Adjustments after carb rebuild

[jwyler]

Hello,

I just rebuilt my carbs recently, and have the bike running, but...

 - It dies when I turn off the choke, even when it's warmed up
 - It runs (barely) really slowly (at like 50rpm it sounds), even though the tach is reading 1500 with partial choke
 - It runs fine with full choke or no choke with throttle

My first thought was to turn up the idle, but the tach's readying high already, and it's always been accurate in the past.  What's going on?

--Jon

[Crimson]

I'm no carb expert, but did you forget any of the little O-rings when putting it back together?

[EvilScooby]

Adjust your air/fuel mixture screws
They say 2 and 1/2 to 3 turns out
There is one on each carb

you may have to drill them out if they are not already, but be very careful
I am using a pic from Kerry's site. I hope he doesn't mind


And also just as Crimson stated, are you sure you put the little o rings back in

[scratch]

Things to check:

Idle screw
Float height using the clear u-tube method
Both mix screws turned out to the same 2 1/2 or 3 turns out
Carb synchronization by the little screw between the carbs on the throttle linkage
The little o-rings underneath the towers of the carburetors black plastic covers
The vaccum tube attached to the inside of the left carburetor and up to the fuel selector (ON/RES/PRI)

[Kerry]

Am I correct in thinking that you made no changes to the carbs beyond a cleaning and a rebuild?  (New gaskets and O-rings, but no change in jet sizes, etc?)

If so, then maybe you have a lean condition caused by how tricky it is to remount the carbs to the cylinder intake boots.  (I have made a sloppy job of it once or twice, and didn't even know what to look for until about the 3rd time.)  Try the WD-40 test (with the bike running):



If the RPMs go up when you introduce WD-40 in this area, then there's a "leak" that's letting extra air and "leaning out" the mix.

BTW - I don't really suspect the forward ends of the boots, since you shouldn't have moved/affected them.

[Kerry]

I am using a pic from Kerry's site. I hope he doesn't mind

Not at all.  Go for it!

[jwyler]

Do you suggest trying these fixes in the order listed in Scratch's posting?  If not, what order would make most sense?

Now that I've got an idea of things that need adjustment, here are some more specific questions.

- Idle screw: do I just warm up the bike, and turn til it's running at 1200 without choke/throttle?
- Can you point me to instructions on how to check the float height?  I recall seeing that somewhere, but can't remember.  Is that necessary if I didn't make any changes during the rebuild?
- How do I adjust the mix screws?  There's no place to grip the copper pieces with a tool from the outside.
- Where's the carb synch screw, and what's the adjustment procedure?

Also, what's up with the tach reading higher than the actual engine speed?

--Jon

[Kerry]

Do you suggest trying these fixes in the order listed in Scratch's posting?  If not, what order would make most sense?

I don't know about the MOST sense, but from easiest & least "invasive" to more effort / time consuming...

No disassembly

1) Idle screw
2) Float height using the clear u-tube method[/list:u]Access requires removal of fuel tank
3) The little o-rings underneath the towers of the carburetors black plastic covers
4) The vaccum tube attached to the inside of the left carburetor and up to the fuel selector (ON/RES/PRI)
5) Carb synchronization by the little screw between the carbs on the throttle linkage

[also requires carb synch tool (or knowledge of a non-tool method) and possibly an auxiliary fuel tank, and a good fan to keep the engine cool][/list:u]Requires removal of carbs and drilling out of brass caps

6) Both mix screws turned out to the same 2 1/2 or 3 turns out[/list:u]

- Idle screw: do I just warm up the bike, and turn til it's running at 1200 without choke/throttle?

Yep, that's right.

- Can you point me to instructions on how to check the float height?  I recall seeing that somewhere, but can't remember.  Is that necessary if I didn't make any changes during the rebuild?

For instructions, see my Float Height page.
Couldn't say whether it's necessary, but once you have a length of suitable tubing it's quick and easy to check.

- How do I adjust the mix screws?  There's no place to grip the copper pieces with a tool from the outside.

See above.  You need to remove the carbs, carefully drill out the brass caps, and then use a normal screwdriver to do the adjustment.  BE SURE TO RECORD YOUR ORIGINAL SETTINGS.  (Make a mark on the screw and count the rotations as you turn the screws all the way in.)

- Where's the carb synch screw, and what's the adjustment procedure?

Once you have the tank off, look at the linkage that joins the two carbs together.  You should see a Phillips-head screw a little closer to the right-side carb.  That's the one.
The actual adjustment is done by turning that screw.  But getting the adjustment RIGHT usually means having some sort of measuring device to monitor the effect of the adjustment.  If you go the DIY carb synch tool route (or use "mercury sticks" from Motion Pro or some other vacuum gauge) you simply remove the little rubber "posts" on the top front right corner of each carb and attach the gauge hoses there.

Also, what's up with the tach reading higher than the actual engine speed?

Good question!  Try lubing your tach cable, and make sure it's screwed tightly to the engine block.  :dunno: