Carb jets for a mile high?

[maparker]

I'm restoring an 81' GS450TX, got it started and it runs and sounds fine, got a few electrical gremlins (mostly corroded contacts) and its way too rich. This bike came from Pennsylvania by way of Indiana and is now in Denver. Even with the air box open and no filter (so broken down I had to vacuum out the remains) the plugs are black. Any suggestions on how far I need to go to get the carbs close? Anybody got a set of jets sitting around that they'll never use that might get me there? Any advice will be appreciated!

[mark m]

What jets are in it now? If it is stock jetting, something else is going on because even at 5000ft it should not be really rich from the factory. You also don't say what your pilot jet is, where your mixture screws are set and which circuit was giving you the sooty plugs.


Mark

[maparker]

Mark M, thanks for the reply:
Not sure what's in it now...didn't think to look when I had the carbs apart. So you think that the stock jets mjght be OK at elevation? The only thing I've done to the carbs is pull them apart and clean...if I didn't get everything cleaned out could this explain the fouled plugs (both are fouled). As far as settings I haven't changed anything, it looks like the mixture screws are still plugged and have never been played with. Should I started with drilling them out, re-clean the carbs, or both?

[mark m]

So you think that the stock jets mjght be OK at elevation?

They were a little lean at sea level, so they should be at least OK at your elevation. Maybe a touch rich, but not horribly so. Rich is a safer condition than lean, so there should be no worry there for the moment.

Should I started with drilling them out, re-clean the carbs, or both?

Not a bad idea to pull the plugs and set the screws to about 2 turns out for a starter. That will be a bit rich for you, but it should run that way.

What you need to do is sort out where the fouling is happening. Your jetting circuits are as follows:

idle - 1/8 throttle is the pilot circuit
1/8 - 3/4 is the needle circuit
3/4+ is the main jet circuit

Set your mixture screws, then put a piece of tape on the throttle housing and mark 1/8, 1/4, 3/8, 1/2 throttle positions, etc. so that you can tell how much throttle you are using and which circuit you are on. Clean and gap your plugs. Go out onto a quiet highway and ride for a few miles on the pilot circuit (basically with the throttle just cracked open enough to make it run). Then stop (preferably by hitting the kill switch and coasting over to the side of the road deadstick) and pull the plugs. Note their condition. Do another plug chop at 1/3 throttle and another at full throttle. This will tell you where your jetting is on each circuit. Then adjust accordingly to even it all off. Report back after the plug chops and let us know what you find.


Mark

[mcconnell]

Does the bike have CV carbs? If so, I would seriously look at the jetting first and make sure it is stock. I moved my stock-jetted GS1100 from Maryland (roughly sea level), where it was a little lean as Mark M noted, to 5,000 feet here in beautiful Colorado and the bike ran better. Not as much power, but smoother running and fuel mileage at least as good as before the move.