After market fuel mixture screws - Kawasaki Forums


Reply
 
 
 
Thread Tools Search this Thread
  #1  
Old 07-11-2018, 12:06 AM
Member
1st Gear Member
Thread Starter
 
Join Date: Jun 2018
Posts: 67
Default After market fuel mixture screws

Been having issues with popping when decelerating on my 250s. I’m noticing my exhaust is getting hotter than usual. I’m reading this is because the fuel mixture screw is set too rich?

Anyhow, I want to adjust the screw in a bit. I’m looking into an aftermarket fuel mixture screw i can adjust without removing the carb but I can’t seem to find any besides some generic ones on eBay and the $20 + $16 shipping* mixture screw sold over at kouba link. Can’t justify the cost for that one.

anyone got any recommendations? I don’t want to have to pull the carb out again if I adjust the screw too lean.

Would those generic eBay screws effect the performance of the carb negatively?

also, will an after market mixture screw made for a kx250 work on the klx250?

thanks

Last edited by Don Tripas; 07-11-2018 at 12:34 AM.
Reply With Quote
  #2  
Old 07-11-2018, 01:31 AM
Senior Member
1st Gear Member
 
Join Date: Jul 2011
Location: Cottonwood, AZ USA
Posts: 1,268
Default

I wouldn't make it any leaner, they run really lean stock.
I don't know anything about the CV... other than one thing.
Reply With Quote
  #3  
Old 07-11-2018, 11:17 AM
Senior Member
1st Gear Member
 
Join Date: Aug 2009
Location: Delaware, Ohio
Posts: 3,255
Default

Okay, I'll catch the usual crap, but that popping on deceleration is normal. Mikuni America, a company that, along with Kiehin, pretty much made about 90% of the carburetors on motorcycles, says properly jetted carbs will still pop. Look for yourself - Mikuni Tuning Backfire in exhaust They tell you what and why.

You can reduce the popping a bit a couple of ways, two will costs you money, the other doesn't. You can richen the idle circuit (pilot jet and idle mix needle adjustment) beyond what is needed. You might get less popping if you block off the air suction valve (reed valve setup above the exhaust port) by plugging it or installing a block off plate. Last and no cost you can slightly crack the throttle and the popping stops while you slow down, it lets the engine draw a bit more fuel.

One question - How can you notice your exhaust is running hotter? Exhaust gasses are around 1200 degrees F, the header will run around 700 degree or so depending on the air flow around it. . It would have to be a dramatic change to be noticeble. I'm thinking most people just become more aware of the heat radiation, with little to no increase in actual temperature. I will say if you let your bike sit for a bit of time idling your exhaust can glow red. Left for a long time it can glow bright red/orange, but within seconds after starting to move, the glow is gone - air flow.. That is the way it is with the single wall exhaust systems. It is the reason you see a lot of cruisers with blued pipes, that's what heat does to chrome. The KLX does have one thing that can cause a hotter exhaust header, that suction system they use to introduce air to the exhaust to burn unburned fuel - pollution. Blocking/removing the system may cool the exhaust a bit.

Interesting thing though, the racers who wrap their exhaust with wrap or have them ceramic coated don't do it just about heat/around the engine, they do it to keep exhaust gas speed up to help in exhaust scavenging - aka better flow. The higher temperature keeps the speed of the exhaust flow higher - faster flow - for better exhaust scavenging. Seems that heat is your performance friend. If you really want to cool the radiation heat from your exhaust, get the head pipe ceramic coated. Some headers for cars and bikes are coated. Best known is Jet Hot. Here's a bit of information on coating and exhaust. I had my 650 header Jet Hot coated and the radiated heat dropped dramatically. It also requires no maintenance, no rust or corrosion. .

Last edited by klx678; 07-11-2018 at 11:24 AM.
Reply With Quote
  #4  
Old 07-11-2018, 01:54 PM
Senior Member
1st Gear Member
 
Join Date: Mar 2016
Location: Texada Island, BC
Posts: 120
Default

Almost all of my bikes that have been tuned for power (some on the dyno) popped on decel
Assuming you dont have vacuum or intake leaks just set the idle circuit using the RPM drop method.

