Dreaded nozzle drip 17056200

[68rs/ss]

Looking for possible solution for new engine/carb. This is fresh 396 BBC and reconditioned using cliff's parts and recommendations.
Engine is 9.5 CR using closed chamber heads, with mild bowel cleanup and good flowing valves. Cam is Crower with 224intake, 232 exhaust, .542 lift intake, .514 exhaust. Lobes are at 112 degrees.
using Q-jet RPM and headers.
This is fresh engine and is on test stand for break-in and carb adjustments before putting in car.

After initial break-in, can not get it to idle down. Primary throttle blades are open too much causing idle drip. Does not run smooth with blades turned down to stop drip. Mixture screws have little effect. Pretty sure no vacuum leaks as all the ports are plugged. Initial timing is roughly 8 degrees.

Carb is as follows.
Jets:79
primary rods: #46 tapered from cliff
Upper Idle air bleed:.070
Lower idle air bleed: .059
Idle tube: .038
Idle down Channel: .053
Mixture screws: .090
Idle by-pass air: .110
Float was set a little high so lowered it to 1/4"
Needle and seat vacuum tested and held for hours.

Looking through cliffs book, seems like the idle down, mixture passages and lower idle air bleeds are all a little small compared to some of the recipes.

Where should I look to cure this?
Thanks.
Phil

[Cliff Ruggles]

Your carburetor "recipe" should be adequate for what you are doing.  Before making any carburetor changes get the idle speed as low as you can and gently "tip-in" the choke flap or place your hand over the choke housing area and see if the engine speeds up and smooths out.

I would also try more initial timing.  Your compression ratio is pretty "low" for the CID and camshaft specs so it's going to enjoy more timing at idle speed.

Do both of those things before adding any more idle fuel......Cliff

[68rs/ss]

OK, I will put it back together for another try. It did smooth out with more timing and it did run better when I put my hand over the carb.
It's a little discouraging hearing the cam is not the best choice for the application. I sent my engine and car details to "cam guy" at company and that's what was recommended.
Do you have any recommendations? Hate to do a cam change, but I do want this to run without any issues. Better to do it now before it goes in car. You've been very helpful in the past.
Phil

[Cliff Ruggles]

You simply don't have enough compression IF you are needing to add a lot of timing and fuel at idle speed for the cam being used. 

Doesn't always make it a bad choice, but from what I've seen with these things if you find your engine wanting a lot of timing at idle, and you aren't making a lot of vacuum without adding a bunch of timing, the cam choice isn't optimal.

Sadly I see a LOT of this sort of thing these days.  Started back when someone (who needed to go very quickly back to their day job and stay the hell off the Forums) came up with some proverbial "brick wall" of 9.5 to 1 compression for these engines if you want to burn pump gas in them.

That statement alone is probably the most inaccurate statement ever made related to these engines......FWIW and IMHO.

Anyhow, next time it's up and running do a vacuum reading at 700-750 RPM with 8 degrees timing.  Increase it to 10, 12, 14 and keep going till it's pretty happy, and take a vacuum reading at each point. 

Once you reach your "happy spot" shut the engine down, let it sit 3-5 minutes and see if it "bucks" the starter on a hot restart........post the results.......Cliff

[Kenth]

You might try the 1965 Impala High Performance vacuum advance (STANDARD MOTOR PRODUCTS VC181) and use full manifold vacuum at idle.
Starts @ 5-7 in/hg and have 16° @ 11-13 in/hg.

This will make a stronger "pull" thru the idle ciruit due to bigger difference between atmospheric pressure and vacuum beneath the trottle blades.

[old cars]

Your cam and compression are alright . Correct timing for the situation is the number one starting point .
Kenth is on the right track if you are using a points distributor and you need more timing with vacuum advance at idle. Like Cliff said post results after stepping up timing with vacuum readings.

[von]

In addition to the above make sure your secondary throttle blades are absolutely closed all the way. Be sure there's a little "slop" in the linkage rod that connects the primary and secondary blades. Hold the secondary air valves (flaps) open by hand and hold the carb up to a light to see if the sec blades are shut tight.

[Cliff Ruggles]

Good advice Kenth but we're a bit early in the game here to start running 25-30 (or more) degrees initial timing.  Before that happens we need to know vacuum readings and how much timing it's going to take to get good idle quality.

The carb already has PLENTY of idle fuel for this application, but we're also assuming no fundamental issues either.

The cam may be "alright" for the application, but that remains to be seen.  It's only around 400CID and dubbed 9.5  to 1 compression.  If it's actually 9.5 to 1 and doesn't make at least 12" vacuum with that cam with only 12-14 degrees initial timing then it's seeing it as s pretty "hefty" camshaft for the combination of parts, or the compression ratio isn't as high as we think it is.

Doesn't mean it woln't work OK, but personally I consider having to run the timing clear off the scale at idle and open up the carbs idle system quite a bit more of a "crutch" fix than a good method of tuning.....FWIW.....

[lightning boy]

68RS, you never gave the main air bleed sizes. Unless I overlooked this.

