what would cause an engine to stumble if you floor it at idle

if i ease into the gas it does fine but if i floor it it dies for a instant and then picks back up

acc pump does work
i do see fuel squirt into the bowls if i move the throttle by hand

plugs are a light tan on the electrode if that means anything

timing is set at 8 BTDC with the vacuum advance unplugged
right at 24 when you plug in the vaccum line

 

.....

 

EverythingScott said..

what engine, carb, intake, cam and car do you have? It makes a difference as well...

 

68 289
stock crank and cam
holley 600

edelbrock performer intake

no black smoke when floored

no pinging or knocking

idle is 800 in drive
1100 in park

 

I agree set everything on carb back to stock setting. majority of times stock setting is pretty good.

Call Holley tech line they are really good at giving pointers. I had a simliar problem and kept playing with carb and no success. Ended up switching out distributor and runs like a champ. Pretty sure it was the vacuum advance.

But I would try the resetting stock first, call Holley. I can't belive though you need to a larger squirter with your set up. 600 is probably on the big size for 289. I've got a 302edelbrock performer, 600 holley andstock squirter andcarb cam was fine. May needa smaller squirter if anything but if you are not see any balck smoke thatdoes not make sense.

You did not say if this just started happening or been that way since you got car.

 

I would suspicion the vacuum advance first before I suspicioned the carb. Your timing is just not right to fire the full butt load of fuel whenever you punch it. The vacuum advance corrects that phenomena so that you do have sufficient fire at the right time to burn the fuel..

 

what do i need to look for vacuum advance wise
right now the ported line is straight to the front of the distributer

i know the advance works because when hooked to manifold vacuum the timing advances to 24 degrees at idle

when hooked to ported it didnt change

 

From your description, you must have the vacuum advance hooked up to manifold vacuum. That's why the timing jumps up when you attach the vacuum hose. Connect it to a ported vacuum source, the timing will stay the same connected or plugged at idle. With a stock cam, you should be able to set your idle to about 750 - 850 in park. With the timing right and the vacuum advance connected properly, if you still have a bogg, I'd lookto the carburetor. You mentioned it's a 600 Holley, it is a vacuum secondary model right?

 

yes
vacuum secondary

i did check to make sure that there was no vacuum at idle going into the advance canister
then the vacuum retard is going into the thermister (or however you spell it)
on the manifold

i was thinking of just capping that off

 

Yes, you don't want any vacuum ports left open. Cap the ones you aren't using.