Timing vac advance

[thejinx]

I have a cheap timing gun off eBay. When I changed from 009 to SVDA I followed the advice and had it disconnected from the carb and the carb plugged. When getting the throttle up to 3500 revs to see where the timing fell it didn't seem to move but once I attach the vac line it will. I am confused. Any help as always appreciated. Thank you

 

[yoda]

Have you fitted a new distributor,or a used one possible bob weights stuck. Does it advance fully with the vac connected.?

 

[thejinx]

Yes it does. I am wondering if it is just a crap timing light

 

[Moseley]

I presume it is a timing light with an adjustable advance knob? What figures are you actually getting at idle and at max advance with the vac can disconnected and plugged?


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[thejinx]

It doesn't have an adjustable knob. I will check again with vac pipe on I am getting 35 BTDC at full revs but if I block the carb vac inlet the light doesn't seem to show any advance. I will try again this weekend to confirm this. What would be the outcome of timing with the vac pipe on

 

[Happystamps]

The reason people recommend disconnecting the vac line is because the vac advance changes with throttle position more than RPM. So, you can't reliably hold it steady.
You should get 28-32 with the mechanical advance only, and another 12 degrees or so for the vac- so time with the vac line blocked, and if you don't get any advance then your centrifugal advance in the distributor is knackered. Then do a suck test for the advance mechanism, and check the carb port isn't blocked by either testing vacuum pressure or just looking at the change in timing when you're holding the revs steady and you connect/disconnect the vac line.
Judging by what you've said so far, your mechanical advance mechanism isn't working, or you've acceidentally fitted an SVSA- post up a pic if you like.

 

[Moseley]

What Happystamps has said above!! I take it if you haven't got an adjustable timing gun that you have measured and marked your pulley to get the advance readings?

 

[thejinx]

I have mate. Got original pulley and marked it up

 

[Hubs]

SVSA distributors just have vacuum advance, no rpm advance. Worth googling the distributor code.

 

[bigherb]

As hubs said could be a SVSA distributor
Single port engines had vac only distributors, easy recognition by the short body height of the distributor.