Engine will only run above 4000 RPM. Carbs or timing?

[madkaw]

my money is still on electrical problem. Kind of fun on-line troubleshooting at someone elses expense-sorry Chris. We'll get it figured out, usually it is stupidly simple:stupid:

Here's a bit of an article pertaining to this. The primary resistance is a HUGE factor for the HEI. It wants much more current than a stock coil(3 ohm) will give. Might not seem like much( 1ohm vs. 3ohm), but as far as amperage it is a lot.

This is an important factor since all the ignition companies we spoke to stressed the idea of properly matching the coil and module. The best way to do this is to use the coil specified by the manufacturer for its specific module. For example, ACCEL offers a stock replacement and two different performance modules for the typical four-pin HEI. Each requires its own coil to create optimal ignition power. What this means is that you should not mix and match coils and modules. In one particular situation, we combined a stock replacement module with a Pertronix coil and the engine just seemed to run flat—as if the ignition timing were retarded, even though it wasn’t. As soon as we replaced the stock module with the matched Pertronix module, the engine instantly responded and was again crisp and fun to drive.

Read more: HEI Coils And Modules - Tech Article - Chevy High Performance Magazine

Edited May 3, 2013 by madkaw

[SteveJ]

Thanks for the link, Steve. I just met someone at the Georgia Z Club meeting who may need to replace the ignition box in his 260Z. I was going to look at adapting the HEI to drop in.

[Wade Nelson]

Disconnect the fuel line and start it on ether. If you can get it to idle on ether it's a carb problem. If it still only runs above 4000 rpms its either a timing or a mechanical problem.

First thing I would do is put a vacuum gauge on it to rule in/out vacuum leaks, mechanical problems, etc. Sounds to me like it may have jumped time, distributor stabbed wrong, etc...

[Zed Head]

A while ago I discovered that GM made an external version of the under-the-cap HEI coil. It's used on a variety of cars and trucks, like the 1977 Nova. It's ugly but it's the coil that the module was designed to use. I've been using it since then with no problems at all and smooth performance. It has a primary resistance of about 0.8 ohms, so probably has a shorter saturation time also, than the 1.0-1.2 ohm Z31 or late 280Z coils.

Accel makes a much better looking version. Search Accel remote mount HEI coil to find theirs.

Here's an image from RockAuto of the AC Delco brand.

Edited May 3, 2013 by Zed Head

[grannyknot]

Was that Pertronix matched for your HEI module? What application was the HEI from?

Is this EXACTLY the way it came off the running engine?

Not sure what coil p/o was using, I have emailed him but no repsonse so far. The first HEI module that came with engine was made by Standard Motor Products.

Since then I have purchased a Pertronix flamethower coil and Pertronix flamethrower HEI module. I assumed they're

designed for one another but who knows.

Chris, any results with cleaned carbs?

Bart

Hate to say it but no change at all, everything the same except now I'm temped to take a sledge hammer to this POS and teach it lesson.

Disconnect the fuel line and start it on ether. If you can get it to idle on ether it's a carb problem. If it still only runs above 4000 rpms its either a timing or a mechanical problem.

First thing I would do is put a vacuum gauge on it to rule in/out vacuum leaks, mechanical problems, etc. Sounds to me like it may have jumped time, distributor stabbed wrong, etc...

Wade, I've only seen either in spray cans, can you describe how to do it, should I empty the fuel bowls?

Thanks,

Chris

[madkaw]

Chris,I would assume they are matched.

[madkaw]

When you did the engine swap, did you actually remove the plug wires from the dizzy?

If so, are u 100% sure #1 wire lines up with rotor at TDC?

I know you checked your order, but does 1 start in the right place?

[Zed Head]

madkaw touches on another possibility, or maybe is referring indirectly. Maybe your timing is just off. Too many posts to go back and see if it's been verified.

By the way, my post #64 was in reference to Steve's post #62. Although, it could apply to anyone looking to avoid all of the module and coil resistance matching stuff.

[Wade Nelson]

I've only seen either in spray cans, can you describe how to do it, should I empty the fuel bowls?

Disconnect the fuel line and block it and/or disconnect electric fuel pump.

Start the engine and when it starts to die from lack of fuel start spritzing ether into either the throat of the carbs (air filter off) , the PCV port, brake booster line, or any other vacuum line that gets it into the intake manifold (ai9r filter on) Big 2-3 second blasts. Keep spritzing to keep the engine running on ether.

You can run a lawnmower or a V8 on ether, brake cleaner, Lysol, WD-40, virtually any flammable fluid out of an aerosol container no matter how SNAFU the carburetors are, water in the tank, anything. Air, fuel, spark, you're simply substituting ether for gasoline as fuel.

If you can idle the engine on short blasts of ether then your problem is with your carbs. If, again, it will only run above 4K, it's a mechanical problem.

I strongly suggest you acquire a $15 vacuum gauge and RULE OUT mechanical problems before you do the above or anything else. Here's a tutorial...

http://www.classiczcars.com/forums/open-discussion-280zx/47347-how-read-vacuum-gauge-30-secs-less.html

In less then 10 minutes you can have your problem diagnosed. Get 'er done.

[grannyknot]

I thought it was time to go back to basics, with the #1 piston at top dead centre this is what I'm seeing,

Is this 10 degrees off or bang on?

Cam lobes look right

The punched timimg marks on this new (15,000km old) sprocket are 5 o'clock=1, 2 o'clock=2 and 11 o'clock=3, isn't the #1 mark suppose to be at 2 o'clock at TDC? Could this mean that the timing chain is already advanced ?

Red marker on distributor housing is where the raised mark on the cap sits when clamped down.

with the rotor on, rotor moves in a counter clockwise. Again, all these pics where taken without rotating the engine in the position I believe to be TDC,

After trying to start it again with no luck I pulled the triples off and re-placed them with a set of SU's from the original engine that worked perfectly before I pulled the old engine. Interesting results.

Using no choke or gas pedal the engine started right up and reved up to 4-5000rpm back down to what I thought was stalled then came back to life and back up to 4000rpm then back down and did this a couple of more times before it really stalled. I have a couple of videos of the vacuum gauge as it does this dance.

Here are the links, First video it doesn't want to start, the revs you hear are the engine on the 2nd video I'm not even touching the pedal!

http://youtu.be/toFAstydu-Y

http://youtu.be/rB79ZnEV8Ec

Edited May 4, 2013 by grannyknot
ever changing scenerio

[madkaw]

Chris,

What is the #1 plug wire in relation to where the rotor is at TDC-that's what I want to see. Is the #1 plug wire lined-up with the rotor???? You never said whether you removed plug wires from the dizzy in all this process of swapping.

I think you seen that it isn't carburation -it's something else. It's ignition-timing or malfunction of spark.

After watching your video-all I can say WEIRD, and that sucks.

I am definetly scratching my head.

[SteveJ]

What happens if you retard your timing a few degrees?