tune up tips please

[billschroeder5842]

So, my little 383 is running rough. I think I have an intermittent miss in two of the cylinders. What gives me this thought is that the engine vibrates pretty bad at 2500 rpms and up and when I squirt the headers with a water spray two of them (1 and 4) take longer to burn off than the others. However, it starts right up with no issues and burn normal oil. "IF" there was a rebuild, it was in 1979.

Tomorrow, I'm going to do the "pop the plug wire off the cap while it is running and see what happens. I'm hoping a bad plug or two is causing a misfire.

Here is what is done to the engine....mild cam, headers, aluminum intake, edelbrock performer carb and electronic ignition.

I bought new plugs, rotors and cap. Anything else I should double check? What should I set my plug gap at?

I feel stupid for asking because as a kid I did tune ups weekly, now it has been a couple of years!!I'm forgetting more than I remember!

Thanks!

[Cooter]

Bill, I don't doubt your 383 might need a tune-up just for good measure, but usually, a bad plug miss would make the engine shake at idle, or very low RPM's...2500 and up sounds like a balance problem or something...

I'd set the plug gap around .035-.040 with stock style points...
Oh and Bill, never feel stupid for asking questions.....

[greenpigs]

Check your plug wires for ohms resistance. Or if you got the spare cash grab some Firecore50 plug wires. Check your fuel filters and replace if they look old, cheap fix. Also make sure your vacum advance is working properly.

[billschroeder5842]

Any good "hack mechanic" ways to check the vacuum advance operation? I've played around with it enough to know that something is not feeling right.
For instance, I tried the distributor hose on both of the two front ports on the eddy at idle and no difference. The right side seems to be "pulling" all the time and the other....well, it can't tell what it does although that is where i currently have the hose.

Something funny....I'll get the car up to about 2500 rpm, disconnect the advance and the motor seems to smooth out. Hmmmm, I though just the opposite would happen where faster the rpms the more advance I'd need.

Cold and wet today in DFW so it is a perfect day to fiddle with the car!

[greenpigs]

You can hook a vacum pump up and check or suck on line and see if you feel anything. Another tip is start up car at night with no lights, the darker the better.  Then pop the hood it should be just as black. If it looks like a light show replace the plug wires and check again.

[TylerCharger69]

Bill, I don't doubt your 383 might need a tune-up just for good measure, but usually, a bad plug miss would make the engine shake at idle, or very low RPM's...2500 and up sounds like a balance problem or something...

I'd set the plug gap around .035-.040 with stock style points...
Oh and Bill, never feel stupid for asking questions.....

There is no such thing as a stupid question....but....without asking...there are stupid mistakes!!!

[71383bee]

Any good "hack mechanic" ways to check the vacuum advance operation? I've played around with it enough to know that something is not feeling right.
For instance, I tried the distributor hose on both of the two front ports on the eddy at idle and no difference. The right side seems to be "pulling" all the time and the other....well, it can't tell what it does although that is where i currently have the hose.

Something funny....I'll get the car up to about 2500 rpm, disconnect the advance and the motor seems to smooth out. Hmmmm, I though just the opposite would happen where faster the rpms the more advance I'd need.

Cold and wet today in DFW so it is a perfect day to fiddle with the car!

The port that is pulling at idle is manifold vacuum.  The other post is ported which should come in at part throttle.  That is where the advance is supposed to connect.  If you connect to the manifold side it will add timing to the motor which should pick up the idle. 

What is the timing?  Initial and total and all in by what RPM?   

[billschroeder5842]

Timing is 10-12 btc

I have the vacuum pulling on the "part throttle" side, so why does the motor seem to be smoother when I have no vacuum at all? What would happen if I just left it off?

[71383bee]

Timing is 10-12 btc

I have the vacuum pulling on the "part throttle" side, so why does the motor seem to be smoother when I have no vacuum at all? What would happen if I just left it off?

I am assuming initial for timing.  That is low.  Rev her up till she stops advancing with the VA unplugged and see where its at. 

Get you timing in line first before doing anything else.  Most mopars like 16 to 18 initial and 34 to 36 total all in by 2500 RPM or so. 

