Rich on #2 and popping/backfiring

Hi all, I've recently picked up a '80 KZ650 LTD and have been trying to work the kinks out. I've found a wealth of information in the forum here, thank you. However, I'm having trouble with popping and backfiring out the 2-3 exhaust. Either 2 or 3 seems to be running rich because gas sometimes drips out from around a bolt on the underside of the 2-3 exhaust where it connects to the muffler. I guess that means I have a hole in the exhaust, huh? I'm assuming #2 is rich because that plug gets carbon fouled and the others don't.I have VM24SS carbs with the accelerator pump.

Here's what I've done so far:
-Checked valve clearances (within spec)
-Installed Dyna S ignition and green Dyna coils
-Did the WG coil relay mod
-Set timing (and double checked a couple times)
-Removed carbs and verified they were clean
-Mechanically synchronized carbs
-Fine synchronized carbs
-Checked float levels by the wet method (within spec)
-Air screws 1.5 turns out

Now, any recommendations on what I should try next? I'm probably too rich on #2 and getting oxygen in through the leaky exhaust, hence the backfiring. Any thoughts on how I can cure the richness problem? I was thinking it might be the accelerator pump diaphram because it's on the #2 carb. Or... I found that the accelerator pump ball bearing check valve in the bowl of the #4 carb is missing. Could this be causing problems? Help! I'm running out of ideas

Hey ericvm,

Have you tried putting your finger atop the enrichment plunger, part #24 in the diagram and giving it a wiggle and push down? I've had these enrichment plungers get stuck open and cause just the problem you're describing.



Hope this helps

KZCSI

Post edited by: KZCSI, at: 2007/03/17 08:39

If you found the check valve ball in the bottom of the bowl, keep in mind there are three bits needed to make the check valve work. The ball, a little brass rod (about 3mm long by 1mm wide) and the clip that holds the ball atop the rod. The clip is GONE... The rod MAY still be in the well that the check valve sits in.

The purpose of the check valve is to stop gas flow unless actuated by the pump diaphragm mechanism. If the check valve is not there, gas just FLOWS as long as the petcock allows. On your bike, I think there is a vacuum petcock so when the bike is running... gas just flows and flows and flows and the check valve is downstream from the float valve so the carb will run RICH RICH RICH... gas will overflow and obviously you have already figured this out.

The only place to pick up a new check valve is in an accelerator pump rebuild kit. Might as well rebuild the pump at this point since you are about to purchase one. www.z1enterprises.com sells them.

I did try jiggling all the choke plungers but no luck there. It sounds like this accel pump check valve is the likely culprit. Sounds like this fix would at least help me get better gas mileage! $$$

I don't think the missing ball/rod is on the carb that is fouling the plug on #2. Does it matter which carb is missing the check valve?

I just did the accelerator pump rebuild and the backfiring and gas overflow has stopped. It runs much smoother now and the accelerator pump seems to be working properly.

Although... it won't idle with #3 now. I'm thinking it's an air leak. could a leak around the airbox to carb boots could cause sufficient leanness to cause this?

Eric, What does it mean, "it won't idle with #3 now"? Does that mean the bike won't idle? Does that mean the #3 cylinder isn't firing at idle?

Are the wires and coils new or used/ Check resistance in the wires. You never know.

It idles, but the #3 cylinder isn't firing at idle. The coresponding exhaust header does not get hot when first starting it up. After a ride, however, the #3 exhaust header is hot - I don't seem to be getting a good air/fuel mixture when the pilot circuit is used.

Maybe check the float bowl service fuel level. Use the quick easy clear plastic tube method with no disassembly required. If level is too high, may cause over rich mixture resulting in soot and quick plug fouling.

ericvm wrote:

... it won't idle with #3 now. I'm thinking it's an air leak. could a leak around the airbox to carb boots could cause sufficient leanness to cause this?

Believe more troublesome leak would be between carbs and holders on engine side (cracks, loose clamp, leaking vacuum plug). Check with motor idling by spraying area with propane gas (unlit), WD40, carb cleaner, or *starting fluid, any of which will be sucked into the intake and cause a change in the idle.



*sorry, Steell

Post edited by: Patton, at: 2007/03/23 00:09

If there is an air leak on one of the cylinders, say #3, the idle would be real high or erratic but it will likely idle. If the #3 cylinder isn't firing at idle, there can be a few reasons...

fouled plug
bad plug wire or cap
plugged pilot jet or perhaps plugged choke fuel pickup
float level
low compression

To check the ignition part, swap #3 and #2 spark plug wires and see if the problem moves. If it moves to #2, then the fouled plug or bad plug wire/cap situation likely exists.

Just replace the pilot jet. #15 VM22/210 type pilot I think. SOME aftermarket pilot jets are junk and put the gas through in a splat rather than a fine spray and just need to be tossed/replaced.

Float level. Check service fuel level for each carb as per your shop manual

Low compression usually means that valves lack clearance; they hang open a bit and the bike won't fire, especially at idle. You can either slap a feeler gauge on the #3 intake/exhaust valves and measure clearance or use a compression gauge and check actual readings.

I checked the float levels, coils and plug wires with a multimeter, and compression. Everything looked good. I ended up removing the air injection system (emissions stuff) and installing vacuum caps where needed. That worked like a charm and #3 cylinder is now firing at idle. The idle is much smoother now than it ever was. This is my first motorcycle, and my first attempt at getting one tuned. I'm looking forward to riding my newly tuned machine. Thanks for the help.