One problem after another! Need help, please.

[Kevin66]

So I've posted on here before about issues my nephew has had with his '66 Ranchero. I talked with him a little while ago, as he just got back to port after a few months away. I'm hoping that some of you guys will take the time to read through this story and offer some good suggestions, because I'm about out of ideas! Sorry that this will be long-winded, but I thought it important that you have all the info if I'm going to ask for your opinions/help.
He's got a completely rebuilt 289 (<500 miles), a good built C4 (3,000 RPM stall converter), and a 4.00 9" posi. The engine has about 9.6:1 c.r., with KB pistons, Pro Comp 175cc cylinder heads, Tri-Y headers, a Lunati Voodoo hydraulic (non-roller) with 227/233 @ .050", .522"/.538" Lift, and a 110 LSA, a Weiand Stealth intake, with a Speed Demon 650 VS carb. Until recently it had a HP289 distributor with a Pertronix III module, and their matching super-low ohm coil, Accel 8.8mm spiral wound plug wires, and Autolite racing 3924's gapped at .035".

In general driving, it seems to run great. Off-idle, mid-range and full power are everything he could want! From a standing start it will boil his 235/60's all the way through low gear until the speed catches up to the engine RPM around 5,000, then it continues to pull hard out past 6,000 RPM. I've never felt or heard a stumble or any hesitation while out driving with him. But there are problems. Gas mileage is dismal, around 8 mpg he said on the last tankful, and the engine refuses to idle properly, despite trying several things to improve a persistent 'roll' in speed.

Thinking that the virtually new BG carb could be at fault, I took it apart for him and looked everything over. I didn't find anything to point a finger at, but re-set the transition slot exposure to the recommended 'square' (.020") on all four throttle blades, and set the 4-corner idle mixture screws to 1.0 turn out for starters. I also dropped Pri & Sec jet sizes by 2 numbers (now 68/76, from the factory 70/78), installed a new 6.5 power valve, and re-checked the float levels to be at half on the sight windows.
Back on the car, things continued pretty much as before. After adjusting the idle speed and mixture screws, the engine idled with a maximum of about 12 inches of vacuum (though often at 10), dropping down to about maybe 8 for a second or so as the idle speed rolled. If I tried to reduce the idle speed much below 1,000 RPM, it would roll worse. It would stay running like that for 5+ minutes in Park, but in gear (at about 800 RPM) it would die after no more than a couple minutes. If I watched the tach while idling, what I would see wasn't a 'flutter' (like a misfire), but rather a quick, sharp drop down to about the 500 RPM range for a half-second or so as the engine rolled, then it would rebound.
I checked the fuel pressure, and it was about 6.5 PSI. If I 'deadheaded' the gauge, by disconnecting the carb from the gas line and plugging just the gauge in, pressure would slowly climb to an indicated 10+ PSI. So I got him to buy and install a pressure regulator, and we set it at 6 PSI, then again set the float levels.

If we pulled the cap off of the manifold vacuum port on the carb at idle, it would speed-up and smooth out somewhat. This suggested that the engine was running rich. In an attempt to get the idle speed down and smoother, I closed the secondary throttle blades so that the transition slots were no longer exposed. This did virtually nothing, so I tried turning the secondary idle mixture screws right in, and adjusting the idle on the primary ones only. This produced a little better idle, but you had to 'put your foot further into the gas pedal' to accelerate while cruising.

This carb has Demon's 'Idle-Eze' adjustment under the air cleaner stud, but it didn't seem to do anything for either idle speed or smoothness. So, frustrated with all this work but no real improvement, I removed the BG carb and installed a new 600 cfm Holley that a friend had. To my dismay, after checking/making all the usual adjustments, the idle still rolled with this carb!

So I'm thinking 'fuel & spark' are the two important things, and decided to look at the ignition. But before doing that, I pulled the plugs (sooty black, as from running rich, not oil fouled, etc.) I did a compression test, and got 160 readings from all eight cylinders. I then verified the 14-degrees initial timing, and the 32 total with 18 in the distributor. Not seeing anything there to indicate a problem, I went back to the carburetor.

He had a 600 cfm Edelbrock carb that was on the car when he got it. Although it had now sat for years, I gave it a try. At first the accelerator pump wasn't working, but once I got the engine running for a few moments, it came around. I found that I could drop the idle speed down to about 800 RPM, and adjusted the idle mixture screws. It seemed to be a little better than the BG carb, but still had that roll to it. Aaarrggghh!

