Lifan 125cc jetting after port Job ???

[jdr.223]

Hi guys. Just did a moderate port job on my Lifan 125 head. Bike kicked over and idled first kick. Revs up when choke is applied.
However, when I attempt to bring the revs up with the throttle, it dies and stalls out. Running a Mikuni 26mm but have an Oko flat slide on the way.

I assume my pilot jet is ok seeing as it starts easy and idles fine. Would I be looking at having to adjust my mixture screw out and adjust the needle clip height?

Thanks in advance.

 

[my67xr]

Welcome to Miniriders,

With it reviving when the choke is on is due to it richening the mixture
With no choke, and you blip rev it, does it hesitate?
If so, it sounds like the Pilot jet need's to be bigger ?
I would be trying a #20 in it if you haven't already done it, the factory fitted #15 Pilot is too small for a standard 125.
You will need to adjust the mixture screw as well.

The needle clip setting effects 1/4 to 3/4 throttle so that should be fine


What size OKO have you bought?
You might be able to jet down a OKO 24mm?

 

[jdr.223]

Thanks. Yeah when it is idling and I blip the throttle it snuffs out.
I've got an OKO 24mm flat slide on the way so I'll try get the Mikuni sorted for now.

 

[8r3nd0]

Probably have an air leak. Check for that around the manifold on both ends. Spray some WD 40 or carby cleaner around the manifold while it is running steady and listen for rev changes. Doubt porting it would make such a difference that you would need to up the pilot straight up.


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[my67xr]

Yeah but the standard #15 Pilot jet's are too small for a stock 125 engine to start with

 

[8r3nd0]

Just saying work your way through the easy fixes first rather then changing the jetting.


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[my67xr]

With it starting and idling ok, then the hole though the middle of the pilot jet is open, it might even be slightly blocked up ?
When you open the throttle and it stall's would most likely be a blockage/restriction in the pilot circuit.
If there was an air leak, it will usually surge, eg revs rise and fall.
But it's easy to check like Brendo advised above.



You'll need to adjust the mixture screw first, and tune the carby to suit the ported head.

Warm engine up, raise idle speed a little, then adjust the mixture screw in or out till the engine reaches the highest/smoothest rpms
while adjusting it listen what the engine is doing, if you turn the screw out and the revs drop, then turn it back in
once you are happy with the way it's running then turn the mixture screw right in till it stops, count how many full turns it was out
If the Pilot jet is ok the mixture screw will be set somewhere between 1.5 and 2 full turns out
any where above or below this, the pilot jet needs to be swapped for a bigger or small size jet.
Usually needs a bigger one



Have you ever cleaned the carby out,all jets and ports etc, then blow it out with compressed air ?
When you blow compressed air in through the 2 or 3 small ports on the filter side of the carby you should feel air coming out one of the holes under the carby body where the jets screw into.
Have you checked that the holes across the jet's are all open ?
Also make sure when you blow it though that the mixture screw and spring is removed from the carby while blowing it out..

 

[jdr.223]

That's the first thing I did when it would t rev up, stripped the carb down and hit it with compressed air.
I will hit it with a good clean dose of WD40 tomorrow and check for air leaks.