Mysterious Timing Issues

[seely]

Hey all, this is my first post, so go easy on me since I am a newbie!

I inherited a 1975 Ford Bronco about 5 years ago and it was running great until about two years ago during an ice storm in Texas. I had driven it in 4WD to get around since the roads were so bad, but the next week I turned it over and couldn't get it to start. The issue seemed to me to be that the timing was not advanced enough. I could get it running by turning the distributor all the way until it hit the water pump, although it had a significant loss of power. I couldn't tell the actual timing because the harmonic balancer had slipped though. I didn't drive it and now I am trying to troubleshoot the issue.

I installed a new harmonic balancer and timing chain (at the time I thought it might have jumped a tooth, but even though there was a lot of slop, it was still aligned at TDC). After doing this, I could see that my assumption about the timing not being advanced enough was correct, now thinking that it had slipped from the cam gear (possibly due to the cold weather/thick oil). I pulled the distributor and restabbed it to give myself more room to advance and I can get it running with a little finnesse.

The only way I can get it running is to retard the timing and then once the engine catches and idles, jump out really fast and advance the timing. It won't start unless I retard it, and if I don't advance it at idle, it stalls out.

Once it idles after this, I timed it with a timing light and am seeing it at 30 BTDC, which seems high, but I read that I should check the timing without vacuum advance. I then pulled the vacuum tube from the distributor and plugged it. Now when I time it, I can't even see the timing markings on the harmonic balancer, except for every once in a while a blip will go by showing me around 10 to 15 BTDC. It also idles really rough without the vacuum connected and eventually stalls. I am getting around 5" of vacuum coming from the carburetor at idle, and have double checked that this is the correct port it should be coming from (I have a Holley 1850-2 for reference). I've also tested the vacuum advance with the car off by sucking through the tube and watching it move and the advance mechanism seems to be working

I am scratching my head, but thinking that it could be that I need a new distributor, although I was hoping to figure out why there is such a significant difference in timing with and without vacuum connected before starting down the path of buying and swapping parts. Any ideas as to what I'm seeing here? Thanks in advance for anyone willing to share their Bronco wisdom with a newbie like me!

 

[DirtDonk]

Welcome to Classic!
I haven’t figured out the main issues yet from what you’ve written, but I’ll think on the little more as well as I’m sure most of the members here.

But to your last question about why it’s advancing when you connect the tube, that’s what it supposed to do.
At least it is if it’s connected to full vacuum rather than ported vacuum.
As soon as you apply a vacuum signal to the vacuum advance canister it advances the timing. That’s what it’s designed to do.
If you’re using the ported vacuum fitting on the carburetor then something is actually wrong with the settings on the carburetor.
Because you should see no vacuum at idle on that port.

Let us know which port you are using and someone more familiar with that carburetor can let you know if you’re using the right one or not.
Or you can take some pictures and upload them to your garage or gallery and we can view them that way.
Assuming it lets you do that right away that is.
I’m not sure if you have to make a few posts before you can do that or not.

To post images directly to your discussion you have to become a contributor for $12 a year.

Good luck! Very odd issue and I don’t think I’ve seen a question like this in a long time. Looking forward to the discussion that follows.

 

[Super D 73]

Check the reluctor wheel in the distributor below the rotor. Pull the cap and rotor then try to move the wheel left to right. It is held in place by a small pin that is known to break and let the wheel become misaligned and throw timing off. Good luck!!

 

[B RON CO]

Hi, X2, 2 on a broken pin on the reluctor wheel, also it is possible to snap the roll pin holding the gear to the distributor shaft. If the ported vacuum port on the right side of the carb is drawing vacuum at idle, I would guess the idle is set too high. After you check out the distributor, I would warm up the engine, remove and plug the vacuum hose and check the timing. @12* BTDC should be a good place to start. Then adjust the idle to @ 700 RPM, then adjust the idle mixture screws, a little at a time, turn them in until the engine stumbles, then out one full turn, the finish with the idle screw on the throttle shaft. Hopefully, there won't be vacuum at the ported vacuum port, and the idle won't change. You set the timing before you adjust the carb, because when you change the ignition timing, you change the idle. Good luck

 

[Brush Hog]

Check distributor hold down bolt. And also check plug wires and firing order. I had some bad timing problems and realized I had a wire in the wrong spot. And also before messing with it more get it back to TDC and start timing and carb adjustments from scratch or you will be chasing your tail.

 

[seely]

Thank you all for your help! To answer a few questions, the problem isn't that the timing is advancing with the vacuum connected, it's that the timing with and without vacuum is completely different. Without vacuum, I can't even get it to idle and the timing light is showing a completely different part of the harmonic balancer (I can't even see any timing markings anywhere) but as soon as I get it to idle with a littl bit of vacuum, I can see it's at 30 BTDC. As for the vacuum source, I have a Holley 1850-2 carburetor and am connected to what is referred to as the "timed source vacuum source" as labeled in the diagram I found here.

