How to do carb tuning

[Sean]

Would like to share some info before the file get into my recycle bin.

 

CV Carb Tuning

 

Follow steps in order....First, dial in:

 

1. Top end (full throttle / 7.5k to redline - Best Main Jet be selected before starting step 2!

Select Best Main Jet

 

To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm.

 

If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.

 

If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small. In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!

 

Do not pay too much attention to the lowend richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the lowend / cruise later - after step 2.

 

2. Midrange (full throttle /5k-7k)

Select best needle clip position

 

To get the best power at full throttle / 5k-7k rpm, after you have already selected the best main jet, If the engine pulls better on a full throttle roll-on starting at

If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k. If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set. Do not pay too much attention to the lowend richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle

/ 5k-7k power in conjunction with the main jets that produce the best power at high rpm. You will deal with the lowend / cruise next.

 

3. Low end (full throttle / 2k-3k)

Float height (AKA fuel level & how to..)

To get best lowend power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum. Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.

 

If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.

 

If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.

Example: change float height from 15mm to 14mm to richen up that area.

REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.

Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.

Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.

 

Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!

If there are lowend richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, also check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs.

 

4. Idle and low rpm cruise

Fuel Screw setting (AKA mixture screws)

There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs use a special "D" shaped driver, usually supplied in the carb recal kit. Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation.

Pilot fuel mixture screw settings, float level AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.

 

If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required. Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated

at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.

NOTE: A rich problem gets worse as the engine heats up.

 

If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.

NOTE: A lean problem gets better as the engine heats up.

 

If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm! Carb tuning is a combination of science, art, intuition and a lot of wizardry. These tuning

kits have been thoroughly tested to ensure easy, trouble-free, optimized performance.

[SRADR200]

my bike use to be easy to start n the rpm does not rise after reaching my destination , but after service it's a bit difficult to start , will die off in idling , n reach my destination the RPM is higher .... do i have to re-adjust my main jet cir-clip to the higher slot or lower slot (currently its at 2nd position counting from the top). .. . .

[Andydy]

thanks for the info.....

[keOnni]

** remove the quote too long.

 

did u get this on de factory jettkit box? lOlx...its de same thing...hehee...

[CoolNard]

could any one recommend where to buy jetting components for the SP150 carb? I noticed that my engine is running on a lean setting, but I realized that the jet needle position is not adjustable on my stock carb & probably my main jet is also slightly smaller...

 

if anyone has done a DIY on their SP150 stock carb, care to share some knowledge/experience...

 

i am relatively new to this forum, but i believe i have gained some useful information from the exchanges...

[Hyde81]

Originally posted by Sean@Jan 18 2003, 06:36 PM

Would like to share some info before the file get into my recycle bin. 

 

CV Carb Tuning

 

Follow steps in order....First, dial in:

........

kits have been thoroughly tested to ensure easy, trouble-free, optimized performance. 

 

u took all this from the factory jetting manual rite ?

 

** edit to remove the long quote **

[fibre]

Originally posted by SRADR200@Apr 19 2003, 02:08 AM

my bike use to be easy to start n the rpm does not rise after reaching my destination , but after service it's a bit difficult to start , will die off in idling , n reach my destination the RPM is higher .... do i have to re-adjust my main jet cir-clip to the higher slot or lower slot (currently its at 2nd position counting from the top). .. . .

dun change the clip position

 

it sounds like too lean idling mixture to me, u need to make the idling mixture richer

 

check this out:

 

http://www.bikechatforums.com/viewtopic.ph...c4c2dc8bed10b32

[Non Stop Racing]

wads e effect for tuning carb ?? faster speed ? o_0 . pls enlight

[SMOKEY]

Tune carb only when you change exhaust system.

Thanks for the notes, good information but very long.

[FLY374]

sorry guys.. off topic abit..

 

read something about washing carb .. uh..

(me a newbie ) ... what is a carb? and how u wash it? or how to maintain it? or .. whatever about it ....

coze i bought a second hand bike.. just wondering is it essential ?

or did i read wrongly? .....

 

i'm riding a daystar. pls help (then after that maybe u can laugh. softly)

hehe .. thanx for the help !

me rally confuse ....

