Doing up a mower engine

[karthead]

Hi all,
I'm building a motorized scooter for a metal project, and was hoping i could get some advice in regards to doing up the engine, i.e giving it more power, and make it reach higher rpms.

You all know what it's like? Whenever I mow the lawn I lift the throttle lever up and down real quick to rev it for shits n giggs, and of course I can barely hear a change in rpm. I want it to rev likea real 2-stroke

Other info: it's a 160cc victa 2-stroke mower like this:
https://media.photobucket.com/image/160cc%20victa%202-stroke%20engine/harry761/bikes/P3130113.jpg
cheers!

[Islander]

Petrol mowers have a centrifugal governor fitted to limit the revs.

[karthead]

[DreadHead]

[jjdugen]

'Generally' the throttle cable does NOT connect to the carb slider directly. There will be an intermediate linkage that is controlled by the centrifugal limiter, this connects to the carb slider. A direct throttle cable will give you 'proper' control, but dont try this with the engine connected to the blades, over-rev them and they might just fly apart!!!
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[Matt-]

[Islander]

[bikenut]

or a wind type, f/wheel has fan for cooling "wind".

pics of engine would be good.

[karthead]

Alrighty thanks all. Upon tearing apart the engine i did notice a rubber tube that connects to the carb from another spot (my memory doesn't help; it was a first semester project)

DreadHead: In case you haven't noticed, I've done better things than rebuild a mower engine

Also i never reconnected the blades to the crank because I new I was never going to use the engine for it's original purpose.

I'm thinking of trying different motorbike engine carbs on them to see how it runs (finding one with the right sized venturi well be difficult I'm guessing). Jetting and tuning the carb will be a chore and a half cause a motorbike carb obviously was never made to go on a mower engine... Somehow i'll need to find out how to properly disconnect this centrifugal microwave thingimobobby.

Assuming a different carb will be ok (i.e mixture, jetting, venturi etc), will there be any decent increase in performance?

[bikenut]

:D tuned pipe??

[karthead]

These aren't photos of MY one, they're off the net.
https://www.outdoorking.com/forum/uploads/usergals/2011/03/full-4730-589-160cc.jpg
https://www.outdoorking.com/forum/uploads/usergals/2011/09/full-5013-3071-wash.png

[karthead]

[DrDonnyBrago]

[jjdugen]

Most of the 'hack' carts that you see at holiday camps etc. use mower type engines. Do a Google, I'm sure that something will come up.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[stevo as b4]

You won't find a tuned length expansion chamber for a 2stroke lawnmower engine off the shelf!
It's not that high on the list of must have options on a new petrol mower lol!

You will have to design, calculate your own dimensions, then cut out the sheet metal into the correct shapes to roll up into cones and weld up. Sounds easy, but I bet there are few people on BCF who could even attempt it TBH, and you need to be confident welder used of working on thin sheet metal sections etc.

as for your Victa engine, well can you still get the parts? It's pretty pointless stripping down an old engine that's probably worn out and then put all of the worn bits back together, as you have achieved nothing that way.

I shouldn't encourage you, but I spent £100 on re-building a Tecumseh 100cc 2stroke engine and re-building the mower it was going back onto. I used new piston and rings, all new oil seals and bearings, and had the block honed, and decked. Pretty sad but I was having a being bored at the weekends stage.

You won't make it rev like a bike engine, as the porting and more importantly the internals are not designed to make bike levels of bhp or rev. Something like a vespa scooter engine would be in a much higher state of tune. If it runs at 3000rpm on the mower, you can probably get it to run safely at 4000-4500rpm with the right mods, but you'd be aiming to get it up the performance level of a small outboard boat engine for example.

On the Tecumseh, I removed 0.8mm from the block face and still had loads of squish clearance. There is lots of improvement you can do to the transfer ports and inlet of most garden machinery 2stroke engine. Just a tip, don't knife edge the throttle butterfly on both sides like I did, as I ended up with a demented mower that idled at 2000rpm, and was a bitch to start.

[karthead]

[DrDonnyBrago]

[karthead]

[pdg]

Those victa motors don't have any governer on them. Very few 2 stroke mower engines are governed, and those that are don't generally use the same type of centrifugal governer like you'd find on a 4 stroke Tecumseh or B&S.

If you bin the crappy horrible plastic excuse for a carb and put a proper one on there you can actually get some usable power without doing much else.

Also get rid of the decompressor - use an old spark plug to bung up the hole. It'll be harder to pull the rope, but it'll start easier and more reliably.

All the bits are still available btw.

These are totally vicious little screamers of an engine and nothing at all like the Tecumseh 2t engines.

[karthead]

[pdg]

In theory, any carb you stick on will be able to work, but you might need to fanny around with jetting - tbh, anything at all is better than the plastic abortion and if you can get a carb off a 125/150/175 2t bike it won't be all that far out. Think about how much it'll get used too, if it's only going to be a few hours here and there then running off 'ideal mixture' isn't going to be too much of an issue - it's not like you'll be relying on it to get to work (hopefully!)

The standard exhaust should be fine really. I know it's far from a perfect design and is made more to fit in the space than to produce maximum power but it does work. If you really want to, you could try getting a minimoto type pipe and stick that on - it won't make things much worse even though it'll be well out of tune.

[_Iain_]

Head over to www.lemonparty.org - i recall them being the people to speak to regarding mower based kart projects, might be worth a look?? I know its not going on a kart, but same principle.
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[karthead]

[_Iain_]

https://onlyhdwallpapers.com/thumbnail/internet_meme_trollface_trolls_faces_troll_face_vectorized_desktop_10000x8136_hd-wallpaper-512654.png
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340