Aprilia rs carb setup?

[2-stroke madness]

hi there, im currently having a full engine rebuild on my rs 125 extrema 1994, reasons for this i seized it, it was running fine, power was great, then one night out it started to 'bog/fail' out at about 11,000, and over a period of a few days, this got worse and the point of 'bogging' out lowered in rpm, eventually only letting me rev to about 3500 rpm, i then changed the plug and it let me run it for a while, still not getting to 12,000 though, nd after about half an hour it clonked out on me, and wouldnt start again for sure, sstripped the engine and this is what i found, i dont have any idea what caused this, mixture? jets? spark plug? im running a std airbox with 34mm VHSB, 153 main jet, iridium br9eix plug, also when i stripped the engine, the main bearings were knackerd, big end gone and small end gone. i just want to make sure this doesnt happen again with my new engine any ideas would be very helpful, thanks
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live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

Forget trying to hit 12k. The red line is at 10750 which is also pretty close to peak power. Revving further you will just be losing power rapidly while giving the engine a really hard life.

From the pictures difficult to tell. That is either most likely detonation (what is your ignition timing set to, and you do realise that an RS that old is set up to use high octane petrol as standard - 97 RON min), or a bit of piston ring / circlip has escaped and bounced around for a bit. Prolonged detonation might also explain the wrecked big and little end bearings (but revving it to 12k would likely accelerate their deaths as well).

If you are thrashing the bike and going to the red line regularly (let alone through the red line) then use a 10 plug. Stock is a BR10EG. Stock jetting for a 1993 bike is 155 main jet, 36 for "min jet", DP266 attomiser tube, K57 needle on the first notch and air screw 1.5 turns out.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

thanks for that ill be putting high octane in all the time now, and if i werent to thrash it all the time would a 9 plug be better?
and how can i find the ignition timing? and also where is the attomiser tube located
thanks alot
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

The number with NGK plugs is the heat range of the plug, which comes mainly down to the amount of insulation around the inner electrode. The lower the number the hotter the plug (for colder running engines) with more insulation, the higher the number the colder the plug (for hotter running engines) with less insulation. A spark plug has a limited range that it works properly in, and if it gets too hot it will blister and fail, while if it doesn't get hot enough it will foul up (and fail). Fouled plug is a pain (but easy to carry a spare).

A 10 is standard and fine normally, but if you are doing lots of low speed riding it won't get hot enough to burn off the build up of carbon on it and will foul up. The 9 should avoid this but might blister and fail if thrashed.

The ignition timing is set by the position of the stator under the flywheel. To alter it you need to remove the flywheel. To check it you use a dial gauge. There is a small hole in the flywheel which matches up with a notch in the stator at the point used for setting the static timing. You use a suitable size pin to lock the flywheel to the stator at this point and check the crank position compared to tdc using the dial gauge (from memory it is a 1.8mm before TDC, but don't rely on that figure without checking it). Basically you get the engine to tdc (there is a bolt under the engine to remove and replace with a longer one to lock it at TDC) and set up the dial gauge. Then remove the bolt and turn the crank back until you can lock the flywheel to the stator and check the dial gauge reading there.

Attomiser tube is in the carb, in the middle of the float bowl. Part number 3 in the following diagram:-

https://www.dellorto-carbs.co.uk/graphics/del16.jpg

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

thanks, ill have to check the timing when i get my engine back, but ive just checked my jets, its got a 155 main, 60 choke, and doesnt have a pilot jet, it has a jet that actually is sat inside the thread, about 10mm down... whats that all about?
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

60 choke jet / starter jet (the Italian translations can get to be a bit strange) is correct. Main jet is within the normal bounds

You can see the min jet as number 7 or number 8 on the previous diagram (not that it is that clear).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

Thankyou for all the advise again
do you reccomend anything when i am running my new engine in, im going to try a 158 main instead of a 155 and fiddle about with the air screw, run it on high octane and expensive 2stroke oil... any more suggestions?
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

The RS runs fairly rich as stock so is fairly safe. Although it you are using an aftermarket exhaust it might help (stock early RS exhaust isn't bad).

