Wide Open Throttle. Actually a log manifold is pretty crude in the world of intakes. They are like a tunnel ram or a 360 degree intake and are only really good at WOT, compound tat by the fact they your runners are only about *3" max and you get an intake that is designed to operate best in an RPM range that is greater than your old nailhead will turn. OK negativity aside, your fuel pressure sounds OK but gauges are only manufactured by the 100 thousands. Before rejetting do two things, first try dropping your fuel pressure down a bit like in the 2 PSI range instead of the max 2.5 PSI. Next make sure that your float level is good carbs are like fuel pressure gauges and manufactured in big numbers. Your description does sound like improper jetting by your description but those are just things I would do before throwing money at it. I would drop 2 jet sizes. One jet size is its running fine but its a little sluggish. Now let us address the freezing problem. I am not trying to be mean here just throwing out some facts. The freezing temperature of modern gasohol is -70 degrees Fahrenheit. Unless you got water in your gas (which is not a problem with gasohol the alcohol dries the fuel in the tank) your fuel is not likely to be freezing. This is a very old myth, when a carb freezes it is not the fuel that is freezing it is moisture in the fuel that is freezing. I have run log manifolds and regular intakes with the heat risers blocked summer and winter for over 40 years and never had that problem anytime other then when I have water in my fuel and only in the dead of winter when the temps are dropping into the single digits. A can of HEAT and you're golden if that is the problem.
Thank I will try those things , and I am running ethanol free gasoline Sent from my iPhone using The H.A.M.B. mobile app
Gasoline without alcohol freezes @-40 to -58 Fahrenheit depending on the additives. I have only been playing cars and motorcycles for about 50 years so I may have missed something but even gas with water in the tank should not freeze in the summer.
I had a slightly OT car and the manifold froze. I was in SoCal, in Oceanside ant it started running roughly. We got out and looked, then looked in amazement. The top of the manifold was frozen. I guess the temp, moisture and concentrated airflow was perfect combo. It took an hour to thaw.
Carburetor icing is weird stuff. It's not good, particularly in aviation. It is most common in temperatures above freezing, maybe into the 40s. Has to do with humidity, altitude and temperature or somesuch. The venturi effect lowers the temp below freezing somehow. I saw it happen once right before my eyes. A bunch of condensation on the carb body turned to frost in just a second or two.
The conversion of fuel from the state of liquid to the state of a vapor is an endothermic process; that is, it requires heat. This heat will be extracted from whatever surrounds the fuel (air, the carburetor throttle body, the intake manifold, etc.). If the temperature of the metal drops below a certain point, which is dependent on both the temperature and the humidity, first moisture (extracted from the surrounding air) will appear on the metal, which if the temperature continues to drop, will then turn to frost (check the low pressure line on your car's air conditioning system when running). Unfortunately, this condition can actually make itself worse if it is the throttle body which ices. Why, because the restricted area (from the frost) increases the throttle air velocity, which pulls ADDITIONAL fuel from the fuel wells that must be vaporized requiring more heat. With stock engines, not GENERALLY a problem with V-8's because the carb sits on top of the engine. High humidity and ambients of about 25~50 degrees F, can occasionally cause icing on stock V-8's. Have seen it a number of times in Missouri where the humidity seems to exceed the ambient (well, it feels like it). However, inline engines can experience icing, if heat is not added, as the carb often sits away from the engine. As I mentioned earlier, for the OP I would try a much hotter thermostat. It might solve his problem. Of course, I am assuming that the carbs have been synchronized and that idle has been set using an exhaust gas sniffer. The fact it runs "better" on that style manifold by disconnecting the two rear carbs sounds "interesting". Jon.
I don’t have an exhaust gas sniffer , I’ve got all 4 carbs hooked back up and air fuel mixture at 1/2 a turn... running pretty good , but plugs still a little black , I’ll try the hotter thermostat, if you think that will help. Sent from my iPhone using The H.A.M.B. mobile app
MORE timing(advance) will cure a LOT of "carb issues"! Jus say'in.......... Crank-in-the-timing until it "rattles" going up a hill in top gear. Back it off a couple degrees and check it again. More initial allows a lower curb idle on the carbs. Cleans up the idle too if you run a "snotty" idling cam. Might help....can't hurt to try. 6sally6
Thank you, running a 401 cam in my 364, to get a bit more performance, I’ll try cranking it up abut more !! It’s all about leaning the plugs out a bit
I think that there's still a bit of confusion about these "air fuel mixture" adjustments of 1/2 or 3/4 turns you are making. These are the IDLE MIXTURE adjustment screws and should affect idle quality only. The idle mixture adjustments will have no real effect on the operation of the main circuit or power circuit fuel mixtures. CarbKing explains it pretty clearly on the previous page of this thread. But also keep in mind that idle mixture adjustments require that the throttle plates be very nearly closed. If they're open too far at idle they will allow fuel to be pulled thru the main circuits and idle adjustments will be largely ineffective. And it also assumes that you don't have some other conditions (float adjustment or damage, leaking needle and seat, excessive fuel pressure, etc.) causing the carb to flood and run rich.
What he said. I have no experience with Strombergs or Nailheads, but I do know that on my 3x2 302 Ford, the little bit of fuel pressure made a big difference, as well as lowering the floats just a hair. It does sound like a jet thing though, to me.
I cant tell from the pic but is that fuel regulator a dial type like this? They come in a lot of different brand names but they are all the same design and the same manufacturer slightly west of Hawaii. If so , take it off and install this one. Regulates accurately to the 2.3 pounds or whatever your strombergs want to drink.
Yes it is a dial type, I’ll change it out ... thank you Sent from my iPhone using The H.A.M.B. mobile app
That is my best advice, at least you will know what you have and solve from there if there is still an issue. That Holley 12-804 is an excellent little regulator. I was having a very similar issue on my car with 3 97's. similar symptoms, Too much pressure was the cause, the Holley was the cure.
Now at least you are in the ball park. Water will freeze @ 32 degrees which you can achieve with thhe proper airflow. You can get hail when the temps are in the '80s, which is tornado weather. But the ice forms well above any altitude that any of our cars will be flying.
It's particularly dangerous in aviation, but it can happen in any carbureted engine, on the ground too. Air cooled engines and murdersickles too. The heat risers and all that coolant through the intake on cars &c., are designed to prevent this. Carburetor icing even occurs when the outside air temps are in the 60° - 70° F range. The ice forms on the surfaces of the carburetor throat eventually restricting airflow, blocking off air to the engine.
I have only been doing this for about 50 years so I may not have seen as much as any other man on the planet. But I have only had one car ice the carb in that time. A stock '64 283 2 bbl in 15 degree weather and water in the fuel, a can of heat cured it. I started blocking my heat risers in about '69, they used to say that you needed to unblock them in the winter but the only problem I have ever experienced was longer warm up times. We used to do it with tin foil balls stuffed down the riser passages in the head. Now you can make that decision with your gaskets most times. Its like I said none of us are ever going to reach hail altitude in our cars. Perhaps my experience is mind over matter, I just don't hold with myths like frozen carbs or heaven forbid vapor lock. Just never had that problem. I have been above 13,000 feet a time or two, but the air was dry and thin. Wished I owned a super charger every time I got up to that altitude. Guess that is a different problem not worthy of this thread