ENGINE TROUBLE

[72HCODE]

You have to be careful here because turning the idle air bleed screws will not prove the power valve is blown.

he's got a DP with secondaries. it may show the secondaries are not adjusted correctly.

in a holley when idle is correctly set with the butterflies closing the transition slots and running just on the idle circuit, the power valve is actually physically shutdown by an internal cam. so if the power valve was blown it would not effect idle. the power valve and jets are on the same circuit. obviously a power valve is only suppose to turn on when a set vacuum level is reached otherwise it will just jam so much fuel into the motor it stalls out.

any mis-adjustment or compensation for a Carb that isn't flowing enough CFM would require the butterflies to be open more then they should be, this exposes the transition slot and starts to turn the power valve area of the carb On, at that point if is blown then you will get black smoke coming out the tail pipes.

Turning the air bleed screws down until off with engine run on, can mean, incorrectly adjusted secondaries letting too much air in, or vacuum leak.

a quick vacuum leak check could also be made if you cusp your hands over the carburator intake and try to choke off the inflow of air. the engine should slow down and stall. if not the engine will run on and you may hear where the vacuum leak is coming from since the engine will be attempting to get all the CFM it can from that leak and not stall out.

now if the air bleeds are set incorrectly you could get a strong gas smell.

or if the carb is set really wacky then you could have heavy fuel smell as well.

basically it still could be a lot of things. i've seen a stuck accelerator pump and i've seen a carb where the one way valve in the accelerator pump broke and gas would drizzle out the shooters and down the motor making it super rich.

timing could effect the idle, what is the idle speed could be too low, what is the vacuum reading at idle, don't know either, lots of variables.

heavy fuel smell could be a leak in the fuel lines, or fuel leaking on the intake, blown fuel pump,

or it can be as simple as a carb adjustment.

ruling out a vacuum leak would be a step forward. hard to do over the net.

we could also have a stuck choke or a blown choke that is just staying on all the time and effecting idle as well. somebody could of also forced the choke on all the time.

also if the holley dp is a 4 corner unit that would drive you nuts on idle air bleed adjustment also.

Guys, one more quick update for the night. I started the car up and it smells super "rich" while idling poorly. it revs up fine. At idle it seems to work really hard and again there is a Strong fuel/ exhaust smell under the good. I wished one of you guys lived here In KC!!

With a Holley carb that sounds like a blown power valve. The simplest way to prove the theory is to turn the idle misture screws in. It should stumble and try to die out, if turning them in has no effect replace the power valve.

 

[JREID2]

Let me ask you guys this. I have a good hot rod shop 20 miles from where I live. Because of my inexperience, I'm thinking of taking it in and having them look at it/ educate me. Would any of the possible issues keep the car from making it 20 miles or more importantly do any damage? I really appreciate all the advice and may still tackle it myself! Thanks.

 

[JREID2]

Let me ask you guys this. I have a good hot rod shop 20 miles from where I live. Because of my inexperience, I'm thinking of taking it in and having them look at it/ educate me. Would any of the possible issues keep the car from making it 20 miles or more importantly do any damage? I really appreciate all the advice and may still tackle it myself! Thanks.

 

[will e]

Hard to say on 'making it'.

Damage it, probably not. Smell the oil on the dip stick. Does it smell like gas? About the only damage you can do is if you are getting so much gas it is washing the cyls and/or getting into the oil.

I think it's a good idea. Do some self study on the internet before heading down.

 

[wwhite72]

There's an old saying, "if yours is the only Cleveland in the shop find another shop." Ha ha. But you might want to visit them before you let them near your engine. Most of the hot rods i have seen are SBC's. but, they might have some blue bloods working there!

 

[droptop73]

You have to be careful here because turning the idle air bleed screws will not prove the power valve is blown.

he's got a DP with secondaries. it may show the secondaries are not adjusted correctly.

in a holley when idle is correctly set with the butterflies closing the transition slots and running just on the idle circuit, the power valve is actually physically shutdown by an internal cam. so if the power valve was blown it would not effect idle. the power valve and jets are on the same circuit. obviously a power valve is only suppose to turn on when a set vacuum level is reached otherwise it will just jam so much fuel into the motor it stalls out.

any mis-adjustment or compensation for a Carb that isn't flowing enough CFM would require the butterflies to be open more then they should be, this exposes the transition slot and starts to turn the power valve area of the carb On, at that point if is blown then you will get black smoke coming out the tail pipes.

