Pictures and some info from a new guy
#1
I am pretty new here. I was asked to show some pics so I hope it works OK.

First is my RED 1972 Mach1 vin code correct. Rotisserie about one year ago with pictures and docs. New seats and covers, carpet, head liner and more. The former owner was mechanically declined so he subbed it all and then tried to assemble the interior and burnt and crashed. He had a new larger radiator and heater core installed, new gas tank, new door panels, windshield, springs/shocks, tranny was checked out.  I was looking for a second winter project so I bought it knowing I would be tearing apart the entire inside and putting it back together slowly and carefully. Some upgrades like LED interior lighting, cd in the glove box, sub speakers mounted on the trunk wall, refinishing the quarter panels and figuring out how to install the fold down seat (in parts). Pull the entire dash and have the gauges re-faced and the clock fixed. He left bolts and screws out everywhere so it is back to ground level here.

The engine is a .30 fresh build 351C, mild cam. I pulled the stock intake and place an Edlebrock dual plane ram air, Holley 600 cfm, new distributor single vacuum, electronic pick up ignition, better coil, Edelbrock V/C, shorty headers which I ceramic coated twice. The dual exhaust was hand built by a pro with throaty flow master mufflers. I am working out a lean stumble (larger discharge nozzle). Automatic FMX. I installed a 1-1/8 front sway which was a great improvement but will probably drill and mount a rear like on my other Mustang. I need to pull the rear new springs and lube the shackles plus the shocks as the squeak a bit. Has a 3.73, 9" posi rear end.

For me I am a retired mechanic/business owner/operator and moved my 9K lift and shop to my Ranch when I closed down. Working on these classics is just fun and good for my head plus they show very well and end up fun to drive in the countryside. We get a lot of snow here so it helps to have a shop with a warm wood stove and 200 watt stereo when I am not moving snow, loading firewood or keeping things running all winter long.

My other Mustang is a 1970 convertible Boss tribute. Original metal and top with 72K on it. Once painted same Grabber Blue with pearl. 347 Stroker from the ground up. Shift kit C4 with a 2800 rpm stall and with posi-loc rear end. Interior has some stuff redone and looks like new of better.  The car is solid and has suspension upgrades to handle the added power which is way more than offered in 1970. Thing is the Boss is basically done now so it does not occupy my time other than detailing it all the time, burn outs, classic cruises, car shows and going for drives in the summer. My wife loves to drive it.

Anyway that is some info and pics


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#2
John,

Nice rides! Thank you for sharing the pictures.  You mentioned you have a "lean stumble" with your engine.  I think I am having the same issue with my car.  I was having some fuel and ignition issues with my car and have broken down twice already.  I just installed a new Edelbrock 600cfm and an old school Echlin dual point distributor.  The car is running much better and the I can feel the performance has greatly improved. I took the car out last night and and I think I felt what you described as a lean stumble.  As I mentioned, I have a new carburetor on the car. Do you think this is in the carb? 

Mike
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#3
(11-15-2018, 09:56 PM)Mustangmike Wrote: John,

Nice rides! Thank you for sharing the pictures.  You mentioned you have a "lean stumble" with your engine.  I think I am having the same issue with my car.  I was having some fuel and ignition issues with my car and have broken down twice already.  I just installed a new Edelbrock 600cfm and an old school Echlin dual point distributor.  The car is running much better and the I can feel the performance has greatly improved.  I took the car out last night and and I think I felt what you described as a lean stumble.  As I mentioned, I have a new carburetor on the car.   Do you think this is in the carb? 

