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Absolute rookie in search of carb help - GS450l 1980

  • Thread starter Thread starter MOC
  • Start date Start date
M

MOC

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I just picked up a 1980 GS450L for a song, and it isn't running right.

It seems like it's running SUPER lean, but i can't seem to figure out how to adjust it. It dies under any throttle , revs a LOT with choke, and spits out the carbs and backfires occasionally.

It starts up nicely with choke, and after it warms up a bit, will idle OK with little or no choke. I pulled the carbs and cleaned the Main jets, Pilot jets, needles, floats, float valves, etc. Everything looked pretty clean. Checked the fuel line for kinks or blockages, everything looks good. After reassembly, I put them back together and back on the bike. Same problem.

Stock airbox installed, with good boot rubber. vacuum hose is in good shape on the way up to the petcock. i can't find any cracks or leaks in either of the intake manifolds. When i say it dies under throttle, I mean only 1% throttle is enough to make it miss and die immediately. Also, and this is what's got me really confused, the plugs look like they've been running rich, but the exhaust doesn't smell rich, or smoke at all.

I can't find the Mixture screws that my Haynes manual describes, and i'm getting really irritated. I know there are lots of threads like this one, and i've searched them for solutions, but haven't found anything that's worked for me.

please help!
 
Could you be more specific? I've been through both carbs top to bottom, all the gaskets look ok, not sure where to source OEM o-rings which is part of the reason i'm here...
 
MOC said:
Could you be more specific? I've been through both carbs top to bottom, all the gaskets look ok, not sure where to source OEM o-rings which is part of the reason i'm here...
Click to expand...

Robert Barr (fine member here) provides a nice kit of carb o-rings.
Look in the "Service" forumn.
Or do internet search for " Robert Barr Cycle o-rings ".
 
MOC said:
...
It seems like it's running SUPER lean, but i can't seem to figure out how to adjust it. It dies under any throttle , revs a LOT with choke, and spits out the carbs and backfires occasionally. .....!
Click to expand...

I am not really certain what carbs are on 450s.

But if like the mukini CV carbs on most GS, the only "adjustment screw" only has small effect on idle.

A bigger adjstment, that you didnt mention, is the float heigth (bending that little tab on the floats that operates the float neddle).
Other than that, there are:
- changing the little washers to raise/lower the main needle
- changing jet sizes.

I am not the one to diagnose the sysmptoms you mentioned.

Go back to GSR main page (not forumn, but GSR mainpage), look for "in the Garage" and then "Carb cleaning series".


.

.
 
Last edited:
It has CV carbs, Dave. cycleorings.com sells the oring sets. Nessism''s rebuild tutorial works for it, there is just half the work. It is mandatory, unfortunately, MOC.
The rebuild tutorial can be found on BassCliff's web site.

For the carb rebuild, use this

For manuals, tutorial, and wiring diagrams, go here BassCliff's web site
 
Last edited:
MOC said:
Could you be more specific? I've been through both carbs top to bottom, all the gaskets look ok,.
Click to expand...
If you didn't dip the carb bodies thoroughly (not just blow gumout thru), it's likely that you have some plugged passages in the idle circuits. These little orifices must be clean or you will have a poor transition as you come off idle.
Best to replace all the 32 year old o-rings in carbs to be safe.
 
big sigh of relief.

I was confident it was pretty clean, but was going to take your guys' advice and dip it. i went back in and checked the float heights while i was tearing them down. I made a float height gauge out of some piano wire and checked each side. The floats were off by 5-6 mm on each side. i adjusted them up to spec, reassembled, and reinstalled, just to see if it would run better.

the bike starts up beautifully now, idles without choke, and revs through the whole throttle range. its still running a little lean, i need to choke it to get it to rev on throttle. I figure this is probably because of the vacuum leak i'm almost certain that i have in the airbox and the intake manifold orings.

I will be traveling in europe for a few weeks starting wednesday, so i cant say for sure when i will be done with this overhaul, but i'm relieved to know that at least it's capable of running at 100%.

baby steps.

Thanks for the suggestions fellas!
 
Just found this thread... haven't been on much in the last week.

Just to clarify on the choke height, the 80 - 82's should be 26.6mm +/- 1mm. The spec's listed everywhere are incorrect according to what I see in the factory manual.

I still have to go compile the info so BassCliff can fix the info on his site. The 23mm level is for the earlier carbs on the 400/425's.

Also, the carbs on these 450's are BS34SS CV carbs and there is a specific write up on cleaning on BassCliff's site by Flaming Chainsaws which will show you what you need to drill out to get to the mixture screws etc.

Anyway, glad she's running much better now, enjoy!
 
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