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FZR 400 Carb Tuning setting etc....

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kirbster

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FZR 400 Carb Tuning setting etc....

PostMon Jan 21, 2013 9:45 pm

Been digging into my recently aquired Canadian model FZR400U. 1988.

Teh bike came with a supertrapp superlight

http://www.supertrapp.com/product_secti ... =425-20160

It had all 8 disks in it. It is a bit loud. It has the stock airbox and stock headers.

Carbs have benn looked through,

Pilot Jet: 20 This i sup two sizes- any pointers on mixture screw settings based on this increase? Stock is 3.5 turns out.
Main Jet: 87.5
Standard needle shape but upgraded to one with 5 clip positions and it is on #3.
Emulsion tubes look like brand new (i bought some Factory Pro to install but will leave teh stock in for now).
Needle valves look good.


Float height seemed way off compared to what i read on here. Rght around 10mm.

The exhaust is very sooty black.

When i had her out back in November, she seemed a bit lean up top but pulled reasonably well throughout the rev range.

Now i was wondering if whoever tuned the carbs was compensating for stock jets by raising the fuel level (dropping float height).

Now that i have set the level to about 12mm, should i worry about being overly lean on top? The increased pilot size should richen up the bottom some. But this could leave the top lean under higher throttle. Correct?

Is anyone here running a slipon with stock exhaust header and stock airbox/filter? If so what have you done in the way of tuning?
As it stands i am tempte dto buy a few main jet sizes (90 and 92.5) just in case i need to do this.

My other option is to remove disks from the Supertrapp to reduce flow (and noise).

Any thoughts from the gurus in here?

I have to replace my carb boots as well, as mine are starting to split. And it is very cold here right now, so it will be a while before i get her started up again.


Any theories would be appreciated.
Thanks
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Evilchicken0

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Re: FZR 400 Carb Tuning setting etc....

PostMon Jan 21, 2013 11:55 pm

First I'd look an find maelstrom (spelling) and see if he does the carb rubbers - I think yours is a genesis so you might be lucky.
If the can is noisey have a look at repacking it. You use stainless wire wool with matting on top. Hold it with stainless zip ties and sealed rivets.
Once these are done I'd honestly say to take it to a dyno and have if setup. By the time you kick the settings around and buy jets - only to reset to stock you'll wish it was just done, I know it costs more but longterm is worth it.
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kirbster

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Re: FZR 400 Carb Tuning setting etc....

PostTue Jan 22, 2013 1:51 am

Carbs are in good general condition. I may need two float bowl gaskets, but have these on order.
I really want to get it close on my own, i understand the dyno tuning thing. but really i dont care about peak power as long as it is running well.
My real question is what happens now that i have adjusted the floats? Will i find it needs a larger main to compensate?
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LiteTekBlair

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Re: FZR 400 Carb Tuning setting etc....

PostTue Jan 22, 2013 2:07 am

Thanks for the plug EC.
I'm LiteTekBlair now. Where will it end?
Anyway back to the subject. I am onto the 1WG and Mr Kirbster is going to be checking my float bowl sample for fit because my 1WG has the wrong carbs. I will post when they are done.
cheers
Blair
Carb seal kits in viton
http://litetek.co
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Evilchicken0

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Re: FZR 400 Carb Tuning setting etc....

PostTue Jan 22, 2013 11:46 am

kirbster wrote:Carbs are in good general condition. I may need two float bowl gaskets, but have these on order.
I really want to get it close on my own, i understand the dyno tuning thing. but really i dont care about peak power as long as it is running well.
My real question is what happens now that i have adjusted the floats? Will i find it needs a larger main to compensate?

Balance the carbs first
Think of the carbs, engine and exhaust as a funnel.
A bigger exhaust means more flow out the bottom - so firstly you need to raise the needle up. If that doesn't make it rich enough then you change the jet (and drop the needle). When I put a can on my 3TJ it didn't need rejetting, that's probably down to the can though.

Dyno's - they're not really about the top power graph, that's the last thing you should look at. Firstly they're about fuelling, they give you a fuel / air ratio on the bottom of the sheet, an experienced opperator will get the best compromise for the engine and they'll do it when the bikes under load. It's up to you but as you see you can do one thing and then have to do something else to compensate. Personally I don't bother, I get it done and leave it, (although I do check the balance at a service), less stress in your day.
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kirbster

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Re: FZR 400 Carb Tuning setting etc....

PostTue Jan 22, 2013 9:55 pm

Evilchicken0 wrote:
kirbster wrote:Carbs are in good general condition. I may need two float bowl gaskets, but have these on order.
I really want to get it close on my own, i understand the dyno tuning thing. but really i dont care about peak power as long as it is running well.
My real question is what happens now that i have adjusted the floats? Will i find it needs a larger main to compensate?

Balance the carbs first
Think of the carbs, engine and exhaust as a funnel.
A bigger exhaust means more flow out the bottom - so firstly you need to raise the needle up. If that doesn't make it rich enough then you change the jet (and drop the needle). When I put a can on my 3TJ it didn't need rejetting, that's probably down to the can though.

Dyno's - they're not really about the top power graph, that's the last thing you should look at. Firstly they're about fuelling, they give you a fuel / air ratio on the bottom of the sheet, an experienced opperator will get the best compromise for the engine and they'll do it when the bikes under load. It's up to you but as you see you can do one thing and then have to do something else to compensate. Personally I don't bother, I get it done and leave it, (although I do check the balance at a service), less stress in your day.


The plan is to get the bike back together once my carb boots arrive. Exhaust is still out for ceramic as well. Hopefully in about 2 weeks time.
Then its fire her up and check fuel levels in carbs. If good, then sync carbs. Adjust mixture screws. If i get a warm day i will take her for a quick run to see how she is running.
Not much else i can do till spring.
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Evilchicken0

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Re: FZR 400 Carb Tuning setting etc....

PostWed Jan 23, 2013 10:26 am

Sounds like a plan - chilly out there isn't it :grin:
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kirbster

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Re: FZR 400 Carb Tuning setting etc....

PostWed Jan 23, 2013 1:46 pm

Evilchicken0 wrote:Sounds like a plan - chilly out there isn't it :grin:


Yup! Not much use in trying to do jetting in -21C. First off you cant feel your fingers, so handling tiny parts is impossible!

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