1966 GT 289 4v - Engine diagnostic

ohiorebel12 · Jul 20, 2013

Looking for help with engine diagnostic. The engine is a 289 4v rebuilt in 1995 and has about 22,000 miles on it. The car sets for long periods of time, but I always make sure the gas is fresh (premium). Cap and rotor are new and it has an original petronix ignition with a stock coil. Timing is set to 8 degrees and vacuum gage reads 15 inches and fluxuates about an inch either way.

For the last 10 years the exhaust trumpets have been black with carbon, meaning when I run my finger over the trumpets it comes out black. When people follow me down the road the tail pipes do not smoke….but the exhaust smells very rich.

I was originally thinking it was the carburetors (4100) and in an earlier post I was looking for a carb recommendation. Most people here thought that the 4100 was the best I could get. Ok I wont argue. This carb was rebuilt by Pony carb several times over the last 10 yrs. I recently confirmed the boosters and jets are correct.

This morning I did a compression test using the following criteria.
Engine at operating temperature, all plugs removed (that was fun- plugs were extremely hot), throttle open, I gave the engine approximately five 2-3 second cranks per cylinder.

The results were in PSI:

Passenger side: 1=149 2=149 3=148 4 =149
Drivers side: 5=149 6=148 7=148 8=149

Attached are pictures of the spark plugs these plugs were in the engine for the last 4 years. Plug numbers 2, 5, 8, look like the have not fired but surely the engine would not run on 5 cylinders or if it did I would know something is up. The car runs down the highway at normal speeds????

Any thoughts?

ohiorebel12 · Jul 20, 2013

I forgot to add that I was shocked to see plugs 2,5,and 8 they almost look like the have not been firing. Surely this would be obvious while running up and down the highway and driving around town.

PrecisionTrans · Jul 20, 2013

First thing I notice is cylinders 2,3,5, and 8 are all running leaner than the other four. You definitely have an issue with one side of the carb. If this is causing a lean misfire, unburned fuel is being dumped into the exhaust, hence the smell.

As for the black deposits in your exhaust tips, that's a characteristic of today's fuels. Look in the tail pipe of a brand new car and you will see the same thing.

Guest · Jul 20, 2013

The following are my opinions based on my experiences only, others will differ.

PrecisionTrans said:
First thing I notice is cylinders 2,3,5, and 8 are all running leaner than the other four. You definitely have an issue with one side of the carb. If this is causing a lean misfire, unburned fuel is being dumped into the exhaust, hence the smell.

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>I agree with precision trans, he made a good call, 2, 3, 5 and 8 are all on the drivers side of the carb. It is supplying some gas which is why it runs ok but still but not as much as the driver’s side due to either an obstruction in one of the passages or different jet sizes from one side to the other. The jets have numbers on them however they often get drilled out over the years in which case they should be checked with a number drill to be sure. You can take them to a local hardware store and check them there if you don’t have these bits, lol. The vacuum passages in the metering block/boost venturi which is held in by the big flat blade type screw on the top of the carb are tiny and often get obstructed or plugged. Take a can of carb or brake kleen with the long narrow nozzle, press the tip right up against ALL the holes and clean the heck out of them. There are two on too that can barely be seen. Spray it into the holes in the top of the carb once the boost venturi has been removed.
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rphudes said:
One other thing that I did not mention is that the heads have roller rockers

Many roller rockers are Chinese and many fail. I personally would only run US made ones. Some of Comp’s are likely made in India as are some of their lifters.
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rphudes said:
they need adjusting. I can hear a few of them clicking.

If you have new comp lifters it is most likely the lifters. If they are adjusted more than 1/2 - 5/8 from 0 they will tick and possibly sustain damage. They are flawed. Other lifters are typically 5/8 – 3/4 from 0.
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rphudes said:
What's a good place to get some smaller jets from?

Your 4 dark plugs do not suggest you have an excessively rich condition, perhaps by maybe 2 sizes max if anything IMO.
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rphudes said:
What's Can you recommend a starting size?

