Do i have enough compression & ID motor

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yzfandy

yzfandy

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Not sure if the compression has gone on my CY motor.

How much should there be or can anyone describe what is enough? For example if i take the pull start off i can turn the the fan/flywheel round and feel compression with a pop sound, but its not exactly the kind of compression i'm used too with nitro motors.

Also how do i identify what motor (cc) i have? Its a CY19106B
 
Look on the side of the head. There will be numbers there that tell what head is on it. The number you gave is a CY serial number.

Compression can be taken with a compression tester. If you don't have one you will not be able to tell by hand.
 
there should be another number like 28-32 on the side of the head hwere it meats the crank case

28 means the crank lenght 28 mm is stock

32 means 32mm piston 23cc

or you can have 30-35

30 means 30 mm crank (+2mm)

and 35 means 35mm piston with a 30mm crank it = 29cc

the second number can be

32 = 23cc

34 = 26cc

35 = 27cc or a 29cc with a 30mm crank

36 = 28.5cc or 30.5cc with a 30mm crank


from my expernice if you asking if my motor has enough compresion to me it means it does not.

there motor needs 3 things to run like any motor

fuel

spark

compression

if the motors getting fuel but will not run it, check spark if its getting spark but will not run its means compression isnt enought to run.

there is a very fine line with these motors from running great to running like crap or not at all,

a good way to tell if the motor runs great when cold then slows down once warm, asuming your tune is ok, it means the engine is worn and is due for a rebuild.
 
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Does the mill start ok? Is it easy to pull the starter? I had problems with my engine ,the compression felt ok but as Benckie said there is a fine line to these things. One member said to put a half teaspoon of two stroke oil down the bore to fire it up,this acts like a piston ring for a few seconds and when you pull the compression is the best there is. Mine fired and ran for a bit but as the oil worn off the engine died. I rebuit the mill with a new headset
and it is running like a dream.
If you are in doubt re-ring it and when you do ,check for scoring aswell.
Good luck.
J.
 
Found 28 on the side of the head so 23cc thanks, that'll make getting a piston ring easier.

Spring has just gone on pull start so cant say really feel what compression is like when it turning fast but last time i tried it didn't take much to get me out of breath.
Reason i suspect compression may be down is it was getting a little reluctant to start but there again the pull start was nearing its end and would only engage halfway through the pull not giving too much in the way of cycles to get gases flowing.

Other reason was its always seemed a little boggy down the low end. Its got a samba pipe on it but wont spin its wheels up, or really get going until a good ten foot. After that i'm being chased away by the grounds keeper for all the tyre tracks in his park.

Here's an old video of what i mean about the boggyness. Bear in mind that it was winter at the time and the ground very wet and slippery otherwise in the dry wheelsping would be near non-existent from pulling away.

http://www.youtube.com/watch?v=aRYdrHQHEDU
 
This is another thing i should have mentioned but the low speed needle didn't seem to do much. It seemed like there was no change to the performance until it was obviously too lean.
I got this of a mate who bought it years back, put about 4 litres through it then it sat in his shed for 2 years. Got a feeling carb may have gummed up so striped that now and rebuilt it.

I'm from a nitro motor back ground but from what i can tell this carb works more like a "real" carburettor, as in its the low speed needle (pilot jet) that needs tuning first? Also reset both jets/screws to 1.1/4 turns each, is that right?
 
After the carb rebuild go back to factory settings and start over on tuning.if it will not tune that might be a sign of a bigger problem. one guy on the 5B forum had to run his LSN about three turns out to get it to run and I think turns out he had a ring problem.
 
I'll go with Hotel on this one, I've just put new heads and rings on all three of my FG's and a new ring in my MCD and they fire straight away and run like new ( flintshire fg.....youtube)
Just re-ring it and shove a new head gasket on (check the bore first for deep scoring) You can get a carb build kit from DDM for buttons and if I were you go for a alloy inlet manifold with TEFLON gaskets to eliminate air leaks,that should do the trick.
Good luck.
J.
 
sounds liike carb issuse, these carbs will not make any difrence once you go past two turns out, any more will not do a thing.

rebuild the carb if you can, they are a tricky bit of gear, i normaly will sugest buying a new 668 carb over a rebuild kit, as there is some things you can stuff up realy easy on the carb rebuild.

if the engines isnt running on 1.5 high and 1 1/4 low theres a problem, with some thing, some times clone carbs are not revery tunible, and some times they block up with crap, and no matter how much you move the needles it will not affect tune, this is a good time to buy a new carb, or rebuild if your confident, but i would sugest rebuilding a clone carb
 
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