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GS450 Rich LH cylinder.

  • Thread starter Thread starter xtlegend
  • Start date Start date
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xtlegend

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Hi all, Just bought a cheap GS450 that seems to be running rich on the LH cylinder. Usually starts up on he RH only (LH downpipe cold) then fires eratically on the LH one. LH plug is sooted up a bit and wet when cold and some black smoke is seen on the LH pipe. Is it possible that the choke is stuck on the problem carb? The choke plunger seems to operate normally. Does about 40MPG instead of the expected 70. Thanks for any advice.
 
The carbs might just need a good cleaning... Check the floats (hieghts and condition) while you are in there. I have had 2 cracked brass floats :(. Also might want to check if the petcock is operating correctly. Disconnect the outlet and put it on 'ON', it should not let gas flow. Do you have a 'PRI' setting? That should only be used when it has sat for a long time...

I get about 40mpg but I have much more open pipes and the carbs had been modified for them. We also haven't clocked the stock 'S' MPG since we bought it. No idea why we haven't, just keep forgetting...
 
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bgmart450 said:
The carbs might just need a good cleaning... Check the floats (hieghts and condition) while you are in there. I have had 2 cracked brass floats :(. Also might want to check if the petcock is operating correctly. Disconnect the outlet and put it on 'ON', it should not let gas flow. Do you have a 'PRI' setting? That should only be used when it has sat for a long time...

I get about 40mpg but I have much more open pipes and the carbs had been modified for them. We also haven't clocked the stock 'S' MPG since we bought it. No idea why we haven't, just keep forgetting...
Click to expand...

Thanks for your quick reply. I've taken the carbs off and just had a close look inside the problem one. All seems pretty good and clean. Nothing seems out of place. Could this be an ignition problem?? The LH plug is definitely wet after trying to start the bike from cold.
 
Dunno... You could remove the plugs test the spark by grounding the plug to the block while connected to the wire, should be a nice strong spark when you hit the starter. If not try a new plug (or the other cleaner one).

Plugs fail real quick if it at one time had run real rich. Too much gas kills 'em.

Are you sure the petcock isn't leaking? if it is it will drip too much gas into the side the bike is leaning to (LH) while sitting.
 
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bgmart450 said:
Dunno... You could remove the plugs test the spark by grounding the plug to the block while connected to the wire, should be a nice strong spark when you hit the starter. If not try a new plug (or the other cleaner one).

Plugs fail real quick if it at one time had run real rich. Too much gas kills 'em.

Are you sure the petcock isn't leaking? if it is it will drip too much gas into the side the bike is leaning to (LH) while sitting.
Click to expand...

I rode the bike 120 miles home after I bought it and it never ran quite right though kept going easily at 50/60/70 mph etc. Seems to 'miss' a bit. So I dont think its a petcock problem. Boy do I wish this bike had points ignition as I could easily iliminate the ignition then!!
 
Not trying to beat this one to death (sorry to sound like I am), but even with a leaky petcock it might run OK. The wife's S ran fine but was leaking while sitting and was bad enough it was putting oil into the crankcase. I didn't notice it until I changed the oil. They are vaccuum operated and should not allow gas to flow at all when no vacuum is applied (hence no 'OFF' setting). Also if the bike sat for a long while and then the petcock was moved dry it has a huge chance of ripping the diaphram.

If you are getting good spark to the cyl I'd guess its either the carbs or the petcock. The petcock is so easy to check that's why I suggested it.

Maybe others have different stuff you can check, but with the 2 bikes I have had, bad floats and bad petcocks have thankfully been as far as I'd have had fail me in this area of the bike.

If you haven't nabbed one either a Clymers or Haynes manual they can be a valuable asset to the 'DIY-mechanic'. I was fortunate to also grab a parts fische, wow it is more helpful than I would have thought :)
 
xtlegend said:
Thanks for your quick reply. I've taken the carbs off and just had a close look inside the problem one. All seems pretty good and clean. Nothing seems out of place. Could this be an ignition problem?? The LH plug is definitely wet after trying to start the bike from cold.
Click to expand...

Did you happen to check the float height? There is a post in the letters to the editor section that I posted the 450 carb specs in. 'OEM carb specs' or something like that as the title...might have to search for it.
 
bgmart450 said:
Not trying to beat this one to death (sorry to sound like I am), but even with a leaky petcock it might run OK. The wife's S ran fine but was leaking while sitting and was bad enough it was putting oil into the crankcase. I didn't notice it until I changed the oil. They are vaccuum operated and should not allow gas to flow at all when no vacuum is applied (hence no 'OFF' setting). Also if the bike sat for a long while and then the petcock was moved dry it has a huge chance of ripping the diaphram.

If you are getting good spark to the cyl I'd guess its either the carbs or the petcock. The petcock is so easy to check that's why I suggested it.

Maybe others have different stuff you can check, but with the 2 bikes I have had, bad floats and bad petcocks have thankfully been as far as I'd have had fail me in this area of the bike.

If you haven't nabbed one either a Clymers or Haynes manual they can be a valuable asset to the 'DIY-mechanic'. I was fortunate to also grab a parts fische, wow it is more helpful than I would have thought :)
Click to expand...

A manual is on its way. I notice that the problem side of the engines carb is the one providing the vacuum to the petcock. Could a knackered petcock feed petrol into the carb and therefore combustion chamber via this route??
 
Yes, with a faulty petcock, its common for fuel to backfeed through the vacuum tube and into the crankcase.

Earl


xtlegend said:
A manual is on its way. I notice that the problem side of the engines carb is the one providing the vacuum to the petcock. Could a knackered petcock feed petrol into the carb and therefore combustion chamber via this route??
Click to expand...
 
Might need to get methodical:)

Might need to get methodical:)

xtlegend said:
Thanks for your quick reply. I've taken the carbs off and just had a close look inside the problem one. All seems pretty good and clean. <snip>
Click to expand...

Although the problem may well be something already posted, you might have to take it from the top (see "Ignition and Carb Diagnostic Procedures for Dummies Like Me!" thread, etc.). To get my 1981 GS 450 purring, I initially tried a few "singleton" suggestions (eg. intake o-rings, air filter/box fixup, etc.), but resorted to zipping through the list.

My last step, a carb rebuild/pilot screw adj/carb sync, ended up getting the bike running great. Even tho my carbs looked pretty clean, the rebuild did the trick. I took some shortcuts (didn't split carbs, didn't touch choke plunger circuit, didn't dip carb bodies - just bowl assemblies), but mostly followed the great carb clean/rebuild doc by John Bloemer.

BTW - Big problem may have been that my float hieghts were perfect for most GS CV twin bikes *except* our 450s... They were about 1.1 inches intead of the .9 they should be... Could also have been crud in one of the many passages I carb-spray cleaned & blew out. You should get your hands on at least a $20 Clymers manual, etc.

Good luck.
 
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Thank you all for your advice - guess what? Its the petcock dumping fuel down the vacuum pipe into the LH cylinder. I took the petcock apart to find bits of foil like metal which I guess is part of the diaphragm. I've bodged it temporarily by cutting the vacuum pipe in half and folding over each open end and securing with a cable tie. This of course relies on the floats shutting off the gas corrctly which they do. In my opinion an over complicated setup where a simple on/off finger operated valve would have done!

Shes purring away nicely on 2 cylinders - cheers!!

Greg J. (Over the pond in the UK!)
 
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