Engine surges - 1971 350

[57rookie]

What would be causing my engine rpm to surge. When cold or hot it surges about a 100 rpm or so consistently like a pulse. I have all original points/coil setup. Need a tune up?? Previous owner had the engine idle jacked up to compensate for stalling when putting the 4spd in gear.
I am thinking I dont want to play with old ignition system and upgrade to HEI but I want to know what causes engine rpm surge first.

[truckster]

It's probably not the ignition. Look for a vacuum leak. It's probably why the idle was high as well.

[57rookie]

Only thing I can think to check is the rubber hose from the vacuum advance on the original distributer and where it hooks up to the carberator. Would this be correct?

[Coley]

Originally Posted by 57rookie

Only thing I can think to check is the rubber hose from the vacuum advance on the original distributer and where it hooks up to the carberator. Would this be correct?

No...you need to check more connections.
Ok...lets go over a few:
1) Are your (4) vertical carb mount bolts relatively tight?
2) Do you have power brakes?....if so, then carefully 'pinch' the vacuum hose running to the brake booster with a pair of pliers. If the surge goes away, or the idle improves...your brake booster or an upper connection is leaking.
3) Is your PCV rubber hose correctly connected and not leaking? (use the same check with the 'pliers' to test this...but be careful, you don't want to compromise the rubber hose)
4) You should have a small vacuum port/tube located on the passenger side of the quadrajet (....do you have a quadrajet?)....is that plugged or is it connected to anything?
5) Are you intake manifold mount bolts all relatively tight?
....post up some pics of your engine from both angles and we can give you some more tips.

All good
Coley

[57rookie]

That is awesome help. Will check carb bolt tightness tomorrow. It is a quadrajet.
No power brakes which I will be adding this winter using a CPP setup.
Here is a pic of the engine but not sure it is all you need.
Thank you for taking the time to help a stranger- much appreciated.

[57rookie]

OK so there is a very small hose about 1" long that goes from the passenger side vacuum port (very small port) to the white diaphragm that appears to control the choke. Could this be the problem area?? It does seem to take a very long time to come off high idle even when warm..... It does seem to have a crack in the very short line... Too small to pinch off to test. Would you happen to know what diameter of this small vacuum line is?? Worth a shot........

[geezer#99]

It's 5/16 inch hose.
Napa has some.
Your surge is likely lack of initial timing and your carb mixture screws need adjusting.

[Steeveedee]

Has it surged the whole time you've had it? In any event, what geezer#99 said is a good place to start. I'd also check the fuel filter.

[57rookie]

Only had it for a month so yes it has done it since I have owned this California survivor....
I will get a fuel filter as it can't hurt to change it anyway. It does seem to be a rythymed surge - seems electrical but I dont know points well which is why I think I will change to HEI.......
Any other suggestions would be great!!

[57rookie]

Only had it for a month so yes it has done it since I have owned this California survivor....
I will get a fuel filter as it can't hurt to change it anyway. It does seem to be a rythymed surge - seems electrical but I dont know points well which is why I think I will change to HEI.......
Any other suggestions would be great!!

[geezer#99]

So. what's your initial timing?

[57rookie]

Not sure have not checked timing yet. I did advance and retard the distributor though while at temp and it continues to surge throughout the advance and retard although less with retarded timing but then it wants to stall out....
Beginning to wonder about fuel restriction - fuel filter possibly.....

[geezer#99]

Have you ever changed a filter in a quadrajet?
If not and you get unlucky you might ruin the inlet threads.
Do the easy stuff first.
Bump your initial timing up to 12 degrees.
Then check the dwell on your points.
Then adjust the mix screws on your carb.

[57rookie]

I have changed lots of filters in a quadajet. No big deal.
I do not understand points and dwell though as i dont have the old dwell meter tool. I can use a feeler gauge though. I think I will go to HEI and not mess with points though.
I could use a good link to how to how to adjust carb idle screws though. Part of the reason why I work on these old trucks is to teach myself how to do stuff like this.
REally appreciate any help. I am a HD Mechanic and used to bid trucks and Diesel engines..........

[geezer#99]

Just search on youtube. Lots of vids on how to adjust your mix screws.