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Author Topic: F4 Jetting  (Read 1554 times)

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Rich

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F4 Jetting
« on: June 03, 2004, 10:35:13 pm »
I have an 00 F4 race bike w/ a BMC filter and Yosh full system.  I just put in a Factory Pro Stage One kit and its kicking my ass.

I went with 145 main jets on cylinders two and three, and 142 on one and four.  I clipped the needles four down from the top.

Initially the bike seemed to run pretty rich.  I had almost no engine breaking.  I turned the mixture in about a turn and a half - two and a quarter full turns out from being all the way in.  It seems much better now, but I'm still a little stumped.  It runs pretty good and power delivery seems pretty smooth.  But it idles pretty odd.  If you just give it some gas it jumps up to about five or six K pretty slow and then drops down to four where it sits for a good five to ten seconds. Even when you are riding it and you let off the throttle it seems to take some time to drop down the RPMs

Any ideas?
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Rich
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Super Dave

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Re: F4 Jetting
« Reply #1 on: June 13, 2004, 05:41:57 am »
Yeah, you've got an air leak, so it's running lean on the idle circuit.

Kind of sounds like you haven't done this before.  Get it to idle decent first.  Then you have to select the proper main.  And you're gonna have to have a nice place to open it up and bracket it in with the correct main jet.  

You've got to have the right main before you can get a feel for the other adjustments.

But look for that air leak or something first.
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Rich

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Re: F4 Jetting
« Reply #2 on: June 13, 2004, 08:53:57 pm »
Airleak.....makes sense.

Where should I look first?  I just synced the carbs today - things got a little better, but still having idle issues.

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Rich
CCS EX GP 179
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Super Dave

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Re: F4 Jetting
« Reply #3 on: June 14, 2004, 02:03:55 am »
Start everywhere.  Anything you took apart...well, that's probably where.  So, the slides, intakes, missing screw, tear in a slide diaphram, etc.  If it wasn't that way before, it's got to be there now.

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Rich

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Re: F4 Jetting
« Reply #4 on: June 14, 2004, 05:27:45 pm »
Actually its been doing it ever since I put the motor back in.  The owner before me didn't torque a spark plug in and it came loose and stripped the threads. I took the motor out, removed the head, and took it to an machine shop to have a thread insert put in it.

I would assume something was leaking after I put the motor back in if this is whats causing the irregular idle.  With that in mind - is there any particular place I should start looking? I truly believe the carbs and airbox are fine - I just checked them again yesterday when I synced them.
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Rich
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Super Dave

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Re: F4 Jetting
« Reply #5 on: June 15, 2004, 05:41:14 am »
Is it mechanical?  Like, the return on the butterflies is slow?  

Sometimes when it's idling normally, you can spray WD40 around the carbs or something and the RPM's will rise...  that will give you an indication of where an air leak might be...
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Rich

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Re: F4 Jetting
« Reply #6 on: June 15, 2004, 11:08:26 pm »
Nope not mechanical.

I stripped it down for the millionth time yesterday and looked over every hose.  It looked like one off the PAIR valve was a little lose but it might have come off from me moving everything around.

In any case, I sealed it up good and put it back together.

The bike seemed to run great initiallly.  I threw on some ghetto street plastic and took her for a spin.  Once it got hot, symptoms returned.  It seems to be putting off a lot of heat as well, which I believe is a result of it running lean.

The idle issues have changed slightly - it will either idle normally or it will jump up to about 3200 and then bounce between 3200 and 3800.  Once you start to engage the clutch it goes back to normal.
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Rich
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Re: F4 Jetting
« Reply #7 on: June 16, 2004, 05:37:08 am »
Have you bothered calling Marc and Leigh at Factory Pro?
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Rich

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Re: F4 Jetting
« Reply #8 on: June 16, 2004, 09:57:27 pm »
I called Factory today - didn't catch the name of the guy I talked to.

He told me he thinks I'm running lean - and to richen it up a full turn.  I cranked it out and will give her a whirl tomorrow.
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Rich
CCS EX GP 179
www.greenlawnracing.com
caferacerinc.com, TC Concepts, Extreme Cycle, Pit Bull, Vortex, Chickenhawk, XT Racing