Engine dies at full throttle

[glenn young]

My son's bike has a problem with full throttle, the bike has a Franco Morini engine 50 cc, that has been ported by a local tuner ( Mr Rivara). The bike is very fast and responds well. However, I have had a Power Blade fitted to the carb to improve
bottom end performance. The carb fitted to the bike is a Dellorto PBHL 24 mm and the engine was ported for this carb.

Since the carb has been modified, when I open the throttle to 3/4 the engine revs reay well however, when I go to full the engine dies, and the revs go up and down.
Is this problem due to either a main jet that is too large or too small ?

I have cleaned the carb out, and the reeds fitted are carbon fibre and are quite thin. Do you think that if I get some thicker ones, this could be the answer.

 

[Red Rider 53]

It could be the spark arrestor if you have one on it. When they get gunked up they will cause the bike to do that. Another thing is you might want to look at the spark plug. My CR80 did exactly what you just discribed. But its tricky because its not that you have a fouled spark plug, the porselen around the electrode could be cracked and that will cause your problem. In that case just pull the old spark plug out and throw it away and replace it.

Hope this helps!;)

 

[glenn young]

Thanks for reply Red Rider, I will check the plug!
All the best Glenn

 

[Jasle]

Actually it really sounds like its too rich on the top end. Also I have seen these symptoms from a bad stator. If you have a spare stator try it out.

But a quick check is to go to WOT and then pull up the "choke" which is actually a fuel enrichening circuit If the phbL is like the phb we get over here in the US. If it gets better then you know your lean. If it gets worse then your too rich.

I suspect this is the case because when you install the "blade" you increase intake velocity pulling more fuel with the extra air. I have seen this on OUR PHB21. We throw a 14mm reducer in for arenacross and have to lean out the jetting.