1966 Mustang 200 ci In-line Six Poor Idle Quality, Runs Rough - Ford Mustang Forum
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post #1 of 9 (permalink) Old 10-11-2008 Thread Starter
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1966 Mustang 200 ci In-line Six Poor Idle Quality, Runs Rough

I have a 1966 Ford Mustang Coupe with an in-line 6, these are some of the issues I'm having:

  • The idle quality is horrible, I thought it may have been because of the breather without the snorkel so I purchased one of those little 6 inch all in one filter breathers which didn't help much at all. So, I tried adjusting the idle and that only helps when the car is first started but by the time it gets warm its awful. So, I put the original filter back on and played with the idle while it was cold but it still idles very poorly the only way the car stays on is if I constantly give it gas.
  • Also, the exhaust manifold appears to be bent. The the old gasket is warn to bits and in most places has just disintegrated. You can see sparks in the space where the gasket used to be and the engine to sputters when it sparks. The manifold is very rusted and I'm afraid if I try to take the screws out they will break, can I fix this problem without replacing the old gasket?
  • Lastly, I drove it on the highway and I noticed that at about 70mph the engine flutters and seems like it's trying to accelerate but just can't go any faster. Overall, the engine runs rough and VERY loud. This is a major problem because when ever I stop I have to put it in neutral and give it gas it or it cuts off and you can hear me from a block a way at least. How do I fix this and increase the mpg by as much as possible?
The car has been in my family for ages and I want to make it a daily driver. What could be the problems and what can I do to get the car running properly? My first time ever working on a car was when I rebuilt the carburetor on this mustang, now I'm hooked.
Do you think I would be able to fix this car on my own? Is this a job for a total beginner like me?
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post #2 of 9 (permalink) Old 10-11-2008
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Ok, for the exhaust problem, I would suggest spraying a VERY generous amount of WD-40 or similar on all the bolts holding it down, letting it sit a couple of minutes, and then trying to take them off slowly.
For the other problems, I have had those. It sounds like you idle, fuel mixture, and choke are off.
Lets start with the choke. When its cold, take the air cleaner assembly off, and see what position the choke plate is in. It should be almost closed. If not that means your choke is off. To fix this, while it is cold, loosen the 3 screws holding that black knob on and turn it counterclockwise so it closes the choke. Also make sure that the one idle screw isn't contacting the cam that is in between the thermostatic spring housing and carburetor body. The screw will be on the drivers side of the car, with the head facing down at the manifold, and it will have a spring on it, just like the mixture screw on the passenger side. If the screw is contacting, then you will need to unscrew it a little bit, you can either do this with your hand, (well I could), or with a spanner.
Fixing the choke is pretty much the first step to fixing it, but I think you really do need to replace the manifold gasket. That would let excess air into the cylinder, and probably cause poor firing. I hope this helps some.
I recomend getting a 66 shop manual if you haven't got one. I am kind of new here too, and for all my questions, at least one person told me to get the shop manual. I did, and trust me it helps alot.
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post #3 of 9 (permalink) Old 10-12-2008 Thread Starter
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Ok. So apparently the choke was stuck open and the dumb mechanic who loaded my car to be sent to me somehow dropped a screw inside the carburetor. Now both of those things are fixed and it idles so low I have to stop sometimes to make sure it's on. The fluttering at 70 mph more than likely was because there was a screw in the carb but I'll know tonight when I drive it. Also, I had a vacuum leak and I'm told that aids to poor engine pressure and that can make a car perform poorly. I fixed the vacuum leak with one of those little rubber tops and it's running ALLOT better but I think I also need to get a better spring on the gas pedal because it's too stiff, it's hard to pump the gas so I'm sure I'm pumping too much when I do. Does anyone know the proper spring to use, if so, can you post a pic because I have NO CLUE what I'm looking for. Also, I have been thinking about having someone bump the timing up because I read somewhere that helps with mpg, does anyone know if that's true? Also what about fooling with the fuel air ratio will that help?
One last thing, Can you point me to the right direction for wiring sources? I want to re-wire the car and ad door and dome lights, power windows and doors, an alarm system, get the interior lights working again and possible a cd player too. What's a cost effective way to re-wire? I have done some reading on ebay what's the difference between 12 & 21 circuit kit? Does it matter if it's a "MINI" I have no clue what most of this means but I'm sure I'll learn as I go.
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post #4 of 9 (permalink) Old 10-12-2008
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Thumbs up