Running in I tend to do 500km at under 5000rpm then add 1000rpm every 100km. Probably a bit excessive though.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

[Kickstart]

Hi

Good question, and one I doubt few can answer on a carefully built new engine let alone one rebuilt.

Couple of heat cycles seems to normally be accepted for competition engines which will likely only have a single ring piston to bed in and where long engine life isn't really something they care about.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[P.]

Not going against God's posts above..

But

What I did with my RS was a completely new top end/barrel and main bearings. I ran that until about 250miles around 5000rpm. After that I started pinging it up to around 7k/8k every now and then, but sitting around 5k normally. Did that until about 450 miles then started opening it up a lot more.

After about 500 miles, was riding as per normal, thrashing the crap out of it, and it was perfect... felt like a totally new bike

[Kickstart]

Hi

Very similar to me, just marginally less distance (and on that I probably am being excessive). I just work in km as that is what the clock reads in.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

thanks for the advice, also now the cold weather is coming in do you suggest anything that could help me keep my engine in tip top shape?
thanks
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

Warm it up properly before thrashing it (and watch out for the temp dropping when the stat first opens).

Otherwise just service it nicely and check for anything wearing out (inlet rubber cracking for example).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

okay thanks still use a 9 or 10 plug? and what do you think to the iridium ones compared to the standard ?
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

With plugs fouling easily I would be inclined to say it is better to replace the plug twice as often rather than use one that could last twice as long.

The spark plug is there to cope with combustion temperature which shouldn't really depend much on air temp. So still stick to the one depending on how you are riding (although if it snows I doubt you will be thrashing it )

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

haha i know im gonna be killing my self if i dont get a good ride out on it, engine should be back with in a 8-9 days, its up at ARD racing in newcastle
getting full piston kit inc conrod and barrel aswell, so cant wait to see what it can do
____________________
live life to the max.... Buy a 2-stroke

[Kickstart]

Hi

As I am sure you are aware, with an RS125 what it can do is somewhat down to how accurate the speed is (or not).

Had 185kmh on the clocks on mine on level ground (115mph). As you can no doubt tell, that shows the speedo as being way out.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[2-stroke madness]

Haha i know what you mean, what years your rs? and what parts you running it with? airbox, carb, jets, exhaust, piston etc
____________________
live life to the max.... Buy a 2-stroke

[P.]

Just as a baseline, mine was a 2000 model, full arrow exhaust, power valve jammed open. Saw an indicated 102, but GPS showed 91. Which is still quick for a little 125

[2-stroke madness]

thats not too bad would you sy its better to have the power valve jammed? personally i love that rush when it opens at about 7600rpm,
just cant beat it
____________________
live life to the max.... Buy a 2-stroke

[P.]

Still get the big power push at about 8k, just think it makes the mid range a little lacking, cant say it bothered me, was always in 50/70 zones, so was trying to keep high revs anyway

[Kickstart]

Hi

Mine is a 1993 bike. One of the first batch in the country (I was friendly with the local dealer, he collected it on a Wednesday and it was still in his van on the Thursday when I popped in - I got it out of the van to look at, then rang the next day to buy it). It is standard (well, other than a blown crank at the moment).

The power valve doesn't really give you top end power. That is down to the porting, exhaust, etc. The power valve just salvages some of the bottom end power to make it usable when otherwise tuned for top end power.

If you jam the power valve fully open you will have a hell of a lot more of a kick at around 7k~8k. You will also have stuff all go when moving off (makes moving off with a pillion on a hill a nightmare).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[P.]

[2-stroke madness]

which ports do you think are best to polish? and ive heard its not a good idea to polish the inlet port to the piston?
____________________
live life to the max.... Buy a 2-stroke