[68rs/ss]

Took Sunday off.
Put carb back together today after checking everything carefully and really didn't see any problems. Although, I've only done a few of these and may have missed something. I wonder if the new idle tubes are plugged or something? I did run this on a 350 for a test fire last year and it did work ok then. So not sure. So, Put it back on engine and tried to do the test that Cliff had suggested. Really could not get it to run smooth enough to get any reliable reading at any initial advance. Vacuum was fluxuating between 10 and 15 in/va. Started at 8 degrees and moved up to 12 or so. Eventually, I did advance it to around 30 degrees and it seemed to work a little better. vacuum there was around 12, but not steady. Was really hard to get accurate reading as engine was "hunting" so bad at idle. I could get it down to 750-800 rpm . Hot restarts are not happening. I do not have vacuum advance hooked up.
It did smooth out when i cupped my hand over the choke to restrict the air flow. Seemed to like this. although, didn't cure it completely.
I've never had an engine this hard to set. I will be trying a different carb and different distributor in the next couple of days, just to see.
I am starting to wonder if I have a intake gasket leaking. It is a new Q-jet RPM and it did need to have some of the intake bolt bosses files down so it would fit.
This engine is a true 9.5. compression. Heads were cc'ed, piston/deck checked at .017 ands a .020 steel shim gasket to get a good quench. There were basically only two forged piston options to choose from, so it was a thought out build. I didn't want to deck block to loose right engine code for my car. So pretty happy to get what I did with the few options available.
If it turns out that this is what the engine personality will be like, I certainly have no issues with a cam change and using my cast intake. I want a strong, fun, reliable street engine. Something that can be driven on a day trip. Of coarse, I will run her through the gears once in a while too..
Main air bleeds are aprox. .113"

So tomorrow, i will get back to basics. Check plugs and may remove intake. Its easy sitting on test stand.
Will keep you posted with any new developments. Thanks for all the help. Definitely learning here.
Phil

[77cruiser]

If it smoothed out by choking a bit, needs more idle fuel or it has a vac. leak.

[Cliff Ruggles]

"Really could not get it to run smooth enough to get any reliable reading at any initial advance. Vacuum was fluxuating between 10 and 15 in/va. Started at 8 degrees and moved up to 12 or so. Eventually, I did advance it to around 30 degrees and it seemed to work a little better. vacuum there was around 12, but not steady. Was really hard to get accurate reading as engine was "hunting" so bad at idle."

If you couldn't get it to idle smooth and decent vacuum there is a fundamental issue someplace probably unrelated to the timing and idle fuel delivery from the carburetor.

Could be as simple as how I cured one today.  Was getting my ars handed to me testing a carb done by a good friend.  It was correctly rebuilt, used my parts, and I went over every detail on the carb and couldn't find any issues anyplace.  My friend told me that it ran horrible on his test engine no matter what size idle tube he tried, main jet or APT setting....Hum?

Testing on my engine confirmed his findings.  The carb resulted in HORRIBLE idle quality so I had him take it apart and make several changes to it and with each test no improvement whatsoever.  I was doing other things in the shop each time he made small changes to it but did look it over closely and couldn't find anything obviously wrong.

Right before the last time it went back together for another test I noticed that the carb had been sealed over the bottom plugs with JB Weld at some point.  I hadn't noticed this earlier, but did ask the builder and he said he just left it on because it passed a leak test so I never gave it another thought.  Just to make sure it wasn't causing an issue I did a closer inspection.  I found that on one side there was a very slight witness mark on the glue and low and behold it was sticking up just high enough it was holding the baseplate away from the main casting when the screws were tightened up.

I ground it down flush, put the carb back together and ALL the problems at idle disappeared.  No more lean idle, surging, hunting, no response with the mixture screws, etc.  Yes, one little detail was causing ALL the problems we were seeing.

For what you are seeing it sounds like a vacuum leak someplace, and probably a pretty decent one as you can't get the engine to be happy no matter where the timing is at.  That isn't enough cam in your build to need 30 degrees initial timing to start to get happy......IMHO........Cliff 

[Kenth]

What type of ignition system? Does it have correct voltage/current to the coil?

[old cars]

"Engine is 9.5 CR using closed chamber heads, with mild bowel cleanup and good flowing valves. Cam is Crower with 224intake, 232 exhaust, .542 lift intake, .514 exhaust. Lobes are at 112 degrees. "

The static CR must be based not only on fuel octane but also intake valve closure point.
If the compression ratio isn't in line with the cam duration , (the closure point of the intake valve) , the dynamic CR, and cranking compression , will consequently be low. This not only kills torque everywhere in the rev range, but also significantly reduces the engines low end output.

A good test to establish that an engine has a high enough CR is to do a cranking test. Assuming that the rings and valves seal perfectly, then even a modest street motor should show at least 180 psi if cam and compression are roughly right. For a regular use performance street motor expect to see 200 psi.

Assuming no pressure is lost to leakage, anything below these levels indicates too low a CR.
For these reasons it is important to follow the CR requirement given for each cam. If for some reason the required compression ratio for a cam can't be obtained choose a shorter duration cam; you will like the results better.

[68rs/ss]

Thanks for all the replies. I did manage to get it to idle with no nizzle drip. RPM hovered between 790 and 840. Vacuum was between 12-13. Initial timing was 12-13 degree's. I will see if i can get it any better tomorrow. Hot restarts are not happening. I went through carb again and changed both top and bottom gaskets. I did find the new base gasket was split and separating. Replaced with old one. This seemed to help.
The past few days, I have been doing alot of reading on cam selection and CR. Thanks "Old Cars" for the reply. So what is a desirable Dynamic CR for a good street engine. My cam card says intake closes at 40 degree's ABDC. used a calculator on line and it came up with 8.78: for my combination (if I did it right).
Phil