Massive vacuum leak

[coop]

I think I have a massive vac leak. if you cover the carb with a piece of paper shouldn't the engine die the darn thing just keeps running. i did check all the plugs and they looked like it has been running lean. I made sure to plug all the vac ports I found one leak at the electric choke it's a Edlebrock 1406 carb it is a small hole beneth the choke body. I sprayed around the carb and intake but nothing changed the intake is a performer where can the leak be coming from. I did have the heads redone they were resurfaced, should of i got the intake done too I used the edlebrock gaskets and everthing lined up, the torque was called out for 25 lbs the factory torque is 32 to 35 lbs. what do you guys think

[Joshpow]

If you have a very big leak, the truck will die. My cap popped off the port on the factory carb spacer on my 72 one time. It wouldn't even idle. You had to give it gas to even keep it running. I've never heard of a piece of paper over the carb killing one before. Vacuum leak tests are usually done with a spray of carb cleaner or similar stuff at likely leak areas. If the spray causes idle changes, you would have a leak there. Also, do you have any hissing noise? Usually vacuum leaks make a hissing noise. My edelbrock carb has never had a proper adjustment since I've had it on my truck. It either idles rich and runs good, or idles good and runs lean. There is no happy median. Yours may just be adjusted a little lean if there is a lean condition. Or, it may be like mine and not tune out perfectly. Does the truck miss or hesitate on acceleration? That is another sign of a vacuum leak. Just a few ideas to help you be sure the truck has a leak, and if so, how to find it. I'm not great at explaining myself, but hopefuly you understand what I am trying to say. Hope this helps.

[fordman]

try unplugging the vacuum to the brake booster and plugging it off.

[coop]

Ok i did what you both suggested, i disconnected the brake booster and plugged the fitting no change. I did disconnect the PCV and that did make a difference with idle. There sounds like there is a small hiss coming from the choke flange shaft sprayed water around it nothing happened. I hooked up a vacuum gauge to it, it reads as follows the needle bounces between 17 - 20 at idle when i bring it up to around 1000 rpm it bounces between 18 - 19. The engine takes right off from idle with no hesitation when you stop and hold it steady you notice the roughness, when you are driving the truck you really cant tell there is anything wrong it feels smooth. and when you romp on it, it takes right off smooth through the gears. When the engine is idling it kinda shakes and thats when you notice the rough idle. Does that sound like a vac leak.

[fordman]

the engine in my parts truck shakes whenit idles also. i figured it needed plugs in it. i havent had time to change the plugs. but it does run pretty good when in gear and i had no hesitation o ranything. and disconnecting my booster didnt do anything to it either.
it couldnt hurt to plug up that hiss in the choke shaft.

[coop]

Right on Fordman I will give it a shot.

[george worley]

Check your timing and vacuum advance,plug your vacuum line to the carb and see if it makes difference. Do you have the line on the right port. should be no vacuum at idle. How is the compression,are all the cylinders pretty much even. It also could be the start of burnt valves. Mine did that when I had a couple of leaking exhaust valves.

[coop]

i did just readjusted the timing it was at 8 btdc i moved it to around 12 btdc and it smooths out and the vacuum needle dosen't fluctuate as much. it seems the more i retard it the smoother it gets and that was with the vac line disconnected, the more i advance it the vac drops and fluctuates more. if you are looking at the front of the carb i am using the right port vac advance for non emission the other port is for emission controlled is it on the wrong port all my engine has is a PCV. i just had the heads rebuilt and the exhaust valve seats replaced for non leaded fuel. i replaced the PCV valve also. i took the truck out for a spin and it runs well just a slight miss now at idle.

i dont know what the timing should be set at i installed a performer cam and it suggests 10 - 12 btdc.

[coop]

George you the man! i just checked the carb port i was hooked to and it has full vac at idle that explains why every time i reconnected the hose to the dist the timing became severely retarded. the other port has no vac at idle i switched the hose and the engine is humming along smoothly. i took it for a test spin and it feels a little more stronger. i still have it at 12 btdc any suggestions?

[george worley]

I set my timing at 10 btc, anywhere between 8-12btc is good . It really depends on what the engine likes the best. Plug the vacuum line when you set the timing,you don't want any vacuum advance at idle. Reconnect the line and check to see if the timing is still the same. You can also hook your vacuum guage up to the port on the carb.You should have vacuum as soon as the throtle opens. There should be no vacuum at idle.

[VirginiaCityFord]

you can advance your timing in small increments until you start to get spark knock on acceleration, then back it off a tad. That will give you all the advance that engine can take and squeeze a little more juice out of it