Issues with Idle

[jim328]

I finally got my bike started after much help from this forum but I now have an issue with the way it idles. Before I started the bike I did the following:
- Stripped, dipped and cleaned carbs
- repaired carb manifolds with liquid tape which worked brilliantly
- repaired holes in exhaust system
- replaced vacuum hose to petcock
- took Yics box apart and sealed it, hoses were in good condition

It started ok and then I rode it around my neighbourhood for about 7kms and it ran up through the revs and gears beautifully with no stumbles or hesitation, the only issue is the idle it varies between 1500-3000rpm with no reason sometimes it would be 1500 and then at the next stop it be 3000 and vice versa. The other thing that I should mention is that the exhaust was leaking where the rear connector pipe connects to the balance pipe, and it is an xz400 which doesn't have the modified airbox. Can anyone point me in the right direction with idle issues? also now that I have sealed the leak in the exhaust it is refusing to start.

[Walt_M.]

Sounds like a vacuum leak but since it is intermittant, can you have a look at your starting enrichening circuit? I'm not sure how the 400 is set up but the US 550 has a plunger that pulls out to open the internal enrichening passages. If the plungers are not positively pushed back, they could move and affect the idle. If they are not getting pulled out, cold starting would be difficult.

[Coil Coyle]

Sounds like a vacuum leak but since it is intermittant, can you have a look at your starting enrichening circuit? I'm not sure how the 400 is set up but the US 550 has a plunger that pulls out to open the internal enrichening passages. If the plungers are not positively pushed back, they could move and affect the idle. If they are not getting pulled out, cold starting would be difficult.

And sychronizing the carbs is next if the enricheners are OK.

$0.02
;)
Coil

[jim328]

Thanks guys will check both, does anyone know what settings the mixture and idle screws should be at? I think my carbs are BD34's if that helps.

[Tiger]

- took Yics box apart and sealed it, hoses were in good condition

:) Cap off the YIC's at the cylinders and try again please...

                    8).......TIGER....... 8)

[jim328]

This may be a stupid question, but what do I cap them off with? Should I use some fuel hose between the cylinders?

[The Prophet of Doom]

Try blowtesting the YICS in water first, and checking that all hoses are firmly in place.  Most people just cap off at the cyl head.  You can buy vacuum caps at supercheap for $4, or use folded over and clamped hoses, or a screw in the end with some RTV.  There is some debate about joining the YICS ports with a single hose.  I found it a bad thing, Inane (I think) thought it was brilliant, so who the hell knows.

My experience with two 400s is that you are a LOT better with YICS in place.

The XZ400 default setting for mixture is 3.5 turns out front and back (+- .5)  This will probably set it slightly rich as you are near sea level.

No point in bringing the manometer round in the weekend unless it's running.  Let me know how you get on

[YellowJacket!]

I tried the vacuum caps on the ports at the base of the culinders but they degraded (probably due to heat and pressure) in just a couple months.  I ended up using a 1.5"length of fuel line and a bolth that fit tight enough to screw into the other end of the fuel line.  Like Roro, I sealed it with RTV just to be sure and stuck each "cap" on their respective port on the motor.

As for fixing a leaking YICS, there are two types of leaks; an internal leak in which gasses move from one chamber to the other and an external leak in which gasses escape the YICS through a small crack in the joint between the two halves.  Both types of leaks can cause the motor to "hunt" for an idle, meaning the idle with fluctuate widely.

To test the YICS, get a foot long length of tube and a bucket or a sink.  Fill the sink or bucket woth water, hook the hose up to one of the ports on the yics and submerge it in the water.  Next, blow through the tube.  If any bubbles come out of the other port, you have an internal leak.  If bubbles come out around the edge where the two halves join, you have an external leak.  Regardless, the repair is the same.

The two halves will have to be separated.  I use a utility knife to carefully score down the seam until I can split it apart.  It takes a long time but gives a good clean edge.  Others have used a saw to cut it in half which works quick, but you have to be careful to get a good straight cut.
Next, I sand down the edges with coarse 80 grit sandpaper to even them out and give a good bonding surface.  I tape an 8x10" piece of sandpaper to my garage floor and put the cut edges down and sand in a cirular motion.  Works pretty quick.
I trace an outline of the YICS on gasket material and make a gasket.  Be sure to cut out the triangular parts on the inside of the gasket but leave the gasket material for the center ridge as both chambers have to be sealed from each other.
Once that is done, I run a bead of red RTV along the edges of the YICS as well as the center chamber divider/ridge and put the gasket carefully in place.  I do the same for the other side of the YICS then line the halves up and clamp them together.  I generally wait about 48 hours before I put it on my bike and I also repeat the leak test to make sure my repair job has worked.
I've done at least 5 or 6 this way and it seems to be the best method for me.  I had tried epoxy and JB Weld too but neither seemed to last long.

David