pvl retarder boxes

[pmb5]

hi,

i'm after some info on ignition retard boxes (as rpm rises the ignition is retarded)

i'v heard of two makes so far, MOTIV and PFP. But i'm not sure what i need.

its a 250 single, 65mm stroke 70mm bore and i ride it between 5000rpm and 9000rpm. (realistic 5.5k to 8.6k)

I run 1.8mm static but the rough range we run is 2.2mm to 1.8mm.

where can i get hold of one of these boxes, can you set where they start backing the timing off from? and how mang degrees per rpm do i want to back off the timing?

also how do i conver timing in mm to degrees cheers

Phil

[Alex Hodgkinson]

Hi Phil,

Firstly what country are you from?

I ask because I'm sure that in the UK, at MSA meetings you're not allowed and form of varyable ignition, so you would not be allowed to run any races with a so-called ignition retarder box on your engine.

What is the 250 engine your using called, and of what induction is it (they do still allow disc-vales don't they?) Also, where are you taking your timing readings in MM from?

Anyway, I'm afraid that this is not a subject I know a great deal about, however the perfect person to talk to would be some called Rex Caurnt from Barwell in Leicestershire. He makes racing igniton systems for bikes and this is his field completely.


Alex

[pmb5]

Hi Alex,

thanks for the reply. I am in the UK, and i had a feeling i was struggling to find information about them because they werent legal at most kart meetings/events.

But i'm not actually using it on a kart, its on a motorbike and the regs are totally open on the ignition system we can run. I'm using a PVL ignition, but i think its slightly different to the ones used on most karts (it runs in the opposite direction)

timing readings are BTDC using a dial gauge.

What other names do they give these boxes then so i can improve my searching?

any information is a great help

thanks

Phil

[pmb5]

ok i've done a bit of ground work, and worked out my timing in degrees:
the featherstone box backs off 4 degrees, will this be way too much. Does a 1.8degree per 1000rpm back off make more sense or can i go more liek 2.5 degrees.

Max power is at about 8800rpm.

tickover is about 3500rpm. whats the osrt of max advance i can run a say 5000rpm? using super unleaded.

1.00MM 12.8 degrees
1.05MM 13.1 degrees
1.10MM 13.4 degrees
1.15MM 13.7 degrees
1.20MM 14.0 degrees
1.25MM 14.3 degrees
1.30MM 14.6 degrees
1.35MM 14.8 degrees
1.40MM 15.1 degrees
1.45MM 15.4 degrees
1.50MM 15.6 degrees
1.55MM 15.9 degrees
1.60mm 16.2 degrees
1.65mm 16.4 degrees
1.70mm 16.7 degrees
1.75mm 16.9 degrees
1.80mm 17.2 degrees
1.85mm 17.4 degrees
1.90mm 17.6 degrees
1.95mm 17.9 degrees
2.00mm 18.1 degrees
2.05mm 18.3 degrees
2.10mm 18.5 degrees
2.15mm 18.8 degrees
2.20mm 19.0 degrees
2.25mm 19.2 degrees
2.30mm 19.4 degrees
2.35mm 19.6 degrees
2.40mm 19.8 degrees
2.45mm 20.1 degrees
2.50mm 20.3 degrees
2.55mm 20.5 degrees
2.60mm 20.7 degrees
2.65mm 20.9 degrees
2.70mm 21.1 degrees
2.75mm 21.3 degrees
2.80mm 21.5 degrees
2.85mm 21.7 degrees
2.90mm 21.9 degrees
2.95mm 22.0 degrees
3.00mm 22.2 degrees
3.05mm 22.4 degrees
3.10mm 22.6 degrees
3.15mm 22.8 degrees
3.20mm 23.0 degrees
3.50mm 24.1 degrees
4.00mm 25.8 degrees
4.50mm 27.4 degrees
5.00mm 28.9 degrees
5.50mm 30.4 degrees
6.00mm 31.8 degrees
6.50mm 33.1 degrees
7.00mm 34.4 degrees

thakns in advance for any help

[Viper Racing]

Here is some info that may be of help.

Firstly a retarder box is ok in UK g/box karting. They are disappearing slowly as people replace them with digital units (they have an ideal ignition curve "burnt" into the coil).
The retarder box is a passive delay circuit, which delays the firing of the ignition by a fixed time. So the faster the engine revs the more the engine rotates in the time that the box takes to fire the ignition hence the spark retards in direct relation to revs.
The disadvantage is that you have to set a large amount of static advance in order to arrive at your desired timing at say 10,000 rpm. This is very harsh on the reeds at low rpm. A delay of about 3 degrees per 1,000 revs is normal.
If you let me know the number off your PVL stator, I may be able to supply you with a digital stator and coil that will give you a better result; you would use your existing rotor. Or I can supply a retarder box. Visit my website www.viper-racinguk.co.uk

Ian