Topic: VB carbs high idle SOLVED w/video

[fdbrat]

Bike at hand:

82 cb650sc
Carbs cleaned throughly/ bench synced
Piston slides move smoothly

New jets:
148 mains (stock 120)
42 slows   (stock   35)
AFR 1 1/2 out
Idle set is all the way out.

Pods... I know, I can't leave well enough alone
Open pipes 4-2
Pipes heat evenly
All cylinders fire, strong spark
Brand new intake boots
New 5k caps and plugs
Petcock vacuum valve has been removed

Problem:
The idle is extremely high. I can only get the idle down by using the choke.
I've checked for leaks with propane. No change in idle.
Plugs are covered in soot, due to having to use the choke.

With choke on, it revs and idles great. I'm sure under load will be a different story.
I cannot take it for a spin yet, due to he fact it isn't registered yet.

What suggestions might you all have.

Thank you for your time.

[goldarrow]

I don't have a 650 bike, but sounds like you're running way lean. 

[fdbrat]

I figure if I add more fuel via larger jets, wouldn't that make the bike rev more?

[Don R]

Have you checked to be sure the cables are properly adjusted with a little slack? Have you checked the slides to be sure they are all at the same height?  um, does the idle screw adjust the idle at all?

[fdbrat]

These carbs are like cv cabs, but there is no rubber. It's essentialy a piston. Vaccum operated.

There is no throttle attached as of yet. I'm using a draw string.

The butter flies are mechanical. And when they open it allows more airflow wich draws the slides up pending on the amount of vaccum.

[fizzlebottom]

Here's what I notice. The book says to put the pilot screws at something closer to 2.5 turns out for the initial setting, get the engine up to operating temp, then adjust them another .25 turns out (I think). Yours are WAY off from that.

But the bigger problem is that I have no clue how the pods & larger jets are changing things. There are reasons that people recommend you stick with the stock airbox. And if you ignore those reasons to trade function for form, you run into problems.

Aside from the obvious, doing a simple bench-sync is where I'd look if you refuse to reconsider the airbox situation. A bench-sync with this particular bike is enough to get it running, but not well. You should consider vacuum-synchronizing the carbs. They may be wildly off, which can just mess with your idle like nobody's business.

And when the vacuum sync doesn't get you where you want, then you're going to end up wishing you'd kept the stock airbox on and jets in.

[fdbrat]

I'll be in the market for vaccum gauges. I did bench sync.

As far as stock goes, the PO thrashed the original box, and the wiring and a bunch of stuff.

It was a basket case. Pipes were cut by PO. As I have welded the battery in a new location a stock box will not fit.

The original slow jets were friction fit. I've tried setting the AFR screw up to 4 out and as little as all the way in.

I agree that it would be good to see where the vaccum is on all four.

[lucky]

Bike at hand:

82 cb650sc
Carbs cleaned throughly/ bench synced
Piston slides move smoothly

New jets:
148 mains (stock 120)
42 slows   (stock   35)
AFR 1 1/2 out
Idle set is all the way out.

Pods... I know, I can't leave well enough alone
Open pipes 4-2
Pipes heat evenly
All cylinders fire, strong spark
Brand new intake boots
New 5k caps and plugs
Petcock vacuum valve has been removed

Problem:
The idle is extremely high. I can only get the idle down by using the choke.
I've checked for leaks with propane. No change in idle.
Plugs are covered in soot, due to having to use the choke.

With choke on, it revs and idles great. I'm sure under load will be a different story.
I cannot take it for a spin yet, due to he fact it isn't registered yet.

What suggestions might you all have.

Thank you for your time.

Of course it idles high!!
You have not even mentioned the slide needle at all!!
The slide needle controls 1/4- 3/4 throttle. Meaning all most all of your driving.
You have skipping over the most important part. The slide needle position.
That 148 main jet is way too large.
Go back to a 120-125 main jet.

As soon as you drop the clip one notch ,which will raise the slide needle then
that high idle will go away.
No point in riding the bike yet.
If it won't run good in the shop forget about taking it out on the road. It is not ready for the road.

[fdbrat]

Agreed, not road ready.  The needle is in stock position. Tho I could. Put the 120 back in and see what that gives me.

I'll report back and let y'all know what happens.

[fdbrat]

I misplaced the 120's, but I had a descent set of 125's near by. So I put those in and reattached the stock air box...

Same problem, the idle is extremely high.

What gives? Do you think a blown head gasket would cause such a problem?

[fdbrat]

Bump.

[fdbrat]

Well I got the bike idling perfect now.
For a conclusion...
The butterflies were at fault. Loosened the 4 carbs from the base plate tweeted it just right so number one would be in line with the other three and massaged the butterflies into place.

Waiting on the throttle cable and grips. A test ride is in the near future.

Here is a video. Enjoy.