Turning the air bleed screws down until off with engine run on, can mean, incorrectly adjusted secondaries letting too much air in, or vacuum leak.

a quick vacuum leak check could also be made if you cusp your hands over the carburator intake and try to choke off the inflow of air. the engine should slow down and stall. if not the engine will run on and you may hear where the vacuum leak is coming from since the engine will be attempting to get all the CFM it can from that leak and not stall out.

now if the air bleeds are set incorrectly you could get a strong gas smell.

or if the carb is set really wacky then you could have heavy fuel smell as well.

basically it still could be a lot of things. i've seen a stuck accelerator pump and i've seen a carb where the one way valve in the accelerator pump broke and gas would drizzle out the shooters and down the motor making it super rich.

timing could effect the idle, what is the idle speed could be too low, what is the vacuum reading at idle, don't know either, lots of variables.

heavy fuel smell could be a leak in the fuel lines, or fuel leaking on the intake, blown fuel pump,

or it can be as simple as a carb adjustment.

ruling out a vacuum leak would be a step forward. hard to do over the net.

we could also have a stuck choke or a blown choke that is just staying on all the time and effecting idle as well. somebody could of also forced the choke on all the time.

also if the holley dp is a 4 corner unit that would drive you nuts on idle air bleed adjustment also.

Guys, one more quick update for the night. I started the car up and it smells super "rich" while idling poorly. it revs up fine. At idle it seems to work really hard and again there is a Strong fuel/ exhaust smell under the good. I wished one of you guys lived here In KC!!

With a Holley carb that sounds like a blown power valve. The simplest way to prove the theory is to turn the idle mixture screws in. It should stumble and try to die out, if turning them in has no effect replace the power valve.

WTH??? Most of what you say I can agree with, but...

A cam that closes the powervalve? I need to see a pic of that. No Holley I am aware of.

 

[72HCODE]

It's built Into the throttle shaft. Cuts the fuel to the jets and power valve when at idle.

Otherwise you would have jets flooding the intake when at idle. Jets and power valve are on the same circuit. The power valve just activates below a set vacuum level to add to the jets flow.

Accelerator pump is the 4th circuit that is mechanically driven.

Idle ciruit is seperate as well. When at idle an engine needs very little air and fuel to stay running.

When you hit the throttle. Butterflies move exposé transistion circuit. Accelerator pump comes on, power valve comes on also in a addition to jets. The accelerator pump shot just overlaps the loss in air , vacuum until the power valve opens and the jets come on.

At cruise steady vacuum only the jets circuit is on. Punch it and power valve plus accelerator pump come on. But after 3 seconds punching it the accelerator pump shot is spent then its the power valves job to keep you going, and it slowly pinches off as vacuum rises after initial acceleration.

At idle only idle circuit. Since the power valve and jets run on the same circuit you would flood the engine at idle. So they much both be turned off at idle. If the power valve was blown then during acceleration and normal cruise you would be flooding the engine with black smoke out the back from unburnt fuel. Most common for a blown power valve major drop in MPG, constant black smoke from tail pipe heavy fuel smell at cruise. Go then major bog off the line possible tailpipe backfire.


As for the OPS car making it to a shop no idea.

First time I went to go to an alignment shop to diagnose my car bouncing up and down when I first got it. My passenger side tire exploded almost lost control of the car at 55mph. Pooped my pants and spent 300$ for a tow to the alignment shop and paid a huge bill for 4 new tires, and an alignment that turned out to be useless.


Here is the problem with a speed shop.

Time is money they may charge 100$ an hour labor it's actually 135$ by me now.

They are walking into a mystery on a car they may have never worked on. So they may spot something obvious but they will not catch everything and you will have a big bill to pay.

They and you have no history with a car. So you will start getting pissed after going back numerous times for a problem they may never locate, plus the cost.

I got raped by a local shop for over 2000$ before I decided to just take matters into my own hands and it took me 4 years to fix my car. Sucks but I learned starting with nothing.

Now I'm just an expert on one car mine, that's it.

I can tell you my car had everything wrong with it. I'm lucky I wasn't killed driving it when I first got it.

It's a tough call because they only way many shops would do it is starting a full ground up restore that's the only way to check the mechanical and know it is solid. A rolling restoration assumes you have history with the car you know it runs good before changing parts.

Basically I would imagine the shop will take the car and first thing is diagnose the compression see if it is in spec then a massive tune up major labor, stuck bolts and broken parts repair.

Then the grace period of you driving it and either the problem went away or did nothing either way your eating the tune up and shop costs and might have to keep going back replacing things.

You have many questions on the car besides the engine. Fuel system, brake system condition isn't fully known. The engine is just a tiny piece really. There might be electrical issues you don't know about as well.

