OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines SUZUKI M120X 2-STROKE HUNTING

Hi - I'm a newbie to the forum and wondering if any of you have experience of the Suzuki M120x engine. Mine is fitted to what we call a Flymo hover mower, it has started to hunt, revving up and dropping off continuously. I can see the govenor rod moving in and out as this is happening. I have cleaned the fuel tank and lines and also checked the carb and gaskets and air filter.

Hi Bampter, and welcome to Outdoorking.

The usual cause of hunting is lean mixture, as you obviously know, since you have been focusing on the fuel supply. Incidentally I hope you cleaned and inspected the fuel filter. However there is another, less common cause: friction in the governor mechanism, caused by, for example, a bent link which jams slightly, something rubbing against a lever, or a pivot that needs to be lubricated.

I suggest you look at the governor mechanism to check that it moves freely, but lean mixture remains the more likely problem. You should be able to verify this though, by restricting the intake air slightly when the engine is hunting, to see whether that clears it up. Most (not all) engines, including yours, have a choke which can be closed a very small amount to make this test. If your engine had only a primer, not a choke, for cold starting you could either obstruct the air filter's intake passage, or remove the air filter and obstruct the carburetor air intake. I do not recommend running engines with the air filter removed, especially if they are running lean, because they may "spit" burning fuel from the air intake, and this is hazardous.

Here is the workshop manual for your engine:
http://golftechs.us/Manuals/Suzuki.pdf

There is a likely cause for lean mixture other than the fuel system: an intake air leak, on the suction (i.e. engine) side of the carburetor. This usually happens in one of two ways: the gasket between carburetor and engine is loose or damaged; or air is leaking directly into the crankcase, perhaps through one or both of the crankshaft seals. In most cases if these are leaking there will be oil around them.

Please try closing the choke slightly to establish definitely whether the problem is lean mixture. If it is, investigate the items I have listed. Either way, let us know what you find, and we can continue the diagnostic process if necessary.

Hi All,

Hope someone can help me. I removed the carb off my Suzuki M120X Rover lawn mower and I cant seem to get it assembled correctly. I have read the service manual but it does not show how to correctly install the linkage arms. Also not sure if both butterflies in the carb must be closed when trying to start the mower.

The mower used to run but was VERY sensitive to the throttle position, then it stopped running completely. There is a strong spark from the plug but I am sure it has something to do with the carb.

Any help would be appreciated...

hello, I love my suzuki's, the arrangement you are having trouble with can be a real pain.
I remove the governor arm to get all the linkages apart.
When I reassemble it, I set the governor up as per the manual, available above.
If you have disturbed the carby, you have to make sure the gaskets are good & sealing when reassembling.
Try not to stretch the governor spring.
Also make sure your choke is fully closing when set to choke or they wont start.

Here is an image.

Thanks for the pic! I came across one at a mower shop today and had a look at the assembly. They had the spring on the governor going to different position.



But thanks for your help, much appreciated!

I'm not sure what you saw at the mower shop, but this is how they are.
Your red circle on the right is where the throttle cable goes.

Your red circle on the left is the governor spring in the centre hole.
Top hole raises engine speed by +150rpm, bottom hole -150rpm.
Good luck.

thanks Mark, I will set mine up again and see if I can get it going. Do you know if the second butterfly in the carb (the one that connects to governor) is closed or open when starting the engine?

G'day dirtbiker, on cold start the throttle plate is opened. Choke plate must be fully closed when you set up your throttle cable.

See figure 1.6 below.

Thanks for the info guys. Tried again this morning to set it up and just not happening. I get a good spark from spark plug and when I pull the plug out it is moist so I assume it is getting fuel into cylinder. Wish parts were not so hard to find as it is a great mower.

It could be the engine seals, you can usually see if the bottom one is leaking.

The seals would have to be pretty bad for it not to start.
A victa with a warped head or dud decomp will still sometimes start provided it not a huge huge leak, If it is they usually pop smoke and flames out the offending orifice.

With the plates in the carb.
The furtherest one in is the throttle plate, full noise is full open.
The outer one is the choke, full open is choke off, closed is choke on.
They both have their own function.