[w1n9]

Originally posted by FLY374@Jun 28 2004, 10:53 PM

sorry guys.. off topic abit..

 

read something about washing carb .. uh..

(me a newbie ) ... what is a carb? and how u wash it? or how to maintain it? or .. whatever about it ....

coze i bought a second hand bike.. just wondering is it essential ?

or did i read wrongly? .....

 

i'm riding a daystar. pls help (then after that maybe u can laugh. softly)

hehe .. thanx for the help !

me rally confuse ....

the full spelling for carb is carburator. it is the connecting part between your filter box and the engine intake valve. the carb serves as a venturi (throat) for taking in air and mixing/controlling the amount of fuel and air into the engine. hope the explaination easy to understand. btw, no need to tune or wash carb if there is no problem with it unless you are into tweaking and hopping up. :sweat:

[shoei]

did u write this up ?

[w1n9]

Originally posted by shoei@Jun 28 2004, 11:43 PM

did u write this up ?

hmm!!? :sweat:

[FLY374]

sigh...

thought is something new or what...

i know what is a carburator ...

(bang my head against the wall.. never thought of this) ...

me even go look up in dictionary for the meaning of "carb" ...

and never think of it as a short form ....hahahaha

 

stupid me... blurr sia...

[AspMonK]

hi, If I change my filter to a free flow how should I tune my carb??? listen??

 

and any recommend on air filter? beside K&N

[jonse]

how to tune carb for sp??

in short term??

too long i see also blur le

[longbow]

Originally posted by jonse@Jun 12 2005, 12:54 PM

how to tune carb for sp??

in short term??

too long i see also blur le

me too want to learn 2-stroke engine carb tuning.....

[TheCockroach]

Originally posted by AspMonK@May 3 2005, 01:13 PM

hi, If I change my filter to a free flow how should I tune my carb??? listen??

 

and any recommend on air filter? beside K&N

 

Hey!

 

K&N are a complete no no with you eh!

 

Try a foam based filter called UNI filters. They are a bit restrictive than the K&N's but still better than the stock ones. K&N an UNI are the only ones I suggest.

 

Regarding tuning, You first have to upjet the carb 'cos the increased air flow will only make your air/fuel mixture lean. Upjet by 5-7 Micro millimeter for the UNI and tune it like a regular CV carb.

 

I'll be hanging around if you have any questions.

 

Peace

DNR --- TCR

 

May the tarmac be in a forgiving mood when you find yourself meeting her. Ride safe.

[TheCockroach]

Originally posted by longbow@Dec 3 2005, 12:21 PM

me too want to learn 2-stroke engine carb tuning.....

Hmmmmm

 

I guess you are reffering to the VM carbs used extensively on 2 strokes.

 

 

Try looking for Mikuni VM slide manuals with the help of your fav search engines and you will find plenty.

 

Happy learning.

 

Peace

DNR --- TCR

 

May the tarmac be in a forgiving mood when you find yourself meeting her. Ride safe.

[encrypto]

Originally posted by SRADR200@Apr 19 2003, 02:35 AM

my bike use to be easy to start n the rpm does not rise after reaching my destination , but after service it's a bit difficult to start , will die off in idling , n reach my destination the RPM is higher .... do i have to re-adjust my main jet cir-clip to the higher slot or lower slot (currently its at 2nd position counting from the top). .. . .

I have a similar problem with my bike. Where is this main jet clip? How to adjust this?

[smalldidi]

u just need to close abit ur Airfuel screw...try it out...if still not so comfortable...just open up ur carb & adjust the slide to higher(mean it can lift higher) thus the pin inside need to adjust lower....

[FijIan WarriOR]

hi guys. really waanna knw how to tune carbs. currently i'm riding a tw200. 4 stroke engine. i wanna change d carb to a vm mikuni kind. any1 can procide me advise oh how to do it or tips even?. also was wonderin abt a kehin 28mm carb(is d same carb as a sp?)

 

[chewelvin]

thx for the infor bro:thumb:

[khoa9876]

should adjust throttle screws first, then adjust idle screws if necessary. If 4engine-line, should not adjust 3rd carb, it is standard carb for adjustment

[iCeLkipS]

This should be helpful!!

 

http://www.youtube.com/watch?v=RYkOCVHGbUw