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Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
I'll be posting up pics of three Victa leaflets I have had in that household for a long time.
I'm going to start off with my favourite.

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Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
1 member likes this: Seanoss
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Joined: Nov 2013
Posts: 6,938
Likes: 278
Forum Historian
G'day MF
That's a great one - The Victa Tuned to BP.

Of particular interest is the Victa Imperial's 80:1 fuel mix.
That mix, to my knowledge, was never commercially available,
but the closest would have been BP Zoom Outboard.

Thanks for posting this!

------------------------
Jack

Joined: Sep 2015
Posts: 2,044
Likes: 145
SENIOR TECHNICIAN & HISTORIAN
G'day Mf and Jack

Yes that's a good Victa leaflet Mf ,I like the mentioning of not turning the fuel tap off to stop the engine as
it causes overheating and wear, so many people say they still do this with line trimmers by emptying the
fuel tank and run until the carby is dry.


Cheers
Max.

Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
Hi CJ,
Originally Posted by CyberJack
G'day MF

Of particular interest is the Victa Imperial's 80:1 fuel mix.
That mix, to my knowledge, was never commercially available,
but the closest would have been BP Zoom Outboard.

------------------------
Jack
I was thinking that's due to being oriented vertically and possibly oil accumulating in the crankcase without the leaner ratio. Still surprised at the amount they reduced it to.
Did you notice the back wheels in the 500 Twin picture? That's the picture that inspired me to swap the rear wheels on my Supreme.

Hi MW,
Originally Posted by maxwestern
G'day Mf and Jack

Yes that's a good Victa leaflet Mf ,I like the mentioning of not turning the fuel tap off to stop the engine as
it causes overheating and wear, so many people say they still do this with line trimmers by emptying the
fuel tank and run until the carby is dry.


Cheers
Max.
so does this mean it's bad for a two stroke to run out of fuel while running?


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Joined: Jul 2018
Posts: 2,085
Likes: 80
SENIOR TECHNICIAN
MF, I am of the thinking that there were a few reasons for 80:1 :

It's going to spend its life fairly low stressed (lowered compression ratio, limited throttle) not ever expected to slash knee high grass like a normal rotary

The engine sits more out in the open for heat dissipation - not couped up with cowl and tank over it

When you are trying to cater to a discerning market with competitors like the sb45, any smoke will be frowned at - especially considering a noise disadvantage already


I personally do run them dryish - that is turn off tap off at idle, listen for when it begins to lean out and kill the ignition.

Hearing people turn them off at flat stick with the fuel tap makes me cringe - though I have personally done it when running out of fuel accidentally

Joined: Feb 2006
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SENIOR TECHNICIAN
I think you're on the right track(s) Tyler.
Several factors must be at play to justify such an outlandish ratio.

Here's my second piece. Someone cut out a piece of the front two pages. If anyone has the complete one could they post it here?
A sample of the most interesting pages.

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Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Joined: Nov 2013
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Quote
I think you're on the right track(s) Tyler.
Several factors must be at play to justify such an outlandish ratio.

G'day MF, Max and Tyler
Interesting enough discussion on the Imperial 2-stroke.
Certainly on the right track except ...

I think engineer Grumpy was on to it back in 2015. He looked to
causality in design as only a gifted engineer would.

I have included that link below.

I think the 80:1 mix was a byproduct of another engineering imperative.
Tracing the causality goes, for me, something like this ...

For the first 6 or so years, the Imperial was powered by a 4-stroke. Why?
I mean, Victa had their horizontal industrial 2-strokes. Why not use them?

Best guess: Victa knew there were problems in mating a powerful
2-stroke to a small centrifugal clutch. Two-stroke power impulses are way
more pronounced than the 4-strokes of similar capacity and primary clutch
engagement would have been 'clunky,' to say the least.

By the late 1960s it seems clear that Victa were aiming for self-sufficiency;
in wanting their own 2-strokes to offer decompressors and recoil starts.

The key design feature is the lower compression ratio for the Imperial.

That smoothed the impulses to an acceptable level (with a smaller,
redesigned clutch).

This created another by-product issue - too much oil!
Best guess: Victa recommended BP Zoom Outboard but the engine
ran so cool that an 80:1 mix was acceptable.