I decided to try bumping the initial timing up a little, to 18-degrees. It was while doing this that I saw something unusual. I now had 14 & 18-degree marks on the dampener, and you could clearly see them under the timing light. But frequently they seemed to 'dance around' a bit, and would then go back to what you expected to see. The #5 cylinder plug boot came close enough to its header tube that it had started to melt, so I'd suggested he install a 6" length of that thermal protective sleeving. I decided we should check that cylinder, to ensure that there wasn't any misfiring going on with it. Simple enough to do, just put the timing light's inductive pickup on the #5 wire and watch the light flash...nice and steady. But then I saw something unexpected. When I turned the light back towards the dampener, I could sometimes see those same two 14 & 18-degree marks (for #1 cylinder) showing up under the light! How could that be, as the two are spaced well apart in the 1-3-7-2-6-5-4-8 firing order?? I checked the #6 plug wire, and saw the same thing. Then I went to the other bank of the engine, and checked cylinder #4, only to again see those same 14 & 18-degree marks under the light sometimes...?

So we then removed the distributor and Pertronix ignition components, going right back to 'dirt simple', with an Accel dual-point distributor, Taylor plug wires, and a 'no-name' aftermarket coil. The car started instantly, and I set the timing up to 18-degrees initial, but that was not before noticing something else. As the engine idled, you could visibly see current jumping from the coil's hi-tension tower over to either of the coil '+' & '-' terminals?? This was despite the thick boot on the hi-tension lead. I had never seen this happen before, but wanted to see if I could get it to stop. So I cut a couple 1" pieces of 1/4" rubber gas line, slit the lower end, and pressed them over the coil terminals. Despite this additional insulation, the shorting continued, but then stopped after a minute or two. How could a points-based ignition have so much current at the coil that it had to find a way to dissipate by shorting to a ground?? The one good thing was that you were no longer seeing those #1 cylinder timing marks show up on any of the other cylinders!

After being thoroughly warmed up, the engine would idle at 800+ RPM, but still had a roll to it. Again, thoroughly frustrated with a lack of progress, and one inexplicable issue after another, we replaced that points distributor with a new Duraspark distributor and an MSD 6A box and coil. I re-installed the Speed Demon carburetor, having decided that if it wasn't doing anything the other two weren't, it wasn't likely the problem. I set the initial timing back at 18 degrees, brought the engine up to 180 degrees, and tried adjusting the idle. This time, I could get it to idle as low as about 600 RPM, but not with the kind of regularity and smoothness that you'd expect from an engine with good compression and a 'fairly' mild cam in it. I could only get a decent idle in gear with all four of the mixture screws set at about 3/4 of a turn out. Any less, and the speed would falter; any more and the roll would be worse. Engine vacuum and fuel pressure readings are the same as before.

Since it'd only been driven a few hundred miles for break-in and trying to resolve some issues, like this idling thing, he wasn't that worried about what appeared to be dismal gas mileage, writing much of it off to prolonged idling periods and trips around the block. But when our recent torrential rains finally stopped for a while the other day, we decided to take it for a longer drive, both to see how everything behaved, and to actually check the mileage. I'm not liking what we came up with!

We topped up the tank with 94-octane premium, and went straight out on the highway to a nearby town. 3,000 RPM with his 25.25" rear tires gets 56 MPH, which is where we cruised. After getting there, he did about a two mile lap up and down the main street of the town at about 30 MPH, then it was back on the highway again. Once back in our city, we refilled the gas tank again. It took 5.64 gallons to do that. Then we get to the confusing part, and the real problem.
I know his speedometer reads low. Where it should be indicating that 56 MPH on the highway, it only shows about 51, suggesting that it's off by about 10%. I reasoned that if the speedo was under-reading, the odometer probably was too. When we had refilled the tank, it was indicating that we'd gone 48 miles since starting out. But his Garmin GPS unit only showed 38.5 miles? So first off, this suggests the odometer was actually over-reading??
If we divide the 48 miles that the odometer showed, by the 5.64 gallons, it comes out to a whopping 8.5 MPG!?!? Even more pathetic, if we use the GPS figure of only 38.5 miles, and divide that by the same 5.64 gallons, it comes to only 6.82 MPG... How could a mechanically good 289, with moderate performance improvements, get that dismal mileage while under light cruising loads??

We checked thoroughly for any gas leaks, right from the tank forward, including gas somehow dumping into the engine/oil, and we see nothing. There is no smell of gas, either when the car is under way, or when it's sitting. There is a bit of a stronger odour when the car is idling, but it's not 'eye watering'. The power and acceleration while driving are great, with no bogs, surging, or any other problems above idle. There's no obvious drag, such as brakes not releasing, and the C4 is working great, shifting up and down just as it should. Has anyone else experienced anything like this? Anybody have a guess as to what is wrong here?

As I mentioned initially, I'm frustrated and stymied here. I have no idea what the problem really is, nor how to fix it. Sorry for such a long-winded post, but I thought it was important you have all this information. If anyone has dealt with this kind of an issue before, or has a good suggestion to offer, I'd be glad to hear it!

