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Hi guys,

Need your help again!! my bikes sick and i really can't work this out. Up until a few weeks ago its been great, aside from the petcock blocking up. so i decided when i got paid i'd treat it to a few mods, namely a proper CNC stack instead of the plastic one i had, a rocket key and a lightened flywheel, new plug, 0.65 and .70 jets to set it up right, the petcock mod with and inline fuel tap, and tapered carb needle with clip moved to the second notch. On stripping the pull start off to do the rocket key/flywheel i found the magnets on my stock flywheel were quite rusty - great i thought, it should run even better than i expected! i put all the bits on but didn't touch the coil as i didnt want to disturb the timing... however on going to test it i couldnt get it running at all, so i came on here and posted my problem, and the most common cause was suspected to be timing (the rocket key is definately in the right place - step facing the front of the bike) so i used the business card trick and reset the timing, after which the bike started allbeit with a few good pulls but i was happy and ready to see how it went with the new mods!

Unfortunely it's actually worse! the big issue is that just as you get to that point in the revs when two strokes make their power and get going it feels like its hit a wall, it tries to pull through sometimes giving a burst of power for half a second or so, but thats it, it doesnt accelerate, just stays at that speed sounding rough. You can also here it at idle, it just doesnt sound like a engine running nicely, with slight pops and bangs as it idles.

So far i've tried the following- refitted the old flywheel (not the original key as i can't find it!) removed the rocket key and refitted with a dab of locktite, redid the timing, changed the reedblock - i have carbon reeds and the orginal metal ones, tried both my carbs - both are immaculate, with the whole range of jets i have as felt it may be a fueling issue, checked my fuel supply system, inline fuel shut off/petcock mod, lines - i run freeline kart fuel line, changed plugs, removed the exhaust wadding, and nothing has helped..

I've sort of convinced myself it has to be timing related at thats the major thing thats been altered but then i'm not sure as it was going well before with that rust on the magnets so clearly the coil is putting out a manly enough spark! and with clean surfaces i'd of thought it should be having an even easier time.. i'm also sure its harder to start at the mo although it could be differcult before.

I just don't know what else to do other than to replace the coil, do you guys think this is the next best step? i've taken some pictures to stop you all from falling alseep at this point.. (everyone loves a picture thread!) anyone see anything of concern?

I'm a pretty patient person but am getting to the point of giving up and buying a stock engine, the thing is i have a decent amount of time invested in this engine as well as a few quid with the mods so would like to see it through, and replacing it will only be a further outlay, btw i'm aware the clutch/flywheel centre bolts are missing in the pics.

barrel;





piston - not looking too good?!





timing






cases/crank

 

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First of all looking at that dome and piston top its no wonder youre not making any power....Carbon build-up robs power in 2 smokers

On the flywheel pic it seems its closer than .020"....Too close is almost as bad as too far away.........

How did you have the head mounted.......With or without the base gasket?

When I mod my engines I replace my coils so the topend is totally refreshed and ready for action..

Do you have the stock exhaust? Did you mod it?

When you installed the reeds you just snugged them and secured them with a dab of loctite......Right?.......If you cranked down on them you most likely warperd the petals and theyre not sealing right

Did you do the reedstop mod?
 

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You have a 40cc engine, they call it 47c, clean it up and new rings. Or put a 49cc top end kit on it. Daves out of them now. I have 4 or 5 kits, I ended up with, somehow.
 

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Discussion Starter #4
Morning guys,

EPR i thought it was probably a 40cc, thanks for confirming! Thats another plus point to buying a new 49cc stock motor, least i'd know i had a decent base.

Cam, i thought the piston/head looked pretty built up!! What would you use to remove this? i did it on my kart using wire wool and metal polish but the head is separate from the barrel on that engine so easy to access.

Interesting note on the timing, i assumed it would either run or not run though, could it be if its too close it would promote poor running instead of just not running at all? i think it maybe an idea to get some gauges on a few buisness cards until i find 0.20, maybe mines too thin!

The head is mounted with the gasket, i thought i remember reading losing the base gasket on a stock motor could make it worse? or should i be looking to refit with sealant only?

I think a new coil is a good idea then regardless..

I have a stock lucky 7 exhaust currently.

