Spits back through intake and exhaust

My Sons 1980 KZ 1000 MKII was having a hard time starting lately. I looked at the spark and it seems weaker than it was, I did do the coil mod and after it the spark was noticeably better, I was getting about 8 volts to the coils before the mod, and am now getting 11.22 Volts, with the battery at 11.88 Volts.

After trying to start it for a while I pulled a plug and it was dry, so I decided to go through the carbs and found a starter galley on one of the bowls was clogged, one pilot was also slightly clogged, and the middle tube in the accelerator pump circuit was cracked. After all of this it now starts right up, but you can not rev it at all until warmed up, and spits and back fires through intake and exhaust at low speed and idle, just like it did before when spark was weak. Also after the carb work I checked for vacuum leaks and there was a gap in the boot to cylinder head on #2 cylinder, re torqued it and noticeably better but can still get a slight raise in idle with carb/brake cleaner. So carb boots need to be replaced or maybe some high temp silicone will fix this, they still seem pliable, not hard or cracked.

I checked all the grounds and the connectors look good. Put a lab scope on number 4 and it was showing 25,000 Volts, did not get to check the other cylinders as the scope shut down on me and I was not able to get it back online. Got it working again so will scope other cylinders soon, maybe tonight if it's not raining.

Also the plugs look great, except #2 looks rich, used my infrared thermometor and noticed that cylinder 2 primary was about half the temperature as the other 3.

Noticeable problems:
1. I have what looks to be weak spark.
2. Slight vacuum leak
3. Cylinder 2 not getting up to temp.
4. Had to move starter switch wire one time to get it to turn over, maybe something here for powering the coils.
5. The kill switch does not shut bike off, maybe a function of running the coil mod?
6. I adjusted the floats by measurement only, could not get the clear tube method to work by using drain nipple and loosening drain plug, have to get the measurment tool. Only slightly adjusted number 1 and 2 a little lower.
7. New AGM battery, would think I would have more than 11.88 Volts with key/headlight on, maybe a charging system check is in order.

Why is your voltage so low? It should NEVER be below 12.something.

If your battery voltage is @ 11.88 Volts, that is a DEAD BATTERY. DEAD.

Here's how it goes:
These are general voltage ranges for six-cell lead-acid batteries:
Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells
1.All voltages are at 20 °C (68 °F), and must be adjusted -0.022V/°C for temperature changes.
2.Float voltage recommendations vary, according to the manufacturer's recommendation.
3.Precise (±0.05 V) float voltage is critical to longevity; insufficient (sulfation) is almost as bad as excessive (corrosion and electrolyte loss)
Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

Yes, check the charging system for sure.

Fix all possible air leaks, after making sure to spray brake cleaner thru all of the carburetor passage ways, and look to make sure it comes spraying out into the carb bore. (I use non-chlorinated brake cleaner as it is powerful on the gas varnish, but will not permanently harm/deform the rubber stuff).

Set air mixture screws, and make sure the gasket rubbers or on the mixture screws themselves.

GoodLuck!

Thanks TeK9iNe,

I thought with the new AGM it should read more, even with the lights on (can't switch off, would have to disconnect).

I will bring a battery tester home tonight and test it and maybe have to go back to Batteries Plus for an exchange.

Or just have them test it, but would like to know before I bring it in what my tester states.

I would think 25,000 volts is plenty of voltage, but my scope was acting flakey.

25,000 is kinda low, but it's hard to measure those voltages since the scope will load it down even with a 1 meg or 10 meg input impedance on the probes. Plus the actual spike you're looking for is very very brief. Once the spark initiates, the voltage drops considerably.

What is your voltage while the bike is running?

I will check this tonight, and try to get to the charging system/battery check done.

Hopefully I can get the scope to work on all four too.

Forgot the battery tester at work and just got home. Will try tomorrow.

Turtle wrote:

...1980 KZ 1000 MKII... starts right up, but you can not rev it at all until warmed up, and spits and back fires through intake and exhaust at low speed and idle, just like it did before when spark was weak...plugs look great, except #2 looks rich, used my infrared thermometor and noticed that cylinder 2 primary was about half the temperature as the other 3.

Noticeable problems:
...
3. Cylinder 2 not getting up to temp...
6...could not get the clear tube method to work by using drain nipple and loosening drain plug....

Would assure valve clearances being to specs, and perform compression test. A leakdown test would be even better. Looking for incomplete valve closure. Especially on cylinder #2.

Clear tube test should work, unless carb float valve is leaking for whatever reason. What exactly does the test indicate?

Good Fortune!

I had the head off about 6 years ago, and ported it and set all the valve clearances, and it probably has 1,000 miles on it since then, so I doubt this is it, but certainly a good idea to still check, I will grab a leak down tester and do all four to verify. I do have a valve cover gasket so I could pull it too.

I saw here somewhere while searching that you could run a clear tube off the overflow nipple and loosen the drain until it comes out the overflow, which does not really make since, but I tried it anyway and could not get any gas to flow out the overflow nipple. So apparantly I NEED the proper tool. Anyone know where to get one cheap? Or how to make one?

I want to make sure I am including everything, I have a Dyna-S with Accel coils, and they Ohm out at 3.45 Ohms.

It seems like the mis-fire was not there when I know I had good spark.

Turtle wrote:

...saw here somewhere while searching that you could run a clear tube off the overflow nipple and loosen the drain until it comes out the overflow, which does not really make since, but I tried it anyway and could not get any gas to flow out the overflow nipple. So apparantly I NEED the proper tool. Anyone know where to get one cheap? Or how to make one?....

With manual slide carbs (believed applicable here), ignore the overflow nipples and use only the drain hole. Even the special tool uses only the drain hole. Without the tool, it's okay to "self-thread" the appropriately sized clear tube into the drain hole.

With some vacuum slide carbs, the overflow nipple serves as a drain when the drain screw is loosened.

Good Fortune!

[Click on image to enlarge view.]

Must have been the vacuum slide carbs I saw the info for. I will try it by screwing a clear hose in and turn the petcock to Prime.

Also now that I mentioned petcock I did notice some fuel in the vacuum tube to the petcock, if that vacuum tube comes off number 2 carb it could be getting adittional fuel and or a vacuum leak. The petcock works, when I turn to prime it fills up the carbs, and when I remove the tank with it ON or RES it does not leak any fuel.

I just keep thinking of more and more issues the more I think/talk about it.