I also note that the Imperial was never fitted with a G4 carby. Victa
stayed with the ol' reliable G3. Why? I think Victa intended the
Imperial be retired the following season.

LINK: https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=62325

Cheers
-------------------
Jack

Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
Hi Tyler, Maxwestern and Cyberjack.
Here's the third one showing the export markets at one point.

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Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Joined: Sep 2015
Posts: 2,044
Likes: 145
SENIOR TECHNICIAN & HISTORIAN
G'day Mf ,Jack and Tyler

The fuel mix is interesting but I probably would have explained it differently.(warning answer may be long winded)

The cylinder head spacer on the Imperial reduces compression , a factory 2 stroke motor makes more HP with a lower comp. ratio
at higher rpm ,the higher compression motor makes it's power at low and mid range (eg governed motor).

The above statement applies to racing 2 strokes and these mowers are not running racing rpm's but the imperial
is an ungoverned motor so I would think it's made with the decomp plate and ungoverned carby so peak power
is achieved at a higher rpm compared with the higher comp governed 2 stroke motor .

I think because the Imperial has it's peak power at a higher rpm by increasing the squish gap this would help to reduce rising combustion temperature and avoids stressing internal parts like the piston and bearings, by having a lower comp ratio.

“Squish velocity has a very pronounced effect on the rate of burning and heat release in two-stroke engines. High squish velocities lead to rapid burning characteristics and that rapid burning approaches the thermodynamic ideal of constant volume combustion. There is a price to be paid for this, evidenced by more rapid rates of pressure rise which can lead to an engine with more vibration and noise emanating from the combustion process. Further, if the burning is too rapid, too early, this can lead to high rates of NOx formation and slow and inefficient burning in the latter stages of combustion. “

A greater squish clearance will decrease wear and tear of the engine , reduce vibration ,result smoother running motor.

If the squish distance is too great then the fuel in the squish band is not burned and the engine runs very “dirty”. It's inefficient and does not produce optimal power.

I would say because the squish distance is increased, to overcome incomplete combustion the fuel mix is set at a higher ratio of fuel to oil.

Also because plenty of squish clearance can reduce heat and allow fuel time to effectively burn off at a slower rate the engine runs cooler thus needing less lubrication.

I did hear a smaller engine needs less oil because of less surface area of moving parts.

The 2-cycle combines two functions in one rotation, it makes the power twice as quickly as a 4-stroke.

See in the graph below how when the standard Victa 2 stroke looses RPM the torque figures increase now with the
Imperial 2 stroke (decomp and ungoverned carby) the torque reading should be at a higher value at a greater rpm when
compared with the standard 125 Victa 2 stroke.



Originally Posted by Mowerfreak
so does this mean it's bad for a two stroke to run out of fuel while running?


The 2 stroke will wear more if the motor stops by running out of fuel just as the 2 stroke wears more it you use
car engine oil as 2 stroke oil instead of specially designed 2 stroke oil but in real terms what
difference is it really going to make possibly the engine lasts one year less?

I don't turn 2 strokes off by the fuel tap but my reason for that is if the engine stops by running
out of fuel lubrication is lost in the engine and putting the mower away in a damp tin shed can
result in rusted internals.

Also I like to leave fuel in the plastic Victa carby as it stops the o rings drying out and leaking.

Cheers
Max.

Attached Images
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Victa full-7392-.jpg (91.71 KB, 42 downloads)
Joined: Nov 2013
Posts: 6,938
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Forum Historian
Hello MF, Max, and Tyler
Mowerfreak, it's serendipity how your Victa docs have inspired
insight by virtue of their contents. They have been provocative!

Tyler certainly got the ball rolling with thoughtful comments too.

The first brochure - the Victa/BP one - has inspired great insight
by Max, way beyond my understandings.

The second one - The Pace Premier Hi-arch [V199] has been
mentioned on ODK, but nothing comprehensive.

The third one - the OP Manual c1970 is a classic example of how
Victa promoted itself in print in the late 1960s and early 1970s.

Max, a great - and important - technical article there!
I have linked to this page from the original article where Grumpy
made his comments. They compliment each other.
Sincere thanks.

Thank you to all.
------------------------------
Jack


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