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Adjust Carbs or Not?

  • Thread starter Thread starter thkbaron
  • Start date Start date
T

thkbaron

Guest
So I have a 1980 GS750L. The carbs have been completely gone through but my bike runs rich. Having said that it's runs great. Maybe a big boggy at the start but honestly that's being picky. All the plugs are pretty carboned up and one actually fouled at the end of the season last year. Should I just say to heck with it and change plugs once a year? Would anyone suggest just running a hotter plug and see what that does. Otherwise I was just going to drop the needles a notch and see what that does. I'm running a completely stock setup.
 
If it were me, i'd go ahead and get the jetting right. My bike runs much better slightly lean than rich. Plus you will get much better gas mileage. However, the first step is to determine where the engine runs rich. Do you know how to do plug chops? Also, make sure valve clearences are to spec and the carbs are balanced. And make sure the fuel screws are set properly then move on to jetting.

Good luck.
 
I'd adjust the valves, clean the carbs, make every other adjustment but that's just me, I really enjoy a bike that runs perfectly and gets great gas milage.
 
BTW Tom, I posted in your engine build thread but maybe you missed it.. did you ever finish the 550 to 650 build?
 
valves are adjusted properly. and all the fuel screws are fine. not really familar with plug chops. seems confusing.
 
Sci85 said:
BTW Tom, I posted in your engine build thread but maybe you missed it.. did you ever finish the 550 to 650 build?
Click to expand...

No, got hung up on a broken Jeep engine, and know I'm working with one arm so just playing with powdercoating a little bit and cleaning out the garage. The 550/650 will be even slower now.
 
tkent02 said:
No, got hung up on a broken Jeep engine, and know I'm working with one arm so just playing with powdercoating a little bit and cleaning out the garage. The 550/650 will be even slower now.
Click to expand...

How do you have just one arm working Tom? How long does that put you out of work then?
 
Well that Stinks! Too bad your not closer or I'd lend a hand. Get better soon!
 
thkbaron said:
... I was just going to drop the needles a notch and see what that does.
Click to expand...
That will lean out the mid-range.

"Plug chops" will test the various circuits in the carbs, one at a time, to tell you which circuit is running rich.

How did you "completely go through" the carbs? Full strip-and-dip rebuild with new o-rings? New "rebuild kits"?

You mention "the fuel screws are fine". What are their settings?

Hotter plugs are just a band-aid to cover up other problems. It is much better to get everything RIGHT and use all the proper stuff.

.
 
Start here:

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Plug chops are a way to take color readings of the spark plugs at different throttle settings so you can determine which circuit is having an issue. You basically find a straight road with little to no traffic and bring along your plug wrench. Then, for checking say the main jet, you would run the bike through the gears at WOT, to redline for about 20s if possible or whatever is safe in the area, and once you are at the point you want to shut down, you pull in the clutch and kill the engine while still holding the throttle in the WOT position. Do this carefully and simultaneously. You are trying to get the plug reading with ONLY that circuit in operation. Once you coast to a stop, pull over to the side of the road or some safe place and pull the plug(s) and write down the color at the tip and the bottom of the porcelain. Then go do it again at half throttle, light throttle, and idle.

You can also do it by "feel" which I do quite a bit and use plug chops for validation.

Good luck.
 
its an odd situation where i would be running rich but have no real performance complaints. haha I bet if I did some tweaking though I would be even more impressed. I'll let you guys know what happens after it warms up outside.
 
Going though the plug chop routine is unnecessary if the bike is stock. Maybe the float needles have weak springs and the fuel level is too high? Also, check voltage at the coils to make sure you have a strong spark.
 
air filter is fine but that was my other thought. I think I'm going to check the float levels before I fire it up this spring. I never messed with that so I'll double check them. Being the bike didn't have a lot of miles on it I'm thinking the springs should be fine. I think I may upgrade the electrical system on it though so that will take that factor out of the equation.
 
The carbs have been completely gone through but my bike runs rich
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Did that include a total tear down, 24 hour soak in carburetor dip and new O-Rings? Your comment about never messing with the floats tells me you haven't. A properly rebuilt stock system should not run rich.
 
If the weight of the float causes the float needle spring to compress, there has been deterioration of the spring and the fuel level will likely be high. It's always best to measure fuel level, not just float height. The process is a bit messy, but not difficult.
 
yeah the guy I bought it from did completely tear down the carbs resync and change all orings. good buddy of mine. but he may have forgotten to check the float level. The bike was sitting for years before he got it so there's no way it would run as good as it does having not done that. If I was smart I'd buy a new bike and take this one bit by bit as it's my daily driver right now.
 
I asked because most people don't soak these carburetors in carburetor dip, thinking carb cleaner will do the job. In the beginning I thought the same until I learned better. I have seen mechanics do the same. A good friend did the same until I stripped them down again and he watched the crud boiling out of the carb bodies soon after they were in the dip.
 
Whether your buddy did it or not you'll be better served to do it yourself. This way you KNOW what condition YOUR bike is in
 
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