OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines VC160 Mark 3 Issues

Hi all

I have an old VC160 Mark 3 mower with a G3 carby. I have replaced the carby with a new unused carby that the local mower shop had as the mower was running badly before that. I took the new carby apart and cleaned all the jets and bowl and replaced the o rings to make sure that the carby wa in good working order. When you spray carby cleaner through the jets it enters the carby fine.

However once I installed the new carby the same problems are still hapening, so I thought I would ask for advise. The problemas are as follows:
1) The mower will only start when you spray 'start ya bastard' into the carby.
2) The engine will then run at full throttle only, although it does sometimes run on idle fine as well.
3) The mower does not run smothly from full to slow or vise verser. it bogs down alot and sometimes stalls.

I know that it is not the carby as I installed it on a mates VC160 Mark 3 and that mower started first pull and ran like new.

I have noticed that the mower maybe leaking out the bottom seal. Would this cause the above issues? The mower does have good compression and once going at full throttle is very powerful and easily cuts through any grass.

I look forward to your reponses.

Do you have the air snorkel installed? I have heard that the G3 carbs like to have these attached for ease of starting.

Hi Joe

Yeah I had the snorkel attached at all times.

firstly carby cleaners and ethanol sprays dont do the plastic carby any good and often eat away at them like acetone does plastic this is because the sprays are designed to dissolve varnished fuel and plastic isn't much better since it is too a petroleum product.

it sounds as if you may have issues with you seals. if they are wet and have a moist ring around the outside thats sometimes a good indication they have gone. another way to tell is to pour a bit of petrol down the spark plug hole and see if it leaks out the bottom seal. you can tip the mower over to test the top one in the same fashion but be careful you dont get too much petrol in the coil as it may eat away at it.the seals only cost about $5 from my mower shop and are easy to install after you pop the blade boss off.be careful when buying the seals as there are big and small ones. from memory , but dont hold me to it the later ones (such as yours) used a smaller seal than early ones. when i say smaller we are referring to outside diameter.

when you assembled the carby did you set the poppet valve to a certain mixture (done by turning the corresponding letter towards the venturi hole) or just pop it in there. in the past Ive had instances where even though the valve isn't set properly it runs well on one unit but not on another. the valve should be set so that the "C" lines up with the venturi from memory but i may be wrong.

Joe was right in what he said because if you look at the air filter housing the diameter of the tube is reduced to about 1/2 inch which is so the engine cant suck too much air and therefore helps create a vacuum in the manifold to activate the decompresser and diaphragm in the carby.

see how you go with the seals first
regards jay

forgot to mention that the top seals do not give as much trouble as the bottom ones and in some instances you need to remove the top 1/2 of the crankcase and top bearing to replace them if they are sitting inside a flange but i cant remember if this is the case on a mark 3. i will have a look on a scrap engine later to see if it applies to you
regards jay

The problem sounds more like lean mixture than anything else (though it could also perhaps be poor compression, due to ring/bore/decompressor problems). Lean mixture can be caused in four main ways: intake pipe air leak; crankcase air leak; blockage in fuel tank/fuel pipe/fuel tap; or carburetor malfunction.

Because your carburetor works well on another mower, it is probably the least likely source of trouble in this case. Since the problem is worst when starting, the single most likely cause seems to be an air leak into the intake pipe or crankcase. Mowernut's specific suggestions are well worth following up, especially since you have some signs of a crankshaft seal leak. That kind of leak matches your symptoms (running better at high speed than low speed, and variable leakage rate) better than any alternative explanation. If the seal is leaking, it needs to be fixed.

Hi Jay

My mower is a 1974 VC160 Mark 3 mower so it has the old metal G3 carby on it. I think the bottom seal is leaking as it looks a little wet when you look at it. I always start the mower with the snorkel on as it is gutless without it. Would a leaking bottom seal cause all ot these problems?
Also the carby is fine as it is in new condition and very clean.
Look forward to hearing back form you.

I have a wierd one that wont run with the snorkel attached at the top, its wierd though.

If your bottom seal is leaky then the bet is the top one is too, and yes that could cause a bit of havoc for you. CHeers Joe.

Hi Joe

Thanks for the response, I will head down to the local mower shop and get a top and bottom seal. Is it an easy job to change the seals?

