I pulled off the old heads and put on some gt40 heads from 5.0 as well as an edelbrock performer intake.  I did new plugs and wires at the same time.  After I put everything back together I don't have a spark...   Initially it looked like the distributor cap was bad.  The spring loaded connection between the cap and the rotor was tired and didn't seem to be making a connection.  I replaced the cap/coil and got a new battery with more cranking amps ( i think 900) at the same time.  Still no spark.  I tested the timing light on a car at this point as well and it does work....   I then replaced the distributor with a davis unified ignition.  The cables from the battery to the solenoid were pretty corroded so I replaced those.  There was some dip in the voltage to the coil with cranking so I got a second battery and connected the hot wire to coil to it to make sure I was getting 12v to the coil.  Still nothing.  The DUI people said that the distributor would need to be spinning ~ 300 rpm to make a spark.  The starter was not doing that so I replaced it (solenoid to) and while the cranking speed is much better Im still not getting any spark.  I cleaned the ground site on the block really well.  I not sure if maybe raising the compression is making it harder on the starter and I dont have enough cranking speed.  I may add another battery I have in the garage to the mix.  I did the test that DUI prescribed on the coil/distributor and it seems to check out.  I emailed them as well.  I'm stumped.

Okay, ignore (almost) everything I said below the dotted line since I thought you had conventional coil and points.  After writing that up, I when back and saw that you replaced the distributor with a David Unified Ignition (distributor).  I thought you had gotten a new coil, not an electronic distributor, so had to look it up.

That said, I honestly don't buy the '300 RPM or it won't spark line).  A standard coil and points will spark (if appropriate voltage) whether it is 5,000 RPM or 1 RPM.  The problem with this all-in-one unit is it is hard to determine where the problem lies, as well as trigger a spark.

You said you have +12v voltage to the unit.  I'm assuming it has the snot grounded out of it so you don't need a separate ground (negative) connection.  However, in this picture https://www.jegs.com/i/DUI/314/M35820BK/10002/-1

 I see red and black wires, so it could be possible that it needs a separate ground along with 12v power.  Make sure you have a good ground; maybe the electronic module is internally isolated and it needs its own ground separate from the distributor body, and it needs to be a good ground.

What's the test that DUI had you do?  I'm curious.  That info will help us understand what is going on, and how that test confirms operation.

There should be a way to confirm that it will generate a spark.  

And even if you installed the distributor incorrectly (not at TDC), the most that would do is to cause a spark at the incorrect time in one of the strokes.  But there should still be a spark.  So that isn't it.

At this point, I suspect a wiring issue (ground), or an issue with the unit.  The problem is you don't have a separate coil so you can test that high tension line or the coil itself.  If it is powered correctly, then either it is not sensing the rotating shaft (pick up), or it is flat out DOA.

Interesting, my '97 with PCM GT40 MPI and electronic ignition still uses a conventional distributor cap and rotor; the 'coil' is part of the ignition module, which is near the throttle body, but it has a high tension line that goes to the center of the distributor just like a convention points distributor (except instead of points it has a pick up that sends the signal to fire a spark to the module).

Let us know.

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IF YOU HAVE STANDARD COIL AND POINTS:

I'd do the following:

1.  Check the points gap?  Are you sure they are opening and closing by the distributor shaft lobes as it turns?  I've had them work lose before on a car and stop opening.

2.  With the ignition on (12v to the coil), you should be able to manually open and close the points with a screwdriver.  The points will probably spark slightly, and if you run the coil high tension output to near a ground, you should get a good strong spark.

3. If you still are not getting a spark and you still have 12v to the coil, jump the negative side of the coil directly to ground).  You should be able to short that negative wire fro the coil directly to ground (which imitates points closing, thereby powering/charging up the coil).  When you un-short it from ground (which is the same as the points opening), you should get a spark out of the high tension line.  If you don't, then your coil is suspect (note:  Don't leave the coil connected to ground for long periods; it may overheat).

4. If you get spark when shorting and un-shorting the coil negative side to ground but don't when you move the points, then you have a wiring problem between the coil and the points.

5.  If you see a lot of points sparking when opening/closing them by hand and you are getting a weak or no spark from the high tension wire, it could be the condenser is bad.  That rarely happened back in the day where all cars had points, condenser, and coil (at least in my case), but you will not get a good spark if the condenser is bad (or it could even be shorting out).  So if you did all of the above with no spark, I'd probably change it.

Let us know what you find out.

Get the VOM back out and check the resistance between a good ground on the block to the DUI. This should tell you if the DUI has a good ground?

A rough calculation for voltage drop with a 5 Ohm resistanve is almost 4 volts. Check the actual volts the DUI is seeing when you are cranking the engine. 

Jim, I take it there is only one wire connection to the DUI, the +12v supply line, and not a separate ground connection (ground is through the distributor).

Let us know when you get a chance on the tests DUI had you do to confirm operation.

Also, the coil and magnetic pick up tests only test static resistance.  They don't have you do a manual energize test on the coil, nor do they have you do anything to confirm that the magnetic pick up actually sends the signal.

I know this is a lame question, but is the pick up wheel/spokes there and lined up to where the pick up sensor is?

