Holley carburettor adjustment needed

Hi Rene -

My first picture (handwritten) is how I had my Holley 4150 (List 4609, 735 CFM) set up during the initial phase of my ownership.  The typed data is how the same carb is currently set up.  It starts good, idles good, runs great.

I have drilled my throttle plates (you can see one of the holes in the picture).  All four throttle plates are drilled.

I’m running a 358 ci (351C bored .040” over), a George Pence recommended Bullet cam.  Compression is 10:1.  I am also running the Blue Thunder manifold.

My buddy Wade helped me set this all up, drilled the throttle plates, and we eventually converted this carb to 4-corner idle by drilling, and installing needle valves in the secondary throttle plate..  nevertheless…

It seems to me if your car won’t even run on start up, and doesn’t idle when you open the secondaries all the way up, very small holes (.136”) in your throttle plates will not solve your problems.

I would be thinking about something like ignition timing. But that’s just me.

I hope this information is helpful to you.

Rocky

Hi Rene,

a Holley carburettor is more tolerant than a Weber in terms of adjustments. A new holley is pre-tuned at the factory and runs as it is, and your engine should start, without backfiring, and not stall below 1800 rpm, the choice of jets, nozzles and power valve, cams, etc. .. are for optimized settings. I think it is necessary to recheck the firing order, recheck the connections and the plugs on the carburettor and on the intake pipe, etc ... before drilling holes in the butterflies and returning the secondary back to adjustment of origin.

When I had a weird problem similar to what you are describing - a lot of smoke, could only keep it running at high rpms etc, it was the distributor cap that had been put on crooked. It messed up the rotor. Worth a quick check.

Thank you for your answers, I will check the whole ignition system before changing the carburetor permanently.

You probably have the wrong Holley carb. I am not specifically familiar with the one that you have but it may be that it has the reverse idle system used to get the idle mixture to 14.6 at idle.

A generic 3310 will probably be the easiest for you to use. It's 780cfm and jetted for a 5 to 5.7L v8, so all you should have to do is bolt it on and idle it down.

What you are also describing in the issues with the carb that you are trying to use now is a symptom of a BIG vacuum leak. So check all of the usual places plus the special Pantera places like the power brake vacuum line (all the way to the front).

...If it has Backfired Through the CARB...Just One Time, You have a Blown 'Power Valve' RUBBER Diaphragm on the Primary Metering Block. Too Much Fuel, Flooding Out! If it is a 'Double-Pumper', there is also a Power Valve on the Secondary Metering Block! Check/Test these by Removing and Sucking on them...No Kidding, they should 'Hold' the Vacuum.

MJ

Marlin is correct. Yes on the power valve as the source if the diaphram is ruptured. . It can be blown out by a backfire while starting but it will also flood the engine since the primary bowl will then dump directly into intake manifold.

The current crop of pv's is so bad, of the ones I've tested around 50% are bad right out of the box. Don't suck on them. Get a Moroso pv tester. If you run Holleys, you need one.

SOME new Holleys, but not all,  have a check valve built into the base plate but they are not 100% effective.

There is only one Holley double-pumper that uses a pv in the secondaries. That is a 4181, 850cfm. The others are all just one and it is installed in the primary metering block.

as doug said, it could be a leak on the air intakes for brake assist, pcv, etc. I think the best thing to do first is to disconnect all those hoses that go to the intake and to the Holleyand put caps in place and do a test.

If you don't already have it, a link in french for the Holley settings:

CARBURATEUR AMERICAIN REGLAGE (free.fr)

@dipascale posted:

as doug said, it could be a leak on the air intakes for brake assist, pcv, etc. I think the best thing to do first is to disconnect all those hoses that go to the intake and to the Holleyand put caps in place and do a test.

If you don't already have it, a link in french for the Holley settings:

CARBURATEUR AMERICAIN REGLAGE (free.fr)

Thank you very much for the link, I think it will help me a lot.

I found a first "leak" of depression, the PCV ME Wagner valve which I haven't adjusted yet since it needs a stable idle, I plugged it and it's going a little bit better.
I'm going to check the power valve because in addition to the backfire there are explosions in the exhaust and flames that come out when I keep the engine speed a little high, not when I release the accelerator but while I hold it a little open.

Thank you for all your advice

@rene4406 posted:

Thank you very much for the link, I think it will help me a lot.

