200 c.i. with auto trans rough idle problem

russell-t

Active member
My 1966 Mustang with the 200 c.i. engine and C-4 automatic has a rough idle problem that is baffling me.

With the engine at operating temp. and idle set to 700 rpm in park,the engine idles fine.

When trans is placed in drive,rpm drops to 600 and stays good for about 5 seconds.

The idle then drops to 300 rpm and acts like it's running on 2 cylinders. Very rough.

When placed back in neutral,idle returns to 600 and runs fine. Placed back in drive...idles for 5 to 10 seconds..then drops back to 300 rpm and rough.

This will happen consistently,every time I tried it, for 5 times. When idle is raised to 850 rpm in park,then shifted into drive..idle drops to 700 rpm and stays there. No rough idle occurs at this setting.
I don't like running the engine this fast,fearing transmission damage.

Timing is set at the top notch..14 degrees.?? Runs rougher at 10-12 degrees. The engine has a new camshaft and the trans was rebuilt. All totally stock.

Ignition is Petronix with all new parts on distributor. Carburetor is stock Holley 1 barrel

Also there is NO vacuum advance at idle. Is this normal for this engine? Tested advance can with vac pump and it works.This is my first Ford and I'm not familiar with how this system operates.

I'm guessing I have a carburetor problem. The carburetor is not original Ford. It's a Holley model 1940. Where is a good source for carb rebuild parts and manuals for same.

Has anyone else had this problem?
 
There isn't much if any vacuum advance at idle and :unsure: Yes yours is a very common problem. Most newcomers to these early Ford six'es just don't understand how the distributor (LOD) and carb's (SCV) work together, it's not the same as the typical vacuum advance systems and requires some different testing. There is an excellent article that will help you in getting to know how they should work ( see below link) and then you will be able to figure out what's causing the problem. When everthing is right and in good condistion a 200 will idle smooth down to 525 - 575 RPM in drive many even lower. Have you done a compression test yet or tested the plug wire resistance? Good luck :nod:

http://www.classicinlines.com/Loadomatic.asp

Stock 1966 Ford Mustang tune up specs

Plugs are gaped to .034, Points are set to 39 degrees Dwell or gaped them to .025,
Base timing is 6 degrees BTDC with a Manual trans or 12 degrees BTDC with a Auto trans, Idle RPM in drive (AC off) 600 RPM (650) with Manual trans 525 RPM (575) with an Auto trans. Numbers in (575) are for engines with California Emissions.
 
I recently replaced the vacuum modulator on my C4.
It was slipping like crazy and had disappearing tranny fluid.
Check the fluid level in the transmission. If it's low, don't bother topping it off.
Get underneath and pull the vacuum hose from the modulator and see if any fluid leaks out.
Have a pan handy and let it drain. Replace modulator if necessary.
If it was sucking fluid up there maybe blow the line out from the top with some air.
 
:unsure: The original poster is located in The State of Penn. so its not likely that his Mustang has the California emissions specs. Though my post did give the tuneup settings for both 49 state (Fed) as well as California as a reference. And without seeing some pictures of the carb and distributor or at least having him post the casting / engineering numbers then there's no easy way to know on a 1966 engine. Good luck :nod:
 
Hi, my gut tells me to look for a vacuum leak. Check all your hoses, carb base, intake gasket, etc for leaks. It sounds like your engine won't run under load. Double check your firing order. Good luck
 
What are your camshafts specs?????
 
:shock: Ok well here is the rest of the story (see the below link) some info I first found out in his other post stating his location and that it's a 1966 Mustang. Still it's not enough info to know what parts combo is being used at this point, as there is no VIN / DSO Code from the Mustang to check, it's unknown as to which model Holley carb or the type of distributor (with Pertronix) that is installed in his Mustang (as there are no pictures or as of yet no casting / enginering numbers of those parts). Having also lived most of my life in SoCal plus other areas of Ca. up until a couple of years ago am well aware of its smog requirements and how Calif. smog systems (the originators) have evolved over time from the very early 1960's as well as the different parts that Calif. spec cars had on them. As a mechanic also repaired many emissions systems and also replaced many missing systems that others had stripped compleatly off, making them ready to pass the Calif. smog tests. Yet even at that after all this many years there is no guarantee that his Mustang is still using all the correct year model or original parts like it was once built with, so yes you could be right.

For original poster after you have been able to ID your carb you can get a carb kit from a number of good places like NAPA, Holley dealer or online, etc. Many times these old carb's have a bad float in them causing flooding so check and test that yours is still good. With age the Brass ones can crack and take on fuel rasieing the fuel level. The Nytro type can also deteriorate and then take on fuel becoming too heavy and as with a bad brass one it sinks raising the fuel level. The carb kits have the rebuild instructions and usally that it's all the info you will need from a manual. Check for excessive throdle shaft wear and for other sources of Vacuum leaks. Good luck :nod:

viewtopic.php?f=31&t=74901
 
2 posts 10 days ago - musta turned it over to the local shop?
 
:unsure: Yep only two posts and looks like he hasn't been here since May 1 maybe he'll come back with more info. :nod:
 
I've discovered that the carburetor on my engine is not the original one it came with.

It's called a Holley 1940 and must have been a replacement for the original.

I'm working to find a service manual for this carb on Ebay.

The distributor has a Petronix set in it and it is set with the correct gap
according to paperwork I got with the car.

The vacuum advance can looks different from pictures I've seen of the original.(Reference factory manual pictures)

I'm working to figure how to post pictures of these items on here but haven't been able to yet.
Clicking on Img in the toolbar at the top of the post doesn't do anything but put Img at the end of the line.
Gotta be something simple and dumb. Have uploaded pictures to other sites and this is the first time I've had problems.

