Slightly confuzzled with off-idle issue By glavey (Read 592 times)

[glavey]

I have a 2011 taotao atm50 with a 72cc bbk. The scooter came from the factory with what was labeled/stamped as a 30 pilot jet and a "secret 60" cylinder/piston. When I had the 60cc cylinder/piston installed, the scooter idled fine and off-idle to mid-range was great.

After I installed the bbk, the same 30 pilot jet now seems... too rich? I seem to have some signs of an overly rich mixture; (slightly) black exhaust, a quick blip of the throttle and the engine bogs and/or dies.

I bought a new carb from scrappydogscooters because I thought perhaps the old stock one had poorly machined internal passages. The new carb came with what was stamped as a 34 pilot jet, but seemed incredibly similar to the 30. I had a 35 pilot jet around and it looks much bigger than either of the supposed 30 or 34 jets.

I tried the 34 jet in the new carb and the off-idle problem was ever-so-slightly improved. I can tune the air/fuel screw and get the highest idle, but when I give the throttle a quick stab, the speed drops below the idle speed and bogs and/or dies.

Now my thinking is that since the 30 jet with a 60cc cylinder was ok, the same jet with an increased volume to fill would be lean, and not rich. Am I thinking wrong?

Also, I should note that I haven't adjusted the needle's height in the new carb, checked/adjusted the valves, or checked the spark plug yet. I can do that tomorrow; today's weather change combined with being around gas and exhaust fumes has given me a migraine.

Thanks in advance.

[Alleyoop]

I tried the 34 jet in the new carb and the off-idle problem was ever-so-slightly improved. I can tune the air/fuel screw and get the highest idle, but when I give the throttle a quick stab, the speed drops below the idle speed and bogs and/or dies.

Try this Start the motor and turn the fuel ratio screw clockwise until it stops, does it kill the motor?
Alleyoop

[glavey]

It doesn't kill it but it idles extremely low; about 900 rpm.

Edit: I found a video on youtube that demonstrates exactly what is happening with my scooter, around 1:20 to 1:26.

[glavey]

Here is a picture of the pilot jets. From left to right; 30, 34, 35. I really can't see a difference between the 30 and 34 jet.

[scootcanic]

Your issue occurs on acceleration and stumbles is how I am reading it. If you back off the throttle about a 1/4 inch. Now pay attention to the engine. If it just settles down and does not gain speed it is rich at that point. If it gains speed when backed off it is lean. If it is where you said it was, in the middle on acceleration, the needle for the main jet will need adjustment.

[Alleyoop]

Jun 14, 2014 15:54:16 GMT -6 glavey said:

Here is a picture of the pilot jets. From left to right; 30, 34, 35. I really can't see a difference between the 30 and 34 jet.

Look at the top of each one your looking only at the defuser part of the jets. The size of the hole going through the whole jet determines the amount of fuel flow.
Alleyoop

[glavey]

Jun 15, 2014 12:00:03 GMT -6 Alleyoop said:

Look at the top of each one your looking only at the defuser part of the jets. The size of the hole going through the whole jet determines the amount of fuel flow.
Alleyoop

Ah that explains it. I feel like a fool now...

I cleaned the carb and all the jets, did a valve adjustment, set the intake to .002 exhaust to .003; no real improvement. I raised the needle one notch and went for a test ride; slight improvement, still a bit sluggish. Raised the needle another notch, more improvement. Low to mid-range power no longer sluggish.

However a new symptom has appeared. When at idle, if I blip the throttle quickly the engine stutters and bogs, the is also a distinct "vraVROOM" sound; if I slowly raise the throttle and let it go the engine rpms slowly drop to idle.

[Alleyoop]

It is LEAN if the rpms drop slow. Turn the fuel ratio screw 1/4 of a turn Counter Clockwise and TEST after each 1/4 turn.
Alleyoop

[glavey]

I will do that tomorrow, I have some around-the-house work to do today.

I was just thinking; could it be the accelerator pump causing the bogging seeing as how it only happens when I quickly blip the throttle?

[Alleyoop]

Yes if you have the pump it could be that, take it off and check the diaphgram it could be ripped, OR it may need adjustment and it is not pushing the rod down far enough to squirt some gas in.
Alleyoop