Off Idle Hesitation SOLVED, Cleaning & reJetting Pilot Jet, Main Jet

[mrbios]

Update:: 05-21-2014 latest results: I was finally able to return to the stock pilot jet #38 with no hesitation. This afternoon I installed #48 for the pilot jet and increased the Main Jet from #102 to #115.  #115 was way to big and the scooter didn't run right.  Tonight I reinstalled #102.

Update:: 05-14-2014 Yesterday I installed a different sized pilot jet #45 and I could feel a minor hesitation.  Today, I removed my carb and drilled the copper plug near the pilot screw so I could stick a wire in the passage.  I used individual strands of 12 AWG Stranded wire 0.019" (0.48mm) ~ 25.5 AWG. The wire barely fits in the thinnest part of the passage.  On a different carb 20 gauge wire (0.81mm) fit with lots of room to spare. See attached pic at the bottom. 


Kymco Grandvista / Grand Dink:



Carburetor Cleaning & Theory three part series:







Keihin CVK30 30mm carburetor - Constant Velocity Keihin (CVK)

Pilot Jet (aka Slow jet) = # 38S --- Part# N424-51B38            $4.99  (Keihin Part # N424-21)   (all sizes are are same price)
Main =                             # 102 --- Part# 99101-116-1020     $3.21  (Keihin Part # 99101-116)

http://www.rockymountainatvmc.com/p/930/24375/Pro-X-N424-21-Series-Keihin-Pilot-Jet-

[Hueffenhardt]

Thanks for sharing. Your post may be helpful to me if I ever encounter that problem.

[allanseth23]

Nice post im having the same problem with my B&W250 for almost a month now I thought Ive cleaned it well until I seen this. Keep posting good info.

[mrbios]

Nice post im having the same problem with my B&W250 for almost a month now I thought Ive cleaned it well until I seen this. Keep posting good info.

Thanks, my goal after really digging into this was to define the problem / symptoms and the solution clearly so everyone else with the same issue can get it right the first time and go back to enjoying their ride.

A few weeks after getting my scoot going great the head gasket blew in my car.  So it is my only ride until I get the car fixed.

Thanks for the feedback.

Paul

[zombie]

Great Job Bios. Kudos for sharing it all.

[mrbios]

Great Job Bios. Kudos for sharing it all.

Thanks Zombie.  An added benefit of the cleaning and increasing the pilot jet is that the scooter always starts instantly (when cold).

[zombie]

I agree. The stock Pilot is sooooo tiny it doesn't like to start w/o the choke. Increasing just 2 sizes is a big difference.

[allanseth23]

Im having a throttle lag problem on my b&w250.  Has anyone experience this? When you give a twist to the throttle its like a second delay for the engine to respond.  Any help is appreciated.

[zombie]

Two thing right off the bat.

Adjust the idle MIX screw to the highest rpm, and back off between 1/8th, and 1/4 turn richer. That is the optimum setting.

Second remove the air box tube that attaches to the Back of the carb, and manually open the throttle several times. There is an accelerator pump on the back right side of the carb that SHOULD be squirting a tiny stream of fuel each time you twist the butterfly open.
That TINY port tends to clog, and sometimes the small actuator rod gets stuck in the down position.

I ride all day every day, and that circuit fails a few times a year on me. I learned to live without it, and just live w/ that little bog.

[tanuki]

Thanks, the videos are good
Ive taken a number of carbs apart in my day, don't call myself an expert but im sure I can deal with this scooter without screwing it up and tearing any sensitive rubber parts if I can successfully remove and rebuild Goldwing carbs..LOL

I looked at my internal carb jets today, nothing clogged, a little sediment.
Cleaned it all up, reinstalled it and started it up..same problem exists, wont rev past idle.
Still have another hose left u8nconnected, its a U shaped junction on the left side of engine bay.
Any pics or info greatly appreciated

[tanuki]

Ooops, I meant to say the RIGHT side of the engine bay.
It seems to have a larger diameter "sheathing" or outer cover on it.
Id really like to know where that tube goes.
I will upload a pic when I get home from work tonight.

Right and Left orientations are assuming that the rider is astride the bike facing forward, at least that is what I was taught early on.

Thanks

[tanuki]

This morning I looked very carefully and long at the engine bay and cant see where the U shaped hose should attach at the smaller end.
At the larger end it is attached to the exhaust recirculation unit?

I took several pics, none will load because they are too big, no success in resizing down to fit.
I just discovered a post in 2013 by tonytode? that has a pic of the hose on question.

[mrbios]

This morning I looked very carefully and long at the engine bay and cant see where the U shaped hose should attach at the smaller end.
At the larger end it is attached to the exhaust recirculation unit?

I took several pics, none will load because they are too big, no success in resizing down to fit.
I just discovered a post in 2013 by tonytode? that has a pic of the hose on question.

I wouldn't worry too much about the U shapped hose.  I misplaced mine and I don't even use it and the scooter runs fine. 

EGR: Our scooter don't have an EGR valve I think you are referring to the charcoal canister purge hose / lines. 

Picture size:  I use the free picture editing program: Irfanview to crop and resize pictures.  Or you can post the picture on another website like I did below.  RIGHT Mouse click the picture and click Save As to save a local copy to your computer.

[tanuki]

My GV 250 doesn't seem lacking in power when on the main jet, accelerates nicely above 4500 rpm.
But..the annoying stumble at about 3000-4500 is proving to be a nuisance so Id like to remedy that.
First I looked at the spark plug and it seems to be running too rich.
When I pulled the carb out again today I noticed or re-noticed I should say, that the float bowl and upper carb body are not aligned in the "usual" fashion.
Maybe Im not up to speed on newer carbs but this carb is cut or bisected at an angle rather than horizontally like most other carbs Ive seen.

Im thinking that trying to get a good/proper/exact float height measurement would be rather problematic on such a carb.
Didn't I see a post about carb float height in which the author was perplexed by the numbers the manual states vs working reality in the carb?
Something about 17 mm and 19mm vs 7 and 9mm?
Any help in getting the float set properly is much appreciated.
Mike Nixon has posted a good clear video on youtube concerning how floats work.

[mrbios]

My GV 250 doesn't seem lacking in power when on the main jet, accelerates nicely above 4500 rpm.
But..the annoying stumble at about 3000-4500 is proving to be a nuisance so Id like to remedy that.
...
Any help in getting the float set properly is much appreciated.
Mike Nixon has posted a good clear video on youtube concerning how floats work.

The main jet is almost never going to be a problem unless the CV diaphragm is leaking or someone messed around with the jet needle and on our 250cc scooters that isn't likely.  Basically, the main jet is easy to clean, is just a hole so there isn't much to go wrong.  However, care must be taken that no parts are bent or lost such as the "needle jet (see my diagrams or watch the videos to see that part).

2000 to 4500 rpms is the prime are effected by the pilot jet.  I recommend cleaning the pilot jet circuit by drilling the copper plug (Carb cleaning video part III).  I don't recommend messing around the the floats because it is too easy to damage them and I think there is nothing to be gained and it just introduces new problems. 

Download and review my carb photos then clean the pilot jet as shown in the part III and report results.


Right click on: Carburetor_Clean_Keihin_CVK30(web).zip
and choose Save As to your hard drive.