GM HEI ICM AND DUAL 32/36 WEBERS ON L28

[jalien]

So many questions!

 

Is anyone using the gm hei ignition control module on a L28? if so, what internally regulated coil works well? Also, should the spark plug gap be the same for FI or carb on a L28?

 

Thank you for future answers!

[datzenmike]

You can use an HEI if the original matchbox or remote igniter was to fail and a new module wasn't available or too costly. EI (electronic ignition) was on all '78 and up Datsuns and most earlier California vehicles. There's no advantage to switching to an HEI if the original EI is working. All L26 and up 260z cars had some form of EI. L28s in the 280zx used a matchbox EI till about '80 when the matchbox module was dropped and a CAS (crank angle sensor) was used. It was still an EI but the ECU did the work.

 

The cols are not 'internally regulated' but for use with  an EI system or HEI you need an EI coil rather than a points coil. The EI coils are 0.75-1.0 ohm primary resistance. This is about half the resistance of a points coil so will flow more current for a hotter spark. Any coil for a '78 and up Datsun will work.

 

Plug gap is generally based on the voltage available from the ignition system. Points ignitions generally run a plug gap of 0.032". The higher output EI ignitions can be gaped wider at 0.038-0.042". Carburetor or EFI wouldn't matter on a stock engine. 

[jalien]

Thanks! We went HEI because the car was completely stripped and the wiring harness was tossed. We were going to go holley sniper but funds dwindled so we settled on dual carbs and hei. The car runs and pulls hard af. chirps the tires going into 2nd, and 3rd. ive seen the rpm gauge go to 8k and hauling ass. the gauge is possibly incorrect 😛

 

all that aside, we do have a major issue. when we blip the throttle, the car wants to die. we are running a carter 4070 fuel pump, located where the original fi fuel pump was. i couldn't tell you what the jetting is on the carbs, but i believe they are stock. we also sputter after we turn a corner.

 

i have not checked fuel pressure yet. carbs were rebuilt except for the power valves 😞 so, im wondering if i need a better coil and or different pick up coil and or spark plug gap. we are using ngk bpr5ey-11 (6937) at the preset gap of .044". we are using a "standard" 1305 coil with internal resistor. its at .5 primary and 8.13 secondary. the coil that was on the car when i got it is 1.5 primary and 10.94 secondary.

 

I hope that info helps?

 

[Crashtd420]

Are you running a return line for your fuel system?

 

Also get rid of that pressure regulator.... looks like the mr gasket and the are pretty much junk.....

 

I use that same Carter pump.... I was using a Holley 1-4 psi regulator but I recently added a return line and removed the regulator.. 

Its rated for the proper psi so I'd try running without the regulator and use the return line.... 

 

Also it might be beneficial to put the tee between the 2 carburetors and the return line before the tee....  

Edited March 13, 2022 by Crashtd420

[Crashtd420]

Ok I see 1 tee between them but I would definitely move that return line off the front carburetor to where the regulator is and see if that helps...

 

[datzenmike]

Faltering when blipping the throttle or exiting a corner has nothing to do with the fuel pump. All the pump does is keep the carburetor(s) full of fuel.

 

The sudden opening of the throttle, the transition from idle to primary running, passes through a zone where the idle can't supply enough fuel for the sudden demand and the primary isn't passing enough air through it for it to effectively generate enough venturi vacuum to suck fuel in. The engine runs lean and stumbles. Most carburetors have a mechanical accelerator pump that squirts a stream of raw fuel into the primary to make it richer, and help it through this point.  

 

With engine off work the throttle several times while looking down into the carburetor.(s) What you should see is a strong squirt of fuel from the accelerator pump.

 

 

The 4070 fuel pressure is 5.5PSI, a little high for a Weber that likes about 3 or just under. It seems to be working fine but this may be a problem later with age. Remember this later if they begin to flood. An inline regulator should fix this but not needed right now.

[jalien]

Thanks! Going to do this today and see what happens...

[datzenmike]

Fuel pump then regulator then past each carburetor and then to return. Cool fuel has to pas both carburetors. What you have look alright. Return line must have a restriction in the end or fuel pressure will not build and fuel will ignore the carburetors and take the easiest path back to the tank. Restriction looks like this... a large pin hole. The return is NOT a pressure regulating device, it's just a small designed leak.

 

 

The return is just a small leak that allows cool fuel from the tank to push over heated fuel from the lines near the carburetors back into the tank. Any gas  bubbles from extreme under hood temperatures will also be pushed back into the tank.

 

 

 

Make the fuel lines to the carburetors as short as possible to reduce heat absorption, maybe insulate them too. Return doesn't matter. If I was doing this I would look at drilling and taping the the near side entrance to the float chamber, plug the other side and run the fuel lines on the fender side as far away from the manifolds as possible. These things get incredibly HOT. Later zx engines had mini fans and ducts to blow cooling air over the fuel injectors and fuel rail.

 

http://images.gtcarlot.com/pictures/85778013.jpg

[jalien]

no go on the fuel line re-configuration 😞

[datzenmike]

It was a long shot. It's workable as is... if you have problems in the summer heat try insulating those lines.

