Vacuum leaks-hunting the SOB down

So have been chasing a vacuum leak for two weeks now, have just pulled and re-installed the intake and carb with a new valley pan and carb gaskets on my Chrysler 383. I have disconnected the PCV valve and also the booster from the manifold and plugged ports etc and it still revs up when I cover the carb, which is a eddy 1406.
Am I missing anything, is there anything internal of the carb that may have cause a vacuum leak.
I'm at my wits end and wondering if I have missed anything. Hope you can offer some ideas.

 

Could be a plugged idle circuit, what kind of carb?

Here is a way to make a smoke tester cheap:

http://www.fiero.nl/forum/Forum1/HTML/081547.html

 

Thanks, edelbrock 1406.
My compressor **** itself last week, if I can get it going will have to give the smoker a go

 

Thanks for the link, very cool.

 

What happens when you adjust the idel mix screws?

 

Drivers side when turned in gave me a change only when almost all in, p***enger side a bit more than that.

I unscrewed the drivers completely and it still ran, the p***enger side killed the engine.

I clamped the fuel line and drained the bowls to see if there maybe something blocking the idle circuit

 

Can I also add..I installed the intake and carb last night and torqued both to spec and fired it up this morning and was able to cover the carb and had no symptoms of vacuum leaks and was able to even kill the motor with my hand over the carb.

After shutting down and later (5 min) re-starting the vacuum leak symptoms re-appeared This also occurred the last time I pulled the intake and I had thought that I hadn't sealed it properly, hence the new gaskets and a re-install. So for it to happen a second time has got me thinking or leaning to internal carb leak or problem..

 

Spray WD40 or such like around where the leak could be. Exhaust smoke will let you know if you found the leak. Starting fluid is less messy, but no smoke, just revs up a bit.

 

This has worked for me - the starting spray is better but obviously more dangerous.

 

I tried the wd40 and nothing jumped out at me but in saying that the idle is a bit erratic currently..one thing I didn't do was cover the carb and then spray so maybe the fluid will temp block a vacuum leak. Will try that tomorrow

 

You can try this too

http://www.youtube.com/watch?v=zMok2y05jNE

 

Here's a possibility; this happens occasionally on FE Fords, 352, 390. It can potentially happen on ANY engine with a manifold hot spot. The heat riser, the port under the runners that gets hot from exhaust, can develop a leak. Yes, it can leak exhaust gas into the intake ports. If you have plugged all vacuum ports, PCV, power brake, etc AND try a different carb. If it doesn't change, you might have a problem with your manifold! I've been fighting a similar problem on my '70 F-100 with an FE, I'm going to switch manifolds soon. Keep this one in mind as a last resort.

 

That's the first thing I do on any engine - plug up that damn exhaust crossover. I don't think he will need it down in Australia

 

Zep:
Just taking a WAG by what info you are giving. But are your Valves lashed correctly if Solid. Or Also if Hydraulic, are your lifter preloads OK?
This could have been changed by a Head Milling, Valve Job, Head Gasket Thickness change. Have seen this before, just sayin.
Also if you are getting different reactions from the Idle adjustments there are some issues at carb. Sounds like you have more then just one issue.
Hey aren't you suppose to be out on the Salt down there??
Good luck
Luke

 

Any chance the leak is in a vacuum line to either dist. Or brake booster ?

 

My favorite method of finding vacuum leaks is a squirt bottle of water. Never had much luck with the other methods. I really like it as you can absolutely drench everything without any safety issues.

 

Thanks for replying, I have been thinking about the AF screws and only the p***enger side killing the motor when removed. If one side of the idle circuit was blocked would that mean the right bank be affected? It has a funny running condition at the moment that is hard to explain but thinking about it could be like four cylinder engine...

Am I right in thinking, would a blockage in a circuit have the circuit/carb pull air from somewhere else internally and simulate a vacuum leak when air horn covered?

 

get your hands on another carb to try. ive been down that road,had issues like that with a carter on my gto many years ago,

 

The hand over the carb does not always meen a vacuum leak it could be a lean mixture from the carb not supplying enuf fuel witch would ack like a vacuum leak I would look at the carb.

 

If checking for vacuum leaks on the intake side of things, we used an unlit propane torch. If the rpms went up, it was ****ing in the propane.
RB

 

I hope your right saltflats and if Im right on my Drivers side bank not getting enough fuel that may answer a few questions. Just bought a can of carb cleaner and weighing pulling the possibly well sealed carb base or gettiing it running and let the engine vacuum **** some **** through. Opinions?

 

You can try taking the mixture screws out and spray some cleaner through the holes and when you get it running rev it up and take a rag or somthing to close of the top of carb so that the engine can **** had on the carb and maybe pull the **** out if that is the problem.

 

What kind of intake is it does it by chance have a EGR valve on it if that thing is leaking it will make it idle like ****.

 

Yeah will try letting the engine **** it through. It's a performer intake and egr is plugged
Thanks again, wish me luck!

 

The left side of the carb feeds cyl 2-3-5-8 the right 1-4-6-7 in a 180 degree manifold.

 

I use a length of vacuum hose one end in my ear and the other end to probe for leak sounds

 

I had some what of the same problem on a 440. Take the rocker arms off. Make a plate to put on in place of the carb. Drill a hole in the plate large enough to put a tire valve stem in. Pump it up with a bicycle tire pump. Start spraying around with a bottle of soapy water. I dont know why, but dish soap works best. If there is a leak, this will find it. Also the eldebrocks with electric chokes have lean idle circuits. Sometimes changing the jetting won't help on these. Ran into that on another 440. Gene.

 

I did this but was unsure what if I could hear the leaks or just engine noise. Is it like getting your ears unplugged, if so I still have a leak on the rhs.

Spraying carb cleaner didn't have the results I was looking for, intake might be coming off again

 

So it could have been carb related but I have resealed the intake with some help from some indian head and while I had the carb off I blew out all the p***ages and jets and put it back together and looks like I have clean running engine again. Thanks for all your input