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Discussion Starter · #1 ·
Hi Guys,

I'm experiencing some issues with my 289 Mustang and need some wisdom. I'm having trouble with vacuum and am experiencing a slight backfire at idle once in a while. I thought it may be bad plugs so I just replaced all of them with new plugs and gapped them at .45. Here is a list of my setup to help identify the issue:

  • Engine is a 289 bored .20 over
  • Ford Racing Cam (Not sure of the specs)
  • Headers
  • Flowmaster Exhaust
  • Edelbrock RPM Intake
  • MSD 6A Ignition Box
  • MSD Blaster Coil
  • Timing is set to 16 BTDC
  • Holley 650 CFM Double Pumper Carburator
When the vacuum gauge is on, the needle is jumping from 10 to 15 and I am hearing a backfire once in a while at idle. When I pulled the #1 brand new spark plug I just installed, I see some oil residue on it and it's pitch black already.

Rebuilding the carb with dropping in smaller jets is on my To-Do list but before I get to that, could it be something else? Would it be the cause of improperly gapped plugs? Bad Ignition wires? bad blaster coil? Something internally with the carb? Stuck valves? Or is it something else?

I realize you can't play mechanic over the internet very easily but if you have been there and experienced this issue, I would love to hear about it.

Thank you.
 

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Yep, sticking valve.
 

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What's the needle on the VAC gauge doing beside jumping> Erratic, drifting etc.?
 

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Discussion Starter · #6 ·
What's the needle on the VAC gauge doing beside jumping> Erratic, drifting etc.?
The needle jitters around between 12 & 13 most of the time (about 8 seconds) and then dumps to 10 then up to 15 for about 2 seconds and then it settles back in the 12 & 13 vacuum area. I can try to send a video if that would help?
 

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Discussion Starter · #7 ·
So let's say it is a sticking valve (I really hope not). What do I do? Is it as simple as some seafoam in the tank and pour a little down the carb venturi? Would that solve it or am I doomed with a valve job in the near future?
 

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So let's say it is a sticking valve (I really hope not). What do I do? Is it as simple as some seafoam in the tank and pour a little down the carb venturi? Would that solve it or am I doomed with a valve job in the near future?
Much depends on the history of the engine. Was any head work performed when those "go fast" parts were installed? How long ago? It may very well be time for a head make-over. Maybe time for a set of "go fast" heads? Any good valve job, done right, is going to cost $500+ . That is, if you farm the work out. Might considering throwing that $500 at a nice set of performance heads?
 

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Discussion Starter · #9 ·
Much depends on the history of the engine. Was any head work performed when those "go fast" parts were installed? How long ago? It may very well be time for a head make-over. Maybe time for a set of "go fast" heads? Any good valve job, done right, is going to cost $500+ . That is, if you farm the work out. Might considering throwing that $500 at a nice set of performance heads?
The history of the engine is it was supposedly rebuilt about 5 years ago and I don't believe any head work was performed because most wouldn't bother doing any headwork to stock iron heads (to your point). Nothing performance related to the heads at least. I believe it was rebuilt on a budget and dressed up with some basic upgrades (Intake, ignition, etc). What's strange is vacuum and idle or backfiring was not an issue up until I changed the plugs. I can re-gap the plugs to see if that solves the issue but what I can't really explain is the oil residue on a new plug. That one does worry me a bit.
 

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The history of the engine is it was supposedly rebuilt about 5 years ago and I don't believe any head work was performed because most wouldn't bother doing any headwork to stock iron heads (to your point). Nothing performance related to the heads at least. I believe it was rebuilt on a budget and dressed up with some basic upgrades (Intake, ignition, etc). What's strange is vacuum and idle or backfiring was not an issue up until I changed the plugs. I can re-gap the plugs to see if that solves the issue but what I can't really explain is the oil residue on a new plug. That one does worry me a bit.
Ok, re-check your firing order. Just double check it. Also, recheck the gaps and the plug wiring integrity. An oily plug is an ominous?
 

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Maybe you crossed plug wires. You mention a upgraded cam. Make sure that it's not a 5.0 cam that you have wired up like a 289/302.
 

