Carb adjustment? Or is it something else? By apothecary (Read 3,005 times)

[alleyoop]

GREAT!! I think just a little tweaking of the Fuel Ratio Mixture scew should take care of the hesitating.

If the Idle is bounceing around goin up and down it INDICATES a LEAN condition.
Have you checked for AIR LEAKS around the carb area. Use a Spray bottle of water and spray individual parts. Intake Manifold, Clamps that hold the carb also Air Fitler tubeing etc..

If no Leaks then RICHEN UP the Fuel Ratio Mixture Screw try 1/4 turns at a time COUNTER CLOCKWISE.
Alleyoop

[apothecary]

Ok I can't find the fuel mixture screw. I tried looking and can't even find the cap that you're supposed to remove to get to it... The only thing even remotely close to an adjustment I can find other than the idle, is towards the engine side but underneath. Not exactly easy to get to and the way it's set up there isn't ALOT of adjusting that can be done. I'll snap a shot of it in a bit see if it's the right one.

[alleyoop]

Yes, on the 250s the Fuel Ratio is underneath by the Intake Manifold side. It is a pain to get to but can be done without turning the carb a little sideways.
You can use one of the small interchangeable screwdriver bits they are about 1" or so in length and it works good.
Alleyoop

[apothecary]

I was afraid of that. Ok well I have a screwdriver set that has a ratchet handle should make it easier. I've also replaced all vac lines with equivilant sized silicon lines. Though what's with the line from the thermostat to the carb then from the carb towards the front of the scoot? Is it supposed to have coolant in it? Or do I have some sort of leak?

I'll attempt to adjust the carb in the morning. I rode her a bit and she hesitates from a stop and pops when slowing down. I also noticed at 20 mph when running steady at that speed it feels like the clutch isn't fully engaging or something. Maybe 20 is the threshhold speed where it doesn't engage yet?

[apothecary]

Ok I can't get the cap of the af screw. Guess I will be replacing the carbb after all. Also a symptom I'm noticing is when I shut it off after running for a bit, about 3-5 seconds after the engine is stopped, the exhaust let's out a nice little pop. Not sharp like a bang or anything but a harder poof type sound like the sound right when a morter type firework is launched. It happens only once each time the engine is stopped.

[apothecary]

All right, I installed the new carb. MAN she runs a WHOLE lot better. There's no pop after shutting the engine off and the idle sounds alot smoother. The acceleration is right back to where it should be. Throttle response is smooth. The only issue I'm still having now is a popping when I let off the throttle and a feeling when I drop down to a certain speed of the clutch? letting go of the wheels finally and allowing it to coast. I think this can be partially the cause of the popping on decel? Once the clutch lets go the engine drops to idle and doesn't pop anymore but until then it pops every few seconds on deceleration.

[alleyoop]

Apothecary,
Now make sure of the sound it makes at deceleration, DOES it POP or is it a BACKFIRE.
Also did you connect the Deceleration Hoses correctly to the CARB, If you didn't that would cause problems on deceleration.
Alleyoop

[alleyoop]

You can give the Fuel Ratio Screw 1/4 turn RICHER see if it stops the popping when you let go of the throttle.
Alleyoop

[apothecary]

Alley,

Reading your descriptions at the beginning, it's a backfire. I have another video of what it's doing now. I think part of the issue is that one of the exhaust bolts loosened itself on me. I'm tightening it up again hopefully it's not destroyed and needing replaced already. It's got less than 30 miles on it so far.

You can hear it about half way through when I let off the throttle. It's a nice popping/backfiring. I'm not sure the difference between the two I guess. Let me know what you think it is. That way I can hopefully start properly diagnosing things.

Ok uploaded the video. If you listen to the beginning I had the throttle wide open and it pops a little there but about 1/2 way through the video, I let off the throttle and you can hear the really loud popping/backfiring.

Also at the beginning you can here it's running full then the RPM drops slightly. That's not me letting off the throttle that's what it seems to do EVERY time. Gets up to a high RPM then drops slightly.

As for the deceleration hoses, I'm not sure which ones are the decel hoses but I reconnected everything just as it was when I took the old carb off.

[alleyoop]

That is a Backfire you are running LEAN, make sure no air leaks where it connects to the motor, and by the INTAKE MANIFOLD the clamps that hold the carb etc..

Alsogive the Fuel Ratio Screw a COUNTER CLOCKWISE about 1/2 turn and see if runs better and does not go to HIGH RPMS.
Alleyoop

[apothecary]

Ok I sprayed starter fluid all over on the carb, the vac lines, the intake, etc. NOTHING. So I think it's fairly safe to say the intake and vac lines aren't leaking at all.

I twisted the AF screw out 1/2 turn as you recommended. It still seems to be doing about the same. The problem isn't noticeable much when the engine is cold but when it warms up coming down from speed the pops and backfiring is still there.

I didn't get a video of it today. I did the adjustment and during the ride it was just too freakin cold for me to try getting video. By the time I got home, I just wanted to get the hex inside.

I do think I need to bring the idle up a little bit. It stalls out when you first start it with the idle where it is. I didn't check the air cutoff internals yet I may take a look at that tomorrow.

I haven't taken it up to speed yet the most I've done was 50 and she feels fin to that point. I know when I first start her if I have her on the center stand, I can rev the engine up then it drops RPMs I'm not sure if that's something being done by the CDI or not since after it drops the RPMs it won't get back up to that higher RPM again.

[alleyoop]

If the scoot has a tach After it is nice and warm at least 5 minutes, set the Idle to 1800-2000 and the REAR wheel is NOT spinning. That also will help on the backfireing so it does not run so lean when the butterfly closes. If the butterfly is a little more open more gas will be allowed to come in and not be so lean when you let go of the throttle.
Alleyoop

[apothecary]

That's probably part of the problem then. Even with the low idle it's got now, the back tire still spins a little. I'll have to see if I can find a cheap tach to put on it for idle setting purposes.

[apothecary]

Ok I've adjusted the idle. It's JUST below the point where I feel the bike want to start moving when sitting without brakes on. I'm still getting some popping when I let off the throttle and it's still giving me a *poof* sound a few seconds after shutting the engine off after actual ride time (not so much when it's not been under load). Do I need to let the air mix screw out a little further? Or should I pop the carb top off and see if the needle has an adjustment I can make on it?

[alleyoop]

There should be a Valve Cover Vent Hose make sure it is not kinked or blocked. The needle is not in play at IDLE, the needle comes into play when you are opening the throttle as more air is let in the Needle(Cylinder) starts to rise out of the Main Jet.

Have you checked the Pipe Flange that connects to the motor for Leaks. If it is leaking there it will always cause backfires when you let off the throttle.
Alleyoop