Mike

Mike,

I recalled the old dual point distributors. If I recall it was an attempt in the early days to work with emissions or try to increase performance. It sort of depended in what ride and what time period. The concept was dropped over time. Hopefully it is a rebuilt distributor with all new springs, plates etc. The dist. in my 72 was older with wear and not reaching the correct over all timing advance. I installed a rebuilt dist and installed the simple electronic magnetic pick on the shaft and breaker plate. That eliminated any and all issues and was very inexpensive.
As for the I guess Holley 600cfm ... if so the accelerator pump cam comes in colors. Mine is orange and each color changes the rate and duration of the discharge profile. The upper most hole is number 1 position which is for cars that run a normal idle around 750. Some modified cars run a higher idle like over 1K. Be sure your mounting screw is in the upper hole for a base warm idle around 750. Mine came with the second lower hole engaged so I redid it. If a change is needed it is best to install the screw into the new hole in the cam while it is off the carb so as to cut the threads into the plastic before hand. Then install.
Next the discharge nozzles can have to small an exit hole. One must remove the discharge nozzle and read the stamped number on it. Be sure to stuff a clean rag into the venturi above the closed throttle plates to catch any washers, gaskets or whatever. Never restart the car is any parts come up missing rather pull the carb and check in the intake first.
I believe most 600cfm have a 33 or .033 same thing. I am stepping up to a 35. This allows for a larger amount of fuel to be shot into the intake over the same accelerator arm travel as before the change out. Engines with modified intakes normally result in longer distances for the air and fuel to flow before entering the chamber so a bit more fuel is often needed to complete the trip with enough fuel still atomized to do the job.

I also experience a slight lean cruise with the new 600 Holley. The car acted like it was hitting a buffing head wind or rough road. Just a bit jumpy. I pulled the metering block and increased the jet size 2-3 sizes up. The jets in the carb when new were not the size they were supposed to be either. That smoothed out the cruise end of the things. Be sure the float level in even with the site port. I like mine to not leak if the inspection screw is out unless I bump the fender with my hip. That is just me. My Blue Mustang needed a fuel pressure regulator to manage the system and I shall see on the 72.

Also be sure to spray small amounts of carb cleaner around the intake gaskets and carb base at idle. If the engine speeds up you have an air leak. A small shot in the venturi can also indicate lean idle if the engine speeds up at all.

That was a lot of typing.....



Be sure the plugs wires and coil wire are in perfect condition as per ohms. I custom cut tall  mine. I also installed a new MSD coil in the 72 to make available more voltage if needed.
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#4
(11-16-2018, 02:56 AM)John Wrote:
(11-15-2018, 09:56 PM)Mustangmike Wrote: John,

Nice rides! Thank you for sharing the pictures.  You mentioned you have a "lean stumble" with your engine.  I think I am having the same issue with my car.  I was having some fuel and ignition issues with my car and have broken down twice already.  I just installed a new Edelbrock 600cfm and an old school Echlin dual point distributor.  The car is running much better and the I can feel the performance has greatly improved.  I took the car out last night and and I think I felt what you described as a lean stumble.  As I mentioned, I have a new carburetor on the car.   Do you think this is in the carb? 

Mike

Mike,

I recalled the old dual point distributors. If I recall it was an attempt in the early days to work with emissions or try to increase performance. It sort of depended in what ride and what time period. The concept was dropped over time. Hopefully it is a rebuilt distributor with all new springs, plates etc. The dist. in my 72 was older with wear and not reaching the correct over all timing advance. I installed a rebuilt dist and installed the simple electronic magnetic pick on the shaft and breaker plate. That eliminated any and all issues and was very inexpensive.
As for the I guess Holley 600cfm ... if so the accelerator pump cam comes in colors. Mine is orange and each color changes the rate and duration of the discharge profile. The upper most hole is number 1 position which is for cars that run a normal idle around 750. Some modified cars run a higher idle like over 1K. Be sure your mounting screw  is in the upper hole for a base warm idle around 750. Mine came with the second lower hole engaged so I redid it. If a change is needed it is best to install the screw into the new hole in the cam while it is off the carb so as to cut the threads into the plastic before hand. Then install.
Next the discharge nozzles can have to small an exit hole. One must remove the discharge nozzle and read the stamped number on it. Be sure to stuff a clean rag into the venturi above the closed throttle plates to catch any washers, gaskets or whatever. Never restart the car is any parts come up missing rather pull the carb and check in the intake first.
I believe most 600cfm have a 33 or .033 same thing. I am stepping up to a 35. This allows for a larger amount of fuel to be shot into the intake over the same accelerator arm travel as before the change out. Engines with modified intakes normally result in longer distances for the air and fuel to flow before entering the chamber so a bit more fuel is often needed to complete the trip with enough fuel still atomized to do the job.