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Discussion Starter · #13 ·
Maybe you crossed plug wires. You mention a upgraded cam. Make sure that it's not a 5.0 cam that you have wired up like a 289/302.
I doubt its the wires as I changed the plugs one at a time but I will double-check it tomorrow. As far as the 5.0 cam, I would have no idea if it is or not. It does sound lopey which I have loved. If it did have a 5.0 cam, how would one configure timing? Advance it or retard it? It's currently at 16 BTDC and it doesn't seem perfectly happy. I tested it at 6, 10, 12, 15 & 18 degrees BTDC. The vacuum gauge was showing the most stable reading at 16 BTDC so I left it there.
 

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You set the timing like you would a 289/302. Make sure you set the timing no with the vacuum advance disconnected and blocked off. I know you say you changed the plugs one at a time. Did you change the wires as well? If they are the same wires maybe you damaged one or two while changing the plugs. Just seems like if you didn't have issues before changing plugs then the common denominator is the plugs or wires. What kind of plugs did you buy?
 

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Discussion Starter · #15 ·
You set the timing like you would a 289/302. Make sure you set the timing no with the vacuum advance disconnected and blocked off. I know you say you changed the plugs one at a time. Did you change the wires as well? If they are the same wires maybe you damaged one or two while changing the plugs. Just seems like if you didn't have issues before changing plugs then the common denominator is the plugs or wires. What kind of plugs did you buy?
The plugs aren't the greatest. They are the only 14mm plugs I found that would fit at AutoZone over the weekend. They are model number R45TS copper plugs. I guess it's possible that the wires could have been damaged during removal or they are just old. I guess it's not an expensive fix to change those as well.
 

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Discussion Starter · #16 ·
The spark plug is an AC Delco Model R45TS. It's a shorty (.460 length) and a 14mm. Maybe the gap is too much on them? I gapped them at .45 in consideration for the MSD box and coil...
 

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The spark plug is an AC Delco Model R45TS. It's a shorty (.460 length) and a 14mm. Maybe the gap is too much on them? I gapped them at .45 in consideration for the MSD box and coil...
FYI, for basic documentation, look at your current firing order and note it. As to the gap, the wider the gap, the more stress is put on the secondary side ( caps, rotor, wires., etc. ) of the ignition system. The more stress, the more tendency for mis-firing due to spark leakage through marginal wires. 8mm wires have heavier insulation, thus, better prepared for wider gaps.
 

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Once you are reasonably assured your wires and plugs are “OK”, and the VAC Issue persists, I would pull the VCs, with the idle as low as possible, watch the action of each valve and its components for any irregularities. Was it a “miss” that caused you to connect a VAC gauge?
 

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Discussion Starter · #19 ·
FYI, for basic documentation, look at your current firing order and note it. As to the gap, the wider the gap, the more stress is put on the secondary side ( caps, rotor, wires., etc. ) of the ignition system. The more stress, the more tendency for mis-firing due to spark leakage through marginal wires. 8mm wires have heavier insulation, thus, better prepared for wider gaps.
Yes, I will be double-checking these steps. I appreciate the input.
 

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Discussion Starter · #20 ·
Okay so I wanted to circle back here and provide an update. If anything, maybe someone will find value from this post in the future.

1. I checked all the wires and they were not crossed. They are correctly set up according to the firing order.
2. I changed the Distributor Cap since some of the contact areas looked worn on the existing one. This didn't solve the problem.
3. I took out the #1 spark plug, checked for TDC with a screwdriver (yes I know, I should use a TDC tool instead) and marked the balancer for TDC again. I did make sure this was done on the compression stroke.
4. I checked to make sure the distributor rotor was marked for the #1 plug.
5. I set the idle mixture screws on the carb to completely closed and then opened 4 half rotations.
6. I set the timing to 10 degrees BTDC. I also tested it at 6, 8, 12, 15, 20. I didn't see any improvement.

After these adjustments, the car started to sound slightly better but still has very low vacuum (10 - 13) and does still backfire once in a while. The next area to check is changing my spark plug wires and MSD rotor. Maybe just do a new coil too? I don't want to replace a bunch of parts that are probably not the issue. I also added a can of Seafoam in the tank and poured some in the Carb Venturi's at a steady RPM of about 1,500 to 2,500. Once I can isolate that ignition and timing is not the issue, I will move on to the carb.
 
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