DCSportbikes.net  
» Help Support .NET!
DCSportbikes Premier Membership for 25$ per year. Discounts! Click here for full information.

Now available in the .NET Shop:



Get your DCSBN Gear!
» Shoutbox
Sorry, only registered users have the ability to use our real-time shoutbox to chat with other members.

Register now, it's free!
» Online Users: 492
5 members and 487 guests
2blueyam, Diggy, dubplaya, Sal_the_man, tonetone
Most users ever online was 4,519, September 2, 2015 at 03:26 AM.
Go Back   DCSportbikes.net > Sportbike Operation > Test and Tune

Reply
LinkBack Thread Tools
Unread
  (#1)
MSF Student
 
Posts: 99
Join Date: April 23, 2003
April 28, 2004, 08:44 AM

I'm confused. I p/u a 93 F2 w/less than 20k miles on it (actually I think it's like 14k miles) from OH. Brought it home to VA and fired it up for the first time. Runs sputtery, like it's running outta gas. Pin 1st gear and you're prettty much ok. But the faster you go in the higher gears, the more you notice it stumbling, to the point where once you get to say 4th, if you upshift you may not really pull anymore. I even went into 5th and 6th on the hwy but they wouldn't really pull and I'd have to go into 4th/5th and pull the clutch in, pin the throttle and pop the clutch just to keep accelerating past the 105-115mph. Wouldn't go past those speeds.

Compression if I'm not mistaken was 135# across the board

AND

Valves are fine

AND

Stock Carbs

Pilot Screws: 2 1/2
Main Jets: 135
Pilot Screws: 40

Kehin Mains.

AND

Stock Pipe

AND

Stock Filter

Spark plugs were replaced and were showing white (lean).

Conclusion: Buy a jet kit? My mechanic says the airbox looks ok but that maybe some of the hoses/holes/ventilation/etc may not be exatcly as should be (maybe missing something?) and that in his experience this may be the cause. If this is the case, would a jet kit alone (and time) theoretically fix it? Only reason I'm duckin a dyno is $$$. As long as it runs fairly smooth I'm fine. This will just be used for stunting and strip, nothing major.

As an aside, it sticks w/my buds 02 gsxr 600 till we shift into 2nd. After that it gets crappy. And I used to have an FZR 600 and this is no where near that was (as it runs now). And I had a gsxr 1100 prior to the CBR. Just thought I'd mention as background reference.

Thanks all,

Ali
  Send a message via AIM to  
Reply With Quote
Unread
  (#2)
GP Champ
 
Twiggy6's Avatar
 
Posts: 2,115
Join Date: December 27, 2002
April 28, 2004, 09:35 AM

Your mechanic needs his head examined. You can look at the airbox and tell if it's been cut or modified. If it's got large holes in it, guess what?

Is there any noticable difference in any of the plugs? If you ride with the choke on, does it run better? Try blocking 1/3rd of the airfilter...run any better?

If Keihin main jets are similar in size to Mikuni, your mains are WTF big. 135s are stage I sized for liter bikes.
  Send a message via AIM to  
Reply With Quote
Unread
  (#3)
GP Champ
 
Twiggy6's Avatar
 
Posts: 2,115
Join Date: December 27, 2002
April 28, 2004, 09:46 AM

You need to search one of the CBR sites for the stock carb set up. What size are the stock mains? Pilots? Mixture screw settings? Needle settings?

You said the pipe was stock. Leave it stock for troubleshooting purposes. Is there an ingnition advancer on the bike? Do you have a stock paper element air filter? Are the carb boots NOT cracked and in good condition? Does it sputter at less then WOT all the way to redline?
  Send a message via AIM to  
Reply With Quote
Unread
  (#4)
GP Racer
 
Bmiester's Avatar
 
Posts: 1,102
Join Date: November 11, 2002
Location: Sterling
April 28, 2004, 10:10 AM

Look here.

http://63.240.54.76/out/Manuals/91-94%20CBR600F2.pdf

This is the F2 manual. Look at it, print it. It should have all the stock specs.


You should probably go to CBRWorld.net as well. They would be more help there than here.
  Send a message via AIM to Send a message via AIM to Bmiester  
Reply With Quote
Unread
  (#5)
boxing twins
 
hayabusafiend's Avatar
 
Posts: 581
Join Date: April 6, 2003
Location: Northern California
April 28, 2004, 12:02 PM

Did someone tell you the jet sizes or did you take apart the carbs and check them yourself? Take the carbs apart and clean them, especially the float bowl.

Gasoline that sits creates varnish that is extremely gummy and plugs up the carb jets. Fouled carbs give you a lean mixture, assuming the bike runs at all.

As Twiggy asks, does the bike run better with the choke on? The choke richens up the air/fuel mixture. If it runs better, then you're currently running lean.

Also make sure you've got spark on all four cylinders.


-- Chris
BMW R1100s
(previous rides: '82 KTM250, '95 CBR600F3, '98 Buell S3T, 2000 Hayabusa, 2008 R1200R)

"Any sufficiently advanced technology is indistinguishable from magic." -- Arthur C. Clarke
  Send a message via AIM to Send a message via AIM to hayabusafiend  
Reply With Quote
Unread
  (#6)
GP Champ
 
Twiggy6's Avatar
 
Posts: 2,115
Join Date: December 27, 2002
April 28, 2004, 12:04 PM

I just remembered that I rebuilt a set of carbs on a CB1000 earlier this year. Well, I should say I just remembered it also had keihins. The mains were 106s and it was a stage 1.
  Send a message via AIM to  
Reply With Quote
Unread
  (#7)
MSF Student
 
Posts: 99
Join Date: April 23, 2003
April 28, 2004, 12:52 PM

The choke doesn't seem to help much either way

I'm about to order a DynoJet kit. I'm gonna drop it off at one of the local shops around here. Fuck it, it won't be THAAAT expensive when it comes right down to it. I HATE this kinda shit! Mark my words next bike will be FUEL INJECTED!!!

The jet sizes were given to me by the mechanic looking at it. All 4 cylinders are firing, that's for sure. I think it has something to do with the airbox. I personally haven't looked at it but you guys did bring up excellent points.

Local shop said that it may not even need a Stage 1 jet kit but I'm gonna pick one up just in case. Worst case, I'll return it or ebay it.

Thanks everyone and if there are any more ideas, I'll be happy to relay them to my mechanic....except Twiggys first comment :o

Ali
  Send a message via AIM to  
Reply With Quote
Unread
  (#8)
Ballaugh Bridge
 
CrazyMotorcycleGuy's Avatar
 
Posts: 6,868
Join Date: September 29, 2002
Location: VA
April 28, 2004, 03:31 PM

Check the fuel and vacuum lines. You may not be getting enough fuel. Like what you described. It will run ok in first to start out, then as work through the gears demanding more fuel, the fuel supply rate isn't keeping up with demand and things get lean.


'08 MARRC Expert Racer of the Year
2009 #3 Combined Overall Championship

  Send a message via AIM to  
Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Powered by vBadvanced CMPS v3.2.3


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Friendly URLs by vBSEO 3.6.0
vBulletin Skin developed by: vBStyles.com
All logos and trademarks in this site are property of their respective owner. The comments are property of their posters, all the rest 2002-2010 by DCSportbikes.net. DCSportbikes.net is owned by End of Time Studios, LLC.