I have rebuilt/jetted etc., over 500 of these carbs. If I needed larger jets than I had available I simply drilled them to the proper size. Yes you can drill jets with no adverse effects on the jets flow providing you don’t drill much larger than the jets size.
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The smallest jet size I have used in these carbs is 52, the largest was 58. The most common for a relatively stock engine were 54 – 56 for 0 – 2000 ft elevation with seasonal temps ranging from 50 to 100 and averaging around 70.
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Klutch · Jul 20, 2013

The black exhaust suggests your carb is slightly rich. But, boy, those plugs sure look clean. In my experience, it's normal to get a little variance on the plugs. Remember, these engines don't have computerized fuel injection.

If your only issue is the black exhaust, I wouldn't worry about it. But if you really want to get to the bottom of this, I would recommend buying some primary jets and trying progressively smaller sizes. Keep going smaller until the engine starts to surge at cruising speed. Then go back up one or two sizes.

I know the guy at Pony Carburetors was good, but there's no way to tell what jets are "correct" when the carb isn't even bolted to the engine. There are just too many variables. So, you really have to dial it in on the engine where the carb sits.

EDIT: The first thing to try is readjusting the idle mixture. Contrary to popular belief, the idle mixture affects the air/fuel ratio well above idle. Get your vacuum gauge out and dial those puppies in!

ohiorebel12 · Jul 20, 2013

One other thing that I did not mention is that the heads have roller rockers and they need adjusting. I can hear a few of them clicking.

I just wanted to get down to the bottom this "rich" running issue before I spend time adjusting the valves. Plus I'm looking for a set of valve covers that I can cut the tops off of so I don't make a mess.

Brian Conway · Jul 20, 2013

Your engine description is essentially the same as mine. I am running at 10 degrees. My plugs are Autolite 45's & gapped at 35. Plugs, all eight, seem to be clean, evenly burning. and are the ' Tan ' color. I have the black residue on my trumpets as well.
I am also running the stock C5ZF-C carb. with the 6.5 power valve. I have never touched the jets and am assuming they are stock. Stock valve train.
The comment about ' today's fuel's ' makes a lot of sense. Brian

ohiorebel12 · Jul 20, 2013

What's a good place to get some smaller jets from? Can you recommend a starting size?

ohiorebel12 · Jul 20, 2013

What causes the oil on the spark plug threads and just above the threads? The valve covers are sealed perfectly.

GT289 · Jul 20, 2013

Motorcraft jets can be had here.........

MOTORCRAFT/FORD/AUTOLITE MAIN JETS

I'd probably bump your initial timing 2 more degrees. Unless you've had the
distributor re-curved, all 289's like more timing. (Don't go nuts though)

GT289 · Jul 20, 2013

I've heard and read various explanations of the "oil above the sparkplug thread" deal
over the years. Including this one today- "While it may look like dirty oil, it isn't, this is unburnt fuel that all the lighter elements in the fuel have boiled off leaving the heavier hydrocarbon components behind. This is not unusual to find even on race engines. I wouldn't have known this myself if I hadn't run acrossed the explanation from a very respected pro engine builder on another site. This "fuel" is here because the seal(tapered seat or gasket) is above the threads but the threads themselves are shielded from the actual combustion process. Almost sounds crazy but it is true."
Don't know about that one.

For the valve covers without lips, I like the Victor Reinz-Dana V/C gaskets for the 289/302. (VS38300HTC) Expensive, yes. Re-useable and will never leak.
On the factory v/c's with lips, we used to glue them with Ford weatherstrip & trim adhesive.
Those also never leaked. I think Gasgacinch for glue now, since the Ford stuff is no
longer available and it would seem to offer similar performance on cork.

ohiorebel12 · Jul 21, 2013

I'll pull the jets out tomorrow and check the numbers. If I recall, the jets are located under the boosters?

ohiorebel12 · Jul 21, 2013

Does anyone see a problem with checking the jet size while the carb is still on the car? I've had this carb on and off a zillion times in the few weeks.

Looks like I just remove the cover, floats, and then remove the jets...

ohiorebel12 · Jul 21, 2013

Ok the primary jets are marked 49F

Should I try a smaller size?

Guest · Jul 21, 2013

How is a smaller size going to correct your lean condition on the drivers side of the carb?

As I previously inferred, I personally have never used a jet SMALLER than a 49 and typically larger but maybe others have.

