Lifan Blowing Air Out of the Carby

[dasqer]

I bought my son a 2nd hand pitpro 125 and when I bought it, it would not idle . The seller told me it was the mixture screw. Got the bike home and adjusted the mixture screw and it worked fine until the next day, I had to adjust the mixture screw again, thought it was the carby idle screw and so adjusted that to no success, got the sh=ts and bought a pitpro 140 which is running fine, swapped the carby's and the 125 still won't idle. Pulled off the valve cover and the bottom one leaked a fair bit of oil( I think I overfilled the oil , got that from other posts) the valves do move when turning the crank,I put the covers back on then couldn't start the bike, it now blows air backwards out of the carby, fuel and all. I didn't muck around with the valves, just turned the crank. could something be stopping them from closing
does anyone have any ideas
The moral is not to buy someone elses problems, I feel like taking the bike back and dropping it on the seller

cheers

 

[Mack]

Remove the timing side engine cover and the cam cover. Check the camsprocket timing mark lines up with the notch in the head when the flywheel is at TDC. Whilst at TDC check the valve clearances. If these are correct then you most likely have a sticking or bent inlet valve. Replacement is easy to aquire.

 

[suzuki_lj80_69]

Hey Mate, I had the same problem with my Kazuma Meerkat, what had happened was that when I was doing burnouts, my exhaust valve nut had vibrated off of the thread, which was pushing the air through my fuel valve, up my carby and out of my air filter.

to fix it all I did was I bought a new valve nut screwed it on, adjusted it and it worked fine, mabye your exhaust nut is loose, or the thread is loose, which is letting air through your fuel valve.

hope this helps.

Tim

 

[marfia]

cheack your inlet valve the one on top it sounds like it is to tight and not closing letting the compretion go back to the carby

 

[dasqer]

Thanks for the answers it was the top valve not closing , I ended up ripping the head off and the valve was not closing up it had a mass buildup of carbon around the valve seat ,Its the first time I've ever done this so hopefully I'll get it back together,
while I have it out is there anything I should do before I put it back. The carbon is really hard to get off whats the best way, I used a wire brush could this harm the chamber?
I havn't taken the valves out, should I do this to clean it better and to check if they're bent?
What about putting it back together, can I reuse the gasket it looks like it is made out of bakerlite and it had an orange strip of silicone on it, i could redo the silicone(if i'm better of buying one I will).
What about putting it back together how do I line it up, to get the head off I took the sprocket off , I hope this is right. I know the exact position that it goes back on.
And thanks for the answers guys.
cheers

 

[Mack]

Is good to be forced into your engines internals...demistifies everything.
You will have to clean the valve and its seat but you do not want to score the seat, otherwise you will end up with the same prob down the track. Because this was most likely caused by incorrect lash setting, is a good chance the exhaust will be suffering similar problem. Best to remove both your valves and do the job properly. To easily remove the valves just depress the spring with a largish socket while holding the head upside down. The retaining collets will drop right out. Clean the carbon off the seats with a hard plastic or very carfully with a soft metal. Then use some mild abrasive paste on the seat with the valve reseated and grind them together till both surfaces have a shiny, clean seating. Then drop in to bike store to have the spring retainers put back in for you. If they don't do it for free definately don't pay more than a few bucks for this, its a 5 min job with the right tool. To reassemble use a new gasket if the old one is at all stuffed. Just make sure you replace the oil galley O ring when you remount the head and line up the dot on the camsprocket with the flywheel (crank) at TDC as previously mentioned and set the valve lash. Don't overtighten the camsprocket bolts and torque the head bolts to 8-9 pounds.

 

[dasqer]

thanks for that Mack.
the gasket looks fine but the orange silicone bead in the channel of the gasket is gone, can I just re-silicone or should I get a new one.

 

[Mack]

May work, may not...for the sake of a couple of bucks I personally don't risk the nuisance of having to go into the head again.

 

[dasqer]

Good idea, will replace.
I just whatched the valve clearance vid that you linked on another thread, I know why this pitty didn't work. The clearance was about 1cm only about 100 times more than what it should be!!

 

[Mack]

well you better do a bit more investigating then. That sounds like the valve is sticking in the guide. I presumed the clearance was too little , therefore not allowing the valve to close properly and so allowing carbon to build up on the seat. But if there was a massive clearance as you say that means after the rocker has forced the valve open the spring should take over and force the valve back to its seat. But if the valve sticks then the rocker returns but the valve does not..giving the impression of huge clearance. You need to remove those valves and inspect the stems for signs of scoring and overheating and check they move freely in the guides. Also check for broken springs.

 

[dasqer]

The adjustment was screwed nearly all the way in.Everything was rocking and rolling before I pulled it apart

 

[dasqer]

All looks good, no bent valves or broken springs I've reseated the valves, although I should have listened to you mack and get the shop to install the valves as I shot the collets across the garage. I found one but lost the other.

 

[dasqer]

just a recap, there wasn't a 1cm gap in the valves it was that the valves were screwed right in causing the valve not to close.
reseated the valves, got them put back in, put the engine all back together and it runs great, idles well, heaps of compression, my son couldn't get me off it!

 

[Mack]

Thats good to here dasqer... most often than not its a simple fix. I'm sure there are heaps of bikes retired early because of an easy fixed problem.