just need to know

[charrington96]

I have a derbi senda 50cc 2 stroke and it seems to be going slower, I used to reach over 50 but now I'm only reaching 40... Its gotten slower as its got colder...
Is it how cold it is as I know 2 strokes are affected by the weather or should I do a compression test
I have just replaced the jet needle as it was knackered and had no circlip from previous owner and it runs 10x smoother
Any ideas?

[Nobby the Bastard]

Colder weather normally means more bang from the engine (cold air is denser than warm air).

You've probably fucked the barrel and piston by caning the tits out of it.

If you hadn't de-restricted it, it would have been fine...
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[charrington96]

I didn't derestrict it, I bought it like it and I dont go out racing around on it

[stirlinggaz]

hi,
do a compression test mate, then post results.
its a 5min job & will tell you a lot.
cheerrs,
GAZ

[charrington96]

Thanks... I know that I'll have to do a top end rebuild if the test is bad...
Won't be done till a while as I have to borrow my uncles

[map]

Could it be carbon build up in exhaust?
____________________
...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Shaft]

[Walloper]

[charrington96]

It is like its just restricted to 40... The power is there but it doesn't get anywhere haha...
How do I know if carbon is built up in the exhaust
I'm 17 and not got quite enough money for a 125 yet

[mysterious_rider]

well compression test it anyway, they are only a few quid. Just over 100psi I think is about right.

It may just need a rebuild.
____________________
KAWASAKIIIII

[charrington96]

Yeah I'm gonna do one just to make sure
I did it with my thumb and there is compression but gonna do a test soon
It doesn't have a problem starting up, starts first time

[c_dug]

If it turns out it needs it rebuilding a 2 stroke is a doddle, if you have the right temperament that is, 17 year old me didn't and made a right mess of refurbishing a TDR250 because of it
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[bikenut]

:D hi dude, all of the above.......

as its a 2 stroke and burns its total loss lub, the exhaust port and exhaust system will "coke up", the black variety rather than powder.

so the exhaust port may be coked up and blocked.....as well as the exhaust system......does the exhaust system gases seem to "fizz" out of the end of the exhaust.....suggesting a blocked system.......blockages will reduce breathing.....but you may have "run out " your engine so do a compression test.
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nuts about bikes

[charrington96]

Thanks I'll have a look while its the weekend... The engine has been blown once before and the top end casing is fried
One problem with the exhaust, its all rusted so I dont wanna snap the bolts...
It is an 11 year old bike now and its done 10k km

[bikenut]

penetrating oil or fluid on those rusty nuts every day ( twice a day ) over a couple of days, then try and undo....or use heat, or split/grind the nuts.....a pic would help.
does the exhaust seem to "fizzzzzzz" as if the gases are fighting there way out??
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nuts about bikes

[charrington96]

I dont really seem to notice, but I can hear the engine more than I used to...
Can hear the piston more

[Walloper]

[charrington96]

I couldnt keep my thumb on it, that's how much compression there is

[c_dug]

You probably want to check it properly anyway, enough to blow a finger off doesn't mean much from a mechanical point of view!
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Nobby the Bastard]

You know how the spark plug is screwed in and there is no screw thread on your thumb?

That's why theres no point testing compression with your thumb...
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[charrington96]

I know but it was to know if it needs urgently rebuilding

[Ichy]

I think you need to check a few bits first before considering a rebuild.

Is the spark plug fitted correctly?

If you block the end of the exhaust does the 'ped keep running or cut out?

Is the air filter clean and fitted correctly?
____________________
https://www.metacafe.com/watch/1972097/how_to_behave_on_a_forum/

[stirlinggaz]

hi,
after compression test, it would be ideal time to de-coke exhaust.

remove whole exhaust off bike & then remove muffler & block up one end of the expansion chamber. (a potato is ideal beleive or not).
then get some caustic soda from b&q,wickes, local hard-ware shop etc.

read the instructions, then read them again

use proper ppe, caustic soda is nasty stuff, good for melting hands etc
once you have the desired amount of mixture, pour it into the spanny, right up to the top. (i should have mentioned this earlier : it works better if one end is blocked & this is at bottom. then just leave it sitting against a wall. overnight preferably.
i then empty out all the crap (& there will be loads of it) & repeat the process.
i know it sounds a bit excessive, but i find the 1st solution loosens off a lot of the gunk & the 2nd solution cleans it out throughly.
i've done it on umpteen 2t exhausts with good results. just dont let it come into contact with alloys,aluminium, skin etc

CAUTION : I take no responibility if op or anyone else for that matter, blinds themselves, burns all the skin from his hands etc

cheers,
GAZ

[Walloper]

[stirlinggaz]

Hi,
personally, i think anyone who owns/rides a 2 stroke SHOULD really own a compression tester.
well worth the 30 odd quid they cost. (i have the gunson kit, which comes with a couple of different sized adaptors)
you can tell a lot by monthly compression tests,
cheers,
GAZ