I took the reluctor wheel off last night and saw that it hadn't slipped. The pin was still in where I assume it should be. I am wondering if maybe the position of the magnetic pickup at ignition (with no vacuum) is causing the rotor to crossfire at another terminal. Then when it gets going, the vacuum pulls it into the normal position where it is timing normally.

A few years ago I had some problems with this distributor and being the newbie I was, took it to a shop. They saw that a piece of the breaker point had broken off and caused a short with the ignition control module. They replaced it with a magnetic pickup (along with a new ICM), and it never quite turned over right since then. I wasn't able to time it since I didn't have an accurate harmonic balancer (although since then I have read about out how to find TDC manually and wished I would have tried that), but my Dad would say that it sounded like it was igniting when the valves were in the wrong position at startup. It still sounds like that to this day when I'm starting it.

I'm wondering if the new part in an older distributor with some wear on the vacuum diaphragm, or an incompatible part, would cause crossfire like this.

Do you all think I am heading in the right direction?

 

[Brush Hog]

I think maybe it won’t idle because it’s at 30 BTDC. That’s why it sounds like it’s igniting when valves at wrong position. If timing marks are correct and you started from TDC.

 

[seely]

I think B RON CO might be correct in that my idle speed might be too high, causing vacuum at idle (pulling it to 30). While timing with vacuum disconnected, every once in a while a blip will go by showing between 10 and 15 BTDC (hard to see because it goes by so quick). My theory is that this is a brief moment where the vibration of the distributor moves the magnetic pickup into a position that briefly stops the rotor from crossfiring. I am going to retime everything from scratch with no vacuum like some of you suggested, adjust idle speed, and then idle mixture before going much further.

If I can get it running without vacuum at the correct timing, my theory would be that hooking the vacuum back up and opening the throttle will pull the magnetic pickup into a different phase and start crossfiring, pulling the timing way out of whack. I'll give that a shot and let you guys know what I find out!

Also triple checked plug order/firing order with my Chilton manual, as that was my first suspicion before going down this rabbit hole.

 

[Broncobowsher]

Make sure the vacuum advance is hooked up. Under the cap that is. I've seen the rod come off and the pickup plate rotates and makes a mess of the timing/rotor phasing.

Did you know Ford put (at least) 3 different timing mark locations on small block? 10, 11, or 2 O'clock. Many were available the same year and model, dependent on what options the vehicle was equipped with. This doesn't matter to a Bronco, until your new parts that may have been for one of those other specs. Did you verify that the TDC marks actually lined up when the engine was at TDC? If you pull the damper bold so you can see the keyway, put that straight up, is the timing mark at least close? Wouldn't be the first time the wrong new parts were used.

 

[DirtDonk]

In case it hasn’t already been mentioned, you are using the passenger side front cylinder as you’re number one, correct?
And when you verify timing marks you can also add your own with a sharpie or better yet, timing tape which gives you almost 360° of timing marks to work with.
But since you set timing tape up yourself, you have to make sure it’s zeroed out correctly.

The likely reason you can’t see the timing marks when the vacuum advance is connected is because typically timing marks are only for the first 10 or 20° and nothing beyond that.

A temporary cure for the vacuum advance blues is to leave the vacuum hose disconnected and plug it with an appropriate sized screw or something.
That way no vacuum leak at the carburetor and no vacuum advance acting on the mechanical advance.
You can then check your mechanical advance by connecting your timing light and revving the engine up while you watch the timing marks.

If the timing light is only flashing occasionally and not rapidly giving you an almost solid light that you can use to read the timing marks, something is wrong with your spark, your spark plug wire, or your timing light.
The flashes should not be intermittent but instead should be very consistent and show the marks every other time they come around.

And as you figured out by the chart, “timed vacuum“ and “ported vacuum“ are one in the same.
I grew up calling it timed, but use ported now more often I think.
Some texts even refer to them as “ported spark” sources.

 

[DirtDonk]

I started along the thought process, but got sidetracked.
You need to find out why the spark is inconsistent and why the vacuum advance pushes it up so high when connected.
Your carburetor idle is possibly set too high which allows vacuum to come through the timed port.
Your vacuum advance could be working too well and pulling the plate too far.
Your mechanical advance might have some broken springs or something, allowing it to advanced too quickly.

So you need to get the timing flashes of the light working properly so you can watch the marks and what they do when you rev the engine.

 

[cldonley]

Your mechanical advance might have some broken springs or something, allowing it to advanced too quickly.

