Well lads, the Scott Bonnar 520 4-stroke mower ain't cutting the lawn like she used to. MT (Mowing Times) have dropped to 17 minutes. Still has an ear shattering note which I'm sure doesn't comly with EPA Regs though.
Thought I'd trick her up a bit so it can keep up with the Victa next door. What do you suggest? Stroke it, or be done with it and fit a blower? Looking for a low 9 minute EMT (Elapsed Mowing Time).
Scott Bonnar Performance Mods
Started by
_Yella-5000_
, Nov 11 2007 03:51 PM
31 replies to this topic
#3
_rorym_
_rorym_
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Posted 11 November 2007 - 04:40 PM
Big port job, expansion chamber and a Flat slide Mikuni...also fit a smaller counter shaft/blade rotor pulley..13,000rpm no worries...6 mins E.T. !! 
R
R
#4
_Herne_
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Posted 11 November 2007 - 04:45 PM
Remove the grass, lay concrete, paint it green, ditch the lawnmower and you will be doing your bit for conservation.
Just think of it, no messy oils and petrol, no noise pollution and you will save the planet by conserving your water. Last but not least it will be easy on the pocket.
Cheers
Herne
Just think of it, no messy oils and petrol, no noise pollution and you will save the planet by conserving your water. Last but not least it will be easy on the pocket.
Cheers
Herne
Edited by Herne, 11 November 2007 - 04:51 PM.
#5
_rorym_
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Posted 11 November 2007 - 04:49 PM
Problem is...he isn't Italian..that wont work...??
R
R
#6
_Herne_
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Posted 11 November 2007 - 04:52 PM
Whats with the ethnic slur on Italians???
You toucha my car and I breaka your face
Hehehhehee.
Cheers
Herne
You toucha my car and I breaka your face
Hehehhehee.
Cheers
Herne
#7
_Bomber Watson_
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Posted 11 November 2007 - 04:59 PM
Right. First thing, new blades. But before you put them on spend a few hours with a wet stone and sharpen the things like razors.
Then weld some bits of metal onto the blade plate for more weight. or just make one out of 6mm plate. Might sound dumb but it will have more momentum thus cutting easier.
Then, because its a four stroke, you can go ape.
Pull the head off and machine it with a 9" grinder. up the comp a bit. Then get a cam out of a bigger one (if available) for a bit more lift and duration. Port it, perhaps fit a carb off a bigger model (again if available). If there isn't a bigger model, just find a carbie off an old small capacity motorbike.
Last but not least get a bit of 1.5" exhaust pipe and make a strait through zoomie header for it.
Should be doing 6-7 min EMT's.
Cheers.
Then weld some bits of metal onto the blade plate for more weight. or just make one out of 6mm plate. Might sound dumb but it will have more momentum thus cutting easier.
Then, because its a four stroke, you can go ape.
Pull the head off and machine it with a 9" grinder. up the comp a bit. Then get a cam out of a bigger one (if available) for a bit more lift and duration. Port it, perhaps fit a carb off a bigger model (again if available). If there isn't a bigger model, just find a carbie off an old small capacity motorbike.
Last but not least get a bit of 1.5" exhaust pipe and make a strait through zoomie header for it.
Should be doing 6-7 min EMT's.
Cheers.
Edited by Bomber Watson, 11 November 2007 - 05:00 PM.
#8
boomfunk
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Posted 11 November 2007 - 05:36 PM
just plumb a NOS kit into it...that will get the bugger movin
#9
_tyre fryer_
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Posted 11 November 2007 - 05:39 PM
Just finished mowing my lawns.
I keep looking at the ol' victa thinking "hhmmmm, wish i could work this baby" then I realise that money could be better spent on my car lol.
I would really like an old mower to pull apart so I can learn more about engines...
I keep looking at the ol' victa thinking "hhmmmm, wish i could work this baby" then I realise that money could be better spent on my car lol.
I would really like an old mower to pull apart so I can learn more about engines...
Edited by tyre fryer, 11 November 2007 - 05:39 PM.
#10
boomfunk
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Posted 11 November 2007 - 05:45 PM
well our last mower we broke the conrod....yes the conrod..made an awful big noise
#11
FastEHHolden
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Posted 11 November 2007 - 05:52 PM
I'm for real here..I have hotted up a few lawn mowers...but if the bloke next door starts modding..you're toast.
- 4 blade conversion
- Remove head gasket, use a sealant and replace the head, you can flatten it more but you need to deck it perfectly flat, after the rough work (emery paper or cement path) you need to use valve lapping paste and a sheet of glass to get it smooth. Check for valve clearance before bolting the head down.
- Grind the base circle of the camshaft and weld the top of the cam follower to build it up...you still need to set the clearances (18 thou inlet, 20-22 thou exhaust.)
- Bigger valves is a bit beyond the scope.
- Remove the original exhaust and run about 6 inches of pipe roughly the same diameter as the port...it will be loud.
- Replace the foam in the air filter with an oiled stainless steel sink scourer.
- Remove the wind vane from the governor..use a strong bit of wire to over ride it.
and that should see you thru.
Victas are heaps easier and respond better to mods.
