derbi senda slow exhaust

[davthegreat]

i have a derbi senda sm xtreme 2005 , i had the normal exhaust on de-restricted and it went about 50-55 and ran fine, ive put a gianelli race exhaust on it and now its slower and even reving right up in 1st and 2nd will only reach like 20mph or a bit more, the performance is decreased and is slower than it was with the original exhaust what do i do, thanks

[mattsprattuk]

change the jetting...
or, just put the old one back on. you hear a lot about people getting better performance from stock than this aftermarket shit
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[rotax81]

you will have to up the main jet. also play about with the needle height until its right.
leave the airbox as standard though as setting up is a lot easier.

try upping the main jet about 15% in size
i.e. if its an 80 main jet, try a 100.
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ZX636C6F road. ZX636C1H track. ZX7R redundant. ZX0.5R minimoto as ornament.
Audi A4 Avant 1.9TDi and VW Transporter 2.5TDi 888 Special (no mot and tax lol)

[stevo as b4]

It's easier to sort out if you had before and after dyno runs with the AFR plotted, so that you can see what effect on fueling if any and where in the rev range that it is effecting it with the race pipe fitted. A decent high performance aftermarket pipe will normally give some gains somewhere, but you will lose somewhere as well. I suspect that the new pipe has sent your jetting home, and that you probably need to upjet for the new pipe.

Presumably you have checked that the new pipe is not restricted, as some aftermarket exhaust manufacturers make E approved versions of their pipes, which do have a restrictor fitted as supplied. You should also make sure that there are no leaks between the pipe and the engine, and pipe-silencer joints, as gas leaks here could make a pipe useless from a performance point of view.

[Ariel Badger]

[davthegreat]

right tomos im gonna look if it is a restricted exhaust, because before i put it on i looked down the end of the pipe and presumed it wasnt restricted, but it is E marked so im gonna have another look to make sure since it goes exactly 30mph- 32mph thats what i think it is so ill check for a washer tomos

as for up jetting if it is a washer which ill bang out tomos does it still need up jetting and what will it run like if i dont upjet it

what do you mean about the needle height are you referring about the mix control on the carb or....

and i have also checked for leaks allover the pipe and its fine, no leaks##

thanks for the help ppl : update tomorrow

[Hutchysrs50]

aslong as you get the jetting right, it will run great

when he says change the needle hight, he means the needle inside the carb, its attached to the throttle cable..

if you follow the throttle cable down onto the carb, there will be 1 screw on the top just infront of the cable, unscrew that, take the slider out and you will see a needle in the middle sticking out the bottem of the slider, there will be a circlip with a choice of 5 differnt slots i think, move it up and down untill you think its at its best.

hope this helps.
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Gilera SC 125 - Current

[davthegreat]

right update

i took the exhaust of today and took out the stupid washer that i didnt expect to be on a after market pipe and it runs alot better set of is well better and runs like it should do hence soved the problem. But only does 50mph still as it did with the stock pipe, but 50mph is in 5th gear and theres a 6th if you shift from 5 to 6 you lose power and decrease speed even if its proper in the right rev range is this to do with jetting, will it go faster (top end) if i jet it right

and does any one have any idea what the original jet is and what to change it to (2005 derbi senda sm xtreme)

15% increase still ok?

and thanks so much for your help

[Hutchysrs50]

stock jet will be 88 i think.

im running the same carb and engine as you, also with a sports pipe.

i have a size 110 jet, but its too big, i would advice getting a jet around 96 - 102

also... 6th gear isnt really a gear to be picking up speed in, its more just to bring the revs down if your just cruzing along. i have a K&N style air filter and a 13t sprocket and mine will go over 50mph no problem.

you got any other modifications fitted?
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Gilera SC 125 - Current

[davthegreat]

ok fair enough ill have to up jet it soon

mine wont go above 50mph for some reason even with a sports pipe is that normal and also my bro said it might have a restricted CDI thats why it wont go above 50

and nah i dont have any other mods atm wanting to get a k&N air filter soon thou

[Hutchysrs50]

yeh like you said, it could be restricted in more than one way.

the air filter probly isnt a good idea, as most people would tell you not to get one, and afew people have problems with idleing ect..

but mines fine anyway..

as for 50mph being normal, most people say 50mph for a 50cc is good... but all my friends with geared bikes and twist and go scooters, most off them get around 55mph, some with good mods will push 60 - 65

the best way to get your top speed up is the sprocket, and there only a couple of quid, you will probly be running with a 12t front sprocket, if you really wona get a faster top end get a 15t front,
but the bigger the front sprocket you get, the slower acceleration you will get, im getting a 14t sprocket next time tho.
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Gilera SC 125 - Current

[davthegreat]

i see, ok

do you know how you tell if your CDI is restricted or not

and ive seen about sprockets where you gain power in one area and lose it in another area, therefor thinking about sprocket change in the near future

do i actually need to upjet if ive just put a sports exhaust on, and what does it do (effect) with a bigger jet

thanks for the help

[Hutchysrs50]

to be honest i dont know how to check, but... iv seen a few people say they have changed the fuses... dont know if that means anything to you or not..

as for the sprockets i THINK they go from size 12t to 15t... i have a 13t on now, which has put my top speed up.. but like i said befor im getting a 14t next time, since you ride the same bike as me, you will know soon as the bike bits 7k revs, they go alot quicker anyway, and in first gear... it hits 7k no problem. so acceleration isnt much of a problem.

you dont need to upjet... but having a stock jet is kinda another way of restricting your bike.. slowing the petrol flow down making the bike slower, the effects should be your bike revs better higher and quiker, and smiliar in speed.
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Gilera SC 125 - Current

[davthegreat]

ok right thanks for all the help

ill have to see about upjetting and sprockets so anyways thanks for the help

[davthegreat]

ow yeah forgot to say what does moving the needle hight actually do then

[Hutchysrs50]

from what i know it makes the petrol to 2stroke mixture weeker and stronger depending on where you put it.

it does make a big differnt to the bikes performance as i found out.

if your gona be changing it and taking it for a big ride... just dont, go along your street and back
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Gilera SC 125 - Current

[davthegreat]

ok thanks

[tutton]

You do need to rejet when modifying anything that lets the bike breathe better on a 2stroke unless your looking to run your bike lean and make it overheat (think it might pop a head gasket if you do a good job on it )
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Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30

[davthegreat]

ok fair enough

[davthegreat]

xps guy ive seen you commenting on other posts you seem to know your stuff is my CDI restricted and should i get a new one

[tutton]

I thought 05 sendas were cdi restricted... my mates drd was...
but if your bikes doing 50 it may well not be,
id upjet and see where you are from there, as it only cost a few quid to upjet, then work from there onwards..
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Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30

[davthegreat]

ok good advise

what are you thinking up 2 or 4 sizes or???

someone said increase jet size by 15%???

[tutton]

Id go by the 15%.
personally.
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Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30

[davthegreat]

ok thanks

will i know if its too big or still too small when i get it on

[tutton]

Too big will mean the bike will bog down whilst on the throttle, will feel like its just loosing power.

What most people do when upjetting is do plug chops, go for a ride, take plug out,
If its a nice choclate brown - its running good fuel to air mix
If its black and sooty - over fueling or over oiling
If its got white bits on it - its running lean/ too hot.

Post pics of the plug when you take it out and bcf will help deciede
____________________
Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30