I also experience a slight lean cruise with the new 600 Holley. The car acted like it was hitting a buffing head wind or rough road. Just a bit jumpy. I pulled the metering block and increased the jet size 2-3 sizes up. The jets in the carb when new were not the size they were supposed to be either. That smoothed out the cruise end of the things. Be sure the float level in even with the site port. I like mine to not leak if the inspection screw is out unless I bump the fender with my hip. That is just me. My Blue Mustang needed a fuel pressure regulator to manage the system and I shall see on the 72.

Also be sure to spray small amounts of carb cleaner around the intake gaskets and carb base at idle. If the engine speeds up you have an air leak. A small shot in the venturi can also indicate lean idle if the engine speeds up at all.

That was a lot of typing.....



Be sure the plugs wires and coil wire are in perfect condition as per ohms. I custom cut tall  mine. I also installed a new MSD coil in the 72 to make available more voltage if needed.

Mike,

I made a mistake above. My new Holley came with 31 discharge nozzle size... not 33. I am tying 35 because it was handy and I dd not need to order it. If it works and the stumble goes away I will wait until next year after it  warms up to over 60 outside. I might try a 33 then or not. Above 60 is the temp range I set up my modifies to run as they are summer only use. It is 34 outside here and they way my Mustangs will operate now  is just not the same so I do not want to pursue a stumble after this discharge change until then. To much discharge size increase can lead to rich exhaust and a feeling the car takes off great but a few dozen feet down the road or less it can pull back on power then come back again. My Blue one has been put to bed now and after a few more days the Red one will be in the shop for interior work and no more off site rides as we pull the insurance back during winter.
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#5
A 600 CFM on a 351C is fairly small.  Not saying it won't work.  But Clevelands tend to like larger carbs than what the math indicates to be needed.  The air speed through the venturies of a 600 CFM carb on that motor should be high enough at any RPM to not need extremely large pump nozzles.  Maybe one size over stock if any.

What is the base timing and the timing curve set at?  Longer duration cams need more initial timing than stock.  That has a big influence on performance and will often fix stumbles on acceleration.  

Another big area that causes stumbles is not having the primary throttle plates set correctly at idle.  You cannot willy-nilly turn the idle speed screw on a Holley carb to set the idle speed.  Approximately 0.020" to 0.040" of the transfer slots on the primary side should be exposed under the throttle plates at idle.  At idle you want the idle circuit running and the transfer circuit to be initialized.  This prevents any delay in the transfer circuit startup and stumbles on mild acceleration.  With the carb off and turned over, adjust the primary throttle plate position and get a feel for how much adjustment there is to still maintain proper position.  After that, for further idle speed adjustment use the secondary throttle plates.  If too much of the transfer circuit is operating at idle two things will occur, (1) the idle A/F might not be responsive to adjustments and (2) during mild accelerations you can exhaust the transfer circuit before the main circuit starts up, then a lean surge or stumble will occur.

Check the power valve size in that carb as well.  Make certain it will open early enough for your motor.  Holley has info on their website for selecting the correct power valve.

There should be no "play" in the accelerator pump lever (linkage) at idle.  The nozzles should start spraying fuel as soon as the throttle is touched.  At wide open throttle make certain the pump diaphragm is not bottomed out.  Common for this to no be adjusted correctly out of the box.  Have you tried different pump cams?  Pink is most common and works for most applications.

Most Holley's need a little tuning out of the box.  After proper adjustments, sometimes one or two main jet sizes and maybe one or two pump nozzle sizes or a different pump cam are needed, if any.  Needing to do more than that is an indicator it's the wrong carb for the application.
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#6
(11-16-2018, 04:14 AM)1969_Mach1 Wrote: A 600 CFM on a 351C is fairly small.  Not saying it won't work.  But Clevelands tend to like larger carbs than what the math indicates to be needed.  The air speed through the venturies of a 600 CFM carb on that motor should be high enough at any RPM to not need extremely large pump nozzles.  Maybe one size over stock if any.