It may seem overwhelming now, that's why you have to work in small chunks. Like now might be backtracking all the lines and making sure they are connected to something and replacing parts that are obviously cracked, leaking or broken. A compression test would be one of the first things you want to do. And inspection of the spark plugs making sure you number them 1-8 as you remove them so you can spot a problem cylinder.

Then it becomes a tune up and inspection under the car, condition of brake lines and fuel lines. Maybe draining some fuel from the tank and seeing how full of rust it is.

Then getting into the carb and possibly rebuilding it or replacing it.

 

[droptop73]

Sorry, 72 H with all due respect many of your posts are spot on. Your post here on carburetion is not one of them.

Actually carburetors ALL work on pressure differentials based on the Bernoulli principle. The venturi causes a low pressure area when the air is forced to accelerate. This low pressure area causes fuel to flow. At low throttle angles the engine runs on the carburetor's idle and transition circuits on most engines this circuit is what the engine runs on until about 2000 rpm. The main circuit operates only when there is sufficient airflow through the venturi to cause the fuel to flow.

Nevermind, it looks like we need a carburetion tutorial. That is a topic for another thread.

 

[72HCODE]

No problem, read tons of books on the subject. Have a few years experience tuning holleys.

Simple test. Start car let it warm at idle. Observe the engine running at idle.

Shutdown engine, open front fuel bowl on Holley pull power valve out, close fuel bowl restart engine. Observe engine will run the same at idle only. Anything other then idle will turn on power valve and jets full blast , most Likely flood engine. It is a tough test because you need to get through initial start up getting the carb off the fast idle cam with the choke fully opened up till that point the jets and power valve is going to leak in until the throttle gets into correct warmed up position and the blades close to the correct warm idle position.

Another thing to consider is a Holley dp with duel power valves and 4 corner air bleeds. If the power valve is blown in the secondaries and the rear butterflies are opened way to far then yes your idle will go super rich.

This Holley power valve argument comes up all the time. In fords, chevies etc.

Holley is now making anti blow out power valves also making a blown power valve rarer then it used to be.

But the OP has a really old Holley design and so it would still be a good idea during rebuilt to change the seals and power valve.

It myth is covered in Holley carburator handbook selection tuning repair. How to build & power tune Holley carburators, how to build horsepower volume 1 david vizard.

A blown power valve is still bad but it will not effect idle unless you have the secondaries or primaries butterflies mis adjusted and opened too far.

The idle circuit is just that a seperate circuit just to idle the engine adjustable for load on the engine at idle only. If the engine is running lean at idle do you tell them to jet up or raise the power valve vacuum open threshold? or start drilling the idle meter circuits out to let more fuel in at idle?

All irrelevant in helping a new person diagnose engine issues with no expirance.

Believe whatever you want I don't want to argue just help a guy with engine problems.

 

[droptop73]

At the risk of being shut down for real this time...

I am not arguing, I am trying to explain basic fundamental carburetor theory to someone who does not understand.

I don't "BELIEVE" whatever, carburetors work on basic physics, not any black magic "turning on and off", You need to study more books and read more posts on websites. I am trying to help with solid, EXPERIENCED carburetor theory. I teach the stuff, PLEASE, you do not understand carburetor theory. LEAVE IT ALONE!!!

That's all... I'll go back to building cars and tuning them.

Let's get back to trying to help someone here.

 

[JREID2]

Well guys I took the car into a speedo shop against your better judgment. WOW! $1711.30 later I still have so many questions. To satisfy your curiosity they did the following... changed spark plugs, distributor, rotor, coil, starter solenoid, starter, ignition box, some bad wiring, rewire choke, adjust choke and carb, replaced battery. So, the car fires right up now, idles better, but two things I noticed. The car still seems to idle rough (not as rough and it doesn't stall out). The speedo shop recommended I replace the carb. to fix this issue. I drove it 30 miles this morning down the interstate with no issues except I noticed when I stomp on the gas, the car hesitates a split second before shooting forward. Could this be carb. related? I had an epiphany after writing a check for $1711.30. I must learn how to do this stuff myself!!!!! You guys have recommended in prior posts some basic tools I need. Please recommend a good mechanical book that can help me identify and learn what I have under my 73 hood. thanks Guys!

 

[marks73]

Chiltons, and the Ford Shop manuals (I bought mine on CD and print out what I need).

