Chevy 305 Emissions

Stuball · Post by **Stuball** » Sun Jul 19, 2009 2:03 pm

Have a chevy 305 in an astro van, running a holley carb, standard distributor etc.

Failed MOT on emissions, High CO 5.9% but fairly low HC, 341ppm

Not sure if its running rich or not due to the low HC.

Any thoughts? (before i start fiddling)

cheers

Stuball

kiwicar · Post by **kiwicar** » Sun Jul 19, 2009 3:57 pm

Hi
probably running rich but with quite alot of ignition advance enabling it to burn the HC to CO but not enough oxygen to burn the CO to CO2.
Mike

Stuball · Post by **Stuball** » Sun Jul 19, 2009 6:45 pm

Cheers for that.

I am a bit unsure about the ignition timing.

Its set at 8 BTDC but with the vac advance connected.

With vac disconnected (pipe plugged) the engine refuses to start, so i wonder if the timing is completely out?

Stuball

sidecar · Post by **sidecar** » Sun Jul 19, 2009 7:04 pm

Stuball wrote:Cheers for that.

I am a bit unsure about the ignition timing.

Its set at 8 BTDC but with the vac advance connected.

With vac disconnected (pipe plugged) the engine refuses to start, so i wonder if the timing is completely out?

Stuball

If your carb has a ported vac take off you could connect the vac canister up to that, I believe that this is more "normal" (At least from what I've read on the Cobra forum)

Also I think that the SBC boys run a bit more static advance than what you're running, maybe 14-18, 36 total.

As to the holley, well once the igintion us setup you could try slowly winding in all the pilot screws until the engine starts to slow down, then wind them out about 1/4 of a turn.

Make a note of the screw settings before you start fiddling!

I'm more of a Rover Bod so I could be talking crap (as normal!)

Pete

Stuball · Post by **Stuball** » Sun Jul 19, 2009 7:48 pm

So should the timing should be set with the vac advance disconnected (and plugged)?

thanks again

Stuball

sidecar · Post by **sidecar** » Sun Jul 19, 2009 8:01 pm

Stuball wrote:So should the timing should be set with the vac advance disconnected (and plugged)?

thanks again

Stuball

If the vac canister is connected to a "ported" port then it should not make any difference. However most people would disconnect it just to make sure that it does not mess up your settings.

Like I said though I'm more of a Rover Bod! Hopefully someone who knows about SBC's will help you out.

My lump does not even run a vac system, I run 12 static but with soft dizzy springs so all the advance is in my 2700 RPM. (32 total)

Pete

Post by **demo2** » Mon Jul 20, 2009 10:07 am

That wouldnt happen to be a purple astro van wud it, black leather interior?

Stuball · Post by **Stuball** » Mon Jul 20, 2009 5:56 pm

Yeah that be the one demo2

(small world eh)

Back on the road after 2 and a half years

Stuball

Post by **demo2** » Tue Jul 21, 2009 11:57 am

I know that car very well, belonged to Vern, a good friend of mine. Used to have a 350 in, i stripped that 305 thats in it. I didnt even know he had sold it.

Stuball · Post by **Stuball** » Tue Jul 21, 2009 8:24 pm

Yeah paul i know Vern.

I work with him

We might actually be able to dust his Cortina off now and get
it on the road

Stuart

Post by **demo2** » Wed Jul 22, 2009 9:35 am

The day that car hits the road will be a miracle,lol that rover aint run for 14 yrs!

Stuball · Post by **Stuball** » Sat Jul 25, 2009 1:11 pm

Managed to solve the emissions, backfiring and stalling problems all at the same time today

Started again with the ignition timing, found that it was 12 degrees retarded with the vac advance disconnected

Reset the static timing to 10 degrees advanced, and its like a new engine

cheers for the help

Stuball