Sign in to follow this  
dr. james

'66 Mustang 289 stumbles and hesitates when driving

Recommended Posts

I have a low mileage 123K '66 Mustang with a rebuilt engine.  The car hesitates and stumbles when driving especially when I come to a stop.  When I stop, I need to keep my foot on the accelerator to keep the car from stalling. The car has Petronix ignition and Petronix coil.

 

Recently, I had the following improvements made to eliminate the problem but they continue: new plugs, new plug wires, distributor cap, rotor, rebuilt carb, PCV valve, fuel line filter, and timing check. My friends at the antique car club suggest I may have a vacuum advance problem but others suggest I get rid of the Petronix additions and switch back to original style points and coil.  

 

This problem is very frustrating and it has reached the point where I only drive the car to leave it at the repair facility but they can't solve the hesitation and stumbling. Other than that, the car is absolutely beautiful because it came from San Diego and has never seen snow or salt.  

 

Can anyone offer me a solution?

 

Dr. James

 

 

Share this post


Link to post
Share on other sites

When you have a problem with a stock car just changing everything or  adding after market components does not seem to me to be the answer-------understanding how your car works and checking all the possibilities seems a better way to go-----it could be one of several problems,,,timing,fuel pump,vacuum, carburator---------------------------some on should invent a after market add on to let the car talk so it can tell you the problem

Share this post


Link to post
Share on other sites

"The car hesitates and stumbles when driving especially when I come to a stop.

When I stop, I need to keep my foot on the accelerator to keep the car from stalling."

 

This definitely sounds like a fuel/air related problem. Float level perhaps or a vacuum leak could cause the same type of issue.

Sorry, it's impossible to diagnose from where I'm sitting but I would check in that direction.

  • Like 2

Share this post


Link to post
Share on other sites

Check the coil.  Seen float level do this too.

 

Modern shops don't know squat from a carb.

 

  • Like 1

Share this post


Link to post
Share on other sites

Recently in the technical section there was a car with a similar problem.  Disconnecting the distributor vacuum advance made it run better.  You may want to try that too.  The modified ignition is another place to look.  Do you know if the plugs were fuel fouled as in black sooty appearance?

Share this post


Link to post
Share on other sites

If you post your zip code, someone may recommend a good shop.  How far are you willing to travel?  

Share this post


Link to post
Share on other sites

Dr. James, we will continue to need updates from you as we attempt to help.  Is the carb a 2 barrel or 4?  Is it a replacement or aftermarket carb or original.  Has there been a time when you did not have the problem?

Share this post


Link to post
Share on other sites

Terry,

 

The car is a c code 289 with a 4 barrel  Ford Motor Co but I'm not sure if that's original.  The carb was professionally rebuilt less than a month ago and the rebuilder said the carb was clean but the float was damaged so he replaced it. When I purchased the car two years ago, it ran fine for a short period but then the hesitation and stumbling began. It was at that point when I started replacing the items mentioned in my request for help.

Share this post


Link to post
Share on other sites
1 hour ago, huptoy said:

If you post your zip code, someone may recommend a good shop.  How far are you willing to travel?  

Huptoy,

 

Thanks for responding to my problem.  My zip is 01970 which is 20 miles north of Boston.  I'm willing to travel a reasonable distance but remember the car runs very rough and the gas mileage is about 10 miles per gallon.

Share this post


Link to post
Share on other sites

I have nothing but praise for the pertronix units and have one in each of my 60s Fords, one of them has been installed for over 10 years now.  I think your problem could be a vacuum leak or too high of a float level causing dripping from the discharge boosters.  Is it also hard starting after sitting for a few minutes after shutdown?  Once warmed up, a 60s Ford in good tune should fire up after sitting for a half hour without having to touch the throttle.

Run the car then shut it off and remove air cleaner lid and look down primary barrels with a flashlight to check for fuel dripping. This will indicate a high float level and cause poor atomization and stumbling.

  • Like 2

Share this post


Link to post
Share on other sites
1 hour ago, TerryB said:

Recently in the technical section there was a car with a similar problem.  Disconnecting the distributor vacuum advance made it run better.  You may want to try that too.  The modified ignition is another place to look.  Do you know if the plugs were fuel fouled as in black sooty appearance?