- 4 blade conversion
- Remove head gasket, use a sealant and replace the head, you can flatten it more but you need to deck it perfectly flat, after the rough work (emery paper or cement path) you need to use valve lapping paste and a sheet of glass to get it smooth. Check for valve clearance before bolting the head down.
- Grind the base circle of the camshaft and weld the top of the cam follower to build it up...you still need to set the clearances (18 thou inlet, 20-22 thou exhaust.)
- Bigger valves is a bit beyond the scope.
- Remove the original exhaust and run about 6 inches of pipe roughly the same diameter as the port...it will be loud.
- Replace the foam in the air filter with an oiled stainless steel sink scourer.
- Remove the wind vane from the governor..use a strong bit of wire to over ride it.
and that should see you thru.
Victas are heaps easier and respond better to mods.
#12
_Bomber Watson_
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Posted 11 November 2007 - 06:14 PM
Ok, im liking boomfunks idea best atm
I even went as far to rig one up on the ol victa down in the shed.
I even went as far to rig one up on the ol victa down in the shed.
#13
boomfunk
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Posted 11 November 2007 - 06:17 PM
your the man bomber !!! 
i like it , what a classic
i like it , what a classic
#14
Com_VC
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Posted 11 November 2007 - 06:18 PM
Maybe try and supercharge it? I've heard those emissions pumps that you often see on VK's would work alright 
I've often had thoughts of injecting my mower, fitting said supercharger and adding starter motor. Or even doing a 10hp engine conversion or something.
I've often had thoughts of injecting my mower, fitting said supercharger and adding starter motor. Or even doing a 10hp engine conversion or something.
#15
_rorym_
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Posted 11 November 2007 - 06:22 PM
Bomber...as usual..you smoke the opposition..Done my man!! Yu Da Man!!
R
R
#16
_Bomber Watson_
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Posted 11 November 2007 - 07:01 PM
Haha cheers guys. i couldent help myself.
I have a couple of blowers sitting around to, shoulda grafted one of them on as well as the nos
Heres one i rigged up years ago on dads old ride on.
Cheers.
I have a couple of blowers sitting around to, shoulda grafted one of them on as well as the nos
Heres one i rigged up years ago on dads old ride on.
Cheers.
#17
_Chaotic_
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Posted 11 November 2007 - 07:23 PM
Just don't do what the old couple in usa did and decide to trim the hedges by picking up the lawn mower and running it over the top.
20 finger tip meat puzzle anyone.
20 finger tip meat puzzle anyone.
#18
RIM-010
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Posted 11 November 2007 - 07:29 PM
That is one of the funniest posts on the internet.
Tim
Tim
#19
_purpleLC_
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Posted 11 November 2007 - 07:37 PM
I have cut down my mowing time to nil since
my mower broke down over a year ago.
My old man comes over and cuts it for me---
he does Ok for an 84 year old!!!!
my mower broke down over a year ago.
My old man comes over and cuts it for me---
he does Ok for an 84 year old!!!!
#21
makka
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Posted 12 November 2007 - 09:50 AM
I hotted up a Victa for something to do once, I had a performance expansion chamber of a old suzuki so I put that on along with an Amal carby that was on our Hodaka (dont ask!) and I did a little bit of a port job and was about to convert it too reed valve but that was too much stuffing around! one thing that really helped get it going better was taking the cylinder off the crankcase and putting it the other way round so that the crank spun away from the intake, not towards it!
i did a few other things to it as well, like a twin spark plug conversion, as you can tell this was before I had my car and all my motor bikes were in pieces!
i did a few other things to it as well, like a twin spark plug conversion, as you can tell this was before I had my car and all my motor bikes were in pieces!
#22
orangeLJ
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Posted 12 November 2007 - 11:13 AM
Careful with the 84 year old mowing the lawn, my step dads father was 73, mowing the lawn on a hot day last january, his main artery in his chest exploded and he died. not a nice thing. and its not like it was really strenuous, but was enough.
#23
FastEHHolden
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Posted 12 November 2007 - 11:35 AM
Umm..thats a bummer..you really know how to put a downer on a fun topic.
For hotting up victa's, run a drill bit thru the inlet port, pour bog into the crank case and shave the head.....you won't be able to stop the thing..they go like stink!!
For hotting up victa's, run a drill bit thru the inlet port, pour bog into the crank case and shave the head.....you won't be able to stop the thing..they go like stink!!
#24
orangeLJ
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Posted 12 November 2007 - 12:21 PM
Nahh, just been really fresh in the mind the past few days and that sprung to mind.
We were running our racing fuel in the old victa and it developed a nasty "rattle"
Well hey, they make us sign to say we wont use it in a "road car" they never say anything about a lawn mower!!
i tried acetalyne injection via a baloon full of the stuff on pops old mower..... it worked, but wasnt too good for it i dont think.
We were running our racing fuel in the old victa and it developed a nasty "rattle"
Well hey, they make us sign to say we wont use it in a "road car" they never say anything about a lawn mower!!
i tried acetalyne injection via a baloon full of the stuff on pops old mower..... it worked, but wasnt too good for it i dont think.
#25
LOWS2
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Posted 12 November 2007 - 12:28 PM
Didnt Azza get an old mower and hot it up in 'Members Projects & Plans' a while back??
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