Scooterotica

Hi,

I have a Series 2 with a Series 3 engine with -

GT186 kit c/w Porcupine head
Varitronic ignition set to 21 btdc at high tick over
30mm Dellorto
- [x] AV264 needle jet
- [x] X13 needle second clip
- [x] Choke 70
- [x] 55 pilot
- [x] 40 Slide
- [x] 135 Main
- [x] 350 float needle valve
TSR Evo exhaust
Pacemaker gears and 17/46 gearing
Readspeed 5 plate clutch
58mm crank
116mm (so base packers)
Squish set as recommended.

I have been massively impressed with this since I built it a couple of months ago, it’s a vast improvement on the previous 190 Suzuki piston type kit I had in before.

It starts easily, runs and pulls well and is a pleasure to ride. There’s just one thing niggling. I went to overtake a car the other day, dropped it into third and gave it a handful but it won’t rev past about 6200 - 6500rpm according to my SIP Speedo rev counter.

Don’t get me wrong, I don’t want to wring it’s neck but I wondered if this is normal? I assume it should rev higher than that so I guess something is restricting its activities a little. It doesn’t bog down or run poorly, it all runs a sweet as a nut. It’s just like it’s ‘restricted’ somehow when it gets to that point.

Can anyone advise what it might be?

Would be grateful for any enlightenment, thanks!

It’s well documented that reed breakage is a major problem with these kits and in some cases the reed actually going into the cylinder bore and the piston biting a crescent shaped chunk out of it.

The recommended work around is to double up on the reeds, maybe this is your problem?

Blimey, I hope not... it’s only done 600 miles!

Could be timing. At 21* you may be retarding under 10*......maybe worth a strobe to check your timing at 6000 revs.

Copied from CamLam:

Timing when the stator is positioned fully advanced will give you around 21 to 22 degrees when the engine is not running (you cannot check this). When you scooter is at fast tick over it will advance around 2 degrees to 23 to 24 (you can check this with a strobe. When fully retarded, depending on how hard your scooter revs, this figure can go as low as 12 to 14 degrees. The thing to remember with the Varitronic is by setting much lower timing, you may loose some top end power, but by running this far retarded your engine will run cooler and safer. The reason we prefer to be this far retarded is the Varitronic by nature of its twin spark system can run hotter, thus the need for more retard. Regarding the possible loss of top end power, you should bear in mind by the time the Varitronic system retards further then 17/16/15 degrees (it does most of its retard at between 4 to 6000 rpm), most expansions will have given up making peak power, so we feel it is not worth trying to hang on to a higher state of degrees as the end result probably will not work with most expansions and gear ratios. The gain in terms of power from the Varitronic is a good increase of power in all bar the top end, so some trade of in terms of power output will be needed in most cases

I see... so it’s a case of I could advance it more possibly but the engine would run hotter and therefore maybe become problematic? At the moment on a warm day the engine temperature sensor which is fixed to the top of the spark plug under the cap with a thin piece of hose reads just over 102 c at its warmest and usually hovers in the late 80’s/early 90’s.

I guess I would prefer it was reliable than squeezing everything out of it. It has plenty of grunt but then it topping out might make sense if that’s the case. I’m not sure how hot is safe...

264 needle jet?
is it weak that may stop it pulling under load; if you drop the throttle a little does it run slightly better

I'd guess the ignition is too retarded as well

A lot of "performance" engines run at 17/16 static so if you aimed for that at 6000 revs it should be ok.

I did noticed a slight surge when I backed off the throttle the other day, does that mean I need a different needle jet? I could also advance the timing more, does anyone know what a safe operating temperature is?

if it was mine I would do one thing at a time richen the needle jet 266 or 268 first then try advancing the ignition; I would set the ignition at 2000rpm around 23-24 degrees