[My427stang]

OK, so everything I would do, you were doing and each paragraph built to some good troubleshooting.

Without being there, here is what I think I recommend, but it's a bit of a guess.

1 - Use a piston stop and make sure your balancer is right.  It doesn't seem like a problem, but if it is spinning like a sheared key, may as well verify TDC the correct way and rule it out

2 - I would probably get to every plug wire with an Ohmmeter and visually inspect the crimps to make sure there aren't some damaged or broken

3 - Verify you have a good path to ground, both for engine and for body, just to rule anything goofy out

4 - Just a note, you ended up getting it to idle at 600, which seems low enough with that cam in a little engine, but just a point, in a 4 corner idle carb, 3/4 out is about perfect, so although 2 corners typically end up at 1 1/8 or so, that's about where I see 4 corner

So I don't have an answer but...if the balancer isn't spinning free, you don't have some intermittent firing and cross firing, we'll have to think some more

[turbohunter]

The two things that come to mind immediately are the balancer and making sure it’s right and together.
And the secondary butterflies. You mentioned that you adjusted the primaries, but the secondaries can get hung open, which may explain a lack of input adjustment.
The electrics are self explanatory, just gotta fix ‘em.

Good luck

[Gaugster]

Great points mentioned so far. My understanding is that the transfer slot adjustment is only for the primaries. So the secondary bufferflies should be closed but not binding shut. If you have adjusted the secondaries to be slightly open at idle it will run pig rich. 12 inch a vacuum seems rather low. 10-12 inch a vacuum sounds like an unstable vacuum signal. I'm guessing all that will improve once the secondaries are adjusted to be closed at idle. I had a first generation Demon 650 that had a bunch of quirks. One improvement was to go to a four hole spacer from an open type. So you may want to think about the carb spacer. Lastly confirm your choke wiring. These days chokes want a legit 12V vs 10V in the ol'days.

[frnkeore]

Did you ever replace the coil? I've never seen that w/o a crack in the tower or moisture conducting the spark, usually with old harden wires.

Have you checked power valve or the plugs after a hard pull? The mileage doesn't sound right, at all.

Of no real help but, the problem with your first dist may be the bushings.

I'm sure that you or your Nephew don't want the trouble or expense but, the easiest way to find the problem, is on the dyno.

[Kevin66]

OK, so everything I would do, you were doing and each paragraph built to some good troubleshooting.

Without being there, here is what I think I recommend, but it's a bit of a guess.

1 - Use a piston stop and make sure your balancer is right.  It doesn't seem like a problem, but if it is spinning like a sheared key, may as well verify TDC the correct way and rule it out

2 - I would probably get to every plug wire with an Ohmmeter and visually inspect the crimps to make sure there aren't some damaged or broken

3 - Verify you have a good path to ground, both for engine and for body, just to rule anything goofy out

4 - Just a note, you ended up getting it to idle at 600, which seems low enough with that cam in a little engine, but just a point, in a 4 corner idle carb, 3/4 out is about perfect, so although 2 corners typically end up at 1 1/8 or so, that's about where I see 4 corner

So I don't have an answer but...if the balancer isn't spinning free, you don't have some intermittent firing and cross firing, we'll have to think some more

Thanks Ross, and I have considered a number of those things. I verified the damper position, and the cam timing, with a piston stop through the #1 plug hole, and a dial indicator. Both seem okay. I haven't as yet put an ohmeter on the plug wires, so I will do that. My thoughts were that with no evidence of any issues above idle speeds, the ignition had to be delivering good voltage to the plugs?
He has a new size #1 ground going from battery to the engine block, and a new ground from the passenger head to the firewall.
The idle wasn't good enough to keep it at 600 RPM, so it's now at about 750 in gear. It's still 'rolling' a little, but not severe or stalling. He may have to live with that, but that fuel mileage is something else!

[Kevin66]

The two things that come to mind immediately are the balancer and making sure it’s right and together.
And the secondary butterflies. You mentioned that you adjusted the primaries, but the secondaries can get hung open, which may explain a lack of input adjustment.
The electrics are self explanatory, just gotta fix ‘em.

Good luck

Okay, so as mentioned in another follow-up post, the dampener has been verified as intact and positioned correctly.
As for the secondaries, they were adjusted too, several times. I had read that, on engines idling below 1,000 RPM with these Speed Demon carbs, that the transfer slots in the secondaries should not be exposed, just the primary ones. I had tried that, but it essentially made no difference. Likewise, closing the secondary idle mixture screws and getting it to idle on just the primary ones, smoothed out the idle a bit, but eroded some of the part-throttle tip-in performance. So the secondaries were set back to exposing maybe .025" of their transfer slots, and the mixture screws readjusted. The throttle blades return consistently to that position, with the oem secondary diaphragm spring pressing on them.
As for the electrical issues, I don't see what's 'self explanatory' about them? Although we've now eliminated the issues of the #1 cylinder timing marks showing up on other cylinders, and the shower of 'zaps' coming off of the coil tower, I'm not sure exactly what fixed each of those?

