OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Decomp valve

Just when you think you have seen it all, something will come along and do your head. My son brought is Powertorque over this morning after asking me yesterday what the hose from the carby was supposed to be connected to. He brought it over and handed me the hose and the plastic adaptor from the end of the decomp valve, then he started the motor and it ran fine. I removed the decomp valve and the valve was open. My head hurts trying to understand this

So they normally need to be connected to the hose to work or do they just work at their optimum when connected?
If it's the former, I can only put it down to a blockage so effective, it has become like a spark plug. It can't be supernatural could it?

Valve is in the normally open, so compression is reduced, vacuum from the carb closes it. This motor does not have good compression to start with but I was gobsmacked when he started it up first pull. I kept the decomp valve and just put a spark plug in the hole, it seemed to have a bit more oomph.

You plainly don't subscribe to the theory of it ain't broke don't fix it. It will still cut your grass, albeit not two feet tall.
But seriously, Victas are always going to have a personality of their own. You get others that won't start no matter how well everything checks out. Some will start on half a pull (love those) and others won't wake up without at least two good persuasive turns with the rope!

I saw one today that a bloke brought over for me to look at. This one is a full crank and when he started it up the noise was terrible. The top housing had completely broken off leaving the valve stem visible. The noise was the valve banging up and down at lower revs but at higher revs it was apparently holding the valve shut so there was no noise. When you think you have seen it all something else comes along

That's right Norm, manifold vacuum keeps them closed after starting but generally compression will also keep them shut, especially at higher RPM's. Positive and negative crankcase pressure can prop them open a bit at low RPM hence the vacuum line to the carb.

I seriously wouldn't mind getting one of those PT heads with the valve hole blanked off. It removes complexity.

Hi Bigted, I haven't looked at a full crank head but somebody at Victa must have done their homework to ensure that if the valve let go up the top, as in this case, the valve couldn't drop down into the combustion chamber and do what we know that does or was it just luck

Cripes that would be nasty. Good thing the Powerchat is a "side valve" design.

It is amazing how tough these motors are that cop so much abuse and just keep going. When I think about the numbers of Briggs motors I take up to the scrap bin compared to the very rare Victa that has somehow rusted solid or been run on straight petrol. Then you have the other situation where I had a bloke bring a little Gardenline mower he had bought somewhere, lost the receipt, used it once and next time he went to start it no go. He also left with a Victa, but now I have none left so little feet have to get busy again

I mowed a neighbour's lawn which had grown to two foot tall throughout, and my 1980s Mustang with thumb latch catcher did it all slow and steady. His green waste bin couldn't take all the clippings, so I brought mine over!
This mower ran on straight petrol once, thanks to silly old me mixing up the fuel cans, and seized up mid mow. I just let it rest a while and fed it the right fuel and away it went continuing to muscle though thick growth as needed.
It probably has some awful scoring on the poor piston and bore!

Yes Norm, too right, they done their homework on the design which doesn't allow for the valve to drop in and damage the piston.

It's an ingenious design from a manufacturing standpoint.
You look at the one piece casting for the engine block and the saving on material and components that goes into it and you can see what Victa had accomplished here with no compromise to performance and minimal penalty to outright durability that would be of little to no detriment to the average punter anyway.

It amazes me as well, the compression can be almost nothing according to the compression gauge and it will still run, can't say that for some of the other brands.

I had a Victa maybe 20 years ago that had so little compression I had to put my finger on the pulley (lanyard type) to stop it from turning while I wound the rope on, couldn't bring it up on compression because I couldn't find it and it had a spark plug in the decomp hole but it ran well and still chewed through the long grass. I retired it and bought myself a new Victa with a Honda on it, but that was a big mistake

Ok now to my next problem regarding decomp valves, all of a sudden there is a run on fixing full crank motors and I'm in need of longer decomp valves. I have plenty of the Powertorque ones so I'm looking at trying to make a few adaptors to raise the valve up. Anybody have any thoughts?

A piece of pipe threaded male one end to go into the head, and threaded female the other, to insert the PT deco valve?
Maybe scavenge the stem from a stuffed PT deco valve and tap the upper end to insert the good one into?
Carefully open up and gut a good PT valve to repair a blown FC valve that is rebuildable, unlike the sealed for life PT variety? There is always a way, but worth the trouble is the question.

So long as the main components [body and poppet valve] are OK, rebuild kits are available, and can be had quite cheaply.

https://www.outdoorking-forum.com.au/engines...ls/victa-decompressor-repair-kit-en72684 - this suits all rebuildable Victa deco valves, which have three clips holding the diaphragm chamber together.

Most times one of these is also required; https://www.outdoorking-forum.com.au/index.p...;cPath=193_514_302&products_id=33881

The PT EN72541A deco valve uses a smaller diaphragm than the EN72135 full-crank one, so it isn't a usable parts source.

Thanks Gadge, I usually don't have time to rebuild things like decomp valves, just need to grab one screw it on and move on, have enough other things to work on than those. An off the shelf adapter would solve my problem with them as I have a bucket full of the Powertorque ones

Why not get some kits if you have some stuffed serviceable FC Valves?! You could rebuild them in front of the TV or with the radio on in your workshop. It wouldn't take long. Or you could just stuff an old spark plug in there and pull firmly!!