I live in Beaver Falls Pennsylvania near Pittsburgh,and I bought the car from a guy who owned it for six years and restored it from Carlisle Pa.
The car has over 200 K miles on it and was almost totally restored.Engine trans were rebuilt and a lot of new stuff was done.
It ran rough at the time I test drove it with the idle problems I've described but it wasn't enough to kill the deal. Now I am on my own.

I've checked the trans modulator with vacuum tester and it holds vacuum. Will be looking for a rebuild kit and will see what happens after that.

I have the cam specs SOMEWHERE and will post them as soon as they reappear.
 
I didn't mention in my reply that my Mustang is a 1966 notchback coupe with the 200 ci engine and a C-4 automatic.
 
W E L C O M E !!! to our sand box. Come on in and play awhile. No bullys here.
Do you think you'll check in here regularly?
If so I bet a back'n forth conversation can have you sorted out fairly quickly…

There is a huge archive of info on these engines on the classic inlines site. Do Not buy from there as that part of the site is being worked on. In 1968 ford changed the carb/distrib. feedback system. The site has alot of info on this. Many here use the ford (falcon) six performance handbook as well as a chilton's or better yet (pricy tho) a ford service manual. I'm not sure which side of the '68 break off date the 1940 sits on but if U have the SCV/LOM system carb/dizzy must match (again, look that up on the CI tech pages).

Many here use the DSII system and a better post '67 carb.
Stick around & some of the ex-spirts (an 'ex' is a has been; a spirt is water under pressure) will answ ur Qs.
:eek:
:LOL:
:oops:
 
I have spent a lot of time adjusting timing and idle settings in an attempt to get this engine to idle smoothly.

My final settings are timing at 12 deg.BTDC and idle in park set at 900 rpm that drops to about 625 in drive.Carb rebuilt.

It still stumbles intermittently and still idles rough. Floats adjusted twice with no improvement. I placed a clear plastic

fuel filter ahead of the fuel pump, (stock mechanical) and placed a fuel pressure gauge in the line between the fuel pump and the carburetor.

On cold startup the pressure gauge reads almost 4 lbs. pressure. As the engine warms up after 15 to 20 minutes the pressure

gauge drops to zero. The engine continues to run rough and there is less than a thimble full of fuel in the clear filter.

Ordered fuel pump and will see if this works. What would cause a fuel pump to fail like this ?
 
chad":1duzmi4d said:
Do you think you'll check in here regularly?
If so I bet a back'n forth conversation can have you sorted out fairly quickly…

There is a huge archive of info on these engines on the Classic Inlines Archive. In 1968 ford changed the carb/distrib. feedback system. The site has alot of info on this. Many here use the Ford (falcon) Six Performance Handbook as well as a chilton's or better yet (pricy tho) a ford service manual. I'm not sure which side of the '68 break off date the 1940 sits on but if U have the SCV/LOM system carb/dizzy must match (again, look that up on the CI tech pages).

Many here use the DSII system and a better post '67 carb.
A visit w/2 wk break and 4 mo break from our discussion make that hard. Do U have regular access to the net to dialogue abt diagnosing the problem?

I'm wondering if the lobe for the arm of the fuel pump is damaged...
 
I now have a ford factory manual 1966 for this car, and it describes low fuel pressure problems.

One of theses is stretched fuel pump diaphram. I'm GUESSING that this may be part of my

problem. Awaiting arrival of a new fuel pump to test this theory out. The fuel pump appears

to be a recent install,previous owner says restoration was complete in 2012. Could this failure

be the result of ethenol in the gasoline? There's no way I can post pictures on this site to

make this any easier. This site doesn't upload pictures like other sites I've been on.

To Chad.. Thank you for your help. I haven't been posting any new results because I've

been running into constant dead ends with this car. Carb rebuild..float adjustments (3)..intake

gasket checks and replacements..idle screw adjustments (100's) mixture screw adjustments...trans shop to check the

transmission...(big $). Timing adjustments..settled on 12 deg. BTDC. The distributor is my next target.

Has petronix setup and doesn't match any of the Ford manual pics of the original with the LARGE vacuum

can. Holley 1940 is not the original carb. It has no spark control valve, just a ported vacuum oriface for vacuum

advance. The engine has a Comp Cam mild cam in it installed by previous owner,guessing one or more lobes might be

wiped. Starting at the top and working down. I'm going to make an effort to check this site every day for replies from

you guys, and I do so appreciate the advice I'm getting here. P.S. Manifold vacuum is between 13 and 14 pounds at 900 rpm in park.
 
To post pictures in your posts there are a couple of ways, the way that Many have used requires a free hosting site. All the info on how to do that is in the below link. Good luck :nod:

viewtopic.php?f=47&t=48863
 
New fuel pump arrived yesterday...installed it....nothing changed. Fuel pressure is 4 lbs at startup,runs for a minute at

high idle then I drop it down to normal idle..about 850 rpm in park. Fuel pressure is now at 3 lbs. After running for about

7 to 10 minutes...pressure is now 0. Engine still runs,but idle is rough. Giving it more gas does not raise the fuel pressure.

Engine speed increases with more throttle but fuel pressure does not move off of 0 and this is a mystery. My next guess is that

I have some restriction in the fuel line or some crap in the tank that is plugging up the intake filter as it runs...then releases

away from the filter as it sits. Any opinions out there ?? :banghead:
 
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