Slight hesitation under constant throttle

[quixotic]

From about 2,000 rpm to 4,000 rpm, it seems like it's either a bit starved for gas or maybe a spark problem.  But when I accelerate (from any rpm's), the problem disappears completely and she pulls very smoothly and strongly (even the typical 4,500 rpm vibration seems to disappear).  I thought I'd next look at the fuel petcock, but I'm wondering if anybody else has any ideas.  


Thanks in advance.

[Barry]

My instinct says it a mixture problem of some sort as ignition issues would not usually improve under the load of acceleration.

But what sort of mixture problem, perhaps an air leak. Does a 79 have the air injection plumbing nonsense or was that later.

How about applying a little choke to see if an increase in richness improves it or makes it worse.  You could remove the air filter to see if a weaker mixture does anything although that is a fairly small effect.

[Luca]

Fuel tap problems would manifest at higher RPM's when the engine demands more fuel.  Usually the problem with a clogged tap is the bike starts to choke at highway speeds.

If you haven't put in in-line filter between the tank and carbs, do that to prevent future problems.  If you've  got a partially clogged idle jet, that can make the bike run poorly when it relies mostly on that circuit.

Are the vacuum ports on the bottom of the carbs properly plugged?  If one is open it will draw air into the manifold.  Whack the throttle and vacuum goes down... less draw through the port.  You'd have a rough idle if this was the case.



But if I had to put my money on something... I'd say you need to check the bowl levels now that you've installed a set of new floats  

...or maybe re-tune your carbs if you tuned them on improper float levels.  PITA, I know, but carb adjustments are always last.

[quixotic]

But if I had to put my money on something... I'd say you need to check the bowl levels now that you've installed a set of new floats

...or maybe re-tune your carbs if you tuned them on improper float levels.PITA, I know, but carb adjustments are always last.

Actually, I'm finding carb synch to be a cool exercise now.  I built my own manometer, and I hauled the bike out into the wind on a coolish day after I installed the new floats (levelled).  The neighbours must think I'm crazy.  One of them said it looked like a drip feed at the hospital.  

Maybe Barry's on to something with the choke settings.  I'm going to play with that on the way home today.  

[montmil]

Evan, it's vitally important that the engine be at full operating temperature before doing any carb adjustments. You mentioned just having installed new floats and it being a "coolish" day -a brisk engine warm up ride of twenty miles or so would be about right.

Again, if the engine hasn't reached it's normal operational temperature, attempting any carb adjustments will be time wasted with faulty results.