Here's what I did:

Bought a complete harness from Painless Performance for my 67 and it was truly painless to wire the car. It took me about 3-4 hours to route it completely, since it's a one-piece unit. Took me a little longer to connect every wire but the beauty is that every single wire is marked as to the component and position it goes into. Plus, the installation instructions are great. My suggestion is that you acquire the shop manual and the wiring schematics from www.fordmanuals.com, either the digital version (color-coded) or the CD version.

As for the timing, I tried bumping it to improve mileage but all it did was to start overheating my engine (also an I6). The shop manual will give you ALLOT of information about your pony and since you said, you're planning on making it your daily driver, why not having every single specification for it, so you can tweak it around to your satisfaction.

I rather walk than ride a Chevy!
1967 Coupe, Std Interior; 200ci Auto Tranny
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post #5 of 9 (permalink) Old 10-16-2008
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Think about changing over to a dual master cylinder, for safety and electronic ingition . Both are great additions.


1966 Mustang Vert., 200 CID I6, Autolite 1100, Pertronix Ignitor I, Candy Apple Red, black interior, black power top with glass rear window, C4 Auto Trans, Scarebird 4 lug front disc brake conversion, dual master cylinder, LED dash, park and tail lights.

1976 Cobra II, 302 CID, C4 auto trans. Blackjack headers, white with blue stripe and blue interior. Restoration process.
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post #6 of 9 (permalink) Old 03-24-2010
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1966 Mustang sprint 200 idles and sputters

My sprint 200 will run good for about 2 or 3 days and then it will randomly start sputtering and will try and die when i press the gas. I took the gas tank out and cleaned it because someone thought it would be funny to dump leaves and twigs in it. After I cleaned it, it ran fine then a couples days later I was driving home and when i stopped at a stop sign it started to sputter. I took it to a friend and he adjusted the distributer and it started running better again. Is there something i can do to where it will run good all the time?
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post #7 of 9 (permalink) Old 01-06-2015
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idle and sputter problem

Wow I feel behind the times replying to a topic that was started in 2008 but I'm sure others still have this same issue like me.

I have a 66 with I6 engine and its doing the same thing even after a new Carb and distributor. There's no screw in the carb that I know of, it just idles rough. I'll have to check the choke on it again. I do know I have to replace the manifold gasket and have the same rusty bolt issue so I was curious if available2Good was able to remove the rusty bolts without them breaking off?
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post #8 of 9 (permalink) Old 01-11-2015
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removing rusty bolts, all you can do is pray, I have removed many a head to drill out broken bolts in my time as mechanic. As to rough idle, the sixes were always a bit rough when idling in gear. I have 65 with C4 and have replaced the distributor with an HEI and had to modify the 1100 carb for the vacuum advance. I also replace exhaust manifold with the 250 manifold. I get 22mpg around town, but not much better at 70-75 due to higher rpms. with 283 gears and 20/75 14's it runs good, and has plenty of pickup.
I am shown as 'apprentice' and worked at ford dealer when these were brand new.
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post #9 of 9 (permalink) Old 01-13-2015
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I got mine to idle and quit stalling out on me with a simple cleaning of the spark plugs. They were very dirty with a lot of carbon build up and some oil on the threads. After cleaning the plugs, getting the timing right, and tuning the carb it runs great.

I still have the exhaust leak which will have to remain until I can get the broken bolt drilled and re tapped when I busted it out trying to remove the manifold this weekend. The other bolts came loose fine but the last one busted.

Other than that it runs pretty good, doesn't burn oil, doesn't blow any smoke from what I can see. I'm going to try a can of Engine Restorer and hope that solves the piston ring issue I may be having with the oil on the plugs so we'll see if they can be saved or if they're totally shot and I end up needing a valve job. I am trying to avoid a rebuild.
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