1980 GS450 Cutting out between 4000 and 7000 rpm PLEASE HELP

[Anonymous]

I just found this forum and hope you guys can help me out. I am working on a 1980 Suzuki GS450 that has been sitting for a long time. I have gotten almost everything fixed. I have the bike running and it runs great up to 4,000 rpm. Between 4,000 and 7,000 rpm the bike cuts out then clears up past 7,000 rpm. I have had the carbs apart 5 times and cleaned them put in new main jets, a new float valve in one carb etc. I did put on two K&N pod filters as the original air box was shot. I also rinsed out the tank with gas because it has some rust in it, added a new fuel filter and new fuel hose, new spark plugs and sync. the carbs. I can't figure this thing out. Can anyone give me some help here, I am about to pull my hair out and I don't have a lot left.

Thank You,
Starbound

[focus frenzy]

sounds like some jetting work still is needed.

[Anonymous]

Tonight I shimed the needle with two washers. The bike runs a little bit better but still not quite right. I don't know if I need to add another washer or go larger on the main jets it has the stock 115 mains in it now and they are new? Does anyone have any thoughts on this?

Starbound

[gsBert]

at what speed is this happening? and at what throttle opening. needles are affected by throttle opening not rpm...

if your flatspot is around 100-120 km/h, blame the pods.

the best advice i can give you is this: (trust me on this one, i've suffered plenty from pod-induced flat spots)
PUT A STOCK AIRBOX ON!

[KEITH KRAUSE]

Just a suggestion, never jetted a 450 personally. K&N's only, stock exhaust.
Try raising the needles about .075".
If 115 mains are stock, try 127.5.
Adjust mixture screws OUT an additional full turn from where they are.
Remove float bowl vent lines and leave the ports open.
Oil the K&N's correctly, with K&N filter oil only.
I'm assuming the carbs are clean, float levels correct and vacuum synched correctly. Clean/tight connections at coils, leads, plug caps. Timing advancer operating correctly.