FJ151v AC52 running badly, light grey smoke

[JeanBaptiste]

Hello all,

First of all, thank you very much for sharing & helping each others so much - it is always nice to see people trying to help others.
Secondly, please excuse my bad english - western french guy here.

I used to run a Kaaz lawn mower equipped with a Kawasaki FJ151v / AC52 engine. It ran pretty well for almost 10 years. When I tried to run it again last spring, it appeared to run badly, despite it was running like a charm at the end of year 2024. Here are the symptoms:
- starting is not a problem, hot or cold,
- there is a power issue, as the engine seems not to run as powerful as before,
- you can hear the engine is not running smoothly, there are like misfires or similar things, almost like a car's launch control system,
- the engine seems to run not as high in rpm as before,
- the sparkplug becomes fouled with dry carbon deposit in like 30 sec, no traces of oil here,
- the combustion chamber was coated with carbon deposit, but a slight layer, not chunks,
- a light, grey smoke is visible at the exhaust, that wasn't here before,
- the crankcase pressure seems higher than usual/designed: when you popped the oil gage cap off and put it down on its threaded interface, without screwing it, you can see it dancing around by the pressure oscillations in the crankcase. Checked the venting system with the elastomeric valve on top of the crankcase, seems to be in good condition.

The oil level is good, the oil has been changed at least 2 times with brand new & fresh oil.

What has been done and did not solve the problem:
- changed the original carb for a chinese equivalent - no result,
- new sparkplug, fresh gasoline of course,
- adjusted the valve clearance to original specs (but the original setting was already good, so no excessive wear detected here)
- changed all piston rings, no result - the cylinder is in good shape, still some crossed-pattern traces of the original honing process visible,
- the decompressor/starter mechanism (decreasing the compression ratio) seems to be free and fully functional, although I do not have a specific method to check it while the engine is running

A year or two before, the carb needle valve was stuck open and gasoline poured into the engine's oil, increasing the oil level up to the point of the engine was smoking badly. But at that time, draining/changing the oil and replacing the faulty needle valve solved the problem.

I'm thinking of the valves guides becoming loose, but this engine hasn't been used so much - maybe 100 hours at max? so I would be surprised of having worned valves guide.
It seems another guy had similar issues on a Kawasaki 180FJ engine here back in 2022, but the thread does not indicate if he succeeded in solving the problem.

Big thanks for any help.

Best,

J.B.

 

[Auto Doc's]

From you description I would suspect there is low compression. Maybe the valves need to be checked for proper seating. Carbon does build up and affect the valve's ability to properly seal.

 

[Tiger Small Engine]

From you description I would suspect there is low compression. Maybe the valves need to be checked for proper seating. Carbon does build up and affect the valve's ability to properly seal.

The Kawasaki FJ is an older engine. Keep an eye on the oil if it is using oil (light gray smoke). There isn’t much more you can do within reason. Run it.

 

[slomo]

there is a power issue, as the engine seems not to run as powerful as before,

You know, on all outdoor power equipment or as in mower engines, you must de-carbon the cylinder/s say every 5-7 years? Could be a reason you are down on power. Or are you used to the engine and maybe not cutting enough? Letting the grass get away from you?

you can hear the engine is not running smoothly, there are like misfires or similar things, almost like a car's launch control system

Possible plug, weak ignition or valve issue. There are 2 TDC strokes in a 4 stroke engine. Are you setting valves on the wrong one?

the engine seems to run not as high in rpm as before

Download your engine manual. Read it cover to cover. Should be a fully detailed carb linkage setup page or two there. Follow it like gospel.

the sparkplug becomes fouled with dry carbon deposit in like 30 sec, no traces of oil here,

Running rich. Is the choke sticking on? Carb float level too high? Does the carb needle hold back 7psi for 30 minutes? Pull the oil dip stick and smell for gas. If you smell gas you have a carb needle/seat issue.

Old air filter? As in the paper element is old not flowing the proper amount of air?

a light, grey smoke is visible at the exhaust, that wasn't here before

She's an old mower. Could be several things. Oil level over full? Tipping the deck up too far? Tipping the deck at all? Will cause oil burning issues.

The oil level is good,

What does that mean? Exactly ON the full mark is what it should be at. Not over and not under.

A year or two before, the carb needle valve was stuck open and gasoline poured into the engine's oil, increasing the oil level up to the point of the engine was smoking badly. But at that time, draining/changing the oil and replacing the faulty needle valve solved the problem.

If you ran the engine too long with fuel diluted oil, poor lubrication resulted. Could be a reason she is a smoker.

 

[Auto Doc's]

What is the off chance there is a little diesel fuel mixed in with the gas? That would reduce power and make the grey smoke you described.

I've seen it happen a couple of times on customer equipment.

 

[sgkent]

changed the original carb for a chinese equivalent - no result

Sounds like we are pulling the lanyard on the parts cannon. The more things you monkey with the harder it will be to find the one thing that caused the issue.

Drain all the gasoline, including what is in the fuel bowl. If the old carb is off, pull the bowl off after marking how it fits, and see if there is debris and corrosion in it. If there is crap in the bottom of the gas tank, it won't matter if you added clean fuel. You'll need to completely clean out the whole fuel system. It was running find you say in 2024 when you put it away. Also look for evidence of critters making a home in the engine. Chewed ignition wires can cause all sorts of issues.

 

[slomo]

Post up a video of it running. Aim towards the muffler to capture the smoke.