I found a first "leak" of depression, the PCV ME Wagner valve which I haven't adjusted yet since it needs a stable idle, I plugged it and it's going a little bit better.
I'm going to check the power valve because in addition to the backfire there are explosions in the exhaust and flames that come out when I keep the engine speed a little high, not when I release the accelerator but while I hold it a little open.

Thank you for all your advice

Yes, the pcv system uses 3-4 inches of vacuum to make it work. I think that you need to hook up a vacuum gauge to help diagnostics.

My vacuum gauge was destroyed by a backfire, I ordered another one.

If you have fire, explosion & flames, it’s not a carburetor problem….

…or a mild vacuum leak!

Especially if it’s coming out the exhaust…

Good luck, have you checked the roll pin in your distributor?

Rocky

as Rocky, if the firing order is OK and if there are flames in the exhaust, I will rather opt  for a lack of advance.

I rechecked the firing order and the connection of the spark plug wires, everything is OK.
It is true that the engine runs better when the vacuum advance is connected and therefore there is more advance.
It seems to me that a really too rich mixture can also cause explosions at the exit of the exhaust when the overflow of gasoline which could not burn in the cylinders comes into contact with the outside air.

Thanks again for all your advice.

@dipascale posted:

as Rocky, if the firing order is OK and if there are flames in the exhaust, I will rather opt  for a lack of advance.

... OR an exhaust valve or valves not seating. What type of camshaft is installed in the engine? Is it a solid lifter or hydraulic lifter?

302 Fords have a history of spark plug wires #7 and # 8 cross firing to the extent that the Ford Engine Assembly Manual shows that they must be separated in the wiring loom on the valve cover. Other Ford engines are not immune from that issue as well.

A problem with the distributor cap such as a crack or the wrong rotor is not out of the question also.

Cam Bullet Racing "GeorgesP" spec, hydraulic roller tappets tuned with very little play, almost like solids.

@rene4406 posted:

Cam Bullet Racing "GeorgesP" spec, hydraulic roller tappets tuned with very little play, almost like solids.

Are you SURE that the valves are closing COMPLETELY? Incorrect valve adjustments are one of the things I would be looking at.

I always prefered solids where I could measure the clearances with a feeler gauge rather then ATTEMPTING to pre-load hydraulic lifters correctly. I always had difficulty with "high performance" hydraulic lifters. They are always a "bear" for me to get right.

I checked the powervalve "by mouth" and it is not destroyed, probably because my carburettor has a protective valve.
I closed the secondary a little so that the progression slot looks like a square.

I increased the lead.

The engine only starts by screwing the idle screw on the primary hands almost fully, when it is running I can loosen the screw up to 1400/1500 rpm, below there is backfire and the engine stalls.

At 1500 revs it takes 36° in advance with the depression connected, backfire below and the engine stalls

The depression is 16 inches, which seems like a lot to me with a cam that has a 285° intake

The engine accelerates slightly when I remove the vacuum gauge and therefore create an additional air intake.

You are kind of isolating this to the carburetor. From your latest post, the carburetor idle circuit is not operating at all.

Is this a new carb or used one being re-applied?

You might want to message Drew Pojedinec on Facebook.

afscarbs.com Web page.

airfuelspart on facebook.

He is one of the most knowledgeable and helpful people that I know of on Holley carburetors. He has mentioned previously that he has brand new Holley carburetors that have had internal problems and incomplete machining and assembly procedures too common to be called rare.

For the moment, try another carburetor.

It is a brand new carburetor.

I have another one that was running when I ran the engine outside the car, a Holley 4160 600 CFM with vacuum primaries, if the same backfires occur I will blow the membrane and gas supply is different as well as the accelerator cable. I'll see if I can adapt it easily.

Recently I had a defective new ngk spark plug, without really believing it, maybe changing the 8 spark plugs. Yes, for me too the depression value of 16 in seems high to me but you measured it at 1500 rpm and not at 800-1000 rpm for your information, with a bullet cam with 226°int and 234°exh @ .050 and a 58° crossover I only have 11-12 of vacuum at 900 rpm. If the engine accelerates with an additional air intake, it is too rich.

@rene4406 posted:

It is a brand new carburetor.

I have another one that was running when I ran the engine outside the car, a Holley 4160 600 CFM with vacuum primaries, if the same backfires occur I will blow the membrane and gas supply is different as well as the accelerator cable. I'll see if I can adapt it easily.

Just get it on the engine. Worry about the details later. If it runs with no problems and will idle then the only component defective has to be the new carburetor. If it is new, it has a warranty on it.