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barnett468 said:
I agree with precision trans, he made a good call, 2, 3, 5 and 8 are all on the drivers side of the carb. It is supplying some gas which is why it runs ok but still but not as much as the driver’s side due to either an obstruction in one of the passages or different jet sizes from one side to the other. The jets have numbers on them however they often get drilled out over the years in which case they should be checked with a number drill to be sure. You can take them to a local hardware store and check them there if you don’t have these bits, lol. The vacuum passages in the metering block/boost venturi which is held in by the big flat blade type screw on the top of the carb are tiny and often get obstructed or plugged. Take a can of carb or brake kleen with the long narrow nozzle, press the tip right up against ALL the holes and clean the heck out of them. There are two on too that can barely be seen. Spray it into the holes in the top of the carb once the boost venturi has been removed.

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rphudes said:
they need adjusting. I can hear a few of them clicking.

barnett468 said:
If you have new comp lifters it is most likely the lifters. If they are adjusted more than 1/2 - 5/8 from 0 they will tick and possibly sustain damage. They are flawed. Other lifters are typically 5/8 – 3/4 from 0.

It is unlikely but possible this is contributing to your problem. I would correct it first since it needs fixing anyway.

rphudes said:
What's Can you recommend a starting size?

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barnett468 said:
I have rebuilt/jetted etc., over 500 of these carbs. If I needed larger jets than I had available I simply drilled them to the proper size. Yes you can drill jets with no adverse effects on the jets flow providing you don’t drill much larger than the jets size. <o></o><o></o>

The smallest jet size I have used in these carbs is 52, the largest was 58. The most common for a relatively stock engine were 54 – 56 for 0 – 2000 ft elevation with seasonal temps ranging from 50 to 100 and averaging around 70.

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What is your elevation? What is your average outdoor temp?
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ohiorebel12 · Jul 21, 2013

Ok, so what size drill bit would I use to check a jet stamped 49 F (primary) and 58 F (secondary)

As A side note, I bought the carb from Pony Carbs many years ago and they are the only ones who have been inside it besides me. I don't think they drilled the jets.

Some suggest I was try to correct a "lean" problem!! I never said I had a lean problem. My problem has and always been running to "rich" you can smell it at idle, at traffic lights, and sitting outside my garage. I've had this problem for years as my original post indicated. Spring, summer, fall and winter it has been running rich for years. I'm just now getting the time to deal with it on a serious note!

By the way, I really do appreciate all the help and ideas everyone is providing me....I just hope we can find a solution!!!

Next weekend I'm going to try and find the time to adjust my valves to at least eliminate that issue from the equations.

ohiorebel12 · Jul 22, 2013

Question: Would running a hotter plug make a slight improvement on the "rich" condition my 289 suffers from? What would be the plug number? Currently I'm using autolite 45's.

Is there a draw back to using maximum gap compared to minimum gap? Presently, I go for the middle.

Guest · Jul 22, 2013

rphudes said:
Question: Would running a hotter plug make a slight improvement on the "rich" condition my 289 suffers from? What would be the plug number? Currently I'm using autolite 45's.

I never use plug temp to correct a lean or rich condition, I correct the problem not mask it.

A hotter plug means your eng will run hotter.

rphudes said:
Is there a draw back to using maximum gap compared to minimum gap? Presently, I go for the middle.

What is your plug gap. Max, min and middle means nothing since we don't know what you are using as a reference point.

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rphudes said:
Some suggest I was try to correct a "lean" problem!! I never said I had a lean problem. My problem has and always been running to "rich" you can smell it at idle, at traffic lights, and sitting outside my garage. I've had this problem for years as my original post indicated. Spring, summer, fall and winter it has been running rich for years. I'm just now getting the time to deal with it on a serious note!

No one said you said you had a lean problem. Four of your spark plugs suggest that you do. See your quote below.
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rphudes said:
Plug numbers 2, 5, 8, look like the have not fired but surely the engine would not run on 5 cylinders or if it did I would know something is up. The car runs down the highway at normal speeds?

rphudes said:
these plugs were in the engine for the last 4 years.

I would start with new plugs so I have a clean slate to judge performance between the two different sides of the carb from.

