[ChuckD]

Hey Gang, I have been wrestling for several years to get this DZ motor to run right. I have been through the carb, curved the distributor, set valves, re-located vacuum advance, and followed most everybody's suggestions. However, I can't understand why I have such a fat-rich idle, and a dying car at hot idle. Above 2500 RPM, it runs just fine, but burns gas like crazy. Oil does not seem to be contaminated.

FYI...the exhaust sat on the garage floor for 3-4 years during a re-do, and when I initially started the car after the engine was done and the exhaust put back on, mouse blew out the tail pipes. This car has great and even compression, clean carb with proper jets and PV, solid ignition, and runs to 6500 RPM without a miss. Idle is set at 950, 14-16 degrees advance initial, and I get 10.5 inches of vacuum. Drive it for 15-20 minutes, and it won't idle, temp is 180-190. Could it be that the mufflers are just internally rusted as the car sits for many weeks/months between drive intervals? Mufflers are 20 years old at least. Help me Obe-Wans!

 

[nashcar]

Do you have the correct PCV valve. Are the floats set correctly. You’re sure the balancer is correct with the timing mark in the right place. The coil and the condenser in the distributor if bad will fail when the engine gets up to temperature. Just giving you my experiences over the years.

 

[DOUG G]

True dual exhaust ? Does the pressure feel the same on each tailpipe ?

Have you tried open headers ?

 

[Yellow69RSZ]

I have to agree in the lines of possibly the coil as I had a coil go bad on a 69 BB and it ran fine when cool and terrible when fully warm. At least its an inexpensive thing to try and rule out, good luck!

 

[1971ls6]

Is it the dz Holley? 2 corner idle carbs with big cams have notoriously been fat. When the motor is cold, it can use the fuel, when hot it is pig rich.

How far out are the mixture screws? Turn them in and see what happens

 

[VI018DZ]

Chuck;
Just my 2 cents worth.
I struggled as you to get a proper tune. Gave up seat-o-the-pants tuning and bought a wideband dual O2 sensor set-up.
Made a huge difference just a few posts here: Tuning a 4053 with AFR

Todd

 

[VI018DZ]

Chuck;
FYI my secondary idle stop had my secondaries closed too much to get the trim screws adjusted for a proper idle.
I'd start there but tough to do without a O2 sensor.

Todd

 

[ChuckD]

Hey folks, thanks for the ideas..

1. I have the mixtures set where it runs best-smoothest-ish
2. The points and condenser are new, and has had the same issue with the old ones.
3. The coil....I will give that a try.
4. I don't have headers, but I wish I did, as I have a neighbor I'd love to annoy.
5. Carb is now off, but I will set floats again, same with secondary throttle plates.
6. PVC is good, and balancer is original as is the timing cover tin.

As I said, runs fine for first 15 minutes, then runs poorly at idle and will die at stops. Will restart but requires WOT to do so.

I will advise any solutions found....and I do plan on putting on a new correct exhaust system next month.

Thanks again!!

 

[Matt 69]

Chuck, just a thought, but requiring WOT for a hot restart might be vapor lock or fuel percolation in the bowls. This has happened to me in the past with Holley carburetors. Just something to think about.

 

[cam67]

Since a mouse came out of the exhaust, what else is in there? A friend had a 64 El Camino that sat for a while. It would never run right. Took the exhaust off and found about 10 pounds of dry dog food that the mice had carried up there.

 

[SoCal805]

2. The points and condenser are new, and has had the same issue with the old ones.
As I said, runs fine for first 15 minutes, then runs poorly at idle and will die at stops. Will restart but requires WOT to do so.

I will advise any solutions found....and I do plan on putting on a new correct exhaust system next month.

Thanks again!!

You ever consider running a Pertronix,, or similar, ignition vs a P&C??

Chuck, just a thought, but requiring WOT for a hot restart might be vapor lock or fuel percolation in the bowls. This has happened to me in the past with Holley carburetors. Just something to think about.

FWIW I use one of these under carb to minimize/eliminate vapor lock.

https://www.amazon.com/gp/product/B00062YBPM/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

 

[ChuckD]

Once again, thanks for the advice! I plan on cutting open the exhaust system, and we'll see what archaeological finds there are! Also, I have an Edelbrock composite -blue spacer/insulator, so that will go on next month also. An updated ignition is also under consideration. Thanks and keep the ideas coming.

 

[VI018DZ]

Didn't here you say what power valves you have and secondary throttle opening? Again trim screws will be ineffective and hot idle runoff without proper setting check those first before you install that carb. I had to pull mine a few times to get the secondary opening to where idle trims become effective. Cured all but very hot day runoff.
Tune for proper idle is tough again without O2.

 

[frankk]

Car stalls at stop sign and runs rich........ consider changing the needle and seats and then readjust the floats.

 

[bob15]

My 67 has a Mallory Unilite ignition system on it (1991 vintage) and found that the module was dying on it and caused similar issues. The car would run fine when the engine was cold, but once it warmed up; it wouldn't idle, starting a hot engine required the gas pedal on the floor as it is was flooded and basically would run like crap below 2,000-2,500 erpm. The issues themselves started after getting stuck in traffic for about 30 minutes (stop & go type traffic).....

I figured out the issue after swapping complete distributors with my truck at the time. Dropped the car one into my truck and it ran like crap, then took the truck distributor and put it in the car and it was beautiful running car again. I then called Mallory in NV and they had me send the distributor to them for a free repair. When they sent me distributor back it had a new module and a ton of dielectric grease under it.


Might be worth looking into the distributor.....

 

[ssrocket67]

I believe the OP is running points, but good advice on the module.

 

[bob15]

Maybe, but the OP said the ignition was solid, which to me equals solid state (electronic).

Even if the OP has points and a condenser.......a failing condenser will also give you very poor performance when it gets hot, though usually seen on a lot older 2 stroke engines such as chainsaws, but can also be seen on cars.

 

[ssrocket67]

Good point. See post #8, the OP mentions new points and condenser

 

[kelley69]

I don,t know what you mean by went through the carb but I feel that is your problem. I "went through" holleys for years and just called some duds. I while back I worked on one that just couldn,t be replaced and had to "go to school" on holleys. Power valves, blocked ports, warped parts, and most important incorrect gaskets. They seem to look the same but they are not.

 

[craigplong]

I have one of those bad boy 302’s. Start by ditching the points, condenser and coil for a Petronix ignition. Second find a box for the original carb and replace it with a new Holley 650 in the correct configuration. Third replace the plugs with appropriate Autolights. Last do not use fuel from the pump. It has 11.5/ 1’s. It needs racing fuel. Let’s remember that motor was built to WOT specs for racing. It’s not mentioned to idle nicely and the carb is way oversized. Then drive it like you mean it.