I'm gonna dis my own suggestion & say it ain't worth the time, as long as you are sure rotor is turning when engine cranks.  If you are getting 12V to input of dizzy & have a good ground, then it is either trigger module or coil.

I assume you have good connection to spark plug wires.  Have you tried to pull plugs & watch for spark from them? 

You replaced starter - are you sure it is turning the right direction?

I worked in a heavy equipment assy factory & we had brand new electronics modules, that had passed testing at supplier, fail every day.  Amazing, isn't it.

Here's a picture of how to do what SNobsessed described for your DUI distributor. (You'll have to rotate the picture or your head 90 degrees)

It's from the electrical section of "The Backyard Hack's Handbook"

It's really pretty easy to do and it'll tell you if the distributor makes spark.

Clamp the distributor in a vise

Clamp a pair of vise grips to the vise

Take a spark plug wire and a spark plug and ground the plug by stuffing it into the vise grips like shown, and hook the other end to any terminal on the distributor

Take a 12 volt battery and 2 test leads and hook the Negative lead to the vise grips. This now has your distributor grounded to the battery thru the vise and the vise grips and the plug is grounded too so it'll spark when you spin the distributor in a little bit.

Now take the other test lead and hook it from the battery positive to the 12 volt feed to the distributor (the red wire in my picture) The Green tach lead in the picture doesn't need to be hooked to anything.

The only thing left to do now is spin the distributor shaft by hand and if it works you'll hear a distinct little "pop" 8 times per revolution and since you have one plug hooked up, you'll see the plug spark once per revolution or every 8th pop.

Now you'll know if it works  If it does, your problem is elsewhere.

Don't forget to unhook the power wire after you're done spinning it.

If it doesn't work, at least you have a new module on the way and since you said you've done all the other tests, that just leaves the module to replace.

If you put in a new module, you'll need some thermal paste/heat transfer paste to spread on the bottom of the new module when you install it, or the module won't last to terribly long.

BTW The distributor in the photo is for a Chevy so the housing looks a little different, but that doesn't matter.

And you'll see that it definitely doesn't take 300 rpm for it to spark

 

This works with the HEI with the coil in the cap, if you wanted to test your old distributor, you'd need to wire up a coil too in order to test it.

So..............That's how an accomplished hack would do it.

It took a lot less time to do the test than it did to write this post 

That is some quality hackery, no doubt.  Yankee ingenuity meets redneck.  Sure y'all not from the South?

JW

Had a situation with a DUI that I installed in a buddy’s 74 SN. 

When he came over with the boat he forgot his key, no problem I had a spare ignition switch we installed and away we went. Installed the unit, new wires, timed it water tested it and it ran awesome. Got back to the house, unloaded the tools reconnected his ignition and away he went. Next day he went to the lake with his family and the boat ran poorly and wouldn’t start then had to get towed.

Long story short.... after testing the next day the dizzy was was getting 12v in the run position, however was getting 0v in the crank and run position. Put my ignition switch back in and it’s been running like a champ for 2 years.

Just a thought...

What style of timing light were you using?  I did the test the other day with an old light that just flashes and it flashed when the plug sparked.

Then I did it with one of them new fangled digital readout advance style lights that reads RPM too...........and it wouldn't flash while spinning by hand although there was spark at the plug. Worked fine on a car, so same results you saw.

I have a little backyard hack distributor machine and if the distributor was at maybe 50 rpm, then the light started flashing so it looks like something in the circuitry keeps the light in the digital timing light from flashing till some certain very low speed

I'd buy a little in line spark checker that goes between the plug and the wire to make it easier to see if the plug is getting spark and crank that thing over and see if there's spark.

Depending on that result, I may have a suggestion or 2 or some more questions also 

Stick that in the end of the distributor shaft and let her rip.

It doesn't really matter, but run the drill in the normal forward direction and that will spin the distributor rotor in the counterclockwise direction that it turns in the engine, if you're looking down at the top of the distributor 

If you have the drill spinning the distributor at 500 rpm for example, that would be like the engine running at 1000 rpm since the distributor turns at half the crankshaft speed.

Then you should see some flashing from the light as you speed things up 

I think it's safe to say the distributor works and if the only way you checked for spark was with the timing light, you should just install it, make sure the timing is roughly set close enough for it to start (#1 at about 5 to 10 degrees before TDC on compression stroke, right firing order(18456273) going CCW around the cap from the correct #1 position and crank it over with the in line spark teste( or a plug) to see if you have a spark, hopefully it starts and you then can use the light to set the timing where you want it like about 10 to 12 degrees BTDC as a good starting point and seeing if you get 32 to 34 degrees total at 3000 rpm

That'll give you 10 at the crankshaft, it all has to do with the distributor on a 4 stroke engine rotating at 1/2 of the crankshaft speed.

JQ

Edit:  turn engine counter-clockwise if RR vs standard.  

I believe he has RH rotation engine, so wouldn't he want to rotate CCW looking at front of engine?

Did you get the proper rotation starter? What direction is the engine cranking? 

