Need help tuning Lifan 140

[locko90]

Been a while but I ended up getting around to working the 140 lifan.
I've got it in another big wheel pit bike.

Running it today it pretty much the same problem still, there's an air leak on the intake manifold.

So I'm going to most likely rip it off and try and get that air leak sorted.

I seen on eBay you can buy the head for a 140 lifan for like 70. Is it that hard to swap the heads ?

Also I have a 125 lifan with a good head on it are the 140 heads the same as the 125 heads "? They look identical


Sent from my iPad using Tapatalk

 

[Trains]

It's not hard to swap heads over, but you will need to get a top end gasket kit also. as for the 140 head on a 125 i have no clue. my67xr would be your best bet here.

 

[mikkh]

The big valve (27mm intake, 23mm exhaust) are the same, the only difference is in the combustion chamber size. You can use the smaller valve heads too, if the bolt patterns fit and the cam gears are the same for example 32 tooth cam sprocket on lifan 140.

 

[my67xr]

Along with the combustion chamber being a different shape, the squish band on the 140 head will be different too, it's wider.
The earlier Lifan 125 head has a different stud pattern to the later head, earlier head will fit the 50cc, 70cc, 110cc as well as the 125, but not the 138cc, 140cc, or 150cc and it also has a 28 tooth cam gear.

A good upgrade for the 140 is the Z40 cam and heavy duty valve spring's, and a high comp piston, it will make quite a difference in power.
You can usually get away with reusing the head gasket too if need be.

When you take the head off, just make sure it's at tdc on the compression stroke
Remove the cam chain tensioner bolt from the bottom of the case, left side of the engine, to make taking the cam chain off easier.
The cam chain bolt has an oil port that run's through it which can block up too, so make sure you degrease and clean them out while you're at it.
And if you get a chance clean out the oil filter screen inside the r/h clutch cover at the front, and take the oil spinner off the end of the crank and clean that out.
The oil spinner is a centrifugal oil cleaner and it'll have a lot of fine grey metallic particle's in it that's been taken out the oil.
You used to be able to buy a lightened spinner for the 140, it help's the engine to rev easier/quicker
Post up a pic of your's if you remember, i might be able to find you one if your interested.
I can send you a link to the Z40 cam/spring kit if you want too.

 

[locko90]

I had the engine running today, and while it was idling I sprayed degreaser all around the intake and seemed there was no change in idol at all.

but when u take it for a ride give it a little bit of throttle and it dies.
ive played around with the carb settings a fair bit cant seem it figger out whats causing the problem, and the carbs ive tried run fine on the 125 I got.

could there be something eles causing this ?

 

[my67xr]

Maybe a blocked filter in the tank, there will usually be one on the fuel tap if you take it off.
I have also seen blocked fuel tap's too, gummed and gunked up, could even be a blocked breather ?

Could be something in the pilot jet, or a bocked hole at the bottom of the pilot jet thread's in the base of the carby.
Wouldn't explain the carby running ok on other engine's though.

 

[mikkh]

The cdi connector could cause issues too. I had similar problem when my primary coil got moisture in it, I took the magneto cover off (for the moisture to escape) for couple of days and it started working again. I had one similar occasion too, but it was caused by sheared off woodruff key.

 

[Trains]

ive had similar problems to this, i'd check your electronics, first off check your spark, you can do this by either finding a spare spark plug and grounding that on your engine. Turn over your engine with your hand and it should give you a constant spark. This could also be your stator/magneto, your cdi or even just a bad ground. Could also be a blocked fuel tap as Craig mentioned, this can be tested easily though by pulling the fuel tubing on and opening the tap, a sufficient flow of fuel should come out. Could also be as simple as a blocked jet though.

 

[locko90]

Thanks for the help guys. Ive got constant spark and good fuel flow. Im not sure where the ground wire is on it. But the kill switch works.

Ive had this engine running decent before. But it used to die at high rpm.
It definitely had a air leak on inlet manifold back then, so i decided to take the inlet off and have a look.

While using one of my feeler guages as a straight edge and pressing it flat on the inlet while shining a torch i can see light coming under the straight edge from the uneven surface.