To break it down.
Carbs start with the fuel in the bowl.
As the air goes through the carb due to careful differences in the size of the bore etc in the carb it makes different pressures and the air sucks fuel out of the bowl through jets up into the air stream. There is also an air passage into the fuel bowl before the throttle plate, so in the fuel bowl is a higher pressure than after the throttle plate.
Its the same deal as how an aeroplane wing works but inside a tunnel with a bowl under it.

Then the air and fuel ratio needs to be right. Thats done with the jetting in the carb. The first thing that affects jetting is the fuel level or float height. This needs to be right. Its all working on pressure differences. Liquids do not compress, air being a gas does.

The throttle butterfly controls how much air can flow through and that controls the engine speed.


So the first thing you need to be sure of if you have had the carb appart is that the fuel/float height is correct.
On a two stroke if you have the oil in the fuel ratio way wrong that effects jetting too. Its burning fuel to run. It burns oil as a by product of how its designed. If you have too much oil you do not have enough fuel. If you have not enough oil you have too much fuel. Not as important with a mower as it is with a high performance bike but it is still relavant.



Given what you just said in the post above. Whats the story with the plug? Id suggest you try two new ones.
Some plugs look good making spark outside the motor. Stick them in a wet damp hole at 6 or more times atmosphere and they dont want to play the game. Ive had new plugs out of the box that dont work.
Ones that look good out but dont work aer usually those cheapie mower shop/part brand type ones and some champion, im not a fan of champion plugs.



To be sure its getting fuel and work out if its lean or rich on the fuel, get a teaspoon of fuel and put it in the plughole. See if it kicks. Try it with the plug you have. Repeat with a new plug.



If you keep an eye out you will find a whole mower for parts for a good price. By that I mean under $50. They do command a bit of a premium. Its taken me a while to collect enough motors etc that I will have enough bits.


What I would dearly like if anyone has it is a PDF or link to an online Parts list for the motor. I have a mate that works at a Suzuki bike shop and he said if I can give the part number he should be able to get me bits.

Yes Bob, When I think about it, I have had a power torque engine running, looking through a gap in the head gasket at the flame inside the cylinder.
I even went & grabbed the misus to show her that one, she just though I was crazy.

Suzuki has no head gasket.

But the seals are on the other side of the piston, so as the piston moves forward there should be high pressure in combustion chamber & a vacuum in the crankcase to draw in fuel.

This would have to affect starting.

I dont have a parts list, just one I have made up over time.
Try the Torro web site in the US, they have a manual but no part no.
Also try the australian site "spare parts online" they have suzuki bits.

Thanks for posting the photos. My rover xl with the Suzuki 2 stroke had a little hiccup yesterday. After pulling the carby apart and cleaning I reassembled the beast. It follows the picture that was posted. I have an issue though. The engine starts fine but I have no throttle control other than applying some choke. The throttle plate is wide open. There does not appear to be any resistance on the governor lever to return the throttle plate to closed position. The outcome is that the motor starts and then runs absolutely flat out. The kill switch still works though. The question therefore is how is the appropriate resistance applied to ensure the throttle plate returns to closed position. Or maybe I am completely off track. Happy to be educated. Thanks.

Hello, I have 2 of these here that I still have to look at.
One takes 4 pulls to start.
The other is hard to tune.

They can be difficult to get right.

I would check your governor set up again.
When you reassemmbled it was the governor shaft all the way to right, then place the governor arm on the shaft so that it is all the way to the right, please see image below.

I have had your problem before. I re-adjusted the governor arm on the shaft slightly. Check it all moves as it should with your finger.

Also are the carby gaskets sealing and not sucking air.

This manual is available from TORO's website.

Surprising, I would have thought there would be a parts list up on the net somewhere. Theres one up for just about every bike ever made.


Thanks for the pics.
Not sure exactly what I need yet.
Have a motor in bits, bought it that way.
Have a motor for bits.

Then i think 2 complete ones on frames still.




I think i have a spare cowling and air cleaner.
But im missing a starter.