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Discussion Starter #1
I have a 69 Z/28 302 and have been having issue with the engine coming off idle. I have owned the car since 1974 and have not driven it much.
Two years ago I went to take it for a drive and I went about 50 yards when the engine just shut off.
I traced the problem to a bad module in the electronic Acell distributor I have on the car. But since it was late in the year I did not replace it till the following spring.
The car then started right up but refused to idle. I cleaned the carb but still had the same issue. I had discovered that this was not the original carb and purchased a used one that I sent out to have it profesionaly rebuilt.
I replaced the carb with the rebuilt one, restored the PCV system, still have the same issue. Only now I can get the car to idle very slowly, about 500 rpm the mixture screws do affect the idle. If I try and raise the idle it starts to lope and eventually will stall. By pumping on the gas a few times I can rev up the engine although when it comes back down as it passes a certain point, it sounds like it will stall but will catch and idle at 500 rpm.
I have been working on this issue for quite a while but now its time I put more effort into getting it going.
At 500rpm I am only pulling about 5 inches HG. I looked for vacum leaks could not find any.
At this point what other trobleshooting tests should I do. Someone mentioned the cam my have jumped time, however I think I would have seen that when I put the timing light on.
I appreciate any help anyone could give. Thanks Bob
 

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When was the last time you adjusted the valves? That will affect vacuum readings. If the motor is stock, you should be pulling 8-9" at 950 RPM on a 302.

It seems odd that if you increase the idle speed with the idle speed screw (not the mixture screw) it stalls? Is that what happened?

alan
 

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Discussion Starter #3
Its been a while since I have adjusted the valves, I will definately try that. And yes its when I raise the idle screw not the mixture screw that it stalls almost seem like when the carb trasitions it happens.. Just seem like the engine will not run between 700 to 1500 rpm. I can keep it running at 2 k with my foot on the gas. If this wasn't the second carb, I'd still be blaming that. It just seemd like the vacum reading is low, maybe because of the slow idle.
One other thing that struck me as odd. I had a timing light hooked up and when the engine goes to stall the light stops flashing. Is it possible I am losing spark at that RPM? Does not seem likely to me.
 

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Hmmm, the timing light should be flashing no matter what. Not sure what would cause the electrical to cut out in that rpm band but if you are losing spark, the ignition system needs to be checked out.

Is it possible the module you installed is bad? Also, what is the state of your distributor cap and wires?

alan
 

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Discussion Starter #6
The Gas is over two years old and its full. It does seem to smell ok though. Thtas one thing I want to do. Maybe use the old gas in my mowers. The guy in advanced auto told me that the timing light may not light if the plug doesn't fire. Sugeested the carb was going so rich at this point that it fouled the plugs. Not sure if I beleive that one though.
 

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If no spark made from the module as the engine is turning, no timing light will happen.
The module installed, does it have high temp grease between it and the plate it sits on inside the dist housing to prevent overheating? Don't use dielelctric grease as DG will stop the transfer of heat.

Spark plugs are probably fouled due to no heat generated to burn off the deposits - needs to be driven to develop heat.

You might need to advance timing to make it run better. Use a vacuum gauge hooked up to the manifold adjust all adjustments for a max reading. As said, it should indicate 9-10 inches of vacuum at 900 RPM.

Go to WOT and 6K RPM should happen within 3 milliseconds............
 

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Will both a hard wire and inductive timing light not fire if the plug is fouled?

But yeah, if the gas is bad, you are fighting an uphill battle. But what do you do with 18 gallons of bad gas?

alan
 

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Have you pulled off the carb bowl to see if there were ugly deposits from the old fuel. Prompted recently by mine running poorly; I recently pulled mine off to discover this. And it did not sit through the entire winter without being run. It was sucking that contamination in. Just to add to your possible electrical problem. You should lose that fuel, strain it and run it through your equipment after mixing it with good fuel.
 

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You could siphon/push out the gas and use it for weed killer along the fence line - just don't use there if dogs/cats are around.

Give it to the neighbors for mower fuel - B&S will run on most anything.
 

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Discussion Starter #11
This weekend I intend to adjust the valves then run a compression check. If still no good will dran the gas. Just that the only time I can work on the car its the weekend. Yeah the module came with some type of grease I put on. Wierd that I never had trouble the the module goes bad the only modern thing on the car now I have all this trouble. The carb was rebulit, never had gas in it till now. And there is an inline fuel filter. I will keep posting untill its solved. Thanks!
 

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Discussion Starter #12
Well since my issues started with an iginition issue, and I have my timing light stop flashing when I raise the idle. I orders a Pertronix Flamethrower 2 distributor and coil. I wanted to restore the vacum advance anyway and the old distributor was full mechanical. One concern was I did niot see the 302 listed under the applications. I can't see what difference it would make.
 

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Make sure you have the right vac can on that distributor. The 302 needs one that is all in pretty early. I will check tonight for the correct spec. As for the mechanical curve, I am not sure of the specs but it is probably easier to have the mech adv. curved on a machine as opposed to the car itself.

