Flat spot 4000-6000 rpm 81 GS450EX

[Guest]

Carbs have been thoroughly cleaned (used a go/no-go gauge on them last clean and all good), bench synced, pilots set, valves all at about .05, good gas (non-ethanol). I'm fine til a little over 4000rpm, then its like the bike starves off and on until 5500-6000 rpm. She is like a real crotch rocket before and after that, it is the only range that the bike is sluggish.... Help on what could be wrong.

No vacuum leaks, all new orings/boots

If it is sluggish before that range, I can't tell. Seems to zip up to 4k-6k then I get the sluggos from that range, then zip/bam up to 9k

I am thinking jet/needle

need advice.

Thanks,

[Nessism]

How many turns open are the pilot screws? All stock? Maybe time to shim the needles.

[Blue Falcon]

How many turns open are the pilot screws? All stock? Maybe time to shim the needles.

LH 1 1/2
RH 1 3/4 - factory spec was spot on for both.

all stock, no mods. stock air box, stock exhaust, stock needles/jets... everything.

[Nessism]

Open them to 2.5 or 3 and see if that helps.

[Blue Falcon]

Open them to 2.5 or 3 and see if that helps.

I'll give it a go in the morning. Just for my knowledge, what size washers for shims....Radio Shack not an option... I have Fastenal and Ace Hardware. Inner/outer diameter or size #

[Nessism]

To lift the needle you need to reduce the thickness of the spacer on TOP of the needle clip. This is because there is a spring pushing up on the needle and the height is set by the plug above the needle and the thickness of the spacer. To lift the needle you need to replace the spacer with a stack of washers thinner than the spacer. Or sand down the spacer by 1 mm or so.

[Joe Garfield]

I'm fine til a little over 4000rpm, then its like the bike starves off and on until 5500-6000 rpm. She is like a real crotch rocket before and after that, it is the only range that the bike is sluggish....

It sounds a lot like a new Suzuki! Only yours can be fixed without a fancy computer...

[Blue Falcon]

Open them to 2.5 or 3 and see if that helps.

left at 2.5 right at 2.75 the flat spot is almost gone... 5700-6000 very briefly. Think its almost time to shim.

[Blue Falcon]

It was my petcock the whole time.... petcock was fine a couple months back, check it this time.... disintegrated when I took it apart. rebuild kit and its working great... no flat spot. what a pain.