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rphudes said:
I'm confused,

Since you are confused and you asked others for help it might be helpful to not try and over think this and simply listen to those that offer you suggestions and do what makes the most sense to you..
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rphudes said:
By the way, I really do appreciate all the help and ideas everyone is providing me....I just hope we can find a solution

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rphudes said:
Attached are pictures of the spark plugs these plugs were in the engine for the last 4 years. Plug numbers 2, 5, 8, look like the have not fired but surely the engine would not run on 5 cylinders or if it did I would know something is up. The car runs down the highway at normal speeds?<o></o>Any thoughts?

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>RICH – You have 4 plugs that are fed by the passenger side of the carb that are moderately dark. This does NOT reflect an abhorrently rich cond, just a mild one in my experience. You can live with it without any noticeable adverse effects other than slightly lower mpg than if that side of your carb ran leaner. A 49 jet will not cause a Mustang to run rich unless you are above around 2000 ft elevation and around 100 degrees in my experience.
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LEAN – You have 4 plugs that are fed by the drivers side of the carb that are almost pure white. This does NOT reflect a rich condition of any but instead reflects an extremely lean one IMO.
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HOW DOES A FACTORY DETERMINE JET SIZES – All factories set up carbs to run on the verge of lean in my experience. Some of the reasons for the following:
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a. to achieve the highest MPG possible. Back in those days the typical highway MPG was around 16. Today it’s around 22. The economy was not great so mileage was a major consideration when purchasing a car. Just 2 MPG could be a make or break deal in my experience. Today virtually no one cares if their gets 22 or 24 MPG simply because the percentage of difference is small.
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b. To meet EPA requirements. In 66 cars in some states were required to have air pumps installed to reduce emissions. Emissions in a car that runs lean are less than those of a car that runs rich.
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JET SIZE – Again I have never used a jet smaller than 49 which means I obviously have also never used a jet smaller than 48, 47, 46 and so on either.
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JET DRILL SIZE – It doesn’t matter much in your case as long as they are both the same size. Again, you have 1 lean bank and 1 burning noticeably richer as evidenced by your 4 white plugs on one bank and 4 brown ones on another.

ohiorebel12 · Jul 22, 2013

This weekend I' ll adjust my valves and change the plugs and then see how things go for a while

ohiorebel12 · Jul 23, 2013

Just so I understand what everyone is saying about the dual plain intake manifold. Please correct me if I'm wrong

1. cylinders 2,3,5,8 are feed by the drivers side

2. cylinders 1,4,6,7 are feed through the passenger side

I search the web and found this illustration

Guest · Jul 23, 2013

rphudes said:
Just so I understand what everyone is saying about the dual plain intake manifold. Please correct me if I'm wrong

1. cylinders 2,3,5,8 are feed by the drivers side

2. cylinders 1,4,6,7 are feed through the passenger side

Yes as I mentioned earlier.

ohiorebel12 · Jul 23, 2013

I decided to change the car gaskets, both the spacer and the 4100 gaskets. I found the intake manifold side channels filled with an oil substance. Is this normal? I do run a PCV from the passenger side valve cover to the spacer and change it often.

So now i'm questioning whether the carb spacer is flip the wrong way.

My questions are

1. Should there be oil in the intake carb mounting channels as the picture depicts?

2. Why is the pcv valve sucking oil...or is it?

3. What is the correct way to place the carb spacer on the intake? Picture 2 or picture 3

Guest · Jul 23, 2013

rphudes said:
I decided to change the car gaskets, both the spacer and the 4100 gaskets. I found the intake manifold side channels filled with an oil substance. Is this normal?

Absolutely, however more common in older engines.

rphudes said:
I do run a PCV from the passenger side valve cover to the spacer and change it often.

There is no need to change it. It might also bre the wrong one which is causing it to have more suction than normal thereby sucking up more oil.

Do you have stock valve covers?

There is a pcv with a foam filter which helps prevent tgis. Also look at adding an aftermarket oil separator.

engine oil separator - Google Search

rphudes said:
So now i'm questioning whether the carb spacer is flip the wrong way.

Flat side goes up. Was it inatalled flat side down?

ohiorebel12 · Jul 23, 2013

Thanks for all the info Barnett468

I have always positioned the spacer flat/solid side up. It was just after finding the oil in the intake channel that I questioned if I have been positioning it wrong

ohiorebel12 · Aug 5, 2013

Update!

Well today for the first time in almost ten years....I decided to drive my mustang about 130 miles ( 70 miles each way) up and down I-75. I have not driven it more then around town in ten years.