 

[hyena429]

Well guys I took the car into a speedo shop against your better judgment. WOW! $1711.30 later I still have so many questions. To satisfy your curiosity they did the following... changed spark plugs, distributor, rotor, coil, starter solenoid, starter, ignition box, some bad wiring, rewire choke, adjust choke and carb, replaced battery. So, the car fires right up now, idles better, but two things I noticed. The car still seems to idle rough (not as rough and it doesn't stall out). The speedo shop recommended I replace the carb. to fix this issue. I drove it 30 miles this morning down the interstate with no issues except I noticed when I stomp on the gas, the car hesitates a split second before shooting forward. Could this be carb. related? I had an epiphany after writing a check for $1711.30. I must learn how to do this stuff myself!!!!! You guys have recommended in prior posts some basic tools I need. Please recommend a good mechanical book that can help me identify and learn what I have under my 73 hood. thanks Guys!

Could be..Did the shop atleast give it a vacuum check? ruff idle and stalling when you punch it..sounds like could be bad carb...Or more to me..Like bad vacuum...Maybe a manifold leak..Or cam went flat, or bad valve, ....did they atleast give it a compression check ? So many things you could discount with a good vacuum check and a compression check...Instead of stabbing money around hoping for a fix."I know i did that before in my younger days"..Vacuum gage is cheap and everyone wrenching on a car should have one anyways....These motors love to leak around the manifold.

 

[JREID2]

Well guys I took the car into a speedo shop against your better judgment. WOW! $1711.30 later I still have so many questions. To satisfy your curiosity they did the following... changed spark plugs, distributor, rotor, coil, starter solenoid, starter, ignition box, some bad wiring, rewire choke, adjust choke and carb, replaced battery. So, the car fires right up now, idles better, but two things I noticed. The car still seems to idle rough (not as rough and it doesn't stall out). The speedo shop recommended I replace the carb. to fix this issue. I drove it 30 miles this morning down the interstate with no issues except I noticed when I stomp on the gas, the car hesitates a split second before shooting forward. Could this be carb. related? I had an epiphany after writing a check for $1711.30. I must learn how to do this stuff myself!!!!! You guys have recommended in prior posts some basic tools I need. Please recommend a good mechanical book that can help me identify and learn what I have under my 73 hood. thanks Guys!

Could be..Did the shop atleast give it a vacuum check? ruff idle and stalling when you punch it..sounds like could be bad carb...Or more to me..Like bad vacuum...Maybe a manifold leak..Or cam went flat, or bad valve, ....did they atleast give it a compression check ? So many things you could discount with a good vacuum check and a compression check...Instead of stabbing money around hoping for a fix."I know i did that before in my younger days"..Vacuum gage is cheap and everyone wrenching on a car should have one anyways....These motors love to leak around the manifold.

No they did not. I had a compression check done before I bought the car a year ago and it was good. I plan to buy a vacuum gauge and check for leaks. more to come.... thank you for your input!

 

[72HCODE]

well you have a bunch of options:

when you punch it and the car hesitates then goes. do you see any black smoke out the back(rich)? or do you hear a pop from under the hood?(lean)

options you could play with the pump shot. you could mess with the shooters or cam for the shooters.

you could adjust the timing 1-2 degrees.

you could change the power valve to open earlier.

if it is a lean hesitation retard timing, if it is a rich hesitation advance timing.

this allows minor compensations to fuel/air mixture problems.

i don't think you have a vacuum leak since the issue is minor.

subject of books:

i read so many books on the subject there really is not a go to bible of sorts, you kind of feel what a car is doing and have a idea of what the problem might be.

there are tons and tons of books on carbs and motor tuning and intake design and carb design, all they will serve to do is confuse you more.

basically a carb is always giving the wrong amount of fuel or air at any given point.

so you have to listen to the engine and the noise it makes.

tools you should have.

Vacuum gauge.

Timing light.

Dwell/TACH/volt meter if you have points or you need to do diagnostics in the engine bay you need the external tach and dwell.

if you have a A/C compressor a Distributor wrench is a good thing.

you can have a alternator voltage meter if you want optional.

then it is just basic tools.

another thing when a car is running badly for a while you get carbon build up in the cylinder heads. drive the car for a few days if possible normally a lot of times the engine cleans itself up and it runs better and better with more mileage on it. make little steps and have patients. drive the car as is for a while and take mental note of how it is working... then later when you make adjustments you can see how things are effected.

I would get the vacuum gauge and timing light and use them to measure your current base line. see what your initial timing is now and see what vacuum the engine makes at idle for a start.

 

[hyena429]

well you have a bunch of options:

when you punch it and the car hesitates then goes. do you see any black smoke out the back(rich)? or do you hear a pop from under the hood?(lean)

options you could play with the pump shot. you could mess with the shooters or cam for the shooters.

you could adjust the timing 1-2 degrees.

you could change the power valve to open earlier.

if it is a lean hesitation retard timing, if it is a rich hesitation advance timing.

this allows minor compensations to fuel/air mixture problems.

i don't think you have a vacuum leak since the issue is minor.

