610 mule spark plug fouls after short use

[bjones]

2007 Mule 610,  owned for 8 yrs and valves were ticking when I got it and had them adjusted twice and this is when plugs began to foul.  I replaced battery (used battery I had on hand) a yr ago and didn't foul a plug for some time and replaced batter (new) with a bigger lawn mower type battery again a month ago and have fouled two plug since.  Had carb cleaned and valves adjusted and still fouls plugs way to often.  Friend has a mule just like mine and his does same thing. Have read this is a common problem with 610 mule.  Any help or suggestions would be welcomed.  Thanks and stay healthy.

[Travis]

I couldn't find the NGK spark plug number used, but it seems like a lot of people recomnend using a colder spark plug in them than the factory plug. It sounds like the heat rating is too high

When the heat rating is too high:

The spark plug temperature remains too low and causes deposits to build up on the firing end; the deposits offer an electrical leakage path that gives rise to loss of sparks.

https://www.ngk.com.au/technical_info/heat-range/

[bjones]

Did you mean colder plug? Some say to use hotter so I'm confused. Before the new battery the plug would be really black and sutted up. Now with newer battery the fouled plugs are white that I think  indicates it is maybe to hot. Thanks for responding.

[Travis]

White plugs means the engine is running very lean and hot.

The battery shouldn't have anything to do with the ignition as it's magneto fired, but it seems like it does.

 

[bjones]

So would you think a colder plug would help, i may give it a try.  thanks

[Travis]

5 minutes ago, bjones said:

So would you think a colder plug would help, i may give it a try.  thanks

I'd say it's definitely worth a try... could be a few $ fix.

[bjones]

I installed a colder plug , original plug is:

BPR5ES, I installed  BPR4ES.  Documented hrs and will see how long it goes. Thanks for responding !!

[Travis]

How's it doing?

[bjones]

56 minutes ago, Travis said:

How's it doing?

So far so good, got around 3 hrs on clock , hope it holds up. Thanks for asking

[Travis]

How's the ol' Mule doing, buddy?

[bjones]

So far so good.  I did have a skip or similar issue but didn't foul the plug.  Was on the road going up a steep hill about 1/4 mile and acted like plug fouled but pulled choke and babied it home and it cleared up before I got home so may have another issue besides plug.  Pulled the plug and it looked ok and didn't foul it so I cleaned it and put back in and has about 7  hrs of run time so the colder plug definitely helped.  Thanks for the follow up

[cliffyk]

Leaving the plug heat range aside--your 2007 Mule 610 (be it a model KAF400A7F, KAF400B7F or KAF400C7F) uses a magneto type ignition system in which the power to fire the plug is derived electromechanically by a magnet on the alternator rotor rapidly rotating past  a stationary single coil  ignition coil--a long winded way of saying it is independent of the vehicle's battery power. You could remove the battery and if you could turn the motor over fast enough (likely just 100 to 200 rpm) it would make a spark.

here are those components:

Here's a link to the ignition system description and test procedures from the service manual--this will let you adjust and test the magneto to determine the underlying problem.

 

-cliff-

[bjones]

Thanks, I am somewhat familiar with this set up. Have a koler two cylinder engine on my 0 turn that would kill a plug after it got hot and it turned out to be the coil.  I put one of those inline plug tester devices on the cylinder and it  showed eractic spark. Do you think my coil could be weak?  I have suspected this but haven't replaced it. Thanks 

[cliffyk]

8 hours ago, bjones said:

Thanks, I am somewhat familiar with this set up. Have a koler two cylinder engine on my 0 turn that would kill a plug after it got hot and it turned out to be the coil.  I put one of those inline plug tester devices on the cylinder and it  showed eractic spark. Do you think my coil could be weak?  I have suspected this but haven't replaced it. Thanks 

Same thing, though the Kohler might have two coils if it's a V-twin (jut one if it's a "boxer"). Using that same tester on the Mule  may reveal something. The resistance tests shown in the manual should be pretty positive.

$43 (w/ free shipping) on eBay for a new genuine Kawasaki part.--p/n 21171-7035 is what you want:

 

Interesting little beasts, these earlty mules--only 400 cc, not much HP (10.5 @2400)--but GOBS of torque at low rpm (22 lb·ft @ that same 2400 rpm!!!).

Peak torque on my 24.4 HP (@ 7500 rpm) Hisun 400 is only 17.1 lb·ft☹️--also @ 7500 rpm, which in reality is an engine speed the CVT will never allow (except maybe when "pedal-to-metal" on an open road somewhere). I suspect real Hp that actually makes it to te ground is more like 15-18. Rubberband CVT efficiency is just 40 to 80% or so depending on a number of factors (drive ratio, belt stiffness, etc.)  In  general hihger "gears" (numerically lower input--> output ratios) are the least efficient.

Here are some interesting charts from a great study "The analysis of an influence of rubber V-belt physical properties on CVT efficiency" by A Kot  W Grzegożek  and  W Szczypiński-Sala of the Cracow University of Technology:

(belt "A" is the most flexible tested, belt "C" the least)

 

 

 

[Travis]

Mule's are definitely torquey,  there are some pretty steep inclines on the property where water runs through and what not, the mule  would probably Idle and climb it if it could.

 

[bjones]

Update, got around 10 hrs and hasn't fouled a plug, fingers crossed. The lower heat number has seemed to help.  Thanks for you guys help. B well

[Travis]

glad to hear it!

[Barry J.]

I was having a similar problem with my mule 610 and reading the posts. My Mule would foul the plug after about a half hour or so. Changed out a lot of parts and spent a lot of time troubleshooting. In the end it ended up being the fuel line. The rubber on the inside of the fuel line was degrading and small particles would hold the needle valve slightly open and flood the motor and foul the plug. I changed the fuel line to a PVC fuel rated line and it’s been working great sense.