I bought my carbon reeds from a shop over here pre-fitted to a reed block so not sure exactly how tight they've been done up, although the reed block they came attached to is noticeably worse quality that my original so i tried to swap them over but one of the bolts rounded, so fairly tight! I'm not convinced they seal properly so have gone back to my stock metal reeds as at least i know they are right. i haven't modded the reed block.
 

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Discussion Starter #5
Looks like a new 49cc engine might be too tempting to ignore.

another problem though, which one to get! i'm looking at a stock 49cc engine with a metal pull start and decent clutch bell - comes with everything and should make a decent upgrade over my 40cc as well as reliable...

link

Mini Moto Quad Dirt Bike 49cc NEW ENGINE Minimoto | eBay UK

However, the same company offer this engine for just £5 more.. it looks too good to turn down going by the spec!! but then i've always been told that if it looks too good to be true it probably is...

link (i know it says item no longer avail but keep scrolling down)

Mini Moto 49cc RACING ENGINE Dirtbike Quad Cag 47cc on eBay (end time 02-Jun-11 10:26:50 BST)

which would you go for??

i also think i've found the modded stock exhaust pre-done for sale, note the belly in the expansion chamber and the shorter front pipe

Mini Moto EXHAUST 47cc 49cc Air Cooled on eBay (end time 12-Jun-11 15:21:53 BST)
 

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Hey, I would go to hkmotos, direct in Hong Kong, they ship international, and there cheaper than hk motos England. They have a Kit for $69 with alloy 2pc head and 44mm, 49cc cylinder, w/ 12mm FC crank, 12mm triangle ported piston. I put my Blue Head Alloy on my stock crank and twisted it. My Blue Demon engine, eats China parts for breakfast. I milled the cyld down about .060" had to grind the top of the piston down & run 2, .020" copper base gaskets, & one head gasket to clear the head.
 

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Morning guys,

EPR i thought it was probably a 40cc, thanks for confirming! Thats another plus point to buying a new 49cc stock motor, least i'd know i had a decent base.

Cam, i thought the piston/head looked pretty built up!! What would you use to remove this? i did it on my kart using wire wool and metal polish but the head is separate from the barrel on that engine so easy to access.

Interesting note on the timing, i assumed it would either run or not run though, could it be if its too close it would promote poor running instead of just not running at all? i think it maybe an idea to get some gauges on a few buisness cards until i find 0.20, maybe mines too thin!

The head is mounted with the gasket, i thought i remember reading losing the base gasket on a stock motor could make it worse? or should i be looking to refit with sealant only?

I think a new coil is a good idea then regardless..

I have a stock lucky 7 exhaust currently.

I bought my carbon reeds from a shop over here pre-fitted to a reed block so not sure exactly how tight they've been done up, although the reed block they came attached to is noticeably worse quality that my original so i tried to swap them over but one of the bolts rounded, so fairly tight! I'm not convinced they seal properly so have gone back to my stock metal reeds as at least i know they are right. i haven't modded the reed block.
Losing the basdegasket does make it run no better than it was but thats where I asked for a reason....the reason is because the exhaust port must be raised to compensate to actually build power and make the mod worth doing...........

The new business cards arent .020"...they are .010" therefore it must be doubled up and not getting set using the folded edge...set the coil from the non-folded edge.........

To remove the heavy carbon build-up I would use either gum cutter or carb cleaner and a stiff brush............

This engine was mega abused and the piston isnt hardly as carbon fouled as yours.........

Long-Live Maxxim Castor 929...!!!!!!!!!!!
 

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♠ ŧŋƸ ƀⱥđ &#
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Boosted306 stage3. Nuff said
 

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♠ ŧŋƸ ƀⱥđ &#
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thats awesome
 

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The only thing that motor needs is a big red coil wire Epr. Im kinda shocked. I figured that would be done on your motors. Lol. Very nice though.
 

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I am glad you brought that plug wire thing, not one of my engine have good wires yet. Got to get on it. I have a 9" piece of Accell 9mm racing plug wire I had left over from the Kawa drag bike, its kind of thick. Have to go to an Auto Store and look at some wires & silicon plug caps.
 

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The only thing that motor needs is a big red coil wire Epr. Im kinda shocked. I figured that would be done on your motors. Lol. Very nice though.

Something kinda like whats on my Polini engine?........lol...I also have the same type on my twin engine project.......




 
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