36 replies to this topic

[ACDodd]

If you are measuring the advance at the crank these are crank degrees and your figures are way off.

Aldon list there figures as dizzy degrees.

Ac

Edited by ACDodd, 20 August 2016 - 10:05 PM.

[racingbob]

If you are measuring the advance at the crank these are crank degrees and your figures are way off.

Aldon list there figures as dizzy degrees.

Ac

ok ta, will get a new dizzy and see what that shows as my advance curve, vacuum doesnt seem to working either ( revs dont drop when i disconnect and still drives ok)

and the pipe isnt blocked, strange car doesnt go to bad but does realy pulls from 3500 - 4000 when on full advance

[Spider]

I've been reading this one from the sidelines.

 

However, just at this point to (hopefully) cut through some of the confusion that I am picking up on I thought I'd jump in at this part of the song.

 

Forget the numbers you guys are reading with the vacuum connected. Disconnect it for now.

 

The Vacuum Connected numbers are leading you well and truly up the garden path.

 

You can 'see' advance now as the engine is unloaded and so making high vacuum in the manifold. This is not at all what happens on the road when you accelerate, you'll have next to no vacuum, so any amount of advance you are seeing now, with the vacuum will not be there when you are accelerating, so this 'added' advance won't be there.

 

While my own thoughts on advance (mechanical) and rates of advance are very similar to those suggested by Adrian here, however, I will say in regards to Bobby's engine at 10.1:1 CR and running 99 Octane fuels - while I haven't run the numbers - I don't think would be an issue, it would have to be very close to where it needs to be, maybe a tad high, but not detrimentally so.

 

Sort the mechanical advance first (with the vacuum disconnected).

 

 

 

 

Only once that's properly sorted, then look to the Vacuum Advance, which if you are going to run on these engines, you'd only want that to give around 6 to 10 degrees of advance (at the crank).

 

Now, if you are running a HIF type Carb and Vacuum Advance, with a Cam that has more than around 255 - 260 degrees of Inlet Duration, you really should rearrange the Vacuum Advance Take Off Port so that there's no Vacuum at Idle and also run it via a fuel trap of some sort, or you could find the Vacuum Advance unit won't last too long. Ideally, this line should have a valve arranged such that any pressure above atmosphere doesn't reach the Vacuum Advance can.

[Ethel]

 

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 

 

 

 

I might have added to the confusion here - the vac connection on most carbs is placed so the throttle disc shields it from seeing full manifold vacuum when it's just idling. When idling, there's no drive via the transmission to ensure the engine passes tdc, so heavily advanced ignition can attempt to push the piston backwards giving a lumpy idle and stalling.

 

You may need to open the throttle a bit to test the vac advance is functioning. As Spider says, an unloaded (idling) engine will max out on rpm before you've got the throttle anything like as open as on the road, so vac advance needs disconnecting to check the centrifugal advance.

[racingbob]

have ordered a new 65d dizzy today so see what that shows at different revs

 

so it should be showing as AC said 14 - 16 at 1500 - not around 5

 

i checked today was showing 20 deg at 3500 plus - dissconected

 

but 33 connected

[ACDodd]

Yes bob, way off.

Ac

[racingbob]

just shows how these dizzys are out

 

bought a new 65d dizzy from powerspark

 

here is the curve

 

VACUUM OFF                VACUUM OFF

 

1500  14  one on there before  7

  

2000  14                                    11

 

 

2500 18                                      15

 

3500 +   33                                   20   ( but vacuum on was 34)

 

car does seem go bit better but not a lot- wierd eh