OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Over revving and under revving cycle

Dear all,

My sister's 2 stroke has developed a habit of over revving and then under revving after it has been running for about 10 mins. During this time, there is nothing you can do to control it, the start lever has no control and the revs are very loud. Only way to stop it is to turn the petrol off. Lawn mower has been a bit difficult to start lately as well. Any ideas what is causing the overrevving?

tiger,

We need more info on the motor like what type Power Torque or older if Victa or is it a Suzuki 2 stroke.

Not a power torque, it's an older Victa.

Tiger,

Here is a few things to look for:

• Check fuel tank cap and make sure that the vent hole is clear
• Check fuel flow from tank to carby
• Check carby main jet for any blockage
• Remove flywheel and check top seal by placing fuel between crankshaft and casing

Try this check list first before we go further.

Do you have a workshop manual?

Thanks, Bruce. Are you talking about the Gregory's manual?

Is the throttle cable connected properly at the carby (since the only way you can stop it is the fuel tap)?

Bruce,

Fuel tank cap actually spurts petrol for a while and then settles down. This happens about 10 secs after starting the motor.
Feul flow from tank to carby is OK.
Not sure how to check the main jet and not sure about what to look for when checking top seal.

Had another look at this mower and I suspected the carby. I took it apart, washed the parts in petrol and dried it with air compressor. It still seems to rev up and down a bit even when the mower is stationary. It is also difficult to start, I can only get it to run by squirting some petrol into the spark plug hole and then by leaving the fuel tap on, it seems to start and keep running albeit with the up and down revving. What do you guys think?

tiger,

If it is not a power torque motor then I would suggest that you check to see if you have any moisture around the bottom seal.

If you can post a picture of the motor it will help.

Hi again Bruce,

I'm not sure how I can get a photo to you but am wondering what the distinguishing characteristic of a powertorque engine would be as it's possible that this is a powertorque engine.

I have taken the carby apart and cleaned it, swapped the primer cap and main jet off a working mower but still the mower over revs and is hard to start. My instinct tells me that the carby is the problem, it is G4 plastic body and these carbys are simple in design. I'll take it apart again but what should I be looking for in order to fix the carby?

Regards,

Tiger

tiger,

What I would be looking for are the following:

1. Crack in the cover for the diaphragm(the one that covers the diaphragm).

2. Look for a hair line crack where the screw goes into the body (the jet screw).

I have had in the past had these issues and it has taken quite a few times looking at it until the light shows it up.

Some times you can not see for looking.

Hi Bruce,

Have got a photo here.

http://docs.google.com/View?id=d8nh9ck_2dq66xxgb

* Remove flywheel and check top seal by placing fuel between crankshaft and casing

Bruce and others, can you give me a bit more detail on how to do the above? I remove the flywheel, and then apply some petrol between the crankshaft and casing, what do I then do?

You can turn the engine very slowly with the fuel on that seal nad if it is blowing little air bubbles, or sucking the fuel into the seal you know its leaking.

Thanks, Joe. Will give it a try if carby tests fail.

Bruce, one more thing, you mentioned before to check the diaphragm cover. I've looked at the manual, what is the name of the cover in the manual?

Just need to know the technical name of this diaphragm cover before I fiddle with this.

Its called a diaphragm cap.

Thanks, Bruce, I have again pulled the carby off. There is no crack in any of the carby parts but the mower will not start. However, if I squirt some petrol into the spark plug hole, it starts and runs until the petrol runs out. Are there any other places to investigate in the carby?

hi all,
have you checked the O rings on the inlet manifold and made sure the screws holding the manifold on are tight? i have had trouble with that before causing air leaks, especialy when the mower is hot.
Regards Jay

Thanks, Jay. I will have a look at these next time I'm over at my sister's place, however regardless of whether this lawnmower is hot or cold, it has trouble starting.