eccsmk
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| posted on 14/12/07 at 10:12 PM |
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kind of engine related question
does anyone know anything about 49cc moped tuning its for my very slow sfera pit bike
many thanks in advance folks
[Edited on 14/12/07 by eccsmk]
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lsdweb
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| posted on 14/12/07 at 10:37 PM |
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Put a car engine in.... :-)
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DavidM
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| posted on 14/12/07 at 10:52 PM |
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quote:
Originally posted by lsdweb
Put a car engine in.... :-)
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iank
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| posted on 14/12/07 at 11:22 PM |
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When I was a kid there was supposed to be one in the area with a 600cc racing sidecar engine (putting power down through a mini wheel/tyre).
On a slightly more sensible note moped engines seem to be equipped with exhausts with 10mm outlets so I'd expect breathing could be improved for
a start (air filter, carb, inlet/exhaust manifold and silencer).
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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balidey
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| posted on 15/12/07 at 12:03 AM |
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Me, I know a bit, as i have been know to race a 50cc moped or two over the past few years.
So, to tune it up you need to do the following. Get the Mallosi catalogue, ring up your local dealer and order one of everything. When they turn up,
fit them all. Done
Seriously though. Step one. De-restrict it. Either (or both) is an additional resonator tube on the exhaust, cut it off and weld up the hole. You may
also have a restrictor washer in the variator. Usually a simple case of removing it.
Secondly, you can ditch the stock exhaust. FOr about £50 to £80 a proper race exhaust WILL make a world of difference. Lighter rollers will be needed,
and these are usually supplied with the exhaust.
Where next? Well, you can get race variators and adjustable clutches too.
Kevlar belt will stop it snapping.
Race barrel, head, piston. About £100 ish for all them in a kit. Again, a very worthwhile mod, but the cheap way is.....
Remove head, remove barrel. Machine about 1mm off the top of the barrel. Dremel the top of the exhaust ports, evenly, about 0.5mm. Re-fit with only
the top piston ring.
Obviously there is a lot of theory you need to understand when doing this barrel work to a 2 stroke, but for a bit of instant 'go' the
above should be fine.
You may need to run with a bit more oil in the pre-mix and maybe a dash of pro-boost to up the octane as you will have uped the CR too.
Working on 2 strokes is fun
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balidey
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| posted on 15/12/07 at 12:08 AM |
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Some pics of me and also Paradoxia0 on here....
http://www.scarabis.com/WitteringPedRace4.8.7a.html
When we did the 6 hour moped mayhem endurance races.
For some reason Mark now prefers 4.2 litre Rover V8's than our 50cc peds
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skodaman
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| posted on 15/12/07 at 12:23 AM |
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Even cheaper we used to junk the head gasket and lap the head on with valve grinding paste and golden hermetite. That raises the cr. You can fit
more base gaskets to raise the exhaust port instead of filing it but this lowers the comp ratio again. Raising the exhaust port gives more power at
high revs but don't overdo it. Lots of fun to be had tuning two strokes. If it's an auto though I don't suppose u want it too
peaky. As above one piston ring reduces drag.IMHO removing baffles etc. just loses what little low down power these engines have though a proper
expansion chamber will help and sounds good as well. Use a good oil and don't use pattern pistons cos they hole rather too easily. Also keep
your ignition timing right or again u'll get holed pistons.
Wow writing this reminds me of my youth. 55mph down a big hill on an AP50 them wert'days.
Skodaman
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Mansfield
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| posted on 15/12/07 at 01:03 AM |
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Oh Skodaman, that brings it all back, they were great days.
In addition to your cheap tuning mods I recall trimming disc valves and bending reed stops on engines of this size. A bigger carb can be bought very
cheaply.
Some of my less sucessful mods were bacofoil stuffed above the gudgeon pin to decrease crankcase volume and a forced induction system using a
'Pifco' type cig lighter powered hair dryer.
They were great days.
