engine wont rev past idle ??

[jackbmx2010]

hi guys, i have been tuning up my 70cc yesterday and just got it running sweet. i went to ride this morning and it starts and idles fine but it wont rev past idle. when i give it throttle it spits fuel out the carby and revs up a tiny bit if i ease the throttle very slowly but thats it. My green wire had come off the coil before i started it up but i re-connected it but dont know if this has anything to do with it ? also if it helps, I had put a new piston and rings in it about 3 weeks ago but its been fine and I went easy for the first 3 hours or so. I am stumped as to what it is as i swapped to another carby i've got and it does the same thing ?

 

[sean01]

check your valve clearances first..

and what were you doing or did you change to tune it?
what carb and jets are you running?

 

[Nuts 4 50s]

Check everything that sean01 said.

Also was the engine cold, it doesnt rev properly if its cold.

 

[jackbmx2010]

The bike was warm, it has a 19mm with standard jets. All I changed was the air/fuel screw and the idle screw. The valve clearances were set when the piston was put in and it is a brand new head aswell. I will do the clearances again and see how it goes. Thanks for the help guys

 

[sean01]

how many turns out is the air/fuel screw?

if this is too far in or out it can cause a drama..

 

[jackbmx2010]

It's 1 1/4 turns out. It was going great on the same settings yesterday with no problems. I left it overnight and now it does what it does

 

[Nuts 4 50s]

Ok what you should do is reset all your carb settings and if its still not running fine pull your carby off and clean it out.

Clean the jets and the bottom of the bowl.

When ever im having tuning problems first thing i do is clean the carb, then work from there.

 

[jackbmx2010]

That's what I thought in the first place so I swapped to a carby that I only used twice but it still does it but I will do that anyway.I will also re-do timing, valve clearances and reset carb settings to eliminate some other potential causes. Thanks for the help

 

[jackbmx2010]

Hey guys, went out and Bought a set of feeler gauges and did the valve clearances. Intake was out a bit and exhaust was out massive and now it goes even better. Also cleaned out carb but still needs leaning out a bit. Thanks guys