You never really said that it's definitely the right starter though

And that's a good thing for sure 

A non digital inductive timing light will work with no issues. You already know the digital  one you have now works when the engine is running (it's not broken)

Here's a good, cheap example with a dial type knob for the advance feature in the link below. The leads are a little on the short side but it works well. Or get your father in laws oldie, it'll work for you.

http://www.harborfreight.com/timing-light-with-advance-40963.html?_br_psugg_q=timing+light" rel="nofollow - link

Maybe try a shot of gas down the carb primary throats. and see if it kicks itself over with that little boost.

Time for another question about fuel delivery, since you have spark  

Way back in post #1 of this thread you mentioned installing an Edelbrock Performer intake.

Did you ditch the 1 inch PCM spacer when you mounted the carburetor to the manifold or did you keep it between the carburetor and manifold? or in other words how is the carburetor mounted to the manifold?

https://www.amazon.com/Edelbrock-2732-Carburetor-Adapter/dp/B000630JXY/ref=asc_df_B000630JXY/?tag=hyprod-20&linkCode=df0&hvadid=309898128610&hvpos=&hvnetw=g&hvrand=7484433107131671709&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011877&hvtargid=pla-569638733036&psc=1

Is your Mr Gasket spacer smooth on the bottom like is is on the top, or does it have funny passages like your old original spacer?

If you're not sure, take the carburetor and spacer off and look at it. (and take a picture to post here)

You should have a gasket between the intake and the spacer and another one between the spacer and the carburetor.

You could have a giant vacuum leak depending on your gasket arrangement and what the bottom of the 1 inch spacer looks like

What works good on the Performer intake is using the flat plate like Gary mentioned with no 1 inch spacer at all.

The plate is needed because of the small, thin seating area on the Edelbrock 2181 manifold.

You would have  a gasket between the manifold and the flat plate and another between the plate and the carburetor.

The PCV hose connection can then be plumbed into the threaded hole in the manifold behind the carburetor. You remove the pipe plug and get a fitting for the hose to hook to. It's in the runner that feeds the #4 and 7 cylinders.

Some people will say that the PCV gases going there will lean the mixture to those 2 cylinders, some will say no problem at all, Plenty have run  that way for years with no issues 

It keeps the height down also when you don't use the 1 inch spacer. The Edelbrock manifold is around an inch taller than the stock one so your height is about the same as original

Before worrying about this stuff though, try starting it with a shot of gas down the primary throats like mentioned earlier so see if it kicks over and runs meaning that your timing is at least close to where it should be. When Mother Nature allows of course 

JQ

Just want to verify what you have. Kinda like a quiz 

Congrats, you passed the quiz and here's the cylinder numbering for the 351W 

I think the first mention of how you have the carburetor adjusted just came today, so how is it adjusted?

It sounds like you put on gt40 heads, an Edelbrock 2181 Performer intake, a new carb spacer and new plugs and wires .

You thought you didn't have spark, but you really did, at least with the new DUI distributor.

You got a free replacement module from DUI 

You verified the rotor spins CCW so the engine is turning the right way.

Timing is now around 6 degrees BTDC and you can see this with the timing light as you crank it over. You're on the compression stroke

You dumped some gas down the carb throats and it sounded like it was trying to start

Did you do this a few times?

Since you mentioned having a compression gauge, what do you have for compression in all your cylinders.

Send me your video of the timing if you want   keno439@gmail.com will get it to me

The spacer is almost entirely smooth with one area that has a little carve out with Mr. Gasket printed in it.  

Thoughts on keeping the spacer or getting rid of it?

Your studs are the right length for the spacer so stick with it as long as the plate is flat on the bottom too.

Probably 1/8 inch pipe threads in the spacer hole. Plug it with a 1/8 inch pipe plug preferably or cover the nipple with a rubber or vinyl cap

Then give it a whirl  

PS timing video looked good

The other end of that hose should have the PCV valve in it and the valve fits in your worn rubber fitting, it should be good for now to see if you get it running since it ran before the work was done

If it were me, I'd remove the right side valve cover. (when looking at the engine from the rear of the boat).

Then remove the spark plug from cylinder #1.  Rotate the engine manually and watch cylinder #1 valve rockers operating. When the piston is at the top of the cylinder after watching the intake rocker close (the rocker comes back up) you are at Top Dead Center at the firing position. Verify TDC with your timing pointer and dampener markings. Then pop the distributor cap and verify the rotor is pointing toward cylinder #1. 

Sly

He has a RH engine and it's turning the right direction which he verified by the distributor rotor going the right way when the engine is cranking over and he says he's using the right firing order and the wires are arranged the right way going around the cap and he knows how the cylinders are numbered. You can verify what he's written earlier in the thread.

He can't post a picture or video here for let's say technical reasons, but he sent me a super slo mo video of his timing light flashing with the timing at 6 degrees before TDC with the engine turning the right way, but that doesn't tell him it's on the compression stroke. People have been taking his word for that with his description of how he checked.

Sounds like a plan...

Remember, when the intake rocker has finished closing, the piston will still be down somewhere near the bottom of the cylinder. You'll have to rotate the engine some more (the compression stroke) and bring the piston up to the top of the cylinder before the pointer aligns with TDC.