[akshye]

A very detailed video showing carburetor in action. Destin has custom-built a transparent carburetor and filmed it with a high-speed camera.

https://www.youtube.com/watch?v=toVfvRhWbj8

"SmarterEveryDay" is an interesting YouTube channel. It also has another video where he runs and records a transparent engine, with a high-speed camera, to explain how 4-strokes work.

[Rahul Bhalgat]

Originally Posted by ashwinprakas

Carburetors are more or less the same in function with minor differences depending on type.

Hello everyone. I request advice from ashwinprakas as well as the other members, for a problem related to my 125 CC gearless scooter. It is Mahindra Duro.

Problem: for the first 10 - 15 minutes of riding after cold start, the engine tends to die in the first 1/8 throttle input.

Supporting information:

1. This is more prominent with load (actual riding) than without load (scooter on the main stand). So the rides tend to be jerky during this period as I have to raise the throttle quickly to beyond 1/8th.
2. After the first 10-15 minutes of riding, the problem vanishes. The throttle then responds smoothly throughout the entire range.
3. The scooter has been serviced at ASC. The spark plug and engine oil have been replaced. The air screw of the carburettor was jammed; it could not be removed. A new carburettor wasn't available immediately, so I procured a used carburator (exactly same model) from local shop who sell the spares after dismantling the bikes. ASC was satisfied after inspecting this carburettor. They cleaned it thoroughly, fitted it and tuned it. The problem started after this.
4. Reduced fuel efficiency. I started getting 33 km/lit on the same trip, where I was getting 38 - 40 km/lit in past. On this 20+20 km long trip, I get to ride continuously in 30 - 50 kmph all the time except signals and occasional crowded traffic. No black smoke visible during cruising or acceleration.
5. This is a Keihin carburettor, cable operated piston throttle. Intake manifold is an aluminium casting. Main jet size 105, pilot jet size 40, both are company default.
6. The ASC could not solve this. So I tuned the carburettor myself. The process: Carburettor cleaned. Air filter and air box checked and found clean. Idling screw set to high rpm. Then the air screw adjusted to a position that gives maximum rpm. Then the idle reduced to 1050 rpm. The problem persists. I even raised the idle to 1140 rpm. No noticeable improvement.
7. The needle clip is in the 2nd groove from the top (out of the 5 grooves). Tried higher needle position (4th groove from top). It solved this problem but worsened the FE to 28 km / lit. So I returned to the 2nd groove from top, which means 2nd position of the needle from the bottom.
8. Even after parking overnight, the scooter starts with second kick, without needing choke. Idling is smooth and uniform. Can idle forever without dying.
9. The ASC / FNG doesn't suspect vacuum leak.
10. Though the choke isn't needed for cold start, the scooter doesn't mind starting with choke on. But if I pull the choke knob after starting, then the engine stalls. On my other three scooters, the engine idles high when the choke cable is pulled after starting.

Request your advice to solve this problem. Yes, the problem is only during the first 10 - 15 minutes after cold start. But this scooter is only used for local errands. So it normally runs only for 10 - 15 minutes at a time.

My other scooters don't have this problem. They don't hesitate on throttle after cold start, yet deliver reasonable FE. Even this scooter did not have this problem long back. It was sitting idle / rarely used for last 2 - 3 years.

Request your inputs / suggestions.

[scorpian]

@Rahul
Its not necessary if the carburetor is cleaned by mechanic its good, i would once again dismantle the entire carb and clean every orifice with a petrol or carb spray.
Replace pilot screw, go to next setting on needle that would be clip in third position.

Check the color of your plug, your plug will tell you a lot about the setting of the carb, if its bone white you are running lean.

In my opinion doing the above with retuning the carb should solve your problem.
Does your cold issue improve if you use the choke?If yes then you need more fuel in the carb so by raising the needle clip you would do the same.

Keep us updated.

regards,
Manoj.