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I have a cub cadet rtz22 with a 22hp Intek. About a month ago it started backfiring through the carb at high rpm. Since then I have checked and gapped the plugs. Checked for good spark. Cleaned the flywheel and coils. I pulled the plug wires one at a time and it is on the left cylinder when you are sitting on the mower. With that and all the easier stuff done, I did a compression test. About 105-110 both side and less than 5 psi difference between the two. I switched plugs from side to side. No change. I switched coils. No change. So that leads me to believe that it is not ignition related. The timing could cause this but since it is basically fixed between the cylinders and only one is doing it that the timing should be fine. Feel free to correct me. So the next obvious choice, at least for me, was an intake valve sticking. I pulled the valve cover and with the plugs out I turned the engine by hand and everything looked good. Nothing tight or loose (just judging from past experience. Nothing official). Pushing in the rocker everything moved freely. Since it is high rpm only, I thought maybe a weak valve spring. I bought a new spring and pressurized the cylinder with about 80 psi and removed the spring. I did not hear and air leakage while doing this. I released the pressure and made sure the valve moved freely. I installed the new spring and I adjusted all of the valves. Turned the engine over a few times and checked them again. Put it together and it started and ran great for about two hours and then started backfiring again. This time it started blowing some blue smoke. I checked the valve adjustment and it is fine. This engine does burn some oil but we check and add as needed every time we fuel up. It has about 500 hours in it.

I am fresh out of ideas.

:welcome:

There is a diode between the two cut out wires.
Disconnect them there and try again.
Problem goes away , replace the diode.
It is there to stop the coils backfeeding a signal down the kill wires and interfearing with each other.
to stop the engine, earth both wires to the block.
A you will be running without the cowel in place keep the time short to avoid overheating.

bertsmobile1 said:

:welcome:

There is a diode between the two cut out wires.
Disconnect them there and try again.
Problem goes away , replace the diode.
It is there to stop the coils backfeeding a signal down the kill wires and interfearing with each other.
to stop the engine, earth both wires to the block.
A you will be running without the cowel in place keep the time short to avoid overheating.

Click to expand...

I will give that a try tonight. Thanks!

Ironhead Dave said:

I will give that a try tonight. Thanks!

Click to expand...

No luck. It didn't change.

Ok cross that one off.
Next pull the flywheel nut / bolt out and check that the 2 halves of the timing ket slot make a perfect square.
If uncertain pull the flywheel and check it.
A small crack & slight displacement can make a big difference to the timing.

bertsmobile1 said:

Ok cross that one off.
Next pull the flywheel nut / bolt out and check that the 2 halves of the timing ket slot make a perfect square.
If uncertain pull the flywheel and check it.
A small crack & slight displacement can make a big difference to the timing.

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I looked at the slot and it appear to be a little worn but after I pulled the flywheel, the key felt tight in the flywheel and the crankshaft.



I tried to attach a pic from my phone but don't know if it will work or not. It is very blurry because I had to trim it way down to get it to fit. I already pulled the flywheel so I can't retake it yet.

Like I said the hole looks big but further down, everything felt real tight when I put it in the slots individually.

I also saw no signs of cracking.

Two things here, I am not clear that you disconnected both kill wires from the base of each coil and a key can be tight in the keyway and be slightly sheared, there must be no mark on the sides of the key.

Walt Conner

OK so exit easy fix No 2
You are now left with valves & cam as it is only happening on one side
If you have an accurate depth gauge , measure the height of the valves and the valve springs,
They should both be the same.
measure the lift again they should both be the same.
Double check these against the right cylinder.
Double check the valve lash.
Pull both pushrods and check them for straitness on a sheet of glass.
On some occasions the alloy rod flexes, random fault and the tips on the rods have ben known to break off.
Again another random fault.
If the head has overheated the valve guides can slip in the head and that is a new head situation unless you are or know a good machinist.
Commercially it is easier & cheaper to replace the head.
Do not order one till you have pulled the head & checked tha gasket and the mating surfaces for any signs of damage.
Not likely with the difference in compression figures quoted.

Tinkerer200 said:

Two things here, I am not clear that you disconnected both kill wires from the base of each coil and a key can be tight in the keyway and be slightly sheared, there must be no mark on the sides of the key.

Walt Conner

Click to expand...

Yes I did unplug both wires. I thought that I had broken the tab off the one coil but was mistaken. The key looks fine. I will try to attach a couple pics of it.



And this is the hole without the key.

Btw....what is the spec to torque the flywheel to?

Ironhead Dave said:

Btw....what is the spec to torque the flywheel to?

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150 ft. lbs, how about I send you a Service Manual for your engine? Address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

bertsmobile1 said:

OK so exit easy fix No 2
You are now left with valves & cam as it is only happening on one side
If you have an accurate depth gauge , measure the height of the valves and the valve springs,
They should both be the same.
measure the lift again they should both be the same.
Double check these against the right cylinder.

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When you are talking about the height of the valves are you referring to the height of the stem sticking through the head? Please explain the lift also.

Thanks!

Tinkerer200 said:

150 ft. lbs, how about I send you a Service Manual for your engine? Address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

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Walt,

I sent you an email to the above address. Did you receive it?

Dave

No, you did understand about putting the address in proper format? I don't use the address in regular form because of spam crawlers harvesting addresses.

Walt Conner

Ironhead Dave said:

When you are talking about the height of the valves are you referring to the height of the stem sticking through the head? Please explain the lift also.

Thanks!

Click to expand...

The height from the floor of the head to the top of the valve.
If the head has overheated the valve guide can shift in the head
If the cam is worn the valve controlled by it will not move as far as the others.
Same thing happens with a bent pushrod for different reasons ( the rod flexes at the bend ) but that usually only happens at speed.