If its running rougher with her connected it could be a vacuum leak.  When you unplug it does it pick up in RPM with the port un capped?   

[billschroeder5842]

**UPDATE**

OOOPPPPSSS.... The mechanic that (usually) does a good job set the initial timing at 39!!!!! No wonder the motor ran bad and shook like mad at any speed. I reset the initial timing at 18 and the engine is very smooth at 2500 ----- all this is when the car is in neutral. I might have a slight miss but my guess is that a spark plug needs changing.

HOWEVER (you knew this was coming) I get no power, back firing when it is in under load and when i try to give it gas. At this point the car is not drivable.

Oh, if it idles for a long time, it will eventually die. It will restart okay, but will not hold an idle for more than 4 minutes or so before puttering out.

The plot thickens!

[Cooter]

You did check the timing at idle with the vac. advance UNPLUGGED right? @ 39 Initial, I wouldn't have thought you could have started it up at all....

[71383bee]

I agree...are you sure that wasn't total?

With the VA unplugged fire it up in idle and take a timing reading...then rev her till she stops advancing and take a reading.

The dying after idling for a while is weird too.  Is it starved for fuel?  How old is the gas in the tank?    

Wait...I just reread your post...do you mean it is idling at 2500 RPM?  That is way too high.  Will it not idle down and if do does it run rough...I would suspect a vacuum leak at that point. 

[greenpigs]

I would check the vacum first, with a mild cam you should have 16' at least.

[71383bee]

I would check the vacum first, with a mild cam you should have 16' at least.

16'...Now THAT's a lot of vacuum!  JK...I know you meant 16"

[HPP]

The engine running good comes down to air, fuel, spark, and compression, at the right times, in the right amounts. As you start checking out those variables, you will eventually find one, or more, that are not right.

Rough idle could be plugged fuel filters (in tank, in line, or in the carb), bad/weak plug wires, bad/weak plugs, or vacuum leaks. A problem that is often overlooked is a bad power brake boster. It can cause idle problems by the massive vacuum leak it generates.

Back fires are ignition or cam timing issues, or blown power valves if using a holley.

Set initial timing at idle without vacuum advance. Rev after setting initial to see initial plus mechanical advance. Plug in vacuum and rev to see total. Vacuum can be adjusted with a hex wrench inserted in to the vacuum cannister.

[TylerCharger69]

I'm wondering if his balancer/dampner has maybe spun giving him a false timing reading??? Meaning the outer portion has spun apart from the center where the rubber insert is??   Ive had that happen before once....I've only seen that a few times in my life, but i s'pose it's possible.

[billschroeder5842]

Tyler--I thought that too as I've never been able to dial in the timing. I just chalked it up to not knowing what I'm doing!

If that is the case, would I be better off timing through a vacuum gauge? I had an old 77 corvette years ago and a guy showed me a trick to time the car through the vacuum gauge as it is a "truer" measure of the motor. I would spin the distributor unit the gauge was steady and about 17--the motor ran smooth after that.

Also, it is funny that VA seems to have limited effect on the distributor. Maybe when it is properly timed it work?

The car idles at 750ish---the 2500 is when I'm revving the motor in park/neutral. It is back fire when in gear.

I'm going to check the fuel pump. Oh, does anyone know will a fuel pump on a 318 work on a 383? Not sure but I have a brand new one in the garage.

The weekend is fast approaching!!

Thanks-I appreciate all your help!

[billschroeder5842]

**UPDATE**
Well I think I found the problem but (of course) created other little issues in my discovery

When I was giving the car the tune up, I popped of the distributor cap and found that the center metal contact on rotor was bent (!) at a weird angel and was grinding against the distributor cap!

I wore through the little "Black ball" contact on the caps and was scraping against the brass. Who know how long that was going on.

Hopefully replacing with a new cap and rotor will solve my weak idle, back fire and overall poor running condition!

Now if only (See little green mean wire in electronics) if can figure out some electrical stuff!

Thanks for your help and responses!

[squeakfinder]

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