[Kevin66]

Great points mentioned so far. My understanding is that the transfer slot adjustment is only for the primaries. So the secondary bufferflies should be closed but not binding shut. If you have adjusted the secondaries to be slightly open at idle it will run pig rich. 12 inch a vacuum seems rather low. 10-12 inch a vacuum sounds like an unstable vacuum signal. I'm guessing all that will improve once the secondaries are adjusted to be closed at idle. I had a first generation Demon 650 that had a bunch of quirks. One improvement was to go to a four hole spacer from an open type. So you may want to think about the carb spacer. Lastly confirm your choke wiring. These days chokes want a legit 12V vs 10V in the ol'days.

So the instructions to set both primary and secondary throttle blades to a point where around .020" of the transfer slots is exposed below the throttle blades, comes directly from the Demon Carbs instruction manual that came with the carb.
I certainly agree that the idle vacuum readings we're getting from this motor seem low, definitely lower than I'd have expected in a new motor with good compression and a camshaft with only 227 degrees duration @ .050".
Not sure about the carb spacer, as it's one of Edelbrock's 'oval' divided ones, rather than either a 4-hole or completely open one??

[Kevin66]

Did you ever replace the coil? I've never seen that w/o a crack in the tower or moisture conducting the spark, usually with old harden wires.

Have you checked power valve or the plugs after a hard pull? The mileage doesn't sound right, at all.

Of no real help but, the problem with your first dist may be the bushings.

I'm sure that you or your Nephew don't want the trouble or expense but, the easiest way to find the problem, is on the dyno.

Thanks for your thoughts here. Yes, three different coils have been used here...the original .032 Ohm Pertronix Flamethrower III, with their ignition module; then an 'unknown' (Chinese?) chrome coil, with the Accel dual-point distributor;  then an MSD 1.5 Ohm Blaster coil with the 6A ignition box.
The power valve has been changed-out twice, from the oem Demon 6.5" one, to a new Quick Fuel 6.5" one, and now a Holley 4.5" one. We found no evidence of gas leaking through either of the first two valves, and both held good vacuum.
I am going to look into taking the car to a respected shop with a chassis cyno. Don't know why I hadn't thought of that before!

[Gaugster]

Great points mentioned so far. My understanding is that the transfer slot adjustment is only for the primaries. So the secondary bufferflies should be closed but not binding shut. If you have adjusted the secondaries to be slightly open at idle it will run pig rich. 12 inch a vacuum seems rather low. 10-12 inch a vacuum sounds like an unstable vacuum signal. I'm guessing all that will improve once the secondaries are adjusted to be closed at idle. I had a first generation Demon 650 that had a bunch of quirks. One improvement was to go to a four hole spacer from an open type. So you may want to think about the carb spacer. Lastly confirm your choke wiring. These days chokes want a legit 12V vs 10V in the ol'days.

So the instructions to set both primary and secondary throttle blades to a point where around .020" of the transfer slots is exposed below the throttle blades, comes directly from the Demon Carbs instruction manual that came with the carb.
I certainly agree that the idle vacuum readings we're getting from this motor seem low, definitely lower than I'd have expected in a new motor with good compression and a camshaft with only 227 degrees duration @ .050".
Not sure about the carb spacer, as it's one of Edelbrock's 'oval' divided ones, rather than either a 4-hole or completely open one??

Trying a four hole spacer is something to consider given the rather low expense. Edelbrock and Holley parts don't always play nice with each other. Spacers can shroud certain channels at the bottom of the carb flange. Then a weak vacuum signal can't be 'used' to meter the idle circuits properly. I'm no expert but that's how I've come to understand it.

[Kevin66]

Trying a four hole spacer is something to consider given the rather low expense. Edelbrock and Holley parts don't always play nice with each other. Spacers can shroud certain channels at the bottom of the carb flange. Then a weak vacuum signal can't be 'used' to meter the idle circuits properly. I'm no expert but that's how I've come to understand it.

Yes, I could do that, but I'm not convinced there would be any real benefit here? If you look at the pictures here, you'll see that the oval shape of the 1/2" thick spacer pretty much matches the shape of the intake carb pad, and maintains the divider between the two manifold planes. Once the secondaries open, they and the primaries are 'blended', on that manifold plane only, the same as they would be with a 4-hole spacer.