Terry,

The plugs are not dirty or sooty but the exhaust pipes that come through the rear valance have considerable soot.  However, the repair facility where I take the car adjusted the mixture control and the soot is decreasing.  The mechanic said I should expect to see some soot coming from a 52 year old car with a carb.  

I may revert back to original points and original type coil and scrap the Petronix ignition and Petronix coil.

 

Thanks for the reply.

Share this post


Link to post
Share on other sites
3 minutes ago, Modeleh said:

I have nothing but praise for the pertronix units and have one in each of my 60s Fords, one of them has been installed for over 10 years now.  I think your problem could be a vacuum leak or too high of a float level causing dripping from the discharge boosters.  Is it also hard starting after sitting for a few minutes after shutdown?  Once warmed up, a 60s Ford in good tune should fire up after sitting for a half hour without having to touch the throttle.

Run the car then shut it off and remove air cleaner lid and look down primary barrels with a flashlight to check for fuel dripping. This will indicate a high float level and cause poor atomization and stumbling.

Modeleh,

 

The carb was rebuilt last month and the shop installed a new float because the original float was damaged. I will look down the primary barrels to look for fuel dripping.

 

The car starts immediately regardless of how long it has been sitting.  A member of the antique car club where I belong suggests a vacuum leak or defective vacuum advance device.

 

Thanks for your suggestions. 

 

 

Share this post


Link to post
Share on other sites

Do you have a standard mechanical fuel pump or has an electric fuel pump been added?  Electric fuel pumps can sometimes overpower the floats in a carb if the fuel pressure is too high.

  • Like 2

Share this post


Link to post
Share on other sites

I was a Ford service technician during the mid to late 1980's; saw every known problem a Ford could have. Your problem: When I stop, I need to keep my foot on the accelerator to keep the car from stalling.  Pretty easy to diagnose, if it were in my shop. 

 

Not familiar with the after market ignition; the stock ford will work great, if  the system is up to Ford specs. Yours may be good, but without checking it I am Not commenting on it.

 

1. I would make sure there is not a vacuum leak.  Those cars sometimes had a vacuum "tree", on the intake manifold somewhere, to have a source of vacuum to operate something, like a vacuum brake booster.  Check there first, a missing vacuum cap or hose off will cause the symptoms, you have.

 

2. Carb just put on ?? Check the base gasket to the manifold, or carb to manifold spacer.  Saw this sooo many times; wrong gasket, or torn gasket.  Same symptoms 

 

3. The stumbling may be a faulty vacuum ignition advance unit. I don't have any idea what you after market ignition has .  This won't affect idle and your stalling at idle; but it will affect drive ability when pulling out from a dead stop. 

 

4. I also would go back and look at the PVC valve. Depending on the emission level and part of the USA where the car was sold new, determines the use of PVC valve on these early 289's. If it is a car that originally had a PVC  make sure it is the correct one.  This problem mimics your symptoms.  Some 1966 289 Mustangs had PVC valves. A PVC valve is Not a one size fits all.

 

5. Of course maybe an intake manifold gasket problem. 

 

6. Maybe something else, but from the owner's remarks, which I added to my post, I am looking first at a manifold/carburetor problem;  gasket, hose, valve, a leak somewhere.

 

intimeold      

Edited by intimeold (see edit history)
  • Like 3

Share this post


Link to post
Share on other sites

I had a 289 I built up with better valves, cam, pistons, headers, carb, heads in other words it was powerful. The best thing I did was put ecklin points, spark plug connectors, distributor cap and coil on it. All of the connections including the points were gold plated. I had a custom made 11 quart oil pan and ran 50 weight racing oil all year, even in the Chicago winters. It started at the touch of the starter no matter how cold or long it sat.  If you go back to the old points system I would check to see if NAPA still sells that setup

 

my two cents says vacuum but you may possibly have a sticky valve. I don’t really know why that came to mind but you may want your mechanic to check it. Just a nagging memory

Good luck 

Dave S 

Share this post


Link to post
Share on other sites

I don't think the PerTronix unit is your problem because it either works or it doesn't.  Just like an off / on switch.  To check for a vacuum leak some where, disconnect all vacuum lines from the carb and plug the ports in the car.  See if the problem goes away.  If it does, reconnect one line at a time and retest until you find the line causing the problem.  Then start tracing that line until you find the problem.  When you reach junction points that split off into different directions, cap all but one line and test again.  It takes some time, but you've been putting up with this problem longer.