Hopefully you can return it locally and not from someone like Summit and need to deal with shipping and Customs again.

In a way, I hope that it is the carb, so that you stop pulling everything else apart.

Again, a generic 3310 is probably what you want. Originally it was a Chevy Z28 carb but is used in many generic forms now.

Rocky's 4609 is actually a version of the 3310. The original application for it was a '69 Ford 428. It was intended to have good street manners and reasonable fuel economy (for a 7L).  Rocky it is worth a few dollars stock to the Mustang group. I wouldn't go drilling on it any more if I were you.

I've run that set up before and frankly don't know why you drilled the throttle plates. That's a modification for a "radical cam" to get it to idle the engine on a street driven car?

The Pantera throttle adapter will work on many old and current Holley throttle levers. It is not rocket science to adapt them.

The 3310 is a 780cfm, vacuum secondary. Originally was a manual choke on the Chevy but is easily converted to an automatic one and it is the "old" type of idle screw adjustment. Not a newer type reverse idle screw adjustment.

There is also a Ford version of that carb on the 69-70 Boss 302 so neither one is too big for a 5.7L.

It is not a terrible idea to get everything running on an 1850. It is a little small and will lack upper mid range and high rpm power but it will be very responsive up to about 4500 rpm or so and is on the lean side so it is good for running in the engine and not worrying about the piston rings not sealing because of too much fuel.

I would actually expect George's cam to produce 16-17 inches of vacuum at idle. That was part of the intention of his design.

I get almost 14 with my Webers on an individual runner manifold and a .606" lift, 244 @.050 so 11-12 means there is a leak in the system somewhere OR the ignition system does not have enough initial advance.

The Boss 302 from the factory used 16 degrees initial advance so that is really a factory engineering admission that the Cleveland heads need some unique timing. That initial timing is really a separate factor from the camshaft timing. In my view any performance "Cleveland" head engine should use at least 14 degrees initial.

I hope some of this helps.

So trouble shooting 101 - you say the engine ran "outside" the car?  Did it run well?  If yes, then what did you change when it was then installed in the car?  These are really pretty simple devices.  Make sure everything is connected, all vacuum ports either plugged or connected and put the old carb that it ran with (assuming it ran well) back on and start it.  You do not need an accelerator cable - screw all of that.  Just hand prime and try to start it.  If you have changed a bunch of stuff since the time the motor was last run, then you have to go backward to see what may have affected this.  OBTW, the picture at the top of this tread certainly is not a new cab with all the black carbon buildup on it.  A base properly tuned 351C at idle should pull approximately 17.00 inches of mercury (vacuum).  The vacuum gauge needle should be rock solid - no fluctuations.   Depending upon what you read (once you get the thing even running) will tell you much more as to what else might not be right (timing, vacuum leaks, plugs, etc.).  A motor that is backfiring that much and flames out the exhaust sounds like either a massive fuel leak from the top end or a stuck value that is causing major running issues.

Perhaps you can walk us through the progression of the motor and how it ran outside the car and then the installation and what changed.  

Here to help if we can.

Pat -

Agree with you, and the suggestions to just pop the old carb on and run it. Rene can fill the bowls through the air vent with a squirt bottle.

Thats my carb in the picture, not Rene’s.

Rocky

The only element that has changed since he was outside the car for a few minutes is the carburettor and that's why I was interested in him from the start. There is also that it now has to drive the gearbox in neutral but without the wheels and there is the full exhaust.
The engine started easily and ran not too badly, in any case much better than now but only a few tens of seconds because there was no cooling, only the full water and the closed circuit swirl tank overflowed quickly. I still managed to set the initial advance to 10°.

There was no backfire.

Since then it has remained a year and a half without turning, the valves are made of stainless steel but could the cast iron seats rust and no longer be watertight?

The new carburettor is all black and full of soot from backfires.

I have to unscrew the 4 idle mixture screws by about 1.5/2 turns and screw the idle speed screw all the way in for it to start, once started I can unscrew the idle speed screw and it runs better when I close the idle mixture screws almost full wealth. If before trying to start I open the primaries just once to get a slight squirt from the accelerator pump, I'm sure to have a backfire on the first turn of the starter.

I also thought about changing the spark plugs and I'm going to check the clearance between the rocker arms and the valves before temporarily fitting the old carb.

The valves and seats will be fine after sitting. I doubt that there is any problem there.