Here is what happened..... before I stated the drive. As before, spark plugs 2,3,5,8 were indicating lean and plugs 1,4,6,7 were indicating rich (very black all al around) see pictures in the beginning of this post.

Well when I got back from the drive....all the plugs were indicating lean! seriously, the were all whitish!

Can I assume that my 4100 is malfunctioning at idle and slow speeds like just driving around town?

Also, I cleaned the tail pipes of all the black carbon dust before I took off for the drive. When I got back they were covered with black carbon dust again. Can I assume the slow driving and stopping at the 3-4 for traffic lights to I-75 and the same amount of lights back with the carb malfunctioning at idle and slow speeds caused the pipes to become black again? even though the plugs performing much better at high speeds. My drive averaged 60-75 MPH.

So much in my faith with Pony carbs....that is who I bought the carb from 10 years a go and who also rebuilt it about 5 years a go!

Any recommendation as to whom I should send it too, to get rebuilt? Perhaps it warped or something???? I need to find someone who knows what there doing.

Helmantel · Aug 6, 2013

rphudes said:
Here is what happened..... before I stated the drive. As before, spark plugs 2,3,5,8 were indicating lean and plugs 1,4,6,7 were indicating rich (very black all al around) see pictures in the beginning of this post.

Well when I got back from the drive....all the plugs were indicating lean! seriously, the were all whitish!

Can I assume that my 4100 is malfunctioning at idle and slow speeds like just driving around town?

Probably. Your main circuit (controlled by the main jets) could be lean on both sides of the carb (feeding all cylinders) but only one side of the idle/transition circuit

Woodchuck · Aug 5, 2013

Okay.... here's my $0.02 worth...

Since you have a GT, I will assume that you have not added a brake booster so we can rule out a vacuum leak THERE..... do you have a C4? Have you checked to make sure the vacuum modulator is holding vacuum?

The 4100 is very efficient at fuel atomization and in the "old" days of "real" gasoline it was common for the tailpipes to burn WHITE and the plugs to exhibit some lead fouling but that's all, when properly adjusted. With today's "crap" gas you can usually see some brown deposits caused by fuel additives. A vacuum leak from a warped carb base could certainly do what you describe as could some crap that may be partially restricting the idle/transition circuits on one side. Bear in mind, also, that lean mixtures take LONGER to burn, so that can lead toward more soot in the exhaust, as can also the additional crapola mixed in with the fuel. What I picked up on was what I feel is an abnormally LOW vacuum reading....I'd expect to see 19-20"hg at idle and steady. It sounds like your reading is floating either side of 15"hg. This can indicate late ignition timing, insufficient spark plug gap, worn valve guides or a combination of all. The OTHER suspect would be a PCV valve that is wrong or defective. However, recognize that PCV opening is INVERSE to engine vacuum too.

Before you go and lean out the carb EVEN MORE, which will further aggravate the problem, I'd think about having your A/F ratio checked with a gas analyzer. You may find that you need to richen up the carb, add more timing, sooner and, if it was me, move your vacuum advance source over to manifold vacuum to start...

Guest · Aug 5, 2013

Are you using e 85 gas

Do you have ex block off plates in intake gasket?

Does id idle fine?

How hot does it get in traffic and also fwy?

Does it hesitate when accelerating hard from a stop or steady speed like around 40 mph.

Did you try to clean circuits out and adjust fuel mix screws like I suggested last week?

ohiorebel12 · Aug 5, 2013

Bartl and Barnett468, thanks for the follow up!

It’s a true GT, 3 speed manual transmission. If I tweak the mixture before I drive it I can get the vacuum up to very close to 19 inches with the idle at about 825, but it won’t stay there if I let the car set for a day or so days.

I’ll try getting some vac hose and run my vacuum advance from the intake manifold directly. The PCV valve I using is off-the-shelf from AutoZone.

I don’t plan on doing anything with this carb until I find someone more qualified than me to evaluate it. When Pony carb sold it to me and then rebuilt it they said it was fine. I think they were wrong.

Are you using E-85 gas

I do not run E-85 gas….I hate that stuff. I have to run that crap in my government car and it sucks. However I do have run the 10% ethanol as there is no pure gas within 100 miles of my town. Although I could mix in some Aviation Gas, but that stuff is 6.75 per gallon

Do you have ex block off plates in intake gasket?
I don’t know what you mean - If I remember correctly I used a regular intake gasket.

