Low idle - motor shakes a lot 355 carby / cam

[Scatman696]

Evening All,

Go easy on me - I’m learning - this is my first 355 carby motor & we are getting to know each other - slowly.

I just wanted to confirm if I needed to investigate more into my motor 355/cam/carby that is shaking a fair bit on Start up when cold. Structurally it appears fine, however is very lumpy and has a noticeable shake when started. It does seem to be running rich atm as well. Once driving it feels smooth with no issues.

Is this just the cam? (Unknown specs)

Could it need new engine mounts?

Or is it a timing issue?

Any advice will be greatly appreciated

 

[bluehighway]

Hard to know where to start... easier to sort when you have it in front of you...could be initial timing ....and as the timing advances its smoothing out....

 

[Scatman696]

Hard to know where to start... easier to sort when you have it in front of you...could be initial timing ....and as the timing advances its smoothing out....

Yeah I have a friend who is a mechanic and said he’ll check the timing. I know it’s running rich at the moment. I have him to do a good check over it all. I know Cams can make it run more lumpy (I just was concerned on how much it does move). Thanks for your insight, cheers

 

[Immortality]

Get a hold of a vacuum gauge, Plug it in and advance the base timing to get the best possible vacuum. Then you can play with the idle speed and mixtures to make it happy.

Stock 308 motors around the VH/VK era had about 6°BTDC base timing but anything with a proper cam will like quite a bit more.

What carb does it have on it?

 

[Scatman696]

Get a hold of a vacuum gauge, Plug it in and advance the base timing to get the best possible vacuum. Then you can play with the idle speed and mixtures to make it happy.

Stock 308 motors around the VH/VK era had about 6°BTDC base timing but anything with a proper cam will like quite a bit more.

What carb does it have on it?

Thanks for that mate. It has a demon carby on it.

 

[Immortality]

I believe Demon carbs are a evolution of the Holley unit. Probably plenty of youtube video's available on how to tune em.

 

[Scatman696]

I believe Demon carbs are an evolution of the Holley unit. Probably plenty of youtube video's available on how to tune em.

Yes. I have already just watch one that did a full installation and tune. Very helpful thank you. Once the timing is sorted and adjustments are made it should be sweet. Cheers

 

[Immortality]

Just remember that if you advance the base timing you also add to total timing at WOT so you will need to check total timing.

What distributor are you using?

 

[Smitty]

Get a hold of a vacuum gauge, Plug it in and advance the base timing to get the best possible vacuum. Then you can play with the idle speed and mixtures to make it happy.

Stock 308 motors around the VH/VK era had about 6°BTDC base timing but anything with a proper cam will like quite a bit more.

What carb does it have on it?

.. a 355 stroker with a cam will need at least 12° of initial timing , sometimes more even up to 18°
but you will need the dizzy modded so it does not go over about 32, 34 max

 

[Immortality]

Even my old 308 with a mild cam was happier with 10° BTDC, never tried more as I was a young padiwan and didn't know what I know now. Hell, having at 6°BTDC was probably the cause of some issues with that car but it was set and tuned by a "reputable" dyno shop here, these days I'm much the wiser. I look at the timing map now (it had a LINK ecu) and it makes me cry, there was soooooo much power/torque left on the table all because said "reputable" shop wired up the distributor wrong which was causing about 6° timing variation at idle!