Kawi 25hp V-twin running rough

[WinterDeere]

The Kawi 25hp V-twin on my ZTR started running rough today, while tooling around the yard harvesting walnuts. This is a low-load chore, but can take a few hours.

I had noticed last week when doing the same activity, that the RPM's seemed to be climbing a bit more than normal on the downhills, mower deck not running. Then today, it started popping and missing. I also found it was under-powered when I finally tried mowing, so I shut it down and parked it in the shop for debug... tomorrow.

I did notice there's a bit of a leak at the rear main seal, but can't imagine it's related. Also, it had backfired harder than usual at shutdown earlier today, just before the missing behavior had started. This motor nearly ALWAYS backfires on shutdown, no matter what you do to try to prevent it, it's been that way since new.

When I start it after sitting, I smell hot or burning oil, but not sure if that's from the exhaust or coming off the external air cooling. Also, behavior is inconsistent, not happening at all when cold, and going in and out when hot. That'll make debug fun.

I put an inductive tester next to each spark plug wire boot, and it's picking up spark on both. Can pull and check actual spark at plugs tomorrow but doubting that's the issue, given how it goes in and out. Thinking first step is to get the mess of air cleaner off the top of the engine, and maybe spray some ether around outside off carb/intake gaskets, see if there's a leak there.

Any advice appreciated.

 

[mjonesnh]

Have a Kohler Command 23 that was losing power when hot. Had 1 coil going in and out. Replaced both coils and issue disappeared. Engine has always backfired also. Found out if I pull choke on when I am turning key to off that it stops the backfire.

 

[oldnslo]

Since happening more when warm or hot would check compression on both cylinders when cold and then again when hot. This should tell you if you have a compression issue vs spark or if your luck is like mine a little of each

I thought newer Kawis had the anti-backfire solenoid on the carb but could be 100% wrong on that belief.

 

[WinterDeere]

Thanks, guys! I should have said, this Kawi is on a 2007 Deere 757 ZTrak, so not that new.

 

[LittleBill21]

sounds like a coil going, do you have a spark tester to see how strong the spark is?

 

[mini14]

while the engine is running and engine cover off spray carb cleaner around the intake gaskets and se if you notice a change in rpm. they were known to leak.same with the carb to engine gasket

 

[WinterDeere]

sounds like a coil going, do you have a spark tester to see how strong the spark is?

Noticing late yesterday that it would stutter when I'd throttle up, I was thinking this could be the issue, as I remember an old car that would behave exactly this way when it needed a new distributor cap and rotor. I have spark testers that will give me a light that I can eyeball, but nothing with adjustable gap that can measure spark strength. Also, since problem is very clearly intermittent, sometimes the engine runs very strong and other times it dies back, this might be a challenge to debug.

while the engine is running and engine cover off spray carb cleaner around the intake gaskets and se if you notice a change in rpm. they were known to leak.same with the carb to engine gasket

Yeah, I think this will be my first step, just because it's an easy test! Also, pulling that huge air cleaner assembly off the top of the engine gives me a chance to clean everything real well and inspect linkage, etc. I really hate the design of these things, the way the carb is totally buried under the air cleaner mounting.

 

[WinterDeere]

Got a spark gap tester on order, for delivery late today 5-10pm.

Gonna be rally pissed if this is just a bad batch of fuel. . Of course all my fuel is fresh, but that which is used in the mower really isn’t shared with any other equipment, so not an easy debug without draining and running out to fetch new.

 

[CloverKnollFarms]

My FIL had a 240 hour 24hp Kawasaki let loose on his ZTR last month.

Sort of surprised.

My commercial Kohler is purring like a kitten, and he hasn't mowed in a month.

Sounds like you got your moneys worth from that motor

 

[Mike1955]

Have a Kohler Command 23 that was losing power when hot. Had 1 coil going in and out. Replaced both coils and issue disappeared. Engine has always backfired also. Found out if I pull choke on when I am turning key to off that it stops the backfire.

Mr mojo I have a Kubota that backfires and I don’t like it one bit. I read on here to idle down before cutting it off. Didn’t help tha I could tell. So I’ll try the choke. Thank you sir

 

[mjonesnh]

Mr mojo I have a Kubota that backfires and I don’t like it one bit. I read on here to idle down before cutting it off. Didn’t help tha I could tell. So I’ll try the choke. Thank you sir

Will add that I do idle down also and then pull choke on while turning key off

 

[RandyT]

Have a Kohler Command 23 that was losing power when hot. Had 1 coil going in and out. Replaced both coils and issue disappeared. Engine has always backfired also. Found out if I pull choke on when I am turning key to off that it stops the backfire.

Kohler engines afterfire solenoids only shut off the high speed jet when shut off not the idle circuit which is why Kohler engines are recommended to shut them off at full throttle, to stop fuel being pulled in from the idle circuit

 

[Mike1955]

I give that a try. Mine is more than a backfire it will run backwards it sounds like. And sometimes vapor lock and I have to remove the spark plugs next time I crank it. I’m afraid it’s hottie tear something up. I even added oxtail but it didn’t help. And I have a new 600 dollar carb on it I may start killing it with the blade on

 

[Mike1955]

I give that a try. Mine is more than a backfire it will run backwards it sounds like. And sometimes vapor lock and I have to remove the spark plugs next time I crank it. I’m afraid it’s hottie tear something up. I even added oxtail but it didn’t help. And I have a new 600 dollar carb on it I may start killing it with the blade on

Sorry about the spelling in the previous post I meant to say octain. Spell check got me!

 

[Racer4]

Kohler engines afterfire solenoids only shut off the high speed jet when shut off not the idle circuit which is why Kohler engines are recommended to shut them off at full throttle, to stop fuel being pulled in from the idle circuit

I wondered what the reason was for the full throttle shutdown. Makes sense now.

My Timecutter HD says to shut down at FT on the sticker next to the key. So that’s what I do. Toro branded (Loncin) V twin.

 

[WinterDeere]

Well, fuel pump is good, and still waiting on spark gap tester, so I went to measure crankcase vacuum, and found it’s at positive pressure. Thinking back, I remember replacing the breather maybe 10 years ago, so I guess it ate another one.

Trouble is, you have to remove flywheel and front motor casing to get at it.

Sounds like you got your moneys worth from that motor

I don’t prescribe to that mentality. I have plenty of motors older than this, and with way more than these 1200 hours.

Compression was checked cool, because I did t want to run long enough to warm it up fully, but shows 75-80 psi. Spec is 57 psi min.

 

[WinterDeere]

Just thinking, I should probably look up leak-down specs for this motor. The high compression could be due to carbon build-up, and not really a good indicator that there’s no blow-by issue.

 

[Yander]

Have you changed the fuel filter. $4 part.

 

[WinterDeere]

Have you changed the fuel filter. $4 part.

Every 12 months. Last change was beginning of this season, about 60 hours ago.

Maybe you just responded before reading ahead, but issue has already been diagnosed to positive crankcase pressure.

 

[WinterDeere]

so here’s a question: what causes these breathers to fail? Getting to the damn thing is an all-day job, engine removal, always precarious with fragile 20 year old wiring harness connectors, flywjeel removal… damn near half the engine is apart before you can even access the breather. Not something I want to repeat too often.

What causes breather failure? Backfiring on shutdown seems like a potential culprit.