36 replies to this topic

[lrostoke]

It'll be down to the cam that gives the mechanical advance inside the dizzy.

 

There are different ones.

 

Under  full revs If you have a 13 degree cam, this will give 26 degrees of mechanical advance. (you double the number)

 

So if the advance is set @ 32 degrees @ 5000 rpm, at rest you deduct the 26 degrees, you get about 6 degrees.

 

If you only have an 8 degree cam in the dizzy, same scenorio at full chat 32 degrees, this would give 16 degrees advance at rest.

[ACDodd]

Your curve is a little slow. I like 14 to 16 at 1500rpm and around 18 to 24 at 2000rpm depending on spec.(vac disconnected figures)

Ac

Edited by ACDodd, 19 August 2016 - 12:00 PM.

[Trissy B]

Interesting.

 

 

I just changed mine to about 32deg at 3500rpm and that gave 24deg @ idle! So almost had what I started with! Almost just did by ear.

 

But drives nicely now! picks up well and 

 

No idea why the idle is so advanced.

[lrostoke]

I'd be checking the weights and cam in the dizzy (under the baseplate) make sure nothings sticking..

[racingbob]

here is what i have mg metro cam stage 3 head 99 fuel

 

vacuum disconected at carb

 

1000 -4

 

1250 - 4.5

 

1500 - 7

 

1750 - 9.5

 

2000 - 11

 

2250 - 14

 

2500 - 15

 

and at 3500 - 4000 advance connected 34

 

doesnt seem bad compared to that chart earlier posted but im no expert on this

[KernowCooper]

Interesting.

 

 

I just changed mine to about 32deg at 3500rpm and that gave 24deg @ idle! So almost had what I started with! Almost just did by ear.

 

But drives nicely now! picks up well and 

 

No idea why the idle is so advanced.

Vacuum still connected ?

[Trissy B]

doesnt seem bad compared to that chart earlier posted but im no expert on this

 

Where is the chart? - would be really useful to see.

 

I'd be checking the weights and cam in the dizzy (under the baseplate) make sure nothings sticking..

OK will do. It might be that I have the wrong distributor...

 

I have the following setup: fairly standard 1275 A+ metro block, standard head (hopefully to be updated to MG), MG metro cam, later 1275 electronic cooper dizzy (maybe SPI but i'm going to check), Stage 1 kit and always use Shell V Power.

 

Vacuum still connected ?

 

Nope - that's all without the vacuum attached.

Edited by Trissy B, 20 August 2016 - 06:57 AM.

[ACDodd]

Both of those curves are way off. Racing bobs is too slow while the other is too short. However if racing bobs is running 10.5:1 then you will want a retarded from optimum advance curve as you have too much compression with modern fuel and that cam. You will need 30deg of advance at 4000rpm (vac disconnected)
When checking.
Ac

Edited by ACDodd, 20 August 2016 - 08:08 AM.

[racingbob]

Your curve is a little slow. I like 14 to 16 at 1500rpm and around 18 to 24 at 2000rpm depending on spec.(vac disconnected figures)

Ac

is that on the timing gun with vacuum off mine shows 7 at 1500 and 11 at 2000, am running no more than 10.1 at the most

or are your figures showing this where figure double to do with something about crank

 

i saw a aldon yellow chart and mine were not far off

[Ethel]

A simple check on the vac would be to reconnect it and see if the advance increases (& retards when removed again). It could be the vac can or baseplate are sticking.

[ACDodd]

I am talking crank degrees.

Ac

[racingbob]

I am talking crank degrees.

Ac

so does that make mine 14 at 1500 and 22 at 2000 at crank which seems ok

 

sorry i get very confused with this

[racingbob]

here is what i have mg metro cam stage 3 head 99 fuel  10.1 or bit less

 

vacuum disconected at carb on my timing gun

is this distributor degrees

 

mine ( timing gun  )                   aldon yellow  ( distributor degrees )

1000 -4                                    1000  4.3

 

1250 - 4.5                               1250   5.6

 

 

1500 - 7                                  1500  6.8

 

1750 - 9.5                               1750  8.2

 

 

2000 - 11                                2000  9.4

 

2250 - 14                                2250  10.8

 

2500 - 15                                2500  12

 

and at 3500 - 4000 

vacuum was then connected showed 34

[NZMini1275]

Timing marks on pulley are connected to crankshaft so would be crankshaft degrees you are measuring
Aldon is distributor degrees as stated
Convert the Aldon figures to crankshaft then compare
Cheers
Dan

Edited by NZMini1275, 20 August 2016 - 08:48 PM.

[racingbob]

Timing marks on pulley are connected to crankshaft so would be crankshaft degrees

was done by a dial type timing gun -  the vacuum advance revs didnt drop when discontected it from carb

 

so does that mean my dizzy curve is to retarded ? and not getting best performance ( like AC said bit slow is that what he means retarded )

 

all this tends to confuse me