Exhaust/jetting issues

[bakirkwold]

My bike has a MAC 2-1 exhaust on it. Its a GS450 L. I built a custom baffle for it. The one it came with had the rattling sound they all have. Anyways, I have a flat spot at about 6-7 grand. It it flat for maybe 1 second then it just takes off. It makes lots of powder at 10. I did shim the needles and move around a few sizes with the main jets. But its the same. Could this be back pressure issue? Any imput would be helpful.

[tkent02]

Are you talking about 6-7 grand with wide open throttle? If so it sounds like one size bigger main jet would do it.

If you are talking 6-7 grand at half throttle it would be a needle position issue.
Have you done proper plug chops to see if its rich or lean?
What other maintenance has been done or not done?

What are you running for intake? Pods, the original factory air box, something else?

[bakirkwold]

Yes at WOT. I am running the factory air box. I have tied taking off the top also. Same thing. The only thing that has not been done is have the valves checked. I hope to get that done sometime this week. Its got 21,000 on it. Could this actually be the issue?

[tkent02]

Could this actually be the issue?

It actually could, maybe, maybe not, the only way to know is to adjust the valves and see if it helps.

Don't know if a flat spot at mid RPMs is likely to be misadjusted valves, but if you do check the valves, check the cam timing while you are in there, then adjust and synch the carbs, check the ignition timing and all of the other stuff, at least you will know where you are at.

If everything isn't done it's just a big guessing game.

I had a Yamaha 650 a long time ago, with a 2-1 pipe. It had a flat spot at about 5,000 - 6,000 RPM, it took off like a shot above that flat spot. I never did find the cause.

I was not as good at tuning things than as I am now. Wish I could take another shot at it.