So im going to hope this still the problem and try have another go at getting this inlet flat.

Sent from my SM-G900I using Tapatalk

 

[my67xr]

Supercheap have a 3 pce mini Diamond file/sharpener set for about $6, they are good for facing manifold's and small stuff.
Keep tapping it against something hard to keep the cutting surface clean
Gripwell Diamond Sharpening Set - 3 Piece, 25 x 75mm - Supercheap Auto Australia


Or if you have one close by, Aldi have the Diamond sharpening block out for $9.99 atm.

[video=youtube;2frr0oEqAw8]https://www.youtube.com/watch?v=2frr0oEqAw8[/video]

 

[locko90]

cheers man ill check them files out when I get a chance.

just managed to get it running pretty good... well out of gear reving it seemed pretty good, after riding it for about 2 mins it just starts to lose power and eventually dies. and leaves me stranded :/

when it dies it will only start again with the choke on and no throttle. then I turn the choke off and accelerate in 1st, if I give it a bit to much throttle changing to 2nd it will completely lose power and die again. I have to ride the clutch heaps it sucks.

I wana metion that the spark plug hole thread is rooted and the spark plug goes in and gets tight but I think theres a leak there aswell all around the out side of the spark plug hole is oil and crap.

could this be causing the problem ?

about ready to give up on this engine again haha cant belive I put it back in a frame!!

oh also there is no lock nut on the flywheel and the shaft its on is a bit bent at the end the sator spark thing isn't the flashest either its been knocked off a few times by the chain and what not.

but like I said before there is spark. but maybe its slightly out of timing I don't know

 

[locko90]

Heres a pic of the head. Pretty sure its all good now.

The magneto is a bit rusty looking and magnet thing has been knocked off a few times. I thought maybe the magnets where to close together so i moved them futher apart. But that just made the spark really weak. Coulnt barely see the spark, There is no lock nut on the magneto and also if i pull on the magneto it moves a bit back and forth, not sure if thats normal.

I think i might need to change the sator thing out from under the magneto. Will i be able to get it off? I dont know how to do it.

Heres the spark plug in it. Its threded and no other spark plug will go in the head only this one fits.

Heres the crap around the spark plug hole i think the spark plugs not sealing around here and leaking oil.

New gaskets no air leaks anymore.

Magneto

Sent from my SM-G900I using Tapatalk

 

[my67xr]

You need a flywheel puller to take the flywheel off
Classic Honda 5's Australia
And buy a new knurled flange nut for when you refit the flywheel too, Jaimie might have them too ^

The gap for the flywheel pick up shoud be pretty small, you can set it using a thin cardboard business card

 

[locko90]

You need a flywheel puller to take the flywheel off
Classic Honda 5's Australia
And buy a new knurled flange nut for when you refit the flywheel too, Jaimie might have them too ^

The gap for the flywheel pick up shoud be pretty small, you can set it using a thin cardboard business card

Where its leaking oil at the spark plug hole could that be causing it to run bad ?

And also the thred on the fly wheel is damaged at the end not sure if i can get a nut on it
Sent from my SM-G900I using Tapatalk

 

[my67xr]

I have temporarily fixed one leaking spark plug which had the same problem as you have, i fitted a 1mm thick, 10mm i/d copper washer on the end of the spark plug before fitting it.

You probably be better off taking the head off and Helicoiling or using a Threadsert to repair it it though, it's more permanent


You could try starting the engine and use a fine file to taper off the end of the thread's on the crankshaft
Then just use a wire wheel in a drill to clean it up so the nut fit's on nice.'

Or you could make your own thread chaser/cleaner easily too.
You need an angle grinder, 1mm thick cutting disc, a vice, safety goggle's, and a spare M10 x 1mm nut.
Clamp the nut in a vice tight, then carefully run the thin cutting disc across the nut, cut it about 1/2 the depth of the nut.
Once you are done you can run the cut side of the nut onto the crank thread's and the sharp edge's from where you cut should clean up and burr's etc that are on the cranks' thread's.
This is a budget diy thread chaser nut, like a Die nut from a tap and die set.
They look similar to this when done, you don't need to cut across it 3x time's, but it can help it align onto the thread's easier.