This likely is all just a bad carburetor. Get the engine running and hooked up on the 4150/4160.  Then work on the new carb.

You do realize that you must set the fuel level on the new carb? The factory procedure puts the level too high and will flow out of the sight plugs as delivered new. That is better with gasolene not containing Ethanol. Here we generally have 10% Ethanol in the gas and it tends to expand the fuel level. At that factory set level, the carburetor will flood the engine.

You want the level just under the sight plug hole. I use an electric fuel pump to provide the pressure with the engine off/ Also you do not want more then 5 psi pressure.

The Pantera should also use an angled spacer under the carb. I think it is 12°? In US built cars the engines were installed in that era on an angle. The intake maniolds were angle cut under the carb to make it sit level.

The drive train in the Pantera unlike the US cars is installed level, so you need to compensate with the angled spacer under the carb to make the carb sit level. I mention that here because that does effect the fuel level adjustment in the fuel bowls.

Thank you Doug and Patt for the information of vacuum value 16-17 in, on my side I will recheck the advance and a possible air intake because on my new Holley 4150 (0-4779), I had problems when opening the secondary, I had backfires in the carburettor, the needle under the secondary nozzle was glued (storage too long?) and the gasoline did not come out or little from the nozzle, I may be damaged the pcv valve or other, I will recheck all that.

Thank you for all these leads.

I have a BlueThunder "Pantera" manifold and so the carburetor is horizontal. There is a half inch spacer.

I set the fuel pressure to 6 PSI and checked to make sure the fuel wasn't overflowing through the level hole. As I write this I realize that I only checked one side, I'm going to check the other.

I find it hard to imagine that the carburetor is the only one responsible for the countless backfires.
I modified the advance 10 times in both directions and it doesn't change much.
I will measure the compression, if a valve is no longer tight I will detect it easily.

If everything is good, all I will have to do is try with the old carburetor.

I purchased this carburetor along with several other parts from an Australian supplier. For certain parts he clearly told me that they were Chinese equipment, not for the carburetor which he assured me was indeed a Holley. Have you heard of Chinese copies?

@rene4406 posted:

Thank you for all these leads.

I have a BlueThunder "Pantera" manifold and so the carburetor is horizontal. There is a half inch spacer.

I set the fuel pressure to 6 PSI and checked to make sure the fuel wasn't overflowing through the level hole. As I write this I realize that I only checked one side, I'm going to check the other.

I find it hard to imagine that the carburetor is the only one responsible for the countless backfires.
I modified the advance 10 times in both directions and it doesn't change much.
I will measure the compression, if a valve is no longer tight I will detect it easily.

If everything is good, all I will have to do is try with the old carburetor.

I purchased this carburetor along with several other parts from an Australian supplier. For certain parts he clearly told me that they were Chinese equipment, not for the carburetor which he assured me was indeed a Holley. Have you heard of Chinese copies?

I have not heard of Chinese Holley copies. I have been told that there have been issues with Holley reproductions of specific "historical carburetors". I HAVE had issues with new needle and seat assemblies. Exactly where they are made is not indicated even in Holley bubble wrapped packages.

I believe the issues are with the emulsion tubes either missing, incomplete or not correctly installed. Those are under the brass plugs in the main body and not normally customer accessible.  YOU should leave them alone. That is a rare occurrence but it has happened enough to notice it.

It was also said that there have been issues with the idle transfer slots on one or two that would effect the idle of the carb. My Holley specialist recommendation was not to send the carb to him for investigation but to return it to Holley under the warranty.

I personally have had the biggest issues with the Viton inlet needle and seats. Sometimes the brass floats colapsing.

The needle and seat seems to have an issue with the Ethanol in the fuel and tend to stick CLOSED after sitting for too long a period of time. What is that amount of time? It is not specific but could happen as soon as two weeks as the fuel in the bowls evaporates.

I have had issues with the old brass type floats and change those to the newer Nitrofil black plastic floats in the carbs that I use.

What will happen with a Holley if the inlet valve sticks closed or you loose fuel flow to the carb, if it is over a certain throttle opening like in WIDE OPEN THROTTLE, the engine will backfire violently. It is powerful enough to blow a hole in a cast piston and possibly even on a forged piston, break what we refer to as the upper piston ring lands, i.e., the small amount of piston just above the top ring.

