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timing
bracey - 31/12/06 at 03:28 PM

how do you know where timing should be after losing the vacuum advance of dizzy when removing old single carb and fitting twin carbs?
cheers
bracey

flak monkey - 31/12/06 at 03:43 PM

What engine? And what cam?

Bit more info needed. Basically you statically set the timing by turning the crank to a certain position btdc and then setting the dizzy up to the firing point on cylinder one (usually marked on the dizzy body and rotor).

If all you have done is swapped the carbs and not changed the cam or anything, leave the vacuum disconnected, you dont need to alter anything.

All the vacuum does is give the engine more advance under acceleration, which improves fuel economy and nothing else!

David

bracey - 31/12/06 at 03:56 PM

its a 1.8 ohc vauxhall with piper 270 cam and twin dellortos jetting in carbs is somewhere near but want to get running so able to get to rolling road

flak monkey - 31/12/06 at 03:59 PM

You need about 12-14degrees idle advance with that set up. That should see you running. Set it up statically then use a strobe to check it and set it as accurately as you can. Expect the idle speed to be about 900-1000rpm with that cam.

David

bracey - 31/12/06 at 04:03 PM

thanks david now with the dizzy been at the front of the engine ,crank pully side which direction is to advance and roughly how far cheers

flak monkey - 31/12/06 at 04:09 PM

If the engine goes clockwise (all except honda do) then the dizzy usually goes clockwise too (check it!). If it does then turn the dizzy body anticlockwise to advance and clockwise to retard.

David

britishtrident - 31/12/06 at 05:38 PM

quote:
Originally posted by flak monkey
If the engine goes clockwise (all except honda do) then the dizzy usually goes clockwise too (check it!). If it does then turn the dizzy body anticlockwise to advance and clockwise to retard.

David


Don't judge every engine by the Pinto it was the exception rather than the rule.

Usual convention in the UK and USA was 4 cylinder dizzies roatate anti-clockwise,

flak monkey - 31/12/06 at 07:26 PM

Fair enough, if the dizzy spins the other way (like i said check it anyway) clockwise to advance, anticlockwise to retard... Not exactly rocket science

martyn_16v - 31/12/06 at 07:34 PM

quote:
Originally posted by flak monkey
All the vacuum does is give the engine more advance under acceleration, which improves fuel economy and nothing else!


It's t'other way round, it adds advance at low load/high vacuum. You should actually see more benefit than just a bit of fuel economy with a properly working vac advance, without it you're not giving enough time to fully burn the leaner mixtures at part throttle. And of course, if you're just throwing in fuel with a set of carbs anything to help waste just a little less is a bonus

flak monkey - 31/12/06 at 07:41 PM

Yes, apologies. I have heard that it is not wise to use vacuum advance with twin carbs, as under vacuum you get a pulse bacuase the vacuum tube tends to be connected to only one runner which can lead to variation in timing.

Up to you, do as you like. Was only a suggestion.

bracey - 1/1/07 at 05:34 PM

with timing advanced getting poor throttle response and bangs and flames from exhaust?