Does id idle fine?
Fluctuates between 725-775

How hot does it get in traffic and also fwy?
Yesterday’s drive on the freeway the temp stayed in the middle of the gauge just before the “M” in temp. If I set at a traffic light on a hot day it would go it will go past the “P” I would not want to be caught in New York City traffic in the summer

Does it hesitate when accelerating hard from a stop or steady speed like around 40 mph.
No. When cruising down I-75 doing 75 I had plenty of gas pedal the car wanted to go faster but the suspension won’t handle it yet. That’s my next project.

Did you try to clean circuits out and adjust fuel mix screws like I suggested last week?
Yes

Any suggestions on who to send the Carb to? When I send it out to get worked on, I was going to buy a new Holley 4160 -600 CFM to hold me over until the 4100 issues are solved. Unless either of you can recommend a better temporary alternative.

Guest · Aug 6, 2013

your advance does not go to intake vacuum it goes to ported vacuum.

when you set fuel mix screws was engine hot?

Check float level, might be high.

it does not sound like your carb needs rebuild. A new power valve wouldn't hurt and check power valve cover for being warped/ put a piece of 320 sandpaper on a granite counter and sand it until flat.

do you have an infra red your engine sounds a little hot.

might need a fixed 6 blade fan from flex-lite p/n 1717p

does it have a shroud?

what is your timing at idle? should be around 8-10

is intake aluminum? if so it needs ex block off plates in intake gaskets if your temps don't get below around 50 degrees when you drive.

is there a carb spacer?

is there a pcv valve?

ohiorebel12 · Aug 6, 2013

your advance does not go to intake vacuum it goes to ported vacuum.

-Right now my vacuum advance runs from the carb to the distributor.

when you set fuel mix screws was engine hot?

-Yes

Check float level, might be high.

-Will check the float level this weekend

it does not sound like your carb needs rebuild. A new power valve wouldn't hurt and check power valve cover for being warped/ put a piece of 320 sandpaper on a granite counter and sand it until flat.

-Will change the power valve when I check the float level this weekend

do you have an infra red your engine sounds a little hot.

-Yes, at idle the passenger side of the intake 1,4,6,7 were running 50 degrees cooler then 2,3,5,8

might need a fixed 6 blade fan from flex-lite p/n 1717p

does it have a shroud?

-yes

what is your timing at idle? should be around 8-10

-I'm set at 12

is intake aluminum? if so it needs ex block off plates in intake gaskets if your temps don't get below around 50 degrees when you drive.

-It's stock...

is there a carb spacer?

-Yes, new gaskets all around

is there a pcv valve?

-New from off the self from AutoZone

Guest · Aug 6, 2013

Right now my vacuum advance runs from the carb to the distributor.

it must have no vacuum at idle.

xxxxx

when you set fuel mix screws was engine hot?

Yes

xxxxx

Will change the power valve when I check the float level this weekend

don't forget to flatten power valve cover, they are always warped.

xxxxx

at idle the passenger side of the intake 1,4,6,7 were running 50 degrees cooler then 2,3,5,8

where did you measure that exactly?

what was the temp?

measure at 1/4 throttle after 1 minute also.

xxxxx

what fan is on it?

xxxxx

is there a pcv valve?

New from off the self from AutoZone

Plug the pcv and try it.

How much does engine rpm increase when it is removed?

If it is more than around 50-75 rpm it is too big. They often sell the wrong size.

ohiorebel12 · Aug 6, 2013

Barnett468, where specifically should I point the inferred laser to get an accurate reading? Just to confirm, let the engine run for one minute and then take the reading?

Guest · Aug 6, 2013

let the eng get to normal driving tempo then hold throttle open 1/4. after 60 seconds it will be as hot as it is going to get, maybe only 30 sec, watch temp gauge.

shoot the ex manifold on every cyl where it comes out head.

shoot front of heads.

reshoot again because eng may warm quickly giving a hotter reading on the opposite side by the time you get there.

what was temp before?

i doubt it's a problem though.

Do both pcv tests!

1966 GT 289 4v - Engine diagnostic

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