1980 GS450 Carb / Air Cleaner Issue

[orion50002001]

Hey, I picked up a GS450 for my Dad for christmas. The bike was in really good condition except for some dirty carbs and a sluggish throttle response.

I took the carbs apart and soaked them in Yamalube. That seemed to help throttle response drastically. Problem is i still have some mid range power issues. The bike runs fine with the throttle cracked open and runs ok with the throttle wide open but It bogs down at part throttle.

I noticed while I was cleaning the carbs that there were some after market K&N filters on them. I also noticed that there are pressure or vacume advance slits on the intake side of the carb. If this is obstructed, even slightly would this cause part throttle problems?

By the way, i shaved the rubber inside the K&N filters near those slits and It may have helped some. I'm not that familiar with this bike so I'm not really sure.

If this wasnt enough detail please let me know. I'll be glad to provide more. Any help is appreciated. Thanks Billy

[SqDancerLynn1]

I'm guessing the last owner put the pods on without rejetting the carbs.
Check to see what jets it has, and what position the needle is in.. maybe raise the needles

[orion50002001]

Cool, I'll give that a shot.

When I bought it the guy said he had tried to re jet the carbs but the bike didnt run well aftwards so he put the stock jets back. I dont really know whether they're stock or not. Or how to tell the difference.

Thanks again. B

[hampshirehog]

It'll need re-jetting / playing with the needles for sure. There's loads of info on here on how to do it (use the search feature) but if you get stuck ask the question and it'll get answered.
I pulled this off the Carb Sticky (at the top of the technical section). Should help you id what your carbs would have been set at when they left the factory:

US 450 models:
Make: Mikuni
Type: BS34SS
Venturi Size: 34mm (1.34 in)
ID number:
ED: 44400
LD, TXD, LF: 44460
Other models: 44110
Idle Speed:
ED, LD, TXD: 1200 +- 50 RPM
Other Models: 1200 +- 100 RPM
Fuel Level:
ED, LD, TXD, LF: 5.0+- 0.5 mm ( 0.20 +- 0.02 in)
Other Models: 6.5 +- 0.5 mm (0.26 +- 0.02 in)
Float Height:
ED, LD, TXD, LF: 23.0 +- 1.0 mm (0.89 +- 0.04 in)
Other Models: 22.4 +- 1.0 mm (0.88 +- 0.04 in)
Main Jet:
ED: 120
Other Models: 115
Main Air Jet:
ED, LD, TXD, LF: 0.7
Other Models: 0.6
Jet Needle:
ED: 5DX87
LD, TXD, LF: 5CDT60
Other Models: 4C2
Needle Jet:
ED, LD TXD, LF: 0-6 (O-6??)
Other Models: Y-6
Throttle Valve:
LF: 95
Other Models: N/A
Pilot Jet:
ED, LD, TXD, LF: 45
Other Models: 17.5
Bypass:
ED, LD, TXD, LF: 1.0, 0.8, 0.9
Other Models: 0.8
Pilot Outlet:
ED, LD, TXD, LF: 0.7
Other Models: 1.1
Float Valve Seat: 2.0
Starter Jet:
ED, LD, TXD, LF: 32.5
Other Models: 30.0
Pilot Screw Setting:
ED, LD, TXD: Preset (2.0 turns out)
Other models: Preset
Pilot Air Jet:
ED: 135
LD, TXD: 145
LF: N/A
Other Models: 1.6
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[orion50002001]

Cool, Thanks for all the great info. I'm going to tear into it this weekend if it warms up a bit. Thanks again.