So most of these Holley issues are now seen by engines that sit dormant after having been run, carbs that have sat new for too long in the box generally in a warehouse where temps run well over 100°F and floats that have not been re-adjusted at first new installation time. Also, heed the caution not to use more then 5 psi at anytime.

Rene: in the US we often see those temperatures in warehouses in the southwest US in the summer. Texas, Arizona, Nevada and even southern California desert areas. Those areas have many storage facilities because of the low tax rates. I can personally verify that temperatures within those warehouses often go to 135°F. Some of the components of items stored there under those conditions are vulnerable to heat exposure.

I've had items come out of there that have "peel off stickers or decals" installed by the factory that now are baked on because of the excessive heat. Australia has become an area where excessive heat occurs regularly as well. So just mentioning these factors in order to give a greater understanding of the variables and to point out that consumers can not assume that because an item is 100% new, it is 100% perfect. This is all part of the new world that we all live in and we all need to be educated and informed consumers now.

Probably the "best solution" with a Holley is to have a spare that is known by you to be good when you used it. That you will need to compare the carb in question to while the engine is running.

If it is dry, i.e., no fuel in it, turn it upside down and listen for the floats, both of them to drop. You WILL hear them and that is enough to ensure that the inlet valves are working. They will not need to be re-adjusted. You can leave the floats alone.

Someone mentioned Weber carbs. Usually on a V8 engine that is referring to a 48 IDA. I have quite a bit of experience with them and actually find them to be much easier and very dependable to deal with verses the Holley carbs.

The issue with them is that people attempt to apply their Holley knowledge to them and they are just a different train of engineering thought and the two trains of thought often do not match.

It's not working yet but I'm making progress.

I measured the compression, everything is OK, between 12 and 12.5 bars on all cylinders. So no problem with valve clearance or sealing.

I installed my old carburetor, it runs a little better, I was able to lower the idle speed to 1100 rpm BUT there are still backfires.

I carefully observed the advance point with a brand new strobe lamp that I just bought, mine was 35 years old and starting to get tired, and I noticed instability and especially flashes corresponding to the spark other cylinders. The explanation for the backfire surely comes from there and moreover the wiring of the ignition box (Pertronix 510) is part of what has changed since the tests outside the car since it is now the definitive wiring.

So I have to look at the ignition side and to begin with could you confirm that my igniter (Chinese replica) is indeed a Magnetic Trigger type

Yes, magnetic sensor, you must have a resistance generally between 300 and 1000 Ohm between the 2 wires of the blue sensor. if I may, I would not have put a Chinese distributor on an engine prepared like yours.

I don't know which stroboscopic lamp you just bought but you have to take quality lamps otherwise you risk having difficulty measuring or instability.

I don't remember reading it but are you sure that the ring on the balancer hasn't rotated? Mis-timed engine could explain much.

The 4v 351-c balancer is notorious for it.

You could try advancing the distributor until the engine smooths out. You could be running now up to something like 45° retarded. Having the outer ring rotated out of sync won't imbalance the engine significantly. The counter balance is on the inner hub. The balancer could have rotated since the time you ran the engine on the stand and the time you started it in the car.

Those things are just "glued on" and with age the glue dries up and fails. If the glue has dried up just the inertia of the engine starting up can shift the ring. Then you would be timing the engine to the wrong spot even though the markings would indicate they are correct.

It sounds like the motor is 180 degrees out.   Further, that is not a Pertronix ignitor.  Not sure what it is.....

That looks like a magnetic pickup for a Duraspark.

John

The damper is new but I still checked against another TDC mark that I made very precisely between the flywheel and the clutch bell when I assembled the engine, nothing has moved.

The ignitor was sold to me as a Chinese copy of a Duraspark by the same Australian who sold me the carburetor, according to him they are well built..... I will measure the resistance of the solenoid.

My strobe light is an Equus 590-51:

https://www.getgoods.com/at-en...a18dd52cb4cde350a915

It was very stable when I used it the first time, the phase shift displayed corresponded exactly to the graduations on the damper. Now it's unstable, so car ignition system or strobe light??? Tomorrow I will try it with another car where I am sure the ignition works correctly.

It seems that if I had shifted the ignition by 180° the engine would not work at all?

I don't know what is going on with it either. I am stumped also.

Did you verify that the roll pin holding the distributor drive gear is not damaged?

Agree that if 180 degrees out it will not run at all.

It's new and I put two inside each other, but it's a possibility.

I haven't replaced the spark plug wires, I may do so, what do you recommend? Rubber? Silicon? What diameter?