OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines 66 Mayfair 125CC won't rev

I can't get my engine to rev. It has plenty of compression (85-90PSI), new points and plug (all gapped and set to spec), a clean carbie with new gaskets (3L carby), float level set according to specs, needle and seat are fine. I've put 2 new condensers in, the first allowed it to rev till the over long lead vibrated out of where I'd poked it, hit the spinning flywheel, bared the wire and blew the condenser, plus, back fired through the carbie and blew he top off the air cleaner (something I'll never be able to replace, it was the original red mesh filtration system. My other thread have pictures). That was a $30 condenser from the local mower shop, lasted 2 minutes. I've now replaced that, I got 5 from ebay for $10.

My exhaust pipe doesn't appear to be blocked though reading elsewhere members say they blow/ spray brake clean through and tap it to loosen carbon then blow it out with air compressor. I have all the necessary equipment.

Another mention is carbon build up on the exhaust port, that appears to be clean. I've had the muffler off and saw little to no carbon build up.

I'm running on standard 25:1 mix I do myself and the fuel is fresh and clean, as are the lines and fuel filter.

I'm at wits end, I have no other ideas and I've been fixing 2 stroke engines and building them for 40+ years (mowers and motorbikes). Usually, I'd go with a blocked muffler and that's about the last port of call later today if it doesn't rain.

Any other ideas?

Crank seals don't leak as is evident by compression readings (plus, absolutely no signs of leakage anywhere on mower).

I need to get my lawn done and spent 1.5 hours yesterday in extreme heat doing the smallest patch of my front lawn (20 minutes worth of mowing under standard, running conditions). It had gotten thick and the mower stalls in long grass even set high.

Hi LEO,double check flywheel key is not sheared after you fitted 2nd condenser.you may not have tightened it up(we are all human and things sometimes happen).as it was fine until original condenser blew. One other thing,and I am mostly thinking out loud! Are there different condensers for 4 and 2 stroke? Reason I ask is I was working on on a 2 stroke with a dead ignition module.i grabbed one that looked the same off a 4 stroke that was for parts,BUT would only start and run 50% at best.replaced it with a 2 stroke one and bingo.later hooked up the the four stroke module to a 4 stroke and it ran fine.

The old victa 85cc (and 170cc) use a condenser of 0.27-0.23uF (where the u represents Greek mu, symbol for micro, giving microFarads)

The 125 and 160cc use a condensor of 1.65-1.80uF but may also have the electronic system (breakerless)

From Gregory's Small engines service and repair manual... Whee, it's already coming in useful!

You may be able to measure the capacitance with an appropriate multimeter. I'm guessing an incorrect condensor, if it allows a proper spark at all, will adversely affect the timing.

Hope this helps,

Cylinder compression readings won't tell you that much about crankcase compression, I fear.

The simple way to test a crank seal is to position the mower with the seal uppermost and level, then dribble a little fuel around the shaft, and turn the crank through one revolution. If the fuel disappears or you see bubbles, it leaks.
I should add that leaky seals usually make them hard to start.

That 'torpedo' style muffler isn't very prone to carboning up, but the outlet should be easy enough to clear with a suitable drill bit or steel rod.
Or use the old 2-stroke motorbike exhaust trick, and burn it out - you probably know that one.

And as Pope says, check the flywheel key - it isn't likely to be sheared, on a Victa 2-stroke, but it does have to be fully seated in the cam notch, to maintain correct timing.

Maybe the following will refresh your memory on 2 cycle operation. Please this is not a comment on your ability it is just that sometime any one of us can forget the basics after years of working on these beasts.

How Two Cycles Works uTube video

I've resolved the issue, it was a blocked muffler. I used brake clean, a block of timber to tap and an air compressor to blow it out and it now revs and runs like a dream. Plus, I'd set the float height on the original carbie but replaced it with another 3L carbie I had in nicer condition. I forgot to check float height on it. The float height was about 1.5-2mm too low but I wouldn't see that making so much of a difference.

OK, my mention of "crank seals as per compression readings", I had checked crank seals when checking the compression a few weeks back. Having an air compressor it's easy to do a leak down test via the plug hole to find anywhere air and fluids escape.

My frustration often means I don't properly express myself. Migraines, strong medication and age don't help.

The mower was starting hot or cold (after 2 weeks under my house)first click. Four winds, prime carbie, one click (Impulse starter), started and idled like a charm. It just wouldn't rev.

My condenser is 0.32uF (read with my multimeter) but they were being sold as early Victa 2 stroke condensers. Despite a difference to what was quoted it runs fine.
I knew the key-way and key were fine, I'd had the flywheel off a few times in the past week. The retaining nut is also sufficiently tightened,

I have a background in electronics and electrical (IT too) but spent the majority of my working life working in the mechanical industry as a mechanic and electro-mechanical specialist.


A 4 stroke ignition module would only fire half as many times as a 2 stroke module.

I am going to convert the mower to electronic module if just for the purpose of not having to remove the impulse starter pulleys bolt and the flywheel nut ever again. I'm having a heck of a time acquiring either, 1/2"BSF screws are like hens teeth and the 1" long stand off nut is as rare and impossible to chase up new.

Thanks for the assistance everyone!

All good that you've found the problem, and sorted it out, Leo.

Not so, in practice - they are triggered by the induced voltage across the coil primary winding, so in common with distributorless car ignitions, they fire every revolution. Just means that a waste spark occurs near the end of the exhaust stroke.

AVB, I suspect that we are at cross-purposes due to terminology.
I've never found THIS type of 'compression test' gauge to be of any real use in indicating 2-stroke crankcase compression. Edit: As you have also previously said, HERE

A leakdown test [or I guess leak-up, if you start with vacuum], with the hand pump setup that you use, is a very different matter indeed, and really the only proper way to go about it.