Valve ? Starting problem ?

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kaevo

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I haven't ridden my pitbike 125cc lifan engine for over 2 .5 years or more but I have just turned it over and given it start here or there.

I decided to start it today, I got it running but it didn't seem to hold revs very well even with the choke on. As well as this when the choke is off and it is idling, when I rev it, there is a very weird sound and causes the engine to die if you hold it on for to long. The sound it hard to explain but its like a very hollow, deep sound.

The reason I ask is the last time I started it, I gave the carb a clean out, and even then it was making this sound when the engine was reved but it was actually capable of idling with out a problem.

Thanks for any help!
 

my67xr

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Welcome to Miniriders,

Wow, long time member, first time poster ..

Drop in and say hello in our Introduce Yourself thread too while your here.

Im guessing it has a blocked Pilot Jet ,or a blockage in the Pilot circuit ?
Probably gummed up from fuel drying up inside it when not being used.
What you could try is take the air filter off and hold your hand over the intake side of the cabyu sealing it off.
Then kick it over a couple of times while blocking the carby.
It will create a vacuum inside the carby and can sometimes clear a blockage.
Your hand will get wet with fuel, just wash it off the try starting it.

It will take a couple of kicks to fire it up,
but if it is running a little better then i'd suggest pulling the carby off, and pulling it apart and giving it a thorough cleaning.
Take the pilot jet, main jet and needle jet out, clean them up, make sure you can see through all the holes etc,
and where the jets screw into the carby, you need to be able to see light through all the holes.
Once the parts are clean, give it all a decent blow out/through with compressed air, including the 2 or 3 ports on the air filter side of the carb

Reassemble it and see how you go

You might want to post up a pic too if you can of your bike/carby if you need any more help.
When was the last time you adjusted the valve clearances too ?

Cheers, Craig
 

kaevo

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Thanks for reply! I will take the carb off and give it a clean, I had a person check/adjust the valves way before I stopped riding. But I shall look at the tech thread and have a go of checking and adjusting the valves anyway.
 

my67xr

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Here is a video that helps explain how to do them.
We recommend setting them at .003" (.76mm) for the inlet, and .004" (.1mm) for the exhaust

[video=youtube;QJciyJRJh8Q]https://www.youtube.com/watch?v=QJciyJRJh8Q[/video]
 
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kaevo

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Thanks! I've got to find the feeler gauge but I shall get them done.

Checked and cleaned the carburetor, no blockages and jets were clean only a little bit of junk at the bottom started the bike up and made the bike idle for slightly longer but no significant difference. Pulled the spark plug out, and gave it a clean and seems to have helped idles for longer but does die after about 45 seconds so I will be replacing it anyway.

I had a ride everything seems okay, but about half throttle it bogs down which I guess could be valves.
 

my67xr

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Did you try my trick i posted above, removing air filter, block the carby mouth and kick it over ?

Have you tried retuning the bike too, eg adjusting the mixture screw?


The valve clearances don't have anything to do with bogging etc, just how noisy the top end (rocker's) is.
If they are too tight, it will become harder to start cold, idle a little off, and be even harder to start when warm, and lose compression too.
A bit of rocker noise is ok, after 5-8 hours or so of use, they will become a bit quieter, this is when you need to check and adjust them if neccessary.


Might be worth swapping the spark plug out with a brand new one, NGK C7HSA .7mm gap.



This diagram shows which circuit operates at what throttle position
I am guessing your needle Jet has some blocked ports across it still ?

images



The Needle Jet is the long once with the hex head that screws into the base of the carby, the one that the Main jet screws into (top pic below)
Check that the 12 tiny ports across it are all open, and that there is no gum inside the main bore of it, or inside the carby where it screws into (2x bottom pics)






 

kaevo

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I didn't try your trick with blocking the carby and I haven't tried to adjust mixture screw. So the needle could still be gummed up, but will try these over the next few days when I get a bit of time and some daylight.

I did go for a ride on it today, let it warm up for a couple of minutes, first 5 minutes it was bogging and couldn't hold idle etc. After that it was running very well had no bogging no matter how much throttle I gave it, and held idle and all I did was put about litre or less of extra fuel in.
 
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