[Edited on 15/12/07 by Mansfield]
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onzarob
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| posted on 15/12/07 at 10:21 AM |
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you'll all be talking about tuning model airplane engines next LOL
...good reading, I wasn't allowed a moped
[Edited on 15-12-2007 by onzarob]
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eccsmk
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| posted on 15/12/07 at 02:20 PM |
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some very good and some very interesting replies guys thanks
so far it's de-restricted the old 12mm carb has been swapped for a 17.5mm version and has a doppler exhaust
we also have a gillera stalker with a 70cc kit here but my little bro wont let me near it as it will!! power wheelie which is quite an experience on a
rev and go ped
[Edited on 15/12/07 by eccsmk]
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MikeRJ
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| posted on 15/12/07 at 03:22 PM |
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quote:
Originally posted by skodaman
Even cheaper we used to junk the head gasket and lap the head on with valve grinding paste and golden hermetite.
Ii also works well on the old side valve Briggs and Strattons
quote:
You can fit more base gaskets to raise the exhaust port instead of filing it but this lowers the comp ratio again.
And it also raises the transfer ports.
Two stroke tuning is a lot of fun, amazing what a few hours with a rifler file can do!
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eccsmk
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| posted on 15/12/07 at 03:59 PM |
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as i dont have much knowledge of two stroke tuning etc can someone post a link of a site where i can gain some knowledge please
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Confused but excited.
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| posted on 15/12/07 at 04:25 PM |
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Don't forget to pad out the crankcase as this will raise the primary compression rato.
Tuning two strokes isn't the science it is for four strokes, it's more of a black art.
I did two identical engines (well as identical as I could measure), back in the day.
Both had the same top end speed, but one would accelerate like hell and the other took a fortnight.
Tell them about the bent treacle edges!
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eccsmk
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| posted on 15/12/07 at 04:56 PM |
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got a 50cc barrel and a dremel ooh deer what will it turn out like?
i can always put the old stuff back if this goes wrong
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balidey
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| posted on 15/12/07 at 06:53 PM |
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Easiest steps are raise the exhaust ports (approx .5mm at a time) and increase the CR by taking material off the top of the barrel, you can usually
take 1mm off with no worries.
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eccsmk
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| posted on 15/12/07 at 07:17 PM |
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thank you been told to not do too much to the top of the ports more to the sides of them i'll keep going and see what works
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eccsmk
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| posted on 16/12/07 at 10:45 AM |
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so far i've made the exhaust port larger skimmed the barrel and head and removed the bottom ring. revs like a loon pain to start now tho.
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Uphill Racer
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| posted on 16/12/07 at 11:15 PM |
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Bloody ell, all our yesterdays. Well............in my yoof when I was tuning a 250cc Ariel Arrow (padded crankcase modded transfer and exhaust ports
ect top speed up by 20mph. Now try to do that today with a file and 3/8 leccy drill on a modern engine). Ok, well it worked, all that extra power
produced more heat............yep, it sised siesed seized siezed......melted pistons...lol.
Took the barrels to be rebored to a shop in Walthamstow (London) that used to race Ducati's (1962). Well I got chating to the old guy behind the
counter who was a race engineer that gave me this gem. In my yoof we used to race a Scott Squirrel (600cc 2 stroke twin circa 1930's) and to
stop it seizing we left the barrels outside to rust. This left tiny pinholes that held oil. Under the rings on the pistons a hacksaw was used to cut
grooves around it. Then another set of grooves below between the grooves above. This lifted oil up the barrel. The pinholes in the bores held the oil.
Result, the fastest 250 on the A127, or it was untill Suzuki shiped over the super 6  .........now........where did I leave the
Tardis........
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eccsmk
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| posted on 26/12/07 at 02:58 PM |
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well so far i have a really high revving engine thats as quick as another moped we have with a 70cc kit on it!!
although the first attempt didn't go well it let the circlip go (which holds gudgeon pin in place) then proceeded to smash the piston ring which
wedged the crank to a stop oops.
i do hold my hands up to that tho as i fitted the clip.
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