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'79 gs850 -- Dies if I roll on the throttle

  • Thread starter Thread starter spacepirates
  • Start date Start date
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spacepirates

Guest
Might be a misleading title, but the gist of it is the bike idles nicely and once it is warmed up, if I roll on the throttle, the bike will bog down and die around 2k rpm. If I'm nice and slow with it, and try a little harder, it revs up ok, but anything mildly aggressive causes it to die.

VM carbs were just cleaned (new o-rings), the previous owner decided it would be a good idea to bury one of the pilot adjuster screws in and break the tip off, so I know I'm working against that (but it idles fine!). I've been trying to tweak the pilot fuel screws 1/4 turn at a time to see if I can get rid of this... "bog" problem, but no luck. Doesn't help that it is a pain in the butt to adjust them while the carbs are on the bike (any tips on that?)

Are the pilot screws even the issue?

Haven't gotten around to making/getting/using a vaccuum sync gauge yet either... :cry:
 
If it dies when you roll on the throttle, your needle setting is probably off and is killing your engine once you leave the pilot circuit. Did you clear that passage with the broken fuel screw? If not, that cylinder may not be getting enough fuel at the idle stage.

Adjusting the fuel screws on a running bike is a hot mess. Tkent does it, but I don't like to grope around under carbs next that hot block. I just set them and adjust at the air screw level. If the fuel screws need turning, I do that once the engine has cooled a bit.
 
After years of fighting the carb and fuel screw I broke down and bough the tool- Should have done it a long time ago- 20$ is well worth it. If your gonna have bikes, I recommend the tool- you can even secure your synch while lock the nut down.
 
Badooka said:
After years of fighting the carb and fuel screw I broke down and bough the tool- Should have done it a long time ago- 20$ is well worth it. If your gonna have bikes, I recommend the tool- you can even secure your synch while lock the nut down.
Click to expand...

What is this mythical tool you speak of? I don't think I've heard it mentioned before.

The needles are in the stock position, and given that the bike didn't have this problem (albeit it had others) when I got it, and that the intake/exhaust is stock (minus some rust holes which are on the list of fixes to do once it actually runs) I figured the stock needles would be good enough.
 
He's confusing the mixture screws with the sync screws

There's a combo screwdriver/wrench that he's referring to

Your pilot fuels shound be 3/4-7/8 out (Z1 has replacements now)
Your pilot airs should be 1 1/2 out

An off idle stumble can be an air leak
 
So buy the new air screw, and a sync gage kit.

Use them.

You'll have decent bike after you do, what you know you have to do.
 
Badooka said:
This is the tool and can be used for all your future carb adjustments. especially 2 and 3. Those were always a headache before this.

http://www.ebay.com/itm/Motorcycle-...Parts_Accessories&hash=item27c825765d&vxp=mtr
Click to expand...

Ah, got it. I have a long flat head screwdriver that works really well for carbs 2 and 3. I was more concerned with the pilot fuel screws on the bottom of the carbs in front of the bowls (on the side closer to the engine). I can't find any easy way to get to them with the carbs on the bike.


As for buying a new pilot fuel screw, the bottom of the old one would still be jammed in there and that seems like it would be a pain in the butt to get out.

I'll take the carbs off the bike and set the fuel screws to the recommended setting. I don't think that setting was in the VM cleaning guide, so I'll double check it. I'll also re-check that everything is sealing properly. I did get new intake O-rings but not boots. That airbox might need looked at though....
 
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