 

If you sill have the problem with all vacuum lines plugged at the carb, you problem is not vacuum lines, so move on to the carb.

 

2 hours ago, dr. james said:

The plugs are not dirty or sooty but the exhaust pipes that come through the rear valance have considerable soot.  However, the repair facility where I take the car adjusted the mixture control and the soot is decreasing.  The mechanic said I should expect to see some soot coming from a 52 year old car with a carb.  

 

You should not expect to see any soot coming from a 52 year old car with a rebuild engine that only had 123K miles on it even if it has a carb on it if the carb is adjusted correctly.  When new (and you have a new engine) the exhaust pipe should be grayish and dry.  I suspect there is a problem in the carb rebuild.  It doesn't make since that the exhaust has soot and the plugs don't unless you are looking at plugs that have not been run long enough to have a soot build up.  Black soot is either a very rich fuel mixture or oil burning from ring blow by or leaking valves guides.  Soot from oil will feel greasy in the exhaust pipe.  Soot from rich fuel mixture will feel dry.  Everything you say leads me to believe it's a rich mixture causing the problem.  Have someone else go through the carb again.

  • Like 2

Share this post


Link to post
Share on other sites

Thinking about this again, look at the carb first.  I don't think the problem is vacuum, because a vacuum leak leans out the mixture.  You seem to have the opposite problem, a rich mixture.  Go for the carb first.

  • Like 1

Share this post


Link to post
Share on other sites
9 hours ago, 61polara said:

Thinking about this again, look at the carb first.  I don't think the problem is vacuum, because a vacuum leak leans out the mixture.  You seem to have the opposite problem, a rich mixture.  Go for the carb first.

 

9 hours ago, 61polara said:

Thinking about this again, look at the carb first.  I don't think the problem is vacuum, because a vacuum leak leans out the mixture.  You seem to

10 hours ago, 61polara said:

I don't think the PerTronix unit is your problem because it either works or it doesn't.  Just like an off / on switch.  To check for a vacuum leak some where, disconnect all vacuum lines from the carb and plug the ports in the car.  See if the problem goes away.  If it does, reconnect one line at a time and retest until you find the line causing the problem.  Then start tracing that line until you find the problem.  When you reach junction points that split off into different directions, cap all but one line and test again.  It takes some time, but you've been putting up with this problem longer.

 

If you sill have the problem with all vacuum lines plugged at the carb, you problem is not vacuum lines, so move on to the carb.

 

 

You should not expect to see any soot coming from a 52 year old car with a rebuild engine that only had 123K miles on it even if it has a carb on it if the carb is adjusted correctly.  When new (and you have a new engine) the exhaust pipe should be grayish and dry.  I suspect there is a problem in the carb rebuild.  It doesn't make since that the exhaust has soot and the plugs don't unless you are looking at plugs that have not been run long enough to have a soot build up.  Black soot is either a very rich fuel mixture or oil burning from ring blow by or leaking valves guides.  Soot from oil will feel greasy in the exhaust pipe.  Soot from rich fuel mixture will feel dry.  Everything you say leads me to believe it's a rich mixture causing the problem.  Have someone else go through the carb again.

have the opposite problem, a rich mixture.  Go for the carb first.

 

9 hours ago, 61polara said:

Thinking about this again, look at the carb first.  I don't think the problem is vacuum, because a vacuum leak leans out the mixture.  You seem to have the opposite problem, a rich mixture.  Go for the carb first.

Dave,

 

When the surging and hesitation problems went unsolved, I suggested to the mechanic who was working on my car that I planned to purchase an Elelbrock Carb to replace the Ford Motor Co carb in the car.  He discouraged me for doing that so I went for a rebuild but the problem continues.

If you owned this car, would you change the carb to an Edelbrock or similar to hopefully solve the problem?

 

 

  • Like 1

Share this post


Link to post
Share on other sites

Hello and greetings from southern NH.

First items I would check, if the car was in my shop:

engine compression and vacuum tests

second, if the first checked out OK:

fuel pressure and volume test

third: ignition system waveform pattern as viewed with an oscilloscope.

Bear in mind that there could be a possibility of multiple problems / misadjustments that may mask the original issue(s).

