Sym jet 50cc Losing power after de ristricted?

[Ben Whitcher]

Hi Guys

I'm looking for some wiz infomation basically ive had this Sym jet 50cc Basix sat in my garden for a while waiting for me to turn 16, so the other day i tried to get it started again took a while and finally after bang's it started. That night i took it out and did 30mph on it with the restrictions on from what i know (exhaust breather pipe) so after this i would like to get it to 40mph + so my father cut of the breather pipe tonight and welded the hole close we then put the bike onto its side and re fitted the exhaust ( i was still holding it though) after this i hit the kickstart and it took a while to start then it started but sounded as if it was dying, so i took it out for a drive quickly and realised as soon as u give it some throttle it pops and feels like the power has gone (but hang on a minute i de restricted it, so i'm a bit confused :S) so basically i brought it back to the house and my dad went on it and from hearing it go up the road it sounds like something is blocking the exhaust or somewhere is loosing power badly as its got nothing now!!!

Sorry its such a long paragraph but some help would be great.

Regards

Ben

[yen_powell]

What breather pipe did you cut off and weld up??
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Blackmail is a nasty word........but not as nasty as phlegm!
XT1200Z and a DR350 in bits

[Hutchysrs50]

[Ben Whitcher]

Hi,

Thanks for quick responce the standard exhaust has a black breather pipe that comes of and out of the exhaust and then back in, Hope this answers it.,

Update: just been on the bike and when i full thorttle it it jumps like the revs go up and down likes its jumping basically and thats where i presume its loosing power also i took out spart plug and cleaned it and it made a bit of differnece but sadly i think i crossed threaded the first 2 parts which im not happy about as it wouldnt go in.

[Hutchysrs50]

[Ben Whitcher]

Hi,

Are you saying the washers are inside the silencer part of the exhaust as tonight we of course cut the breather pipe off and looked around the exhaust for washers but there wasnt any, and most people say around the web that these bikes dont have them ??? so..

Furthermore i think my dad sorted the spark plug out thankgod but the jumping is what we are banging are heads together about as when we used the bike before restrictor pipe removed we had nothing like this jsut a slow bike then when it was removed the thorttle twists more but on the part of it twisting more (giving more power than before breather pipe was removed) it jumps.

[Hutchysrs50]

[Ben Whitcher]

Ok Well ill tell my father also could it be when we got told to take off the variator and remove the washers (that arent on these bikes) the rollers fell out but i dont think that is going to affect the preformance as it wasnt doing it before we cut of the pipe, furthermore people were saying around the web that it could be where we had the bike on its side the spark plug cable has come loose or something like this :s

[c_dug]

I could be all sorts, when you say jumping is it...

A) starting at 7k rpm and jumping to 9k rpm randomly

or

B) starting at 7k rpm an cutting to 5k rpm randomly?

Numbers are randomly chosen but if it is randomly rising i would expect it to be something slipping, i.e. drive belt slipping.

If it is randomly dropping to me it would suggest something electrical like as suggested a loose sparkplug cap.

To be honest with what you have told us so far it could be alot of things.

c_dug
c
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Ben Whitcher]

Hi, Well i dont have a rev limiter unfortuently but the bike revs to nearly full power then the extra bit i quess what gets me to 40mph is reving higher then dropping, reving higher then dropping, there is no constent rev which is therefore giving me less power from the bike.

[Ben Whitcher]

Update : Today going to buy new spark plug as this one is 4 years old and maybe whats causing the problem but still could do with some expert help to give me tips on what i could check on my bike?

Thanks

[yuri2085]

Maybe i am mistaken but welding closed a hole which is used for 'breathing' isnt going to increase power?

Or does the hole somehow reduce breathing?

[Ben Whitcher]

Think about it a breather pipe is used to take away power, so if i remove it like lots of people have done instead of buying sports exhaust it will give me more power as im taking away the restriction.

But my dad welded it nicely and shut so no air or exhaust gas is going to get out that would decrease the power its got to be something else, and i need somone to tell me what basically. But no1 seems to know

[ToGGoT]

Struggling to figure exactly where you cut without pics of the exhaust.

This https://www.bikechatforums.com/viewtopic.php?t=123858#1522539 ?

