I NEED HELP! - running 5km/h MAX

[mack_t]

hey guys...i have a problem. i just installed my 70cc cylinder, metrakit pipe and a 21mm carb. it starts and idles fine. however when i accelerate, it goes SLOW...about 5km/h for a few feet and shuts off/dies.

could it be the mixture screw on the carb?

i have not installed the roller weights as i cant get to the variator (cant unbolt the bolt) nor have i installed carbon fibre reeds.

anyone know whats wrong with it?

btw...i had the stock carb before and it ran about 60km/h.

[XPS1210]

you got fuel going into the carb?

Is it bogging or does it simply just die out?

bogging would lead me to look at the rollers and springs in the tranny.... simply dying out would make me think fuel supply...

then there is always the issue of did you hook the carb up right and/or is there air leaks causing it to be really lean...?

[mack_t]

how do i check if fuel is getting to the carb? the gas tube is black. do i have to do something to let the fuel flow.

my carb should be hooked up right. all tubes are connected and everything else is connected.

as for the rollers, i think i'm going to purchase the variator locking tool or is there another way?

i will play around with the carb/mixture screw some more and see what happens.

one more question....can i still run my 17.5 stock carb with this setup?

[XPS1210]

pull the fuel line off the carb, there should be a small amount of fuel that will come out...

then it should stop after about 10 seconds...

crank the motor... with the fuel line off, the vacuum should cause the petcock to open and allow fuel to flow freely... Have a gas can handy... to catch the fuel.

[mack_t]

thanks jared...i did what you told me and it seems like my carb is getting fuel and the bottom of the carb is also filled with fuel so i'm guessing the fuel is not the problem.

i wonder what else could be causing this super slow ride.....i put my stock 17.5 carb back for now...it runs about 60-70km/h

[Zuma-Zuma]

What jets are you running in the 21? What airbox? Needle position?

If it runs with the other carb, its the new carb giving problems. Since its off, check the needle/seat inlet for blockage. I'm guessing its just an imbalance of fuel and air.

The other thing is try and run it on the stand. If it rev's under no load, your'e close on the adjustments.

[mack_t]

What jets are you running in the 21? What airbox? Needle position?

If it runs with the other carb, its the new carb giving problems. Since its off, check the needle/seat inlet for blockage. I'm guessing its just an imbalance of fuel and air.

The other thing is try and run it on the stand. If it rev's under no load, your'e close on the adjustments.

the main jet is 92. stock airbox and the needle position is at 2 from the top. my carb also included a 105 jet that i havent tried.

i dont think theres any blockage - will not from the needle anyways.

i tried running it on the stand, same thing...it rev's, wheel spining but it doesnt seem that fast and then it dies.

[florida derbi rocket]

What brand carb is that 21mm?..it sounds like you might need to Down jet a couple sizes..92 main on a 21mm carb flows a good amount of fuel...On your 17.5 you would be running a 90-120 main..Your airbox is stock?..try taking the cover off and see how it runs. you might need to drill holes. Edit..I don't recall ANY Derbi owners on here with a 21mm..I could be wrong.

[mack_t]

its a metrakit Dellorto 21mm. i forgot the jet size on my stock carb - someone told me it was 60?. i have drilled 2 tiny wholes when i installed the 21mm carb...about half a cm each. it might be too small though.

anybody know where i can buy jets for my stock AND 21mm carb? apprently they are different sizes. the stock jets are bigger than my 21mm jets so they dont fit.
someone said i can use Mikuni jets? how do i know what size will fit?

[florida derbi rocket]

Dellortos use 6mm and 5mm main jets. Can't use Mikuni jets

[XPS1210]

still sounds like fuel...

maybe your bogging from to much fuel... when you twist the throttle does it "blaa....." and that's it?

[new scooter fan]

well i am working on tuning the same parts but decided to try with the stock carb i jetted up to 87 main jet and it was running well but the bottom end wasn't that crisp but top end was about 65mph on my speedo.Then i tried a 95 main and an open eliment filter and it bogged and would never get going.Just wondering if a 17.7mm carb is big enough or if i should get a 19mm.

