Rejetting necessary after third party exhaust?

[guile]

He messed it up! Tell him to fix it FREE. At least have him set it back to stock. I never have a mechanic adjust my carbs. They only make it worse. Its easy to change a jet or raise a needle. Idiot should have left everything alone & just put in next size up main jet. I can't tell u what to do as I don't know what it is he really did or didn't do?

The only thing changed is the mixture-screw. I turned it back 360 degrees clockwise, but no real change.
I learned that starting it the way I used to by twisting the throttle does not work anymore. It floods the spark.
However, it does sometimes pick up when I don't twist the throttle. Not ideal, but better. any idea how that change came about?

[sissy mary]

I never touch my throttle. Starts right up every time. Turn the key and do not hit the start button until the fuel pump stops clicking. This will prime the carb with gas. 

[guile]

Thanks Sissy, I will do that and hope it is the answer.
 Strange though that it would never start before without twisting the throttle.

[guile]

Thanks Sissy. The exhaust is not yet installed. Hopefully it doesn't pop!

Because of the annoyingly loud popping of the exhaust I changed the main jet. The manual says the main jet is size 108. The Dutch Kymco Impoter said it is size 118. When I opened the carb it was indeed 118. I changed it to size 125. Less popping now, but still there. Should I go even higher now?
What size (approximately)?
Will this change fuel consumption?

[guile]

Sissy?

[sissy mary]

If it still pops? I would say go up one more size? Pull the plug, if white it's lean. It should be light brown to tan. Dark brown/black/covered in oil, to rich. Make sure there are no leaks where carb connects to filter/breather housing, and where carb is clamped to where it go's to the head of motor. If these are not tight u could be sucking air, and this would cause bike to run lean and burn up engine/valves etc. I would make sure everything is tight/sealed good from manifold (round doughnut gasket), at header pipe, and all the way to where pipe clamps to muffler also. Make sure the manifold/gasket is tight where the intake mounts to the head also. Any leaks could cause this?  

[guile]

Thanks Sissy. I will go in and check all that.
Does changing the main jet size have any influence on fuel consumption?

[zombie]

YES! Not enough to matter tho. 3-5 Km per tank maybe...

[guile]

Thanks zombie

[zombie]

You're welcome.

[guile]

If it still pops? I would say go up one more size? Pull the plug, if white it's lean. It should be light brown to tan. Dark brown/black/covered in oil, to rich. Make sure there are no leaks where carb connects to filter/breather housing, and where carb is clamped to where it go's to the head of motor. If these are not tight u could be sucking air, and this would cause bike to run lean and burn up engine/valves etc. I would make sure everything is tight/sealed good from manifold (round doughnut gasket), at header pipe, and all the way to where pipe clamps to muffler also. Make sure the manifold/gasket is tight where the intake mounts to the head also. Any leaks could cause this?

I put in a larger main jet, size #130. But it still pops very loud The pops seem to be more muffled though, as if more on the inside of the muffler (closer to the engine?).
I checked for airleaks, but all is fine.

Should I go an even higher size main jet??

[ce]

Since it pops on deceleration and at low RPMs, you might do better to replace the pilot jet to a 40 from the stock 38.

The slow speed jet is running the engine until about 1/4 throttle, and that's where it pops.

I have a Leo Vince exhaust with a 40 pilot, and it popped too much with the 125 main jet, so I have a 120 main jet now. It still pops, but not as bad, and usually only one big pop after shutoff.

You can also tune the idle mixture screw to refine the low end, turn it clockwise until it stops, then back it out 2 1/2 turns and see how it performs, then you can go in or out accordingly. Out is rich, in is lean.

[zombie]

There are two screws on the left side of the carb. The smaller one is the idle mix, and the larger one is the idle speed.

Turn the small mix screw all the way in till it lightly seats. Then back it out 2 turns. That should get you started. You may have to hold the throttle slightly open to keep it running. If that is the case turn the larger speed screw clockwise till the bike idles.

Once you get there turn the smaller mix screw in either direction. (slowly about 1/4 turn at a time).
The object is to increase the rpm w/ that small screw. If the idle falls, turn the other direction.
If the idle goes too high turn down the larger screw, and continue w/ the smaller screw till you get the best rpm.

If that small screw is closer to the engine intake it is a fuel adjustment, and needs to be turned 1/4 turn counter clockwise AFTER you have gotten the best rpm from it.
If it is on the air box side of the carb it is an air adjustment, and needs to be turned 1/4 turn clockwise AFTER the best rpm.

Both of those 1/4 turn settings will enrich the idle, and prevent lean stalls.

When you change your main jet you will not need to fiddle w/ this again as it only effects idle.

Show this post to your mechanic friend. It might help him make a better living, or at least keep a few friends around...

[guile]

Since it pops on deceleration and at low RPMs, you might do better to replace the pilot jet to a 40 from the stock 38.

The slow speed jet is running the engine until about 1/4 throttle, and that's where it pops.

I have a Leo Vince exhaust with a 40 pilot, and it popped too much with the 125 main jet, so I have a 120 main jet now. It still pops, but not as bad, and usually only one big pop after shutoff.

You can also tune the idle mixture screw to refine the low end, turn it clockwise until it stops, then back it out 2 1/2 turns and see how it performs, then you can go in or out accordingly. Out is rich, in is lean.

It does not pop at low rpm's, but it does pop on decelration after high rpm's.

[guile]

There are two screws on the left side of the carb. The smaller one is the idle mix, and the larger one is the idle speed.

Turn the small mix screw all the way in till it lightly seats. Then back it out 2 turns. That should get you started. You may have to hold the throttle slightly open to keep it running. If that is the case turn the larger speed screw clockwise till the bike idles.

Once you get there turn the smaller mix screw in either direction. (slowly about 1/4 turn at a time).
The object is to increase the rpm w/ that small screw. If the idle falls, turn the other direction.
If the idle goes too high turn down the larger screw, and continue w/ the smaller screw till you get the best rpm.

If that small screw is closer to the engine intake it is a fuel adjustment, and needs to be turned 1/4 turn counter clockwise AFTER you have gotten the best rpm from it.
If it is on the air box side of the carb it is an air adjustment, and needs to be turned 1/4 turn clockwise AFTER the best rpm.

Both of those 1/4 turn settings will enrich the idle, and prevent lean stalls.

When you change your main jet you will not need to fiddle w/ this again as it only effects idle.

Show this post to your mechanic friend. It might help him make a better living, or at least keep a few friends around...

Thanks zombie. Will this get rid of the popping? The engine runs fine there's only the the (annoyingly loud) popping sound.