Pilot Screw?

MYSCTR · Post by **MYSCTR** » Mon Jul 08, 2013 12:01 am

Picked up a like new 2009 Buddy 150 with 225 miles that sat idle for 2 years. Started right up and ran great so we gassed it up, added Lucas and at 269 miles it decided to run no more.

We pulled the carb and cleaned the jets and carb, put it all back together and we were off again.

The problem comes in now that we are getting a back-fire through the exhaust when we back off the throttle coming up to a stop. We have adjusted the idle to where it idles pretty low once warmed up yet we still seem to be a bit rich. I am thinking the jets are really clean yet there has to be some way to back the gas mixture down.
Would the airflow / gas mixture need adjusted after cleaning the jets?

We did read through: Idle Adjustment and Torque

topic18606.html

This was very informative and pretty helpful. Just don’t want to jump in messing with something if I am overlooking something else.

Thanks for any input.

OldGuy · Post by **OldGuy** » Mon Jul 08, 2013 2:58 am

Sounds like a cool scoot.

There is also such a thin as crackling, or lean backfire, which comes from the mixture being lean. This is common on some high performance 4 stroke dirtbikes. I don't know if this applies to you, but you should be aware of it.

I you are getting a lean backfire then the mixture is quite lean (I hesitate to say too lean, because that is debatable). If you are getting a traditional backfire then it is too rich.

Did you check the air filter? You should take a look and be sure there aren't any rodent nests in there.

Also, the automatic choke may be stuck on. You may need to take it to a dealer and have them take a look.

lovemysan · Post by **lovemysan** » Mon Jul 08, 2013 3:04 am

I find the idle mix screw not very sensitive. I find the highest idle speed point. At that point Generally I'm able to move the screw either way about 1/4 turn before effecting idle speed so I set it in the middle. I also find the pilot jet is the hardest part to get clean. I worked 5 minutes with air and berrymans b12 to clean one Friday.

I bought a d-tool for my 2009 idle jet but ended up swapping it out with a slotted version. You could grind a slot with a Dremel.

fatcharlie · Post by **fatcharlie** » Mon Jul 08, 2013 7:03 am

I'd clean it again... I usually find an ultrasonic cleaner and some vinegar to work wonders on cleaning a carb.

Tear it down, I'd remove the jets, emulsion tubes, and adjustment screws (Remember how many turns out from lightly seated) and drop everything into an ultrasonic. Let it run in warm water for 10-15 minutes, then rinse and carefully blow out/shake the water out the passages.

Put it all back together and re-tune the carb... get it idling and warmed all the way up. Once the bike is nice and warm, set your idle to ~1700 RPM. (I highly suggest a tachometer for tuning). The turn the pilot screw in or out until you hit MAX RPM (You should find a peak in there somewhere.) I usually find the peak and then turn the screw in about 1/16 - 1/8 of a turn (Depending on how much of a change it makes in the idle RPM), then re-set your idle screw.

Since the pop is occurring as you shut the throttle off, it sounds like the transition from the main jet to the pilot jet is causing a lean condition until the idle stabilizes... this will cause fuel that is well off from the desired fuel/air mix to travel into the exhaust, where it is nice and hot... and pop as it encounters more oxygen combined with the heat. This can occur since your pilot may be too lean for thorough combustion, but not so lean that the motor can't idle.

Out of curiosity... why do you think you are too rich? If its from the smell, then a lean condition that I described COULD (not always in my experience) cause a "gas" smell from the exhaust. Relying on smell alone can turn you the wrong way... you could always drop some coin and hook up a wideband o2 sensor... but probably overkill in this case.

OldGuy · Post by **OldGuy** » Mon Jul 08, 2013 2:43 pm

Have you pulled the plug out and checked the color? This is probably the best way to see what is happening with the mixture. Black means too rich; tan is just right. Gray is tending toward lean.

Tocsik · Post by **Tocsik** » Mon Jul 08, 2013 3:31 pm

One other thought: I agree you should pull the air filter cover and take a look in there. But, it's also possible there's an air leak around the air filter cover or in one of the hoses. If that's the case, you could be running a little lean which can also give some deceleration popping.

Robbie · Post by **Robbie** » Mon Jul 08, 2013 9:29 pm

To the OP...... You are describing 'Afterfire'
Rarely carburetor related, it is primarily caused by a air leak in the exaust system.....like a leaking head to pipe gasket.
The air is drawn into the leak point while throttle is closed but bike is holding engine rpm up.
Because the throttle is closed, fuel is drawn into the combustion chamber but not burned due to inadequate air......the unburned fuel is then thrown into a hot muffler.....any air leak will cause the the fuel to ignite and there is your 'Afterfire pop'

Tighten or regasket the exaust.

Rob