Copied this from a motocross forum

Quote:
You start out with an engine that is turning high RPM with a carb that is open, flowing freely. Next, you close that slide. This has the effect of creating a tremendous vaccuum in the intake manifold (CHOKE!). This vaccuum does curious things:
1. It pulls air and fuel from wherever it can--including the idle and low speed jetting in the carb.
2. To counteract the vaccuum, air will take the path of least resistance--including sucking exhaust gases back into the combustion chamber during valve overlap (the brief period of time that the exhaust and intake valves are open at the same time.

So what does this mean? Well, now you have a disproportionate rich mixture heading for the cylinder AND what little oxygen is drawn in is further diluted by gases that are coming back into the chamber from the exhaust valve. The result is poor, incomplete combustion! Depending on the temperature of the exhaust pipe and gases, reignition is possible once this mixture is introduced into a more oxygen rich environment. This produces the "pop."

Why does a lean running engine have a tendency to excessively pop? The exhaust gas temperature of a lean engine is substantially higher than one that is running on the rich side ( an EGT probe will show this). Therefore, the high EGT serves to heat the pipe more and the gases themselves become a much better source of re-ignition. By richening things up, you are cooling down the exhaust temp and therefore reducing potential re-ignition sources.

Any 4 stroke engine--even those that are flawlessly tuned will pop on decel. It is harmless, but can be annoying--granted. However, I would never alter the jetting of an otherwise performing motorcycle to get rid of it. Go by the seat of your pants and the color of your spark plug rather than the popping as an indication of the jetting of your scoot!

Last edited by RageHardIntoTheBendies; 07-11-2018 at 02:00 PM.
Reply With Quote
  #5  
Old 07-11-2018, 02:48 PM
IDRIDR's Avatar
Senior Member
1st Gear Member
 
Join Date: Oct 2010
Location: SW Idaho
Posts: 4,311
Default

To add to the above, the pilot circuit has very minor fuel input above half throttle and being a little rich or lean on the idle circuit would not be the cause of an overly hot exhaust. It's just not enough to make a difference.

Adjust the idle circuit to have the best off-throttle snap and best no-throttle idle. Don't adjust it for decel popping. As some here advocate, it can be done...sure...but as Mark RageHard note, it's not the right way.

Last edited by IDRIDR; 07-11-2018 at 02:52 PM.
Reply With Quote
  #6  
Old 07-11-2018, 02:56 PM
Member
1st Gear Member
Thread Starter
 
Join Date: Jun 2018
Posts: 67
Default

Quote:
Originally Posted by klx678 View Post
Okay, I'll catch the usual crap, but that popping on deceleration is normal. Mikuni America, a company that, along with Kiehin, pretty much made about 90% of the carburetors on motorcycles, says properly jetted carbs will still pop. Look for yourself - Mikuni Tuning Backfire in exhaust They tell you what and why.

You can reduce the popping a bit a couple of ways, two will costs you money, the other doesn't. You can richen the idle circuit (pilot jet and idle mix needle adjustment) beyond what is needed. You might get less popping if you block off the air suction valve (reed valve setup above the exhaust port) by plugging it or installing a block off plate. Last and no cost you can slightly crack the throttle and the popping stops while you slow down, it lets the engine draw a bit more fuel.

One question - How can you notice your exhaust is running hotter? Exhaust gasses are around 1200 degrees F, the header will run around 700 degree or so depending on the air flow around it. . It would have to be a dramatic change to be noticeble. I'm thinking most people just become more aware of the heat radiation, with little to no increase in actual temperature. I will say if you let your bike sit for a bit of time idling your exhaust can glow red. Left for a long time it can glow bright red/orange, but within seconds after starting to move, the glow is gone - air flow.. That is the way it is with the single wall exhaust systems. It is the reason you see a lot of cruisers with blued pipes, that's what heat does to chrome. The KLX does have one thing that can cause a hotter exhaust header, that suction system they use to introduce air to the exhaust to burn unburned fuel - pollution. Blocking/removing the system may cool the exhaust a bit.

