Over revving after full throttle and top speeds

[DAMIEN1307]

Unless your fouling plugs an 8 or even 9 ngk is perfect.

I would have to disagree with that assessment based on many, many years as an ASE certified master mechanic, at least on cars and trucks...lol.

This is a pic of my perfectly burning plug at present and all my plugs have looked like this on all my CGs for almost 10 years now running the NGK-B6HS, recommended spark plug...most of these engines come with those Z-4 Cinese plugs which are a heat range hotter equivalent to a B5HS...Im running a 32:1 ratio using Amsoil synthetic Dominator 2 cycle racing oil with a stock NT carbie...runs great as you know and has been to 47 MPH before i chickened out...lol...DAMIEN

 

[Ktm pipe]

Will try to run a colder plug definitely worth giving it a shot.. Doubt it's a slow return on the carburetor slide cause it does it when it's shut

 

[Chainlube]

Will try to run a colder plug definitely worth giving it a shot.. Doubt it's a slow return on the carburetor slide cause it does it when it's shut

If the slide is closed, then you have an air leak. Once it's running, spray a little carb cleaner on the intake manifold where it meets the cylinder and carb. If the revs change then you have an air leak. Any kind of spray will work, mist of water, WD40, open propane torch, etc.

 

[Ktm pipe]

I've did that test with carburetor cleaner seems fine it's raining really bad at the moment so can't test now ... Maybe I need to run a real filter rather than the velocity stack?

 

[Chainlube]

I had a similar issue to what you're experiencing when I rebuilt my spitfire, it took it for ever to come down to idle. I'll see if I can find my notes on tuning my SUs, it may or may not be related.

 

[Ktm pipe]

Ok

 

[Street Ryderz]

Yd100 reeds and 21 mm oko dirt bike pipe the bike idles fine until I put a heavy load on full throttle top speed runs the problem I'm having is when I come off full throttle engine revs really high for about 20 seconds only does it with hard runs any suggestions please??

This is because the fuel supply can't keep up with demand and leaves the float bowl low on fuel and there for lean for a moment after the wot running, this will also lean out the wot run if sustained so be careful. I have pictures of a modified petcock to help eliminate this issue somewhere here on the forum though that's still not really working for me and a better petcock is required with a better flow rate (more volume).

 

[Ktm pipe]

Thanks that makes sense my float level is slightly low at 19.8mm oko recommend 19mm

 

[Ktm pipe]

It's still doing it only when I push the throttle to the limit maybe cause I don't have a 3 transfer port..Who knows???

 

[Ktm pipe]

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