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1981 GS450L Idle and starting issues

  • Thread starter Thread starter Buddybud425
  • Start date Start date
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Buddybud425

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I recently bought a 1981 GS450L that was pretty rough, the carbs were nice and dirty, and I found a mouse nest in the air box, it would run at 4k rpm with throttle pinned when I tried starting it (before I knew there was a nest in the air box). So I just cleaned the carbs, got new intake boot O-rings and put it all back together today, and the bike won't start well, I need to give it some throttle to get it to start and if I let off it dies, but it is fine once revved up to about 3k rpm and up. I have tried messing with the one screw under the carbs and it has been tough to find a good position for it. The bike has clean carbs, new O-rings, new NGK B8ES plugs gapped to .032 as the specs state, new battery, and new air filter in the clean air box, if anyone could help it would be greatly appreciated.

I was thinking maybe the adjustment screw isn't assembled properly or...

Thanks,
Blake
 
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How did you clean the carbs- these things have tiny passages that get clogged (and stay clogged) and resist quickee cleaning? Hard starting means your "choke" circuit passages ain't passing fuel- there's a tiny feed hole in fuel bowl bottom, did you ensure that it's open so fuel can climb up ?
have you adjusted valve clearances?
 
I cleaned the carbs by dipping them in chem dip, then blowing through the passages with carb cleaner, small wire for the jets, and compressed air at the end. I haven't adjusted the valve clearance yet but it should be done in the near future as the bike has ~21k miles on it and I don't know much of the history on it. Is there anything else other than choke passages that could be causing the starting issue?
 
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Also, when I do start the bike and rev it up, it bogs a little and then goes nicely after 3-4k rpm, could I adjust the throttle cable to fix the starting and give more throttle when the bike is idle?
 
I have narrowed the problem down to fuel related issues, but I know the carbs are clean, but maybe the float height is wrong? I took it for a ride and it died when I let the rpms dip too much, making me push it home since it didn't start. I took the plugs out and they are black and dry, so I think the bike is running rich when it starts up then drains all the gas out and dies from running lean?
 
Well it might be running rich above 3000 rpms or so, but if it can't stay running when you back off throttle, then it isn't getting enough fuel thru its idle circuits. As I mentioned the passages are tiny. Have you seen this link? Pay particular attention to the mixture screws on carb side that let you adjust idle mixture delivery.

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
 
tom203 said:
Well it might be running rich above 3000 rpms or so, but if it can't stay running when you back off throttle, then it isn't getting enough fuel thru its idle circuits. As I mentioned the passages are tiny. Have you seen this link? Pay particular attention to the mixture screws on carb side that let you adjust idle mixture delivery.

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
Click to expand...

I did actually realize that although I dipped the carbs and cleaned all passages, in the link, the needle jet and adjustment screw on the side(I didn't know about this) were left in and most likely destroyed the orings on those
 
Are there for sure mixture screws behind those aluminum plugs? I don't want to drill into my carbs only to find out I mess something up
 
Buddybud425 said:
Are there for sure mixture screws behind those aluminum plugs? I don't want to drill into my carbs only to find out I mess something up
Click to expand...

The very first step in tuning these bikes, especially if you don't KNOW the history is to check/adjust the valve clearances. If you didn't tear the carbs down completely before dipping them, it probably need to be done again correctly.
 
download

I was wondering if the plug just beneath the choke rod with the hole in it comes out/if I have to drill it out to get access to adjustment screws, low quality pic, but I hope someone can help, cause in the link tom203 gave it said something about drilling it out, there is one on each carb
 
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