Help with my Aprilia rs 125 main jet!

121game121 · Two Stroke Sniffer Joined: 15 Dec 2010 Karma :

Basically im completely new to bikes. I bought an aprilia RS 125 and the guy said it needed a new battery and Main jet to get the bike starting.
I bought the battery and main jet. Fitted the battery on fine.

But not sure where to fit the main jet on the carb. Its a delorto 28 carb.
I looked at manuals online and was wondering if i should unscrew the screw at the bottom of the black box on the carb and fit the main jet on and how do i fit it on?
And i bought a 110 size main jet. Is that too big or too small? How would i know.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Main jet sounds a bit on the small size, but wondering why the seller said to replace it. They shouldn't wear out so normally replaced to adjust the fueling if the bike has been tuned.

The black bit at the bottom of the carb is the float bowl. It will be full of petrol (unless it has been drained and the petrol left turned off). The large brass "bolt" at the bottom of it (uses a 14mm spanner) holds the float bowl on, and also holds the main jet. If you take out the large brass bolt you will find the main jet screwed into it.

All the best

Keith
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GSTEEL32 · Traffic Copper Joined: 24 Feb 2010 Karma :

I'd think a 120 main jet would be more suitable for a standard set up. choke jet will be 70, idle 62.

I'm suprised it didnt come with one...... Very odd if the truth be known as they're so cheap to replace....

I suspect you haven't been told the full story by the seller....

121game121 · Two Stroke Sniffer Joined: 15 Dec 2010 Karma :

Hi thanks for the advice. Bought the haynes manual.
Yh it was really fishy, because there is a main jet already there but he said there wasnt one thats why it wouldnt start properly and he had to push start it on the buying day. But changed it anyway to 120.
I bought the bike off ebay for £750 1999 model. So dont mind doing abit of work to it.

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

sounds like you were had...........
i'd start from the beginning, get a new spark plug, better still get 2. a NGK BR9 & a BR10, avoid the iridium ones, just stick with the copper/iron tipped ones for now.
while your there, get a compression tester (if you dont already have one) & get it tested.
as difficulty starting etc can be a sign of low compression & tbh rs's need the top end done fairly often (compared to most other 2t learner bikes anyway)
anything under 120psi & your going to have to, at the very least, replace rings.
use a decent tester, not one of those shove in type. (i use the gunson kit & its been very good)
another common rs issue is the battery, it needs a good charge to start (pity it doesnt have the kick start like the sp) & the lcd voltage screen is notoriously inaccurate, so test it with a multi meter.
oh, & download the rs125 WSM & the rotax 122 manual (im presuming its a 122?), they are far better than the haynes manual.
let us know how you got on,
cheers,
GAZ

121game121 · Two Stroke Sniffer Joined: 15 Dec 2010 Karma :

Okay il work on it from next week, weathers too bad atm. It says on the specs the spark plug is NGK BR8?
Also if i did have to replace the rings is it a difficult job and what are the costs?
Could you give me a direct link to the Aprilia manual/s as i searched on here for manuals but no decent ones found & yh its a 122.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

You want an 8 in a restricted bike and a 10 in a full power bike.

Doing the rings isn't that difficult. Gentle afternoons work once you have done it a few times. Few bits are a pain (such as getting the springs back on that hold the exhaust on). Just be very careful the rings are in the right place and held in while you lower the barrel in place over the piston.

All the best

Keith
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stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

hi,
Keith's right, 8 for restricted & BR10 for FP, but i've always used BR9's & all my rs's were far from standard, but i use my bikes for commuting & use BR9's, like it suggests in rotax manual.(10's foul easier, imho, & especially those silly priced iridium ones)
maybe im getting too old & dont ride as fast,lol
cheers,
GAZ
ps : the manuals are over on 125cc sbs,iirc. (i have them on cd rom)