650L w/flatside


4 replies to this topic
  • pjpoo

Posted January 26, 2007 - 11:36 AM

#1

I made a post about tuning my bike which the previous owner had put together. It's pod-filtered and has a full exhaust (which leaks). Riding the bike, it stumbles hard in the mid-range and a bit in the low range. I've had it stall out completely when whacking the throttle open to pass, etc. Comments left suggested that there is no way to effeciently tune a CV carb with a pod filter.

Enter the flatside. Is this really the best option for tuning with pod filter? I'll jump for it if so, because as I'm a n00b to carbs, any tuning I should have to do should be a bit more remedial. Also, going back to the airbox would be a pain and just as expensive probably, as the snorkel and connection from carb to airbox has been cut out and eliminated completely. And the battery and fuses were moved to the air box. I would have to source an entire air box with snorkle, etc, as well as a battery box.

http://www.xrsonly.c...emart&Itemid=77

XRS Only will more or less set up the flatside for your setup AND include extra jettings for any changes that might have to be made! This seems like a no-brainer, win-win situation to me. $230 for a carb that can be efficiently tuned and already set up....versus the pain and time of trying to tune a cv carb that won't ever be efficient anyway, or the extra time and money to put the bike back closer to stock...

Advice? Any reason to not do this?

  • oldchvytrx

Posted January 29, 2007 - 03:17 PM

#2

I made a post about tuning my bike which the previous owner had put together. It's pod-filtered and has a full exhaust (which leaks). Riding the bike, it stumbles hard in the mid-range and a bit in the low range. I've had it stall out completely when whacking the throttle open to pass, etc. Comments left suggested that there is no way to effeciently tune a CV carb with a pod filter.

Enter the flatside. Is this really the best option for tuning with pod filter? I'll jump for it if so, because as I'm a n00b to carbs, any tuning I should have to do should be a bit more remedial. Also, going back to the airbox would be a pain and just as expensive probably, as the snorkel and connection from carb to airbox has been cut out and eliminated completely. And the battery and fuses were moved to the air box. I would have to source an entire air box with snorkle, etc, as well as a battery box.

http://www.xrsonly.c...emart&Itemid=77

XRS Only will more or less set up the flatside for your setup AND include extra jettings for any changes that might have to be made! This seems like a no-brainer, win-win situation to me. $230 for a carb that can be efficiently tuned and already set up....versus the pain and time of trying to tune a cv carb that won't ever be efficient anyway, or the extra time and money to put the bike back closer to stock...

Advice? Any reason to not do this?


<<<<<<<<>>>>>>>>
I know you probably don't want to hear this (and it'll start a long and protracted argument from the gadgeteers), but the fact the stock carb is a "CV" or vaccum slide constant velocity type is not the problem with your "stumble" you have jetting issues. Possibly as simple as clogged jets. The CV is a very efficient, dependable and forgiving unit and one of the reasons it is used on this bike is that is not altitude sensitive and will support a broad range of bolt on mods. My XR "L" is extensively modded and STILL retains the 42.5mm Keihin CV carb with a DynoJet kit. It runs out exellent and has been ridden at altitudes of 700'ASL (home)to 8000' ASL with no changes in tuning. It will cruise @ 75 mph all day or chug @5mph down a rocky stream bed while getting an average of 45mpg. It'll also whip the neighbor's Sportster in a drag race with Dunlop 756 knobbies still on it!
I'm quite aware there are better carbs for making HP like flatslides or an Edelbrock unit. It sounds like this is the way your wanting to go but I just wanted to put my 2 cents worth in in defence of a fine fuel mixer like the Keihin CV.:applause:
:ride: :ride: :ride:

By the way, don't install the Mikuni that XR's shows in their catalog as pictured..... it'll leak like heck!
(It's upside down)..:naughty:

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  • XR650L_Dave

Posted January 30, 2007 - 10:23 AM

#3

<<<<<<<<>>>>>>>>
I know you probably don't want to hear this (and it'll start a long and protracted argument from the gadgeteers), but the fact the stock carb is a "CV" or vaccum slide constant velocity type is not the problem with your "stumble" you have jetting issues. Possibly as simple as clogged jets. The CV is a very efficient, dependable and forgiving unit and one of the reasons it is used on this bike is that is not altitude sensitive and will support a broad range of bolt on mods. My XR "L" is extensively modded and STILL retains the 42.5mm Keihin CV carb with a DynoJet kit. It runs out exellent and has been ridden at altitudes of 700'ASL (home)to 8000' ASL with no changes in tuning. It will cruise @ 75 mph all day or chug @5mph down a rocky stream bed while getting an average of 45mpg. It'll also whip the neighbor's Sportster in a drag race with Dunlop 756 knobbies still on it!
I'm quite aware there are better carbs for making HP like flatslides or an Edelbrock unit. It sounds like this is the way your wanting to go but I just wanted to put my 2 cents worth in in defence of a fine fuel mixer like the Keihin CV.:applause:
:ride: :ride: :ride:

By the way, don't install the Mikuni that XR's shows in their catalog as pictured..... it'll leak like heck!
(It's upside down)..:naughty:



I do know that the CV unit is finicky with regards to turbulence in the air flow- not sure if a pod filter exacerbates that or not, but I've seen it reported in a few places.


Dave

  • oldchvytrx

Posted February 02, 2007 - 12:54 PM

#4

I'd say you're probably right Dave. I didn't take into account the airbox mods or change in aircleaner.
I never had much trouble getting pretty consistant performance out of the CV I ran on my old short tracker. It came off a 70 CL450 DOHC and I used a 6" Filtron foam sock behind a 2" velocity stack without an airbox. The 74 XL250 motor this was mounted on made 42 hp on a Webco water eddy chassis dyno.... the best the 70's had to offer!?
I tried a 36mm Mikuni and 1.75" Lake Injector Carb and neither had as consistant hp or easy to keep tuned as the Keihin CV.
The Lake made better hp up top but too darned finicky. If it wasn't perfect the midrange perf suffered terribly.

  • daddyk

Posted February 06, 2007 - 06:43 PM

#5

I also run XS650 Yamaha street tracker and CV carbs on them have a know problem with pod filters. The problem is that if you push the pod to far on to the carb, the lip in the filter blocks the vacuum port to the diaphragm on top of the slide.Some people would trim the lip a little,not push it on so far or try another style pod.The best way to test if it's the pod is to run it without it on and see how it works. Street only of course





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