Hunting idle?

[the_Journeyman]

Here we got with yet another fueling question.  I'm gonna be an expert on carbs if I ever get this thing running right.

1999 Monster 750, OEM Mikuni carbs, almost new (maybe 1500 miles on them) emulsification tubes, 35,000 miles. 

Settings:  Stock mains & pilot, needles shimmed about 1mm richer, air screw about 5 turns out on both carbs.  Does the same thing at 5.5 turns out.  At 3 turns out, I get a stutter at low RPMs when I whack the throttle open, seems to be a lean issue as it gets worse at 2 turns out.  Idles better at 2 and 3 turns out though.  Pulls like a maniac once off the pilot circuit, as in power wheelies with a slight bump in the road in 1st gear.

The Idle hunts, as in sounds normal and then slows down and sounds labored, comes back up and goes back to the slow labored sound.  No real pattern in how long it sounds normal or goes form normal to slow & labored.

Where to start?

JM

[take risks]

Mine too. 
But I have just started looking into it.
2007 695
When I start it, choke is on it wil jump up to 3k rpm back down to 2k then up again.

[Howie]

easy stuff first, check  for vacuum leaks and sink throttles.

[the_Journeyman]

I have done a sync, and I've got new diaphragms.  All the vacuum tubing seems good too from visual inspection.

I've got some new plugs, I'll toss those in and see what happens.

JM

[ducpainter]

What is your warm idle speed set at?

[the_Journeyman]

No tach, so I have no idea.

JM

[ducpainter]

Try raising the idle a bit and see if it helps.

The screw is a fuel screw, and 5 turns is pretty far. I'd go in to 4 turns.

Keep in mind that needle position affects pretty much all ranges on those carbs, and they came form the factory really lean. If your needle has adjustment grooves I'd drop the clip another notch (raises needle) and try it.

A jet kit would help that bike.

[the_Journeyman]

I was thinking I was a bit far out and should go up a size on the pilot.  No notches, but I've added a shim under the OEM washer, I could easily add another, but it does run REALLY good once you get off the pilot circuit.  I'll run the fuel screw in a turn and see if I get any lean missing.

I'll turn the idle up a little and see too.

JM

[ducpainter]

I was thinking I was a bit far out and should go up a size on the pilot.  No notches, but I've added a shim under the OEM washer, I could easily add another, but it does run REALLY good once you get off the pilot circuit.  I'll run the fuel screw in a turn and see if I get any lean missing.

I'll turn the idle up a little and see too.

JM

I have a set of stock needles with adjustment grooves from a 900.

Wanna try them if you don't get it sorted?

[the_Journeyman]

I may if fiddling with the idle & moving the screws back to 4 doesn't get me anywhere.

JM

[the_Journeyman]

Seems I have two options.  Hunting or hanging idle.  When I bring the speed up where it sounds about right, it hangs a few hundred RPM high once I blip the throttle.  When it's down when it doesn't hang, it does the hunt/sound labored thing.

1)  Could I have shimmed the needle TOO high?

2)  I'm also burning oil it seems, would blow-by make tuning impossible?

Why can't this be simple?  I've got a riding trip next week!

JM

[Howie]

The needle doesn't affect idle.  Idle mixture screws, main and pilot jets will though, as well as float level.  How are the spark plugs?

[the_Journeyman]

Can't remember when I put new ones in last.  I have a set I got last week I'll toss those in.  Here's what one of them currently looks like:



Gotta love a good macro lens!!!

JM

[akmnstr]

I've battled this problem for years and on my bike it came down to a gasket leak were the intake manifold meets the head.  Here is how I found the problem.  On a tip from my local auto parts store I sprayed carb cleaner at all of the connections on the intake system downstream of the carbs themselves.  The engine revved higher when it was sucking in the carb cleaner through the leak.

[koko64]

Plugs have some deposits. If rich enough at idle you wash a little oil off the bore and add oil deposits to rich fuel deposits. How bad is the oil usage?

Normally idle will hang when lean, but an overly rich idle mixture with a high idle speed to compenxate can cause another type of 'hanging' also. 

How are your float levels? Hope they are ok. 14mm is correct from memory.

Turn down the idle speed so it just idles and adjust for the fastest and strongest, most even sounding  idle speed with the idle mixture screws on fresh plugs. Set your speed after that as you may have it too high to compensate for rough running, but you want to hear the idle clearly speed up when you turn those screws in the right direction.



Let us know how you go.