View Full Version : Carb adjustments, spark chop, drilled airbox and some other useless about my bike =)

04-01-2006, 07:48 PM
Sorry to bring this carb adjustment thing up again...

Tomorrow I'm gona reinstall my Athena 75cc cylinder and Dellorto 21mm carb to my bike. I got the right kind of manifold and I am able to fit the carb to the original airbox. I have Aprilia RX. Same engine as RS but you cannot use RS manifold in RX becouse it is straight and doesn't leave space for filter becouse the shock is so near. Anyway I got the RX version malossi manifold which is bent like the original so now I'm able to try out with the original air box instead of a thick metal net =)

I tried other jets with this metal net but could'nt get the bike run properly. I tired various main jets and with 105 it seemed to run OK with high revs. Spend hours looking for the right size and finally made out for a spin. Runned pretty good. Maxed out 105km/h to the gauge but then head gasket tear apart somehow and let all the cooling water to the engine but now I'm back with new manifold, new gaskets and an airbox. Now I now that I must be realy careful with the head gasket and grease it up before installing. Strange tho that it run fine about 1000km...

Anyway I found out this plug chop thingie and I am going to give it a shot. I'm now using a number 8 sparkie should I use 9?

Let's see if I got it right... First you warm the bike properly and after that drive with full thorttle on 3rd or 4rth gear? Cut the power when on high revs and let it roll. I was wondering could it be done by putting the back tyre in the air and reving with 4rth gear? In RX you have a "sidestand" whics lifts the back tyre in the air. Or does this spark chop need some floating air to be done correctly? If it's possible, how many seconds of high reving will do the job? Don't have a temp gauge so it's hard to tell when enough is enough and don't wanna seize it =)

So if I am using original airbox is it a MUST to drill holes or does it perform fine just like that? I also ordered a better breathing airfilter. Here's a pic of it...


Should I use it inside of the the airbox or just go with the original filter? It would need very much modifieing to get rid of the original airbox becouse it contains the battery and is part of the side desing of the bike. Most crappy thing in RX imho.

Here's a pic of my bike. Kind of old fashion. Would wanna paint it and do a lot of other things do it but don't wanna get more attention from the cops. I get pulled over a lot. Maximum speed for a moped here in Finland is 45km/h so it's always a long talk with them =) Depends on a cop in here you can get a motorcyckle tax if your moped runs over 65km/h. That can be almost 1500 euros. Kinda shitty. No license needed tho. Just got to be over 15 to ride. This turned out to be kinda long story... Hopefully some of you can answer my questions.

Here's a pic of my old lady. First owner. Mods in the sig.


04-02-2006, 05:19 AM
Use at least a number 9 spark plug, if not a ten. Keep the original airbox, dont need to drill holes in it. I wouldnt put it on the stand, just go out for a ride, any gear will do really, not sure how long to keep it full throttle, I'd say about 10, dont take my word for it though, then hit the kill switch(dont let the bike come back down the revs) pull over to the side of the road and take plug out. Perfect mixture should be a coffee kind of colour. A darker brown/black colour means its running too rich. A whiter colour means its too lean. There are various webpages around that show the different colours of the plug tip, look on google.

04-02-2006, 12:48 PM
Yeah did a search and found the colour map of plugs. What about the filter I have? Should I put it in the box (I think RX airbox is bigger than the RS), use the original or use nothing at all?

04-02-2006, 12:56 PM
Not too sure really, probably safest to use original.

04-05-2006, 07:50 AM
It doesn't seem to work at all. Yesterday I tried 100 main jet for the carb. On first and second gear it doesn't rev high and after that the running isn't realy very smooth at all. Today I tried 95 and it was better with second gear but didn't rev eather with first. When the motor was cold it did idle but when it warmed up it didn't at all. When warmed up it didn't rev high at all with that 95 jet. So what the heck should I do? I'm running the stock airbox.

04-06-2006, 09:44 AM
I got a new spark plug. It's number 9 and that helped with high revs. Runs good on high revs and also revs with second gear. When I rev it and then let go of the gas the engime seems to cut off. I'm running with 90 jet now. It also smokes alot and theres some oil coming from the exhaust and it doesnt run with midle revs and runs like shit with first gear. So should I go for a bigger or a smaller main jet? I don't think the spark chop will do any good coz it runs fine with high revs on 3rd, 4th, 5th and 6th gear. I would realy need some help guys! =) Could the oil pump be fucked up? Getting too much 2 stroke oil?

I cant make it idle with this 90 jet. With 100 it was possible.

04-06-2006, 10:38 AM
I think you need to adjust the needle position on the carb. And why would the main jet affect idle? Thats a seperate jet.

04-06-2006, 01:55 PM
I tried changing the needle position. I lowered it couple of steps but it didn't have any effects at all. It doesn't idle even thou I tried to screw the idle jet from the beginning to the end. This is kinda odd. Mayby the oil pump gives too much oil to the engine? I haven't touch that at all. Should I go for premix? If I do that, how will I disable the pump? Stick a nail in the vent? =)