GS400 Boggs down from half to full throttle

[motorjunky]

I have searched the threads and cant find anything that helps. If anyone can tell me what the problem is with a 1981 GS400T. It starts. Idles and accelerates very well up to about half throttle. From there on if I try to accelerate, it boggs down. If I let up on the throttle back to half or so, it seems to pick up again. I have cleaned the carbs twice with no difference. This bike was bought - not running -from a college student who only rode it around town (???) Yea I know, you dont have to say it. I have tried it with and without the breather element, no difference.
Help

[psyguy]

assuming the carbs are clean, and if you're running pods? you may be lean on the main jets

[BassCliff]

Greetings and Salutations!!

Hi Mr. motorjunky,

The easiest way to sort things out is to use stock parts and settings. If you have modified the exhaust or intake then jetting changes are necessary. Have you cleaned the carbs fully and properly? Float height set? Using an inline fuel filter? Vacuum and fuel lines good? Details will follow. Also check valve clearances, coil and timing specs, petcock, etc. Here's my "welcome thang"...

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[spyder2120]

just jumping in. you dont really know me but welcome back basscliff, i hope your recovering well and thanks for your web site.

[motorjunky]

Can anyone tell me where I can find out the stock jet sizes (the main in particular) that this is supposed to have.

[Spyderman]

Can anyone tell me where I can find out the stock jet sizes (the main in particular) that this is supposed to have.

also check to see that your mechanical advance is working properly so that as engine RPM increase the timing advances it should move freely by hand

[mxhead]

sounds like your float level is too low. no fuel when calling for it.

[mxhead]

k&n should be able to tell you stock jet sizes, and try dynojet, vance and hines or possibly a savvy motorcycle dealer. tell them to look up the carb and what jets it takes

[PoppaDre]

Seems like you are having the same problem as me. I got my carbs cleaned last year, and new plugs and battery. This year they tested all my electrical and found a less then 100% coil that i replaced. $200 later for the coil still no improvement, GS1100GK suggested i test the battery at different times and to report them. I am hoping to get that done tomorrow after work, and i will let you know if it helps when all done. Best of luck, let me know if you get 100%

[chef1366]

May be ignition related.
Coils?
Igniter?
Trank triggers?

[snark]

Before you go nuts I've had the same exact problem. Turned out to be bad gas. I'm actually wondering if the blended crap they have in Pittsburgh is causing the problems...they actually put warning lables on the pumps now.

Anyhow...I threw a bottle of Gumout in the tank the next time I filled up and the problem went away. I hope that's all it is for you.