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Yet Another Jetting Question

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

Anonymous

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Helllo All,

I have a 79 gs 850 it's rejetted (forget with what) open pipes. Believe me leaness is not a problem. Bike runs great. However, when I blib the throttle slowly at idle everything is good. But when I twist the throttle quickly at idle threr is a notable hestitation. Is it the piolt jets or what?
The carbs have been set, and everything else is within spec.

Thanks
 
Had the same thing on my zx. I bet the vacuum tube going from the top of your #2 carb to your petcock is crimped. Make it run in the smoothest organic curve you can get. This hose is what turns the fuel on when the engine is running. If that fails, check the vent in the gas cap. I didn't have to touch that so I'm not sure how to fix it. You can test it by seeing if the hesitation occurs with the gas cap off (if you're crazy enough), if it doesn't, there's your cause.
 
Re: Yet Another Jetting Question

A 79 GS 850 would have VM mechanical slide carbs. Those carbs are throttle position priority. The short explanation is that with constant vacuum (CV) carbs, the carbs automatically adjust to induction vacuum which is changed by movement of a throttle plate which smooths out the transitions. With VM carbs, there is no throttle plate and the slides are raised by throttle movement. Induction vacuum changes directly with slide position. Consequently, you can blip the throttle faster than the intake system can adjust to the changing pressures. When you instantly blip the throttle open, the slides get yanked up, vacuum momentarily dips to zero, flow faulters, then the engine reacquires the correct flow and catches. The result is the "hesitation". If the carbs are well adjusted, the hesitation range is small. That is normal and due to design, it is not something that can be completely eliminated.

Earl


quietone said:
Helllo All,

I have a 79 gs 850 it's rejetted (forget with what) open pipes. Believe me leaness is not a problem. Bike runs great. However, when I blib the throttle slowly at idle everything is good. But when I twist the throttle quickly at idle threr is a notable hestitation. Is it the piolt jets or what?
The carbs have been set, and everything else is within spec.

Thanks
Click to expand...
 
Yep. That's a fact. You can "gag" these carbs if you turn the throttle too quick. In normal riding, you won't ever open the throttle quite as quickly as you do just sitting there blipping away. A short hesitation is normal.
 
What if you get that with CV carbs...what does that mean?

Dm of mD
 
I don't think I'd worry about it if it's that minor. If it's bothersome and you have to adjust for it, then you've got a problem.
 
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