 

Gas has several components that all boil at different temperatures some as low as 100F. Ethanol boils at 175F others all the way to 400F. Most of the time under hood temperatures are well under boiling point of water but on hot summer days after shut down is what's called heat soak and it gets very hot. There is no fan or movement of air and there are things like the exhaust manifold that is 600-700 degrees. Hot air is trapped under hood with hot engine. 

[jalien]

i had a couple of mechanic friends take it for a spin after the alteration. they were thoroughly impressed of how it handles, except for the main issue. one suggested i try a hose from valve cover to forward carb and a hose from crank case vent to balance tube. do u think maybe i need to install the the water plumbing for the intake manifolds for atomization? i did notice that if i set the choke and get to 2200 rpms, i can blip the throttle all day. also, we are getting the stream of fuel from the accelerator pump.

[jalien]

So, I need to bottleneck the return? that makes sense.

 

 

[jalien]

so we tried a new coil, an edelbrock 1.4ohm 42kv. we changed timing to 20btdc. we disabled the fuel return and still cant blip the throttle. we gapped plugs to .035". btw, plugs were covered in black soot only after about an hour of run time? still not able to blip the throttle.

[datzenmike]

There's an old saying that 90% of electrical problems are caused by the carburetor and 90% of carburetor problems are caused by electrical problems.

 

 

HEI or even the stock matchbox modules use a coil with 0.75 - 1.0 ohms. This will draw more current through them and make a hotter spark. Hold the coil wire near a ground and turn the engine over with the starter. You should get a 1" spark at the least.

 

Twenty degrees advance is almost twice what's needed.

I'm not sure it would even run that advanced so this begs the question are you setting it correctly? Perhaps misreading the timing marks? It's easily done. Timing is about 12 BTDC on an L series. I imagine the L28 is the same or close. Too much advance will fight the engine. Find out what the stock advance is and stick with it or you may combine two problems making it even harder to diagnose.

 

Black plugs are a problem...

Make sure the chokes are fully off once warmed up, that's the source of the over rich sooty plugs is my guess. If the chokes are off then the plugs should self clean themselves while driving. (at least 20 minutes on the highway) If the chokes are off and the plugs still black then that is a problem. Perhaps over jetted or carburetors are flooding while driving. Flooding may be from too much fuel pressure. Webers like under 3 PSI. Take the air filters off and rev the engine and hold at 3,000 for 30 seconds. Watch to see if the carburetors over flow.

 

 

On 3/12/2022 at 10:28 PM, jalien said:

 

 

 

all that aside, we do have a major issue. when we blip the throttle, the car wants to die. we are running a carter 4070 fuel pump, located where the original fi fuel pump was. i couldn't tell you what the jetting is on the carbs, but i believe they are stock. we also sputter after we turn a corner.

 

 

 

Stuttering...

Blipping the throttle or balking or stuttering when stepping on the gas exiting a corner in second and low revving is classic indication of accelerator pump not supplying enough fuel. Look down the carburetors and work the gas pedal. You should see a strong squirt of raw fuel.  

[jalien]

Soo, no overflowing that i saw. set timing to 12 btdc. changed back to the ignition coil i was using before. acc jet is squirting fine. still no go. after turning off the car i checked pooling in carb adapter. it was like 3/16" deep. float bowl had about 1/2" of gas inside. it does seem like when we double blip the throttle it will rev quickly instead of a slow rev. makes me think we need bigger acc jets?

[jalien]

also, my current acc jets only squirt into primary. do i need the dual flow jets instead?

 

[datzenmike]

Only need the primary on the 32/36.

 

51 minutes ago, jalien said:

 after turning off the car i checked pooling in carb adapter. it was like 3/16" deep. float bowl had about 1/2" of gas inside. it does seem like when we double blip the throttle it will rev quickly instead of a slow rev. makes me think we need bigger acc jets?

 

You took carburetor off and there was 3/16" of gas in the adapter?????? Don't the Webers bolt directly to the intake? without an adapter?

 

Find out the correct float level for a 32/36. 1/2" of gas seems a little low.... 

 

[jalien]

well, probably with the floats actually in, the depth of ga will rise. these webers do not bolt directly to the stock intake manifolds and need an adapter. its weird. i personnaly dont like it. the webers are downdraft, i think thats why. 

 

[datzenmike]

So what's this about 3/16" gas sitting in the adapters?

[jalien]

probably because the adapters are like a p trap and some gas just doesn't make it? attached is a pic

[datzenmike]

Not seeing any adapter plates on these.

 

That much gas doesn't seem right. Combined with black sooty plugs this would indicate flooding.

[jalien]

those manifold adapters bolt right onto the stock intake manifolds at the flange, making it a long trip to the chamber. it does seem like too much gas pooling. but, if it was flooding constantly wouldnt it not want to start or run like crap. the engine starts up right away and stops right away. when we are driving, it sounds good and pulls hard. 

[jalien]

so, from this pic, u can see how the adapter manifold bolts to the stock manifold.