[mack_t]

well i am working on tuning the same parts but decided to try with the stock carb i jetted up to 87 main jet and it was running well but the bottom end wasn't that crisp but top end was about 65mph on my speedo.Then i tried a 95 main and an open eliment filter and it bogged and would never get going.Just wondering if a 17.7mm carb is big enough or if i should get a 19mm.


ok...so it sounds like theres too much fuel. i guess i'll down size the main jet to like 87 or something? any suggestions on jet sizes?

btw....would 1.5 mm make a difference? (17.5mm vs 19mm)

edit: i found out my stock carb has 80 main jet and it runs 60-70km/h - so if i find a bigger jet like new scooter fan, it should be fine right?

[mack_t]

ok...so i just tried to balance the fuel and air by taking out the stock airbox. it wouldnt even start.

so back to the stock carb for me....hopefully it doesnt seize my engine.

[mack_t]

i just went for a test run with my stock carb...i hit 100km/h down hill and can do about 80km/h on a straight.

the acceleration is not as good as before though. i am guessing that stiffer clutch springs can fix that.

i'm planning to upjet my stock carb like new scooter fan and drill holes in my stock airbox until i figure out the 21mm carb.

[new scooter fan]

Hey Mack i spent all weekend trying to get a foam filter to work with a 95 main jet in my stock carb but it just bogged so it was back to the 87 main jet and stock air box it goes pretty well but a little slow on the take off.You could also take out the plate on your carb intake side i heard that lets more air in keep me posted and good luck

[mack_t]

ok..so i spent all day trying to get the 21mm carb to work once more. i have tried 88 and 82 main jets. both with same results: this time, it wouldnt even start. it sounds like the engine cant ignite. sounds the same as when i unplug the spark-plug wire (the wire that connects to the top of the spark plug)

anyone know whats up?
again...back to my stock carb. i also tried to take out the cover of the airbox and it accellerates very well...but in about 30 seconds, it dies out.

[Scoot-FloorDaa]

Are you using the stock manifold with the 21mm carb? I'm not sure about derbi but I've heard the largest carb with the stock manifold on many scoots is 19mm. Just a thought as I may be way off on this one.

[str8dum]

have you put in a new plug? whenever it bogs, i always put in a new plug. Once i get a bog my plugs never seem to run right again, regardless of tuning.

[mack_t]

@str8dum
no...i havent tried a new plug. i guess i'll get a new one and see what happens. the plug is all the way in...i triple checked the plug everytime.

@Scoot-FloorDaa
yea..i'm using the stock manifold. it could be the problem...maybe i should switch to 19mm?

[str8dum]

doesnt matter if the plug is in. You cant see when it fouls . Plugs are only $2. I change mine everytime I rejet to make sure that its not the plugs thats causing the problems.

[mack_t]

ok....i @#$%in give up :angry: _-_-_- _o :mad:

i just tried a new sparkplug with the 21mm carb.....nothing...same symptom, same noise :(

i tried just about everything and nothing seems to work and i'm all out of ideas.

anyone know what the stock carb for the Derbi Atlantis (2005) main jet tread size it? is it M6 tread or M5 tread?

my last resort is to upjet the stock carb. if that doesnt work, i'm gonna go back to ALL STOCK..which i dont feel like doing :mad: :angry: ;no _o _-_-_-

[Zuma-Zuma]

Try and look into the carb with the scoot off. Make sure that when you give it full throttle, that the slide actually is all the way open. Sometimes cable play doesn't give you full throttle. Its worth a look.

[mack_t]

yea...thats the first thing i check when i installed the carb. the cylinder thing goes all the way to the top when i give it full throttle.

[Zuma-Zuma]

If all else is good, its possible you could have a casting flaw. An internal passage may not be open all the way, or casting flash could have blocked it. Total dissasembly, and close inspection may help. It sounds like an interesting problem to troubleshoot, too bad you don't live closer.