Bike Jetting

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Bike Jetting

Post by difflock123 on Fri Jul 30, 2010 7:03 pm

I know there are some bikers on here so wanted to ask a quick question...

I have a Suzuki DRZ400S
Stock Mikuni CV Carb
DEP Freeflowing end can

The bike has been dynojetted to suit the above setup (a little bit richer than it should be really but nothing to worry about)

I have modded the airbox so instead of a 1" x 2" hole, its got a 3x3" hole Smile

I have altered the clip position on the needle and up to it starting to really use the main jet, it runs brilliantly...

However, when it goes onto the main jet circuit it runs out of all power so its running lean...

The stock main is a 142.5
If its got that, what do you reckon would be a good idea to change the main jet too?
I reckoned a 150/152.5

But if its already got a 150 main, do you reckon a 160?

I am not looking for perfect tuning as long as its slightly rich when on the main jet, I dont mind Smile

Any thoughts?

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Re: Bike Jetting

Post by rich the mechanic on Fri Jul 30, 2010 9:20 pm

Have you got a free flow air filter if not tape the bigger inlet up a bit and see if it gets better. are you sure its leaning out as going rich can have a power loss as well as lean gets a slow - no power burn where as rich gets a fast no power burn.
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Re: Bike Jetting

Post by difflock123 on Sat Jul 31, 2010 9:59 am

Its definitely lean...

Because I discovered the bike had got a dyno jet kit setup for the DEP can and stock airbox, I lifted the needle from the second clip down to the 4th clip down.
To get more fueling in the midrange...

The pilot circuit needs a slight adjustment on the fuel screw, but nothing much.

The only problem, is since opening up the airbox (4.5 times bigger intake hole area) the main jet just doesnt get enough fuel through...

It ran a bit rich on main jet before (checked doing a plug chop)

So with the extra airflow into the carb, it definitely needs a bigger main jet...

I think I will get a 155 main and stick that in and see how it goes...

Forgot to add, that its got a foam filter in it...

I did a plug chop as well, and currently it came out white, which is definitely lean...

The way it just stops really, when the main jet comes into play, to me says that it isnt getting anywhere near enough fuel, so I think a drastic increase in jet size is required...

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Re: Bike Jetting

Post by rich the mechanic on Sun Aug 01, 2010 8:32 pm

right don't go to mad on uping the jet size try up 2 sizes first and see how different it feels and runs its very easy to go for much more than is needed and miss the sweet spot on the way.
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