125 4-stroke thumpstar not revving out - HELP !!!!

chiefmew · L Plate Warrior Joined: 06 Jul 2007 Karma :

Hi. Can anyone help me please? I have a 125 4-stroke thumpstar and it does not rev out. I have replaced the head twice and it will start fine but will not rev out. I was told that my timing was great and that the head gasket needed replacing so i changed it but it is still the same. I have put new oil rings in it, piston rings and even changed the cdi coil along with a spark plug. I cannot understand it so can anyone out there help me please? Thank you. Crying or Very sad

Odie · World Chat Champion Joined: 24 Jul 2004 Karma :

What do you mean by "rev out"?
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hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

have you got a cv type carb or flat side?
if its a cv then pull the top off the carb and check the diaphragm is still in good condition
has it got an electronic advance or a mechanical type??
check that also.
if its not advancing it won't "rev out"
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chiefmew · L Plate Warrior Joined: 06 Jul 2007 Karma :

It's exactly the same as a honda step through c-90 engine if this helps anyone to help me. Some one is telling me that the valves are out but i am not too sure.

biker_king · Renault 5 Driver Joined: 28 Jun 2007 Karma :

sounds like your fuel mixture is rich, is their any smoke from the exhaust, iff their is blak smoke it is running rich, clean the carb and adjust fule mixture.

chiefmew · L Plate Warrior Joined: 06 Jul 2007 Karma :

Hi. Yes it does smoke a bit. I will try this and get back to you to let you know if there is any change. Basically whats happening is that the bike will start with no problems at all but once i rev the throttle it starts to cough and splutter. It will tick over o.k as well. This is the first time i have done a 4-stroke and it has done my head in so far! Laughing

It sounds as if it is sucking in air but i cannot seem to work out where from. I have checked all seals and gaskets and put sealant on them. This bike has had 2 heads put on it and it still does the same thing. Could it be an electrical problem? or is it something so obvious i can't see it! ( typically happens to me - always turns out to be something simple! Laughing

). Thank you.