What is the base timing and the timing curve set at?  Longer duration cams need more initial timing than stock.  That has a big influence on performance and will often fix stumbles on acceleration.  

Another big area that causes stumbles is not having the primary throttle plates set correctly at idle.  You cannot willy-nilly turn the idle speed screw on a Holley carb to set the idle speed.  Approximately 0.020" to 0.040" of the transfer slots on the primary side should be exposed under the throttle plates at idle.  At idle you want the idle circuit running and the transfer circuit to be initialized.  This prevents any delay in the transfer circuit startup and stumbles on mild acceleration.  With the carb off and turned over, adjust the primary throttle plate position and get a feel for how much adjustment there is to still maintain proper position.  After that, for further idle speed adjustment use the secondary throttle plates.  If too much of the transfer circuit is operating at idle two things will occur, (1) the idle A/F might not be responsive to adjustments and (2) during mild accelerations you can exhaust the transfer circuit before the main circuit starts up, then a lean surge or stumble will occur.

Check the power valve size in that carb as well.  Make certain it will open early enough for your motor.  Holley has info on their website for selecting the correct power valve.

There should be no "play" in the accelerator pump lever (linkage) at idle.  The nozzles should start spraying fuel as soon as the throttle is touched.  At wide open throttle make certain the pump diaphragm is not bottomed out.  Common for this to no be adjusted correctly out of the box.  Have you tried different pump cams?  Pink is most common and works for most applications.

Most Holley's need a little tuning out of the box.  After proper adjustments, sometimes one or two main jet sizes and maybe one or two pump nozzle sizes or a different pump cam are needed, if any.  Needing to do more than that is an indicator it's the wrong carb for the application.

The 351C I own has the two barrel heads which fall under the four barrel heads. Intake ports are smaller and valves are smaller. I have no desire to spend loads of money on four barrel heads unless I built this motor from the bottom up. It is a  new stock motor .30 over and has a mild cam. personally I have no desire to build  stroke for this 72. IMO the year does not justify the expense... maybe when they come of age more? I will know if the discharge increase does it. Holley also advised to switch it up at least two - three sizes from stock for what I was doing. They also recommended the 600 or 650 cfm. I personally prefer under slight carbureting  than over carbing. Once I am rolling it handles the pedal to the metal and passing gear just fine.

This is all guess work even when one knows stuff. Usually you end up with extra parts left over from trying.
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#7
What's the ignition timing set at, initial and total?  I only ask because a #35 nozzle is fairly large for a small carb on a 351 CID motor.  Usually larger nozzles are needed when larger carbs are used on smaller CID motors because it takes more engine RPM before the main circuit starts up.  Also the larger nozzles are more often needed with single plane intakes because the signal to each venturi is weaker than with a dual plane intake.  I run a 650 CFM mechanical secondary Holley HP style carb on a 351W.  Runs fine with only #28 nozzles.  A 700 CFM Holley mechanical secondary carb also works great on the same 351W motor.  The 700 CFM carb needs #31 nozzles.

Where is the stumble, directly off idle, mid to upper RPM, etc.?  Not saying the #35 nozzle won't fix the issue.  But, it might be covering up something like an ignition timing issue.
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#8
(11-16-2018, 08:44 AM)1969_Mach1 Wrote: What's the ignition timing set at, initial and total?  I only ask because a #35 nozzle is fairly large for a small carb on a 351 CID motor.  Usually larger nozzles are needed when larger carbs are used on smaller CID motors because it takes more engine RPM before the main circuit starts up.  Also the larger nozzles are more often needed with single plane intakes because the signal to each venturi is weaker than with a dual plane intake.  I run a 650 CFM mechanical secondary Holley HP style carb on a 351W.  Runs fine with only #28 nozzles.  A 700 CFM Holley mechanical secondary carb also works great on the same 351W motor.  The 700 CFM carb needs #31 nozzles.

Where is the stumble, directly off idle, mid to upper RPM, etc.?  Not saying the #35 nozzle won't fix the issue.  But, it might be covering up something like an ignition timing issue.

