1966 Mustang 200 ci In-line Six Poor Idle Quality, Runs Rough - Ford Mustang Forum

LinkBack Thread Tools
post #1 of 9 (permalink) Old 10-11-2008 Thread Starter
Classic Member
available2good's Avatar
Joined: Oct 2008
Location: Jonesboro
Posts: 2
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?

available2good is offline  
Sponsored Links
post #2 of 9 (permalink) Old 10-11-2008
MACH I Member
Classic Member
V6 Member
66Sprint200's Avatar
Joined: Jul 2008
Location: Moon Township
Posts: 2,624
Send a message via Skype™ to 66Sprint200
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.

1966 Mustang Sprint 200 "Oliver"... factory fog lamps, factory rally pac, off the road for restoration.

2005 Mustang 4.0 litre... Airaid CAI, Honeycomb taillamp panel, more mods to follow.
66Sprint200 is offline  
post #3 of 9 (permalink) Old 10-12-2008 Thread Starter
Classic Member
available2good's Avatar
Joined: Oct 2008
Location: Jonesboro
Posts: 2
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.
available2good is offline  
post #4 of 9 (permalink) Old 10-12-2008
Classic Member
67sustang's Avatar
Joined: Jul 2008
Location: El Paso
Posts: 77
Send a message via Skype™ to 67sustang
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
67sustang is offline  
post #5 of 9 (permalink) Old 10-16-2008
PONY Member
Mustang II Member
Classic Member
RagHead's Avatar
Joined: Sep 2006
Location: West Monroe
Posts: 471
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.
RagHead is offline  
post #6 of 9 (permalink) Old 03-24-2010
Classic Member
classic200's Avatar
Joined: Mar 2010
Location: Midwest City
Posts: 2
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?
classic200 is offline  
post #7 of 9 (permalink) Old 01-06-2015
66MustanginAZ's Avatar
Joined: Jan 2015
Location: Sierra Vista
Posts: 52
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?
66MustanginAZ is offline  
post #8 of 9 (permalink) Old 01-11-2015
james65coupe's Avatar
Joined: Apr 2013
Location: south east us
Posts: 91
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.
james65coupe is offline  
post #9 of 9 (permalink) Old 01-13-2015
66MustanginAZ's Avatar
Joined: Jan 2015
Location: Sierra Vista
Posts: 52
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.
66MustanginAZ is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

For the best viewing experience please update your browser to Google Chrome