Interesting thing though, the racers who wrap their exhaust with wrap or have them ceramic coated don't do it just about heat/around the engine, they do it to keep exhaust gas speed up to help in exhaust scavenging - aka better flow. The higher temperature keeps the speed of the exhaust flow higher - faster flow - for better exhaust scavenging. Seems that heat is your performance friend. If you really want to cool the radiation heat from your exhaust, get the head pipe ceramic coated. Some headers for cars and bikes are coated. Best known is Jet Hot. Here's a bit of information on coating and exhaust. I had my 650 header Jet Hot coated and the radiated heat dropped dramatically. It also requires no maintenance, no rust or corrosion. .
Ive become aware of these changes in the last few weeks. I got the bike with 14,500 miles on it and have been using everyday since I got it - bout a month and half ago. Prior to hitting 16'000 miles, I had no pop on decel. And since the popping started, my bike has been running a bit odd. Occasionally the bike will have trouble starting ... even with the choke pulled out. and sometimes die on me when idling at 1200 rpm at a red light.

and as for the headers getting hotter .... this is something Ive become aware of when the popping showed up. Maybe its me trying to diagnose the popping w very little knowledge.
Reply With Quote
  #7  
Old 07-11-2018, 03:06 PM
Klxster's Avatar
Senior Member
1st Gear Member
 
Join Date: Jun 2013
Location: North Texas
Posts: 2,434
Default

Don, I hope you've enjoyed reading the responses to your problem and your questions - they are the usual "first responses" a member will get concerning decel popping..

Now, lets give you the facts and knowledge you need: Decel is fueled by the pilot system - whose other function is to fuel your engines' idle. There is one other instance where the pilot system plays a role in fueling your bike - whenever you "jab" on the throttle, the pilot system is responsible for providing a little "shot" of fuel to get your engine "cooking" ( a simulated accelerator pump shot that has nothing to do with the fuel screw - only the transfer ports of the pilot system )...

As such, decel fueling has nothing to do with "jetting", "properly jetted", "changing jetting", "spark plug color", etc etc etc etc etc etc etc etc....

To reduce or eliminate decel popping, get better throttle response, and improve low RPM power ramping, you must richen the pilot system ( on the KLX).
1. Remove (and cap off) the air injection system.
2. Insure that all exhaust joints are fully sealed and not leaky.
3. Set the fuel screw to 3.5 turns out .

Depending on your altitude, you've just eliminated all popping or (at sea level) reduced it significantly. To fully rid any remaining pops, install the #40 pilot jet and put the fuel screw to 1.75 - 2 turns out..

No need for aftermarket fuel screws, etc etc.. You set up the stock fuel screw correctly - and never touch it again.. Remember, all the fuel screw does is fuel idle and decel - nothing else - thinking it does is ignorance and/or delusion..

Last edited by Klxster; 07-11-2018 at 03:24 PM.
Reply With Quote
  #8  
Old 07-11-2018, 03:08 PM
Klxster's Avatar
Senior Member
1st Gear Member
 
Join Date: Jun 2013
Location: North Texas
Posts: 2,434
Default

Oh, ok Don.. Your pilot system seems to be failing you... Time to learn the CVK, tear it down and clean it..
Reply With Quote
  #9  
Old 07-11-2018, 03:36 PM
Senior Member
1st Gear Member
 
Join Date: Aug 2009
Location: Delaware, Ohio
Posts: 3,255
Default

Like I said, the usual crap from people who think they know more than the companies that make the carburetors or motorcycles.
Reply With Quote
  #10  
Old 07-11-2018, 03:52 PM
Klxster's Avatar
Senior Member
1st Gear Member
 
Join Date: Jun 2013
Location: North Texas
Posts: 2,434
Default

You know me, I always gotta throw facts at all the fiction..

It's not yall's fault that cleverly written articles fool ya - they fool most.. Properly jetted carbs, dyno tuned carbs, etc etc, can still pop on decel - that is a fact. And this is because shoddy/ignorant tuners don't include the fuel screw / pilot system in their "tuning efforts"..

Properly jetted CVK's can decel pop - but none of them have to..

Last edited by Klxster; 07-11-2018 at 03:56 PM.
Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Fuel bowl screws 44snot24s KLX 250S 14 08-16-2014 10:55 PM
Idle mixture screws EdsGPZ New Member Area 8 10-06-2009 03:08 AM
Mixture screws ? ? CroNiKRoCkeT07 ZZR 600 10 09-29-2009 02:35 PM
after market air filters crash972 General Tech 1 05-10-2005 01:42 AM
ex500 after market parts toad1025 Ninja 500R 9 04-02-2005 08:38 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 Off
Pingbacks are Off
Refbacks are Off


Advertising
Featured Sponsors
Vendor Directory

All times are GMT. The time now is 01:58 PM.


© 2018 MH Sub I, LLC dba Internet Brands
We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.