Currently timing is stock as per the manual. Advance curve reaches 34-36 degrees at higher rpm. Advancing the timing has caused issues because I tried it. This is an issue which happens before the timing can hardly even change. A sudden backfire is often a lean condition because there is not enough fuel being introduced in to the sudden demand for air before the metering circuits can respond and deliver. The timing does advance quickly as I crack the throttle with my adjustable timing light because it is ported and has weights to. This is strictly a very fast full throttle from a stop hesitation and often a backfire. If I take off a with a bit less throttle it pulls just fine. It will even scratch tires when shifting gears. After several miles per hour and up it works alright with a sudden throttle even down to engaging pass gear. The 35 is being tried because it was locally available to try. To get a smaller size would require days as to shipping and my window of testing is closing with snow. I never pass absolute judgement on these modified car engines etc in real cold weather. I set them up to run at 60-70 degrees and above because that is when they get driven now. I understand some of your points and they are well taken. I always only try or do one fix at a time so as not to cloud up the results. I have about a week with shipping to get a direction on this minor issue before the car gets layed up for interior work for the winter and the insurance is cut back. I truly suspect this will end up a spring to do item for me ;-0
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#9
34 total is fine.  Might run better with more initial timing than the stock 6 deg. BTDC.  But then you need to recurve the distributor to limit the total timing.  Sometimes simply disconnecting the vacuum advance is enough to limit the total advance on a stock distributor.  There are articles on how to recurve stock Ford distributors.  Crane also makes a spring kit and adjustable vacuum advance.  Most people run as much initial as possible, start at 10 degrees BTDC and move up and down as needed.  Then not use a vacuum advance if the mechanical advance by itself will get it to about 34 degrees total.  I ended up at 13 degrees BTDC initial and 21 degrees mechanical for a total of 34 degrees.  Only drawback of increasing the initial timing is you might need a PMGR high torque starter.  The original style Ford starters sometimes crank slow after advancing the ignition timing.

Holley nozzle sizes represent the orifice diameter, unlike Holley main jet sizes.  If you have number drills and a pin vise you can take a smaller nozzle and open it up.  With larger nozzles, some say at #35 and some say #40 you need a hollow nozzle screw to flow enough fuel.
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#10
(11-16-2018, 10:07 AM)1969_Mach1 Wrote: 34 total is fine.  Might run better with more initial timing than the stock 6 deg. BTDC.  But then you need to recurve the distributor to limit the total timing.  Sometimes simply disconnecting the vacuum advance is enough to limit the total advance on a stock distributor.  There are articles on how to recurve stock Ford distributors.  Crane also makes a spring kit and adjustable vacuum advance.  Most people run as much initial as possible, start at 10 degrees BTDC and move up and down as needed.  Then not use a vacuum advance if the mechanical advance by itself will get it to about 34 degrees total.  I ended up at 13 degrees BTDC initial and 21 degrees mechanical for a total of 34 degrees.  Once drawback of increasing the initial timing is you might need a PMGR high torque starter.  The original style Ford starters sometimes crank slow after advancing the ignition timing.

Holley nozzle sizes represent the orifice diameter, unlike Holley main jet sizes.  If you have number drills and a pin vise you can take a smaller nozzle and open it up.  With larger nozzles, some say at #35 and some say #40 you need a hollow nozzle screw to flow enough fuel.

I have the Crane part number. There has not been any great amount of change to this rebuilt 3351C. Decks were not milled, head just rebuilt. Stock pistons, crank and rods. Some cam change was mentioned to an RV cam but I can not prove that. Te specs are not provided just the cam name. I need to recheck manifold vacuum since the intake/carb and header work. Was around 12. This slight hesitation is since the complete install so I go back to the install part first. mainly the carb. I always go back to the last things done as suspect.
My other mustang is in a whole different league and I had to modify the Holley a bunch and ultra sound clean it as it has been screwed with. I needed to change the power valve because it pull 7 inches or so of vacuum. It runs like a scolded dog now ;-) I sense this issue is a minor issue to resolve and I will try an over size discharge nozzle to see if it effects the issue in any way. I think I mentioned the hollow bolt above in my previous postings. i doubt the distributor is a cause to. Time will tell and I sure do not want to over think this thing. It is so close to working just fine.  Thanks.
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