Scooterotica

Hi Guys, I have a mk1 P2 with a polini 207 kit, standard but drilled carb and a RHS JL. Kit has done 1000 miles now so safely run in, yesterday however it ran so hot at half to three quarter throttle it ran on for about 10 to 15 seconds aferI swithched it off
Running fully synthetic at 3%. Any ideas?

Whats your timing set at ? Jetting ?

You could try this more fuel = cooler engine (stops the carb bowl from running dry at full chat)

http://scooterotica.org/forum/viewtopic.php?f=8&t=10869

Now it's run in are you sure the jetting's right , plug chops/ dyno etc , also the timing is it correct ,could need retarding some more . Also could it have been a one off due to shite unleaded , do you use decent super unleaded or just whatever's cheapest at the supermarkets .
Plug should be a B9ES or other make equivalent, i would say a B7 or 8 is probably too hotter grade plug for it especially if going on long thrashes on hot days and while that wouldn't cause the problem it certainly wouldn't help.

hungdog wrote:Whats your timing set at ? Jetting ?

You could try this more fuel = cooler engine (stops the carb bowl from running dry at full chat)

http://scooterotica.org/forum/viewtopic.php?f=8&t=10869

Yeh good point you can get all the bits from sip for this mod, cosa si 24H carb float cap and needle ,and spacer if required.

cit205 wrote:

hungdog wrote:Whats your timing set at ? Jetting ?

You could try this more fuel = cooler engine (stops the carb bowl from running dry at full chat)

http://scooterotica.org/forum/viewtopic.php?f=8&t=10869

Yeh good point you can get all the bits from sip for this mod, cosa si 24H carb float cap and needle ,and spacer if required.

Guys thanks very much, why have tuners gone back to SI carbs, wouldnt I be better running a 26 or 28 MM dellorto?

cit205 wrote:Now it's run in are you sure the jetting's right , plug chops/ dyno etc , also the timing is it correct ,could need retarding some more . Also could it have been a one off due to shite unleaded , do you use decent super unleaded or just whatever's cheapest at the supermarkets .
Plug should be a B9ES or other make equivalent, i would say a B7 or 8 is probably too hotter grade plug for it especially if going on long thrashes on hot days and while that wouldn't cause the problem it certainly wouldn't help.

Scoot has been on Dyno and was not showing any issues, just when its run on road, I will re check jetting as it was set up on dyno on the safe side with quite a rich set up, I always go for decent unleaded petrol not the cheap stuff, you may save 50p on fill up at cheap place but can hole a piston!
Its just frustating as casings have not been done yet, plan is in winter but I don't want to do that if cant solve issues as is.
Carb has had float bowl mod and a reedspeed chamber top, and it has not changed a thing.

At risk of sounding a bit controversial though, a dyno isn't the road ,if it were me i'd check the plug colour with plug chops and look at the timing and back it off a bit then see if it still does it, and also see if it does it more with a lower fuel tank than a full one ,which could show up a fuel flow issue.

I'm no tuner and i only speak from experience but personally i've never had much success with si carbs on kitted 200's with expansion pipes, i always ended up with something like a phbh 28 .
On T5's though i've found using the si carbs with kits etc fine .

At the moment though, my money's on your timing being too advanced

cit205 wrote:At risk of sounding a bit controversial though, a dyno isn't the road ,if it were me i'd check the plug colour with plug chops and look at the timing and back it off a bit then see if it still does it, and also see if it does it more with a lower fuel tank than a full one ,which could show up a fuel flow issue.

I'm no tuner and i only speak from experience but personally i've never had much success with si carbs on kitted 200's with expansion pipes, i always ended up with something like a phbh 28 .
On T5's though i've found using the si carbs with kits etc fine .

At the moment though, my money's on your timing being too advanced

Brilliant, thanks for this will have a look, it has got a SIP fast flow fuel tap

dazbo wrote:

cit205 wrote:Now it's run in are you sure the jetting's right , plug chops/ dyno etc , also the timing is it correct ,could need retarding some more . Also could it have been a one off due to shite unleaded , do you use decent super unleaded or just whatever's cheapest at the supermarkets .
Plug should be a B9ES or other make equivalent, i would say a B7 or 8 is probably too hotter grade plug for it especially if going on long thrashes on hot days and while that wouldn't cause the problem it certainly wouldn't help.

Scoot has been on Dyno and was not showing any issues, just when its run on road, I will re check jetting as it was set up on dyno on the safe side with quite a rich set up, I always go for decent unleaded petrol not the cheap stuff, you may save 50p on fill up at cheap place but can hole a piston!
Its just frustating as casings have not been done yet, plan is in winter but I don't want to do that if cant solve issues as is.
Carb has had float bowl mod and a reedspeed chamber top, and it has not changed a thing.

Hi Dazbo,
First thing is who did the cylinder head mods & what volume was in the cumbustion chamber when fitted?
Next you say that there were no problems when on the dyno (Who did the work?) What Co2 % did they set it at & did they check the carburation at various throttle & speed runs? If they did & all was ok running about 6% Co2 that should be rich enough. That leaves only an air leak into the motor unit when closing throttle on the over run causing pinking/detonation!

Many years ago when thwe imported these kits 1987 the standard cylinder base gasket is a thin hard alloy gasket. It was found not to compress & seal the base joint like the thicker & softer standard base gasket. On striping the motor a few times due to detonation damage to the piston, The cure was using a silicon jounting compound Loctite 5910 which has a temp range upto 250'C. All this because the crankcases were not flat across the vertical crankcase cylinder base joint!
The tell tail sign is what looks like oily deposits which look as if they have come from the exhaust stub from blowby!
It was actually fuel getting blown out of the base joint & road dirt covering it, but when you shut off then air is taken in.
A very costly 2 weeks trying to find that problem!

As for jetting we used a larger slow runner jet 55/100 replacing the 55/160 standard. BE3 ataomiser,135 main jet, Air Jet enlarged to 180 from 160. this was using the Si 24/24E carb with a Cosa carb top & float needle. Air filter element undrilled above the air jet.

Next thing to check is how good your rear suspension unit is? Not all of us are light weight Italian riders!
With you & what ever luggage etc on the scooter check with fan cowl slots are still level & not vering upwards to the rear & disapearing behind the panel as this means your suspension unit has too soft a spring fitted, thus letting the carb float level come higher than the base of the fuel tank so when the fuel level is low you have fuel starvation due to no fuel flow from the tank!
Stopping the scooter & checking the fuel level? All will seam too be ok as the carb has filled back up when you get off the scooter!
There are a lot of Vespa scooter riders that do not realise that this is happening when loaded for a rally weekend.

I hope this may help you sort your delema out before getting a holed piston!

sorry to hijack a thread but cant see what im looking for,, i have fitted a sip speedo with temp guage but no idea what to high a temp is