I recently had my 1990 Blaster rebuilt (.40 over), and while I was in the buying mood, I decided to buy a racing carb. I got a Keihin 28pwk carb.My mechanic told me that this carb requires a lot of air to run right. He gave me 2 options: 1)take the whole air box off and slide a little filter onto the carb. or 2)Leave the air box on, but take the lid off. So I decided to do the first option. It ran great and I had no problems with it, except for dirt. I was worried about the reliability of my engine, so I decided to put the air box back on, W/o the lid. on take-off, it was a lot more responsive, but when I would quick shift (required), it would start to bog a little and sputter. It didn't do this when the box was off. Please tell me what could be happening when it does this.

Jeff

 

It sounds like it isn't jetted right.

 

That might be it. My mechanic jetted it w/o tha air box, and now I have the air box. I'll try that
thanx