ToGGoT
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2005 BMW R1150R

[Ben Whitcher]

Wait ill take a picture for you and post it up on here.

Hi the picture uve got there i havent cut of that part it was a another piper running of the side of my exhaust pipe which i presumed is a breather pipe to restrict preformance ill try to get a picture but due to it being chopped off it might be quite hard,

Link to Pictures = https://www.2shared.com/uploadCompleteFlash.jsp?sId=DdYcFcqha5Ph3G7F

[Ben Whitcher]

? Anyway seen where ive gone wrong ?

[c_dug]

I just want to point out before you read this post that im not a scooter mechanic, im just applying common sence and what little mechanics i know.

Link isn't working, im pretty sure i have seen the pipe your talking about on a gilera runner when i was younger, think my friend closed his one up too so i don't /think/ that is the problem, that is going back more than three years now so i may be wrong.

Just so you know im not a scooter expert by any means so this could be wrong but this:

[The Artist]

Link isn't working.

Upload them to here or photobucket or something. I doubt it is a breather pipe. It is probably a pipe that just disrupts the exhaust waves, I forget what they are called but you cut it off and weld the hole shut. My moped had one.

Once this is done, you usually need to re jet the carb and remove the restricting washer from the variator assemble.

There are lots of guides on how to do this all over the internet.

Where abouts are you located?

[Ben Whitcher]

Positive stuff thanks im located in winchester/hampshire we havent got round to stripping the carb yet after 4 years of not being done (this bike has been sat for 4 years in my garden untill the other day) when i started it up, also there is no washers in the variator on these bikes so finding the restrictors is even more difficult.

Lastly i understand you guys saying about being 16 (which i am today) but 30mph isnt enough when i basically live in he countryside, around town thats fine but ive got hills all around me and speed makes a difference.

Keep the posts coming guys still not got a solution.

[Ben Whitcher]

ok pictures uploaded to Photobucket dont know which link it is so will post most.

Link = https://s262.photobucket.com/albums/ii90/MadMan_065/
https://i262.photobucket.com/albums/ii90/MadMan_065/jacket024.jpg
https://i262.photobucket.com/albums/ii90/MadMan_065/jacket025.jpg
https://i262.photobucket.com/albums/ii90/MadMan_065/jacket026.jpg

All links to the 3 pictures.

[The Artist]

Looks like a wave disrupter thing I was talking about before.

You will need to re jet the carb to make this work properly. Go up about 5 but buy a few so you can play with them to see which works best.

e.g. if it is size 60, buy a 63, 65, 67, 68 and try them all

[Ben Whitcher]

Ok do u mind putting it in simple form, ha ha so i need to take carb out clean it (jets etc) and it should be fine and then replace the jets but where can i get these from and how will i know what size ?

[The Artist]

Ok, remove the carb.
undo the float bowl (usually 4 screws) on the bottom of the carb.
Then in the middle will be a brass circular thing. Quite small. Looks like these but usually brass
https://www.scooterparts4less.com/web_gas/4stroke_carb_jets_logo.jpg
It will have a number on it. Unscrew it with a flat head screwdriver.

More can be purchased online https://www.adrenalin-pedstop.co.uk/cp-JETS__CARB_PARTS-4827.aspx

Be careful not to lose any small parts and don't scratch anything with your screwdriver.

[c_dug]

Edit: Beaten to it

In very simple terms...

Because you have removed the restricton in the pipe the engine can now flow fuel and air more freely, the carb as standard is only set up to let a certain amount of fuel through at full throttle, you need to compensate for the de-restricted pipe changine the current main jet for a bigger one.

Allymoss might be able to clarify on this bit but i think if you remove the jet it should have a little number ingraved on the side of it? Anyway when you have found out the size of the original a bike garage should be able to order you some bigger jets

Im going to take a guess that the bike wasnt drained of petrol before it was left to stand, if so it is well worth cleaning it out as the petrol will have solidified. Be careful when dismanteling the carb because the screws are made from a soft metal, make sure you are using the right size screw driver!

c_dug
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Ben Whitcher]

Excellent guys, most people of said about the fuel it had a full tank to my suprise when i got it running again i think its nearly ran out but i topped it up with fresh fuel so as soon the shitty fuel gets used it should run ok ? i quess and furthermore do i have to buy new jets or is there any way around this problem ?