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Carb Needle Setting?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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You guys have been so great with my low compression question, I thought I would ask another. 82 Gs750, I re-jetted after replacing old filter with a K&N and put a Vance/Hines 4 into one header with meg. with no muffler. I like the color of the plugs with the 127.5 mains. I have not lowered or raised the needle. Should I? If so why?
 
If your not experiencing any drivability problems such as lean surging, backfireing and such, and it idles as well as pulls strong and the plug color is close to a light tan. I wouldn't bother changing the needles.
 
If the mains are right and it drives well, no need to fiddle any more..you have hit the jackpot!! I would only fiddle with it if you suspect it is right on the edge of acceptable (eg takes a while to warm up and run cleanly, plugs seem too lean looking after an extended cruise etc)
 
It does take a long time to warm up in my opinion. I don't take extended rides on it. Mostly just 1/4 mile at a time. If it is not really warm it will really bog if I try to bring up the RPM. Once it is fully warm, it pulls hard the entire 1/4 mile.
 
The needles control mixture from about 1/4 to 3/4 throttle. If it cruises nicely and responds to the throttle it's probably okay. The only way to know for sure is an extended ride and check the plugs.
 
Take your bike to a shop with a dyno and have them either tune it or do a couple of runs and you tune it using the graph that they give you.
Going by an ASS dyno will not give you the real info you need. Also "reading" your plugs is only effective for the main jet. To do this properly you need new plugs and a nice long stretch of road. This isn't the most effective jetting tool but it does get you in the ballpark.
 
meanman said:
Take your bike to a shop with a dyno and have them either tune it or do a couple of runs and you tune it using the graph that they give you.
Going by an ASS dyno will not give you the real info you need. Also "reading" your plugs is only effective for the main jet. To do this properly you need new plugs and a nice long stretch of road. This isn't the most effective jetting tool but it does get you in the ballpark.
Click to expand...
I am curious to know why reading your plugs is only effective for the main jet. Could you mean that it is only effective to read the main jet when running a flat out 1/4 mile. Or did i mis understand what you said.
 
It would be too difficult to read your plugs for Needle setting as that would mean running a given rpm at any given point on throttle opening. This simply means too much human error in holding (on a variable venturi carb) the throttle strictly in one position long enough to leave deposits on the plug that can be visibly "read". Even more difficult on a CV carb.
Hope this answers your question.
 
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