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Can't figure out correct fuel mixture? Please help.

CBR 600F3 1995 - 1998 CBR 600F3 Forum

Can't figure out correct fuel mixture? Please help.

  #1  
Old 07-03-2017, 04:29 PM
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Default Can't figure out correct fuel mixture? Please help.

Info:

97 CBR F3
​​​​​​Denver (5k average riding elevation)
Yoshi slip-on
K&N filter

She couldn't get above 10k rpm under load no matter what I tried (in neutral she would just fine).

​I put in larger mains (140 142 142 140) huge jump I know but the PO had them jetting 138 140 140 138 already and I felt she was running lean before I opened the carbs up. I threw in the larger mains just to see while I waited for the smaller ones, and she now can make it to redline but I have to hold WOT for a bit and she struggles to get there.

Throttle position has so discernable impact. I can crack it wide open and she'll climb just fine until 9k and start to sputter up to redline. Any ideas?
 

Last edited by Kevin Hamilton; 07-03-2017 at 04:54 PM. Reason: Grammar
  #2  
Old 07-05-2017, 12:58 PM
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Originally Posted by Kevin Hamilton View Post
Info:

97 CBR F3
​​​​​​Denver (5k average riding elevation)
Yoshi slip-on
K&N filter

She couldn't get above 10k rpm under load no matter what I tried (in neutral she would just fine).

​I put in larger mains (140 142 142 140) huge jump I know but the PO had them jetting 138 140 140 138 already and I felt she was running lean before I opened the carbs up. I threw in the larger mains just to see while I waited for the smaller ones, and she now can make it to redline but I have to hold WOT for a bit and she struggles to get there.

Throttle position has so discernable impact. I can crack it wide open and she'll climb just fine until 9k and start to sputter up to redline. Any ideas?
Hi , just checking the sizes in the manual and they show 130 and 132 for above 5000 feet and 132 and 135 for below 5000feet, also check through you DAI system ,seem to remember someone had a problem with that as well
 
  #3  
Old 07-06-2017, 12:25 PM
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Originally Posted by CaBaRet View Post
Hi , just checking the sizes in the manual and they show 130 and 132 for above 5000 feet and 132 and 135 for below 5000feet, also check through you DAI system ,seem to remember someone had a problem with that as well
Thanks Cab, I just ordered some new mains and pilots. What is a DAI system? Dual air induction?
 
  #4  
Old 07-06-2017, 12:31 PM
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Originally Posted by Kevin Hamilton View Post
Thanks Cab, I just ordered some new mains and pilots. What is a DAI system? Dual air induction?
Hi DAI (Direct Air Intake) rather like the ram air system, the solenoid is connected to the speedo , but riders usually do the clean air mod taking out the solenoid, pics on You Tube
 
  #5  
Old 07-06-2017, 03:18 PM
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Originally Posted by CaBaRet View Post
Hi DAI (Direct Air Intake) rather like the ram air system, the solenoid is connected to the speedo , but riders usually do the clean air mod taking out the solenoid, pics on You Tube
Alright so I've learned how the solenoid works, I've learned how to take it off, I've learned what the solenoid inventor's favourite colour is. But I haven't read anywhere WHY you would bypass it?

Also, if I were to bypass it, would I have to rejet? I also have the fuel pump bypassed, for what it's worth.
 
  #6  
Old 07-06-2017, 03:37 PM
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You don't have to take the solenoid off, that was a suggestion
 
  #7  
Old 07-06-2017, 05:06 PM
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Have you tried re-shimming your needle?
 
  #8  
Old 07-06-2017, 05:59 PM
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Originally Posted by Kevin Hamilton View Post
Info:

97 CBR F3
​​​​​​Denver (5k average riding elevation)
Yoshi slip-on
K&N filter

She couldn't get above 10k rpm under load no matter what I tried (in neutral she would just fine).

​I put in larger mains (140 142 142 140) huge jump I know but the PO had them jetting 138 140 140 138 already and I felt she was running lean before I opened the carbs up. I threw in the larger mains just to see while I waited for the smaller ones, and she now can make it to redline but I have to hold WOT for a bit and she struggles to get there.

Throttle position has so discernable impact. I can crack it wide open and she'll climb just fine until 9k and start to sputter up to redline. Any ideas?
It doesn't make any sense that a normally aspirated engine with no significant changes to the engine is running lean. At 5000' you've only got 83% air density. You'd most likely be running rich. You should be looking at going to smaller jets not larger.
 
  #9  
Old 07-07-2017, 11:56 AM
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Originally Posted by CaBaRet View Post
You don't have to take the solenoid off, that was a suggestion
I know, I'm essentially wondering if there would be any downside to taking it off; if it cuts out a variable with no discernable loss then hell yeah I'll scrap it.

Originally Posted by hamlin6 View Post
Have you tried re-shimming your needle?
Didn't know you could, there's no clip notches on mine and I thought you could only shim it richer (washers) without moving a clip.

Originally Posted by IDoDirt View Post
It doesn't make any sense that a normally aspirated engine with no significant changes to the engine is running lean. At 5000' you've only got 83% air density. You'd most likely be running rich. You should be looking at going to smaller jets not larger.
That's what I was confused about initially but I could have sworn it was running lean with how she was running and the fact I have an aftermarket filter and pipe (probably less of an impact on a/f ratio than I first thought). Unfortunately, for whatever reason I somehow didn't even notice the richened main jets the first two times I pulled the carbs so I ordered the bigger jets prematurely.

​​​​​​​I'm going to order 130s, 132s, 135s, and probably 38 slow jets. Should I put anything else on that order before I place it? I'm sick of paying S&H for small mistakes. Thanks guys.
 
  #10  
Old 07-07-2017, 08:44 PM
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Fuel pump bypassed, high speed issues, thinking you're lean.... Is it possible you're just not getting the fuel required at higher throttle?
 

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