I suppose you could try a new Edelbrock carburetor, this might be akin to a surgeon giving you a new heart, without first running a battery of tests.

Best of luck.

 

Share this post


Link to post
Share on other sites
16 hours ago, dr. james said:

Terry,

The plugs are not dirty or sooty but the exhaust pipes that come through the rear valance have considerable soot.  However, the repair facility where I take the car adjusted the mixture control and the soot is decreasing.  The mechanic said I should expect to see some soot coming from a 52 year old car with a carb.  

I may revert back to original points and original type coil and scrap the Petronix ignition and Petronix coil.

 

Thanks for the reply.

How much soot are you getting? Dismissing the presence as a common condition to carbureted cars is a suspect conclusion.  Too much soot means you are running rich.  I would then revert back to Modele's comments about your float level.  Does your vacuum advance have a leak?  I'll read comments above to see if that has been mentioned.  Otherwise, it is time to take your carb apart and check the rebuild.  Can't always trust that a service won't make a mistake.

  • Like 1

Share this post


Link to post
Share on other sites

BTW Carter/Eidelbrock aftermarket carbs are set waaay rich. For a stock 289 a 450-500 cfm would be about right. What you describe sounds more like a lean stumble than rich. Tom has it right, would just add a tailpipe sniffer, but suspect few others have an O'scope any more. Chassis dyno would help also.

Believe the original carb was an Autolite/Holly.

 

ps have several Pertonixs - they are excellent devices that replace the points so the vacuum advance is still functional. On a premium gas V8 I like about 10-12 initial and 38 at 3000 rpm mechanical. 10-16 vacuum is good. 

Normally a Pertronix system includes a high power coil that is not suitable for a points ignition.

 

pps an engine does not care how old it is, proper maintenance is everything. My Judge is tuned a bit hotter than stock.

Edited by padgett (see edit history)

Share this post


Link to post
Share on other sites

did you or a previous owner install an electric fuel pump?  What pressure does it supply, if there is a pump?

Share this post


Link to post
Share on other sites

The first step in any tune up should be a compression test. What were the numbers?

 

Once the condition of all the cylinders is know and corrected as required there should be a systematic sequence of tests, repeated each time a car is tuned.

 

That's a tune up on a known car. A strange car requires a deeper start point. My first test on a completely unknown car is a cold pressure test of the cooling system. I once had a rough running '59 Caddy show up with all kinds of speculative diagnosis from ignition to carburation. When I put pressure on the cooling system and heard water running inside the engine I knew where to start.

Share this post


Link to post
Share on other sites
5 hours ago, kgreen said:

did you or a previous owner install an electric fuel pump?  What pressure does it supply, if there is a pump?

KG,

 

I have every repair invoice for this car for the past 37 years.  The invoices fill two 3-ring binders and I've looked carefully at each one but I don't see any bills for an electric fuel pump so apparently the fuel pump must be the one that came with the car.  The engine rebuild receipt clearly shows a new oil pump and water pump but no mention of fuel pump.

 

Thanks for your comments.  I will eventually solve this problem.

 

 

 

 

 

 

Share this post


Link to post
Share on other sites

Lots of good ideas, however (opinion) the best ideas are testing. In order:

 

(1) Compression test

(2) If the compression is good (rebuilt engine), check the valve settings (spring tension, clearance, if applicable)

(3) If compression and valves are good, check the ignition, ESPECIALLY with an aftermarket ignition. Would suggest returning to original components for the test. We have solved hundreds of customers "carburetor" problems by having them replace a pertronix with points and condenser!!!!!

(4) If all of the above is good, verify the idle settings (dwell, timing, idle mixture)

(5) After that fuel pressure test. Compare results to the specifications in your factory shop manual. If you don't have a factory shop manual, acquire one!

(6) If all of the above is good, a vacuum test at idle, and off-idle. Again, compare results with expected results.

 

And remember, the white tailpipe of yesteryear was lead residue. A well-tuned car with todays fuel will have a dark or black tailpipe, and if driven around town and never driven at speed, the tailpipe will be sooty.

 

Finally, an engine with a "perfect" carburetor and a defective ignition will be very rich, as there is insufficient spark to burn all of the fuel.

 

Have fun. Very enjoyable to overcome a problem. Do not give up, but more testing and fewer replacement of parts will lead to better results.

 

Jon.

  • Like 3

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this