Jump to content
Sign in to follow this  

FCR 39 – Keihin - WOT Bog 1/4 to 1/2 second

Recommended Posts

Bike: 2003 DRZ400e

Carb: FCR 39 – Keihin

Altitude: Sea Level

Main Jet: 142 (I’ve read this needs to be 155)

Pilot Jet: 45

Starter Jet: 65 (I think, it was hard to read)

Fuel Screw: 2.25 turns

AP: Functioning (Steady stream for about 5 seconds if cracked full)

Plug: New NGK gapped at .029

Exhaust: Stock

Airbox: Wide open, choked out, and everything in between.

 

Idle: Excellent

Low Range: Excellent

Mid Range: Excellent

High Range: Excellent

Rapid WOT: ¼ to ½ second bog.  This is just enough to reset my preload and launch me directly into the object I was intending to clear.  Damn near broke my melon last week trying to clear a downed tree.

 

 

When I quickly crack the throttle, there is an instant bog.  I’ve pulled and cleaned all jets, cleaned air filter, checked accelerator pump, opened and closed air box, replaced and gapped plug.  Managed to get it to idle a bit more clean, but she still bogs when I crack the throttle.  Everywhere else, it hums along perfectly…does anyone have a suggestion?  I’ve read that the 155 main jet is stock for sea level, but I’d prefer to have confirmation from the geniuses around here.

 

Thanks!

Edited by fiBishop

Share this post


Link to post
Share on other sites

First off, you don't ride a bike that way, from zero to wide open throttle, so stop trying to tune for that, as it will drive you insane.

Secondly, only test under load; testing on the stand means nothing

Thirdly, it will always bog if you are in too low of an rpm, then WOT...can't remove that.

 

You need to post and read in the DRZ thread, as this bike is hard to jet perfectly; you need to know all the tricks,,,,,and most never get it just right

You cannot up-tune a carb with stock pipe and intake...you must uncork

Share this post


Link to post
Share on other sites

First off, you don't ride a bike that way, from zero to wide open throttle, so stop trying to tune for that, as it will drive you insane.

Secondly, only test under load; testing on the stand means nothing

Thirdly, it will always bog if you are in too low of an rpm, then WOT...can't remove that.

 

You need to post and read in the DRZ thread, as this bike is hard to jet perfectly; you need to know all the tricks,,,,,and most never get it just right

You cannot up-tune a carb with stock pipe and intake...you must uncork

Troll much?  Seems like you need a hug.

 

To your first point, I do ride that way in technical conditions when I need a quick burst of power from slow speeds/low RPM...IE crawling through a wooded area and needing a shot of torque to clear a downed tree.

 

Your second point is absurd.  

 

Third you're right and I wasn't completely clear.  It's not necessarily WOT, it's simply going from low to high range RPM.  

 

I've managed to get the majority of the bog out by moving down one groove on the needle to richen the mi.  I'm also going to buy a custom jet kit for the stock pipe.  I may at some point go aftermarket, but I'm not going to bother with it for a few HP when I have other mods that have higher priority.

Share this post


Link to post
Share on other sites

...and again, it will never run right till you uncork it....cause stock it's designed for the stock CV carb

 

...right, and when you need to clear a downed tree, you are at 2500-3000 rpm before you provide throttle, not idle.

 

...and yes, with no load on the motor, the vacuum condition of the carb are completely different (very low) and it will act in a way the is irrelevant

 

...moving the needle to correct bog will cause other problems....specifically, a rich mid throttle.

 

Lean bog is 100% accelerator pump.....which you haven't even mentioned....which must be modified from stock, and has nothing to do with vacuum...and that is why it is there, to give you acceleration in near zero vacuum conditions.  You need to upgraded it to 2008 specs (2008 crf250r parts) and tune it (leak jet size, diaphram pin length) and time it (pump timing screw under the throttle wheel cover)

 

If you don't want advice, don't ask for it.

 

 

I'm done with your rude ass

Edited by TheKoolAidMadeMeSick
  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×