Who knows what the specs are for the 302?

alan
 

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Discussion Starter #14
Think I can set it to one of 3 settings on the vacum. I can also change the springs on the mechanical. All in all I should be able to see if this is my issue or not. And if someone knows the specs that would be helpfull.
 

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The best vac can for your engine is the Echlin 1810 which is also know as the DR305 or B28 can. It starts to come in at 3-5" of vacuum and is fully deployed by 8" of vacuum. It will add in 8* (16* crank) when fully deployed. I tried 3 different cans on my Z and this was the best. It solved several problems of drivability I was having.

According to the manual, you should have 16* (32* crank) total advance. According to the manual (and this is 1969 so the curve could be to meet emissions for 1969), you should have 11* @2200rpm, 16*@4400rpm. These are distributor figures, double for crank degrees.

Here is a link for the can:

http://shop.oreillyauto.com/productdetail.aspx?MfrCode=NIE&MfrPartNumber=DR305

So there you have it.

alan
 

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Discussion Starter #17
I Finally got around to replacing the Accel superstock Distributor with the Petronix. However it did not fit. I could not get it to sit all the way down on the deck of the intake manifold. The Acell fits fine. I still had play in the distributor shaft going up and down, so I do not think it bottomed out on the oil pump. Back to the drawing board. Think I may get a stock dist and convert to electronic. And I really don't think this is my issue. Just a guess.
 

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If this were me, I would install a point distributor, doesn't matter where it came from, its just a troubleshooting aid, install it, start the engine and run curb idle up to 1200-1500 rpm and with a vacuum gauge attached to manifold (full time) vacuum, advance the timing for max vacuum reading.

Engine should smooth out. Then slowly decrease idle, you may have to retard timing also. Once under 1000 rpm, adjust mixture screws for best vacuum. No action from idle screws, either rpm still alittle high or metering plate needs a cleaning along with the immulsion tubes on the carb body, those little brass holes in the venturis.

As primary plates close further to curb idle, the secondary plates may need to be cracked open to allow more air. there is a setscrew on rear pass side of throttle plate for this adjustment. Might use a feeler gauge to substitute, then remove carb and unscrew the setscrew and install from top for easier adjustment, from the top rather than remove the carb and adjust from the bottom. You'll see what I'm trying to explain.

In the end, 900 rpm with about 9-10 in. of vacuum at idle, or whatever the engine needs, it will tell you.
 

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If this were me, I would install a point distributor, doesn't matter where it came from, its just a troubleshooting aid, install it, start the engine and run curb idle up to 1200-1500 rpm and with a vacuum gauge attached to manifold (full time) vacuum, advance the timing for max vacuum reading.

Engine should smooth out. Then slowly decrease idle, you may have to retard timing also. Once under 1000 rpm, adjust mixture screws for best vacuum. No action from idle screws, either rpm still alittle high or metering plate needs a cleaning along with the immulsion tubes on the carb body, those little brass holes in the venturis.

As primary plates close further to curb idle, the secondary plates may need to be cracked open to allow more air. there is a setscrew on rear pass side of throttle plate for this adjustment. Might use a feeler gauge to substitute, then remove carb and unscrew the setscrew and install from top for easier adjustment, from the top rather than remove the carb and adjust from the bottom. You'll see what I'm trying to explain.

In the end, 900 rpm with about 9-10 in. of vacuum at idle, or whatever the engine needs, it will tell you.
dam your good ,you can tell your old school! :hurray:
 

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If this were me, I would install a point distributor, doesn't matter where it came from, its just a troubleshooting aid, install it, start the engine and run curb idle up to 1200-1500 rpm and with a vacuum gauge attached to manifold (full time) vacuum, advance the timing for max vacuum reading.

Engine should smooth out. Then slowly decrease idle, you may have to retard timing also. Once under 1000 rpm, adjust mixture screws for best vacuum. No action from idle screws, either rpm still alittle high or metering plate needs a cleaning along with the immulsion tubes on the carb body, those little brass holes in the venturis.

As primary plates close further to curb idle, the secondary plates may need to be cracked open to allow more air. there is a setscrew on rear pass side of throttle plate for this adjustment. Might use a feeler gauge to substitute, then remove carb and unscrew the setscrew and install from top for easier adjustment, from the top rather than remove the carb and adjust from the bottom. You'll see what I'm trying to explain.

In the end, 900 rpm with about 9-10 in. of vacuum at idle, or whatever the engine needs, it will tell you.
Someone posted last year or it on Holley's web site that the secondaries should be just cracked open ever so slightly via the stop screw, 1. to prevent the butterflies from wedging in the carb bores and 2.to keep them from figuring into the idle circuit but I can't remember for the life of me what it was? Like .040"? Or was it to keep them just above the transfer slots or just below them? I have it written down in my files somewhere.

alan
 
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