Topic: Cb650 dies at 5500 rpm

[lucky9]

Hi,

Ive taken over a scrambler project and having some problems with the engine.

It's a rc08 but with at pd51c carb.

4-1 system and airbox removed.

The pilot jet is "standard" 95.

The engine starts great. But when I rev it over 5500 rpm it just bludders and dies. The sound is like it opens up something. Kind of like the sound of a automatic decompression.

But if I use the choke at approximately half it revs fine and no bad sound.

So, obviously it doesn't get enough fuel or something like that.

My first question is, what's the standard "setting" of the choke? Should it be no tention at the wire or should the choke be semi closed (some tention at the wire) as standard?

Second, should I change pilot jet? And to what?

The carbs are fine. I've cleaned them with ultrasound and checked everything.

Please help.

[robvangulik]

You just need a larger main jet and/or a decent air filter(box)

[lucky9]

Kind of thought so...

Any idea on how much bigger?

[robvangulik]

As the standard main jet for a 79/80 650 is 92 or90 (and the pilot 35) start with 110 or so, the exact size you'll have find out experimenting yourself! The later 650's have 118 and 120 in VB44 carbs....