I to have an odd 1995 Victa Commando that will only run with the snorkel removed - it runs great though - as soon as you put the snorkel on the mower stops.

from my experience the main reason Ive had for victa only running with the snorkel removed is air flow issues either with a wasps nest in the top part of the snorkel of a blocked air cleaner. try removing the cartridge and seeing if it helps.
as to the seals it is indeed a good idea to replace both but for the top one the top bearing needs to be removed which means dismantling the whole engine. the reason for this is because the old victa engines have a roled flange that the seal sits against so you cant get them out from on top.
regards jay

Hi all

I have ordered the parts and they should arrive soon. How do you go about taking the blade assembly off on this mower? I can lossen the blades nut the motor still turns over when trying to reomve the rest of the bolt once it has been loosened.
I was also thinking while I had it apart that I would replace the piston rings and decarbonise the cylinder head etc..
Would doing all this make the mower ruun great or is it just worth replacing only the seals and gaskets?

Also are these engines simple to work on or are they a real pain, I would just like to know what I am in for.

VC Victa, I'm not entirely clear on what is happening here. Are you saying that when you loosen the center bolt that holds the blade plate to the end of the crankshaft, holding the blade plate to keep the entire plate and crankshaft from rotating, once the blade plate comes loose, continuing to turn the bolt rotates the crankshaft? That would mean the bolt was tight in the thread in the crankshaft, which shouldn't happen unless perhaps it is rusted.

This sounds a bit tricky to deal with because the blade plate will get in the way. If you can, try holding the crankshaft to keep it from turning (i.e., apply a Stillson to the outside of the blade plate boss on the crankshaft. Do not hold the crankshaft itself - you'll mess it up so it will make it difficult to replace the lower crankshaft seal). If you can't do that, a rattle gun (impact wrench) will do the job - you may be able to borrow one, or take the mower and a suitable socket to the local tyre store for the ten-second job of removing the screw.

Hi Grumpy

You are correct once the nut becomes loose the whole crankshaft turns you try to lossen the nut further, this prevents the nut from being able to be removed as the crankshaft is spining.

I thought that I could put some nylon rope into the cylinder head to prevent the engine from turning over so I can remove the nut. Would this work okay?

I don't recommend that, VC Victa. Depending on just how tight the thread is, the load on the piston crown (or perhaps even the connecting rod) might be excessive. Most likely the thread is not all that tight since it has already moved a bit, and your method would be fine, but it relies on you not applying enough torque to the bolt to break anything. There is also a risk that some fibres of the rope would end up jammed between the side of the piston and the cylinder wall, and you'd have to remove the cylinder to remove them.

It isn't a terrible idea, but it is a bit risky. If you can get a Stillson onto the boss, it can't hurt anything. Similarly with the rattle gun. The only risk with either of those methods is that, if the bolt is really seized, it will shear off in the crankshaft. If it is that tight it will shear whatever you do. You should put some penetrating oil (preferably Penetrene) on the bolt thread and let it soak in for an hour or so, to minimize this risk. Then you should tighten the bolt again and work it back and forth, so the oil gets worked into the full length of the thread. (There are ways to remove the stub of a sheared thread, but they are difficult and likely to damage the thread in the crankshaft.)

the rope trick can work well. i have used rope + a breaker bar in the past to get me out of trouble. otherwise a rattl4 gun works great too.

Yeah a rattle gun is the go.

The main problem with the rope trick is that, depending how much rope you feed in, the piston might be close to top or bottom dead center when you apply torque to the bolt. If this happens it is using the crank/rod/piston as a force magnifying system to increase the force on the piston crown, potentially to astronomical levels.

If the amount of rope is just right, the piston should be right at mid-stroke when you apply the load, and the force on its crown is only the force you put on the breaker bar multiplied by the length of the bar and divided by half of the engine's stroke - that is, the piston crown will probably only see around ten or twenty times the force you put on the breaker bar. However if you don't feed in so much rope, and the piston is near top dead center, the force on the piston crown will be hundreds, or even thousands, of times the force you put on the breaker bar. This is much, much greater than the force it takes to crush the piston crown.

In other words, it might be OK if you understand the mechanical principle and therefore feed in the right amount of rope - but if you don't it is quite likely to crush your piston, and may even break your connecting rod as well.

Hi Grumpy and all

Well I got the bolt of with the use of a mates air gun.
But now I don't know how to take the blade boss off the mower.
Is there any easy way?

I've never done the job on a Victa 2 stroke so you will need confirmation from one of the guys with the right experience. I am under the impression that the end of the crankshaft where the blade boss attaches is tapered, and the blade boss is retained by the taper. If that is correct (and you should be able to see the taper if it is held that way) it is rather similar to removing a car front suspension ball-joint. You hold a large steel block against one side of the blade boss, and strike the opposite point on the blade boss really hard with the biggest hammer you can handle with one hand. You need both block and hammer to be square against the side of the blade boss, and exactly opposite each other. One or a very few good whacks will make the boss pop off the taper.

You can either use an anvil or two hammers because the blade boss is on a tapper and you will need to hit the boss by holding one hammer against the boss and hit it with the other.