dont really feel like constantly having to fiddle with the jets (its a fiddle time consuming job)

So, if the main jet is 142.5 what size would you reckon to get the power back?
I was thinking a 150~152.5

If its already a 150, a 160?

Thanks...

[Sphere]

Try a DRZ tuning section of an appropriate forum? I've found one in Dutch, but not much use to you.

[IgorVigor]

Already tried them...

They werent much help really...

Always on about buying this kit, and that kit :S

I got a bit fed up in the end, so drilled the main jet, and its fine now....

[andrewaust]

I got to this thread a little late, when I'm jetting I usually go by steps of 5 ie; 150, 155, 160 etc for main jets.

If I cannot source the jets "usually get them cheap by a UK supplier on ebay" I have a jet drill set which does the job.

Jetting can be tricky as you sometimes have to play with jet needles, pilot jets as well as main jets, then with the new carbs your looking at fuel pumps, leak jets and air metering jets on the bell-mouth of the carburettor.

Then we get fuel injection on the newer bikes



A

[IgorVigor]

But on a petrol engine, you cant beat a nice carb
I dont like any electronic fuel injection and the only mechanical injection I like is on a diesel

Even my S3 Land Rover SWB has been modded and instead of the stock zenith, its got an SU HS6

I havent given up on a diesel bike, far from it...its just I dont have the money at the moment to build one
I had to get rid of the Escort Diesel before I had a chance to remove the engine due to circumstances....

Oh well....

As for the jetting, I am just happy its all working
I worked out the large jump after reading a lot of info..
As stock the bike runs quite lean, so a 142.5 stock is lean, BEFORE modding the airbox and different can...

Fitting a high flow can (before I got it) and then cutting the intake bigger, requires a big jump..
They need a 145~147.5 as stock really...
Its on basically a 156~157 which is a tad rich, but it works well, so I am happy....

Thanks for the input though