I thought the same thing...No way im loosing vacuum or compression ..When i tossed a ton of money at my mustangs top end..checked timing..Then got a new distributor...New plugs and wires....Then all new carb and manifold...My car was doing the same thing..It was hesitating only a bit when i punched it ...No smoke...No puffs or anything...was even idleing a little ruff...But not bad...I had freinds follow me around to see if any smoke come out of my car...nothing...Idle kept getting worse as months went buy...I kept throwing money at every little part on the motor...I could of saved my self a ton with a simple vacuum check...My car's cam was flat and my rings where loosing the battle with a bad hone job..vacuum gage was all over the place..They did not cross hatch it...Perfict circles...I was loosing compression.....And i had zero smoke...Cheap vacuum gage is a good thing to have before you start ripping the carb apart...And tossing around money..Just my 2 cents

 

[Mister 4x4]

How old is the gas? Have you gone through all of the gas the previous owner sold with the car yet? Everything listed so far could very well be issues that need addressing, but if you've got a tankful of nasty old gas, it's going to run like crap until it's gone and the fuel system cleaned out.

You also didn't mention if they'd changed out the fuel filter [or not].

If you have new and clean gas, and a new fuel filter, the rough idle and 'hesitation then takes off' when you stomp the pedal sounds like a carb rebuild to me - if nothing more than to get the jets cleaned out and a new accelerator pump in there. If the car sat for a long time or has a lot of miles on the latest carb rebuild, the seals are likely going brittle and there probably a nice coat of varnish inside of everything that passes said gas, causing things to operate sporadically... not smoothly like they should.

$1700 for a 'tune-up' [that didn't even fix the problem] on a car from a period of time that's one of the easiest to track down issues. Wow... I'm in the wrong business. For that kind of money, they [also] should've rebuilt the carb and changed the fuel filter. I mean, it's an hour of time (mostly spent while doing something else while the hard parts are soaking in carb cleaner) and a $25 rebuild kit on one of the easiest carbs in the world to rebuild (MC2100 being easier).

Shakes head - sorry Brutha... I know you're new at this and gotta do what you gotta do. It's times like this I wish we all lived closer to each other.

 

[Chris Womack]

A few weeks ago I got my 73 Mustang 351 Cleveland out of the garage. It ran great driving down the road, but at idle it ran real rough. It never died, but very rough. Yesterday I got it back out of the garage, same thing, idled very rough. I started it three different times and I can't seem to figure out what's going on. On the 4th time, the car wouldn’t start?? I hear an odd noise toward the back left of the engine compartment that I don’t recognize. Of course this was only when I had it running. Any ideas?

How long has it been in sitting?

Is this noise coming from your starter motor? I have found my starter solenoid sticking once so that starter's bendix was not retracting (maybe my starter is bad if it is not allowing the starter's gear to disengage). It was trying to engage with the flywheel when the engine was running. It is fine now.

I have also experienced rough idle caused by vacuum leaks, one of the rubber block-off caps on back of intake manifold was cracked from heat and age. The same thing on one of my vacuum block-offs on my Holley carb.

Looks like you have received great advice and I agree -- the best thing is to get a good manual and the recommended tools and do it yourself (with available help from site members).

 

[Kit Sullivan]

Ok, there is a simple problem that Holley's are prone to and it flummoxes mechanics ALL THE TIME.

The fuel bowls and metering blocks/ plates (depending on the model of carb) on each end are held on with four horizontal 5/16" ( or 8 mm) screws on each end of the carb, eight screws in total.

There is a screw in each corner of both bowls.

These screws can get slightly loose over time due to consistent vibrations. The cork gaskets can also become fuel-soaked and soften, and then compress, also leading to loose screws.

If these screws are just loose enough, fuel can leak internally from the cruise curcuit into the idle circuit and you will NEVER be able to achieve a stable idle. As RPM increases, the engine smooths out because is now running on the cruise ( the correct) curcuit.

You cannot see or smell this internal leak, so there is no obvious way to detect it.

Simply give each screw a little snugging up and your problem may dissapear.

I have seen this problem piss off many seasoned mechanics over the years.

Its worth a shot.

 

[Widowmaker00]

For hesitating when you punch it id suggest just small simple adjustments. Play with the timing, add or subtract 1-2 degrees. Check for vacuum leaks as others have said. Stuff like that.