View Full Version : Kawaski 25 hp vertical engine on Hustler Super Z popping and dead battery

08-28-2009, 06:09 PM
Yesterday no problems. This moning dead battery, barely enough to turn little red light on by key. Tried jumper box, enough to turn over a couple turns a let out a HUGE backfire. Got a new battery, no problems for about 2 hours. Startin popping a few times at one job, finished no problem. Next job stats fine, when you put any load or move the throttle up fast pops and hesitates. 13.86 volts at the battry running. 12.6 right now sitting. Any ideas where to start? Bad coil that shorted out possibly? Thanks for any help.

08-28-2009, 06:42 PM
When was the last time that you adjusted the valves on this engine?
Valves that are out of adjustment will cause back firing. Once the engine is running did you check the battery voltage?


08-28-2009, 06:53 PM
With it running full throttle 13.86.
If it was the valves it wouldn't have killed the battery or started right after a dead battery, right?

08-28-2009, 06:58 PM
I agree that you may have more than one problem. I believe that misadjusted valves will cause the backfire. 13.8 is good battery voltage so the dead battery is something non related.


08-28-2009, 07:14 PM
move the throttle up fast pops and hesitates

Move the throttle up and while it's popping/hesitating SLOWLY apply the choke, If it smooths out the carb most likely needs to be cleaned inside. A leaning carb can cause these symptoms and still crank just fine.

08-28-2009, 07:26 PM
I'll try that.

08-30-2009, 12:13 PM
That didn't work. It only pops or stumbles for a second and then clears up. With the blades on it runs rough the entire time. Thought maybe it was a coil, pulled each plug cap off one at a time and it just made it worse.

08-30-2009, 12:26 PM
There may be an anti-backfire solenoid at the base of the carb. Check out carb parts diagram. I don't know that this is the problem. It could well be something else. I'm new to the anti-backfire solenoid and it's full function. I do know it's a $100.00 + item, not to mention the repair time.

08-30-2009, 12:34 PM
Aren't they either stuck on or off?

08-30-2009, 03:05 PM
Aren't they either stuck on or off?

In most cases yes.....

Replace the spark plugs first and try it again, If it still acts up let it cool and check the valves as ericg mentioned;


08-30-2009, 03:44 PM
Thanks. I will try plugs and then check the valves. I just don't understand why eithere would be the case when I started with a dead battery and why it just suddendly started. If it was the valves wouldn't it slowly come on and wouldn't it usually get hard to startif the valves were getting out of adjustment?

08-30-2009, 03:48 PM
The valve adjustments have all to do with the compression release so a valve or vales being out of adjustment could lead to hard starting. The dead battery is a separate issue. Listen to Restorob as he is the master of small engines.

08-30-2009, 04:05 PM
I am trying everything said above. I am just trying to understand the "why" behind some of the suggestions so I can learn.

08-30-2009, 04:16 PM
As ericg has mentioned twice, It sounds like you have/had two different issues here. A strap in a battery can blow at any given second, When you tried the jumper and it only turned a couple times it most likely didn't turn fast enough to generate proper spark until the last second thus the back-fire.

A back-fire can cause carbon to break loose from the piston and or valves, This carbon can get stuck under a valve seat and cause a mis-firing cylinder. Back-fire can also cause bent push-rods and broken baffles inside a muffler which can cause a restriction in exhaust and cause missing and loss of power.

It appears you have the starting issue solved for now. Since the battery has noting to do with the running of the engine other than holding the fuel cut-off solenoid open for fuel to enter the carb main circuit, We are trying to help get to the bottom of the run issue.

A spark plug is the easiest cheapest thing to start with when having run issues, That's the first thing I replace so is why I suggested it.

If you find any valves way out of spec check the push-rods......

08-30-2009, 04:53 PM
I understand what you guys are saying about them being unrelated and just working on the problem that is current. It is just hard forme t factor out the first problem when dealing with the second, but I guess thatis just the best way to deal with them is one at a time. It does make sense to have the backfire cause something else. I took the plugs out and won't be able to get new ones until tomorrow, I will check the valves after that if it doesn't help. One quick note. When the problem first started I checked a plug and it was dark brown. After screwing with it all day and taking the plugs out this time they were white like it's running lean.

08-30-2009, 05:39 PM
After screwing with it all day and taking the plugs out this time they were white like it's running lean.


A recap of what's been done;

You preformed the applying choke test I posted, That shows the carb is not leaning out.

You performed the pull each plug wire test on your own (which would have been my next) and that shows both coils are firing.

If you have ample fuel and ample spark do you have ample compression ?

The plugs may look like it's running lean if the valves aren't opening fully to pull in enough fuel.

The fact that it happened suddenly is leading me to believe you have a mechanical failure (valves), Could I be wrong ? Sure..... But no one will know until there checked and eliminated as a possible cause.

I have put the dead battery issue on hold because it's much easier to perform a charging system test on a properly running engine, A ill running engine can/will give false results. Therefore once the engine is running properly attention can be reverted back to the battery/charging system issue.

08-30-2009, 07:10 PM
I found a local auto parts store that had the plugs. Put them in, and as for now, it runs perfect. True test tomorow mowing all day. Driving it around the garage it seems to be the solution. The gap was still OK on both old plugs, guess one of them was fouled or cracked??? Could the backfire have cracked/fouled a plug? Thanks for all of your help. I will update in a day or two to confirm whether it is fixed or it comes back. I will check the valves tomorow anyway, I looked and it's been about 400 hours since last check.

08-30-2009, 07:41 PM
Good deal, Now put your multimeter across the battery and read the voltage, Then start it and give it full throttle then read it again. Post the before and running voltage readings.....

08-31-2009, 08:44 PM
12.5 and high 13's

08-31-2009, 10:24 PM
With those numbers it looks like it was just time for your battery to take a dump, Should be good to go now.

09-09-2009, 12:07 AM
The first day after I thought it was fixed the popping or boggong slowly came back. Was OK for half a day and once it started it gradually got worse. Was OK enough to finish out the week. Over the weekend checked the valves. They were in spec. So I had a good set of used coils from a different engine so I tried those. After a full day of mowing it has been running perfect. Hopefull this if the end of the story and it was the problem all along. Thanks for your help.