I've seen this before, along with too much vacuum at the timed port causing your timing to go off the chart. Take a really good look inside your distributor, it really sounds like there's a problem in there. Look for signs of arcing inside the cap, and make sure you have have good solid connections. You may have two problems, too much advance and something causing that intermittent spark.

 

[seely]

I think you all are right, I might be getting ahead of myself in trying to make assumptions without checking the basics first (idle speed too be too high seems to be the foremost problem). I double checked to make sure I'm at the #1 spark plug and according to the Chilton manual it should be correct (passenger side front sparkplug).

Also, I am actually getting a pretty consistent spark with the timing light, as well as a spark tester I used to double check. The intermittent part has to do with what I am seeing during the flashes of the timing light. With no vacuum, I am seeing a bare harmonic balancer (with consistent flashing) and then a blip of the timing markings every once in a while.

I am not sure if I have mechanical advance or not. I can't see any plates or springs in the distributor, but it does look like there is evidence of carbon from arcing inside the distributor. I can't post pictures right now it seems, but here is a link to a similar distributor from Napa Auto Parts. Thanks again everyone for helping me troubleshoot, it's been a real puzzler for me but I'm learning quite a bit!

 

[DirtDonk]

Ford distributors use the flyweights and springs underneath the main plate. Not up top like GM distributors do.
So yes, you won’t see them unless you disconnect and remove things.
You can only tell their action externally by twisting the rotor and watching it spring back. Or by watching the timing light flashes on the damper ring.
Speaking of which, if you’re only seeing the marks occasionally can you tell if when you’re not seeing the marks the flashes are moving to different points on the ring? In other words consistent flashes, but at different points? That would indicate something wrong inside the distributor.
Loose weights, or other broken components. Allowing the spark to just happen whenever.
This should also result in rough running.

So as a quick test, pull the cap, grab the rotor and gently twist in either direction. Does it feel rough or nacho? Smooth? Does it spring back all the way consistently?
And while you are at it, look for anything else loose or out of adjustment. I think we need to see pictures of what you have inside your distributor. What’s outside is good to know, but what’s inside is more important.

These are just generally good things to know.

 

[seely]

There's a bit of an oily spot that I could see on the harmonic balancer (residue from when I installed it) that stayed in the same spot when timing with no vacuum. The little blob looked stationary, which makes me think it might not have been moving around (except for the blip where I could see the side with timing markings).

For the rotor, I can't twist it clockwise at all, but I can twist it counterclockwise about half the distance between reluctor arms (not sure how to describe this well). Feels generally smooth when doing this, but I did notice that it doesn't quite snap back all the way and I can move it with my fingers just a smidge more before it's all the way back to where it was. I have a bit of play with the vacuum diaphragm using my fingers and a bit of upward vertical play with the distributor shaft. I might try and take the rest of the distributor apart to see the mechanical advance underneath if you guys think that is worth it.

 

[B RON CO]

Hi, I wouldn't take the distributor apart yet. I would put a sharpie mark on the distributor housing directly under the #1 plug wire terminal. Next, remove the cap and turn the engine over by hand until the rotor is pointing to the mark. Now look at the timing marks. They should be very close. If they are close, mark the balancer with a dab of white paint. If they are not close report back. The engine should run and idle fine with the vacuum hose removed and plugged. One step at a time. Good luck

 

[Brush Hog]

Did you install the correct harmonic balancer when you replaced the old one? Sometimes these complicated problems are just goofy mistakes. I know because I have made hundreds.

 

[blubuckaroo]

I had a similar problem with my '77 last year. I had the Duraspark pick-up coil fail. I bought a new one from NAPA, and it advanced my timing a lot. I found out there are more than one pick-up coil for these, in spite of what the parts guy at NAPA says. I finally got a good replacement from Parkland Performance Ford in Tacoma WA. They were able to sort out which Duraspark distributor I had. http://reincarnation-automotive.com/

 

[seely]

I felt like I had enough to go on to take the easy way out and try a new distributor and now the timing issue I was seeing seems to be fixed! I am going through the steps to set the timing/tune the carburetor to get it running well.

Last night I set the timing to 12 BTDC without vacuum and set the idle rpms to 700. Then adjusted the idle mixture and it was running great. I took it to the store to fill up with gas and get a celebratory snack, but this morning I can’t even get it to idle in drive without it stalling. My thought is it’s just a bit more fine tuning, but it shouldn’t be as hard as all the rest of the work I’ve put in so far.

Any more tips on tuning my Holley carb are appreciated, and thank you everyone who gave me suggestions and advice!

 

[Broncobowsher]

So issues in the morning. Cold engine? How do you have the choke setup?