Tip & How-To about 2008 Lifan Delta 250 V Twin

How to adjust carb settings

Hi Charlie.
Operations to be performed depends on how much tuning is needed.
Carb setting regulates the ratio between air and fuel in the mixture aspired into the cylinders.Optimal air/fuel ratio is usually around 14(air) to 1(fuel). I illustrated the complete job with cleanup and jet replacement and adjustment. In some situation you do not need to perform complete tuning, which involves taking apart the carburetor. In that case perform basic regulation setup using the two adjustment screws at one side of the carb. Adjustment simple procedure starts from part 2/Adjustment. A good approach is first doing adjustment using idle and thickener screws. Then do the whole tune up if the simple adjustment does not work.
The complete tuning is based on carburettor cleanup, regulation of main jet and idle jet and needle setup.

Part 1 : Complete tuning and cleanup:
1. Take apart the carburettor,
2. Undo the float chamber(6 in diag) held by screws (26 in diag).
3. Clean bowl with with carb cleaner (put a lot of it in the bow, wait a bit and dispose it-finish the job with a cloth if needed) . Clean floats (nr.4) and other parts using carb cleaner and cloth.
4. Use a flat screwdriver to remove the main jet screw (placed in the chamber, held by big golden screw, goes between the floats). Spray the main jet. You must be able to see through it.
5. Use the carb cleaner to clean the accelerating pump and all the other parts inside the part. Needle and small parts must be cleaned. Clean the idle jet, which is the smaller golden screws. If you have a compressor blow into the jets (you can blow them even without compressor, but follow H&S).
6. If possible replace main and idle jets. Sometimes you may like to replace the jet with a bigger one to get a richer mixture.
7. Adjust the needle if needed. A lower needle settings means a richer mixture.
8. Remove idle adjustment screw (7) and main adjustment screw(31), clean them screw them back in without tightening and perform part 2. Leave the screws about one and half turn from all way in.

Part 2: Tuning and minor cleanup - Here you mainly operate on idle and air (thickener) adjustment screws (8 and 12 in diag)- Start from here, if this does not work, do part one:

1) If the engine runs start from idle adjustment: screw or unscrew the idle regulator to adjust the idle speed, the screw is placed to one side of the carburetor and has a spring (part 12).
Keep idle least slightly higher than the minimum needed. Example, if the engine stays on slightly below 1000 rpm, set idle to a bit higher with engine revving above 1000 rpm.

2) The thickener, placed near that of the minimum screw regulates the air flow. Tighten the screw and unscrew 2 turns from all the way in. Do regulation from this position.

Here carburetor diagram and part list. The diagram is taken from service manual. The manual for Lifan 150 (does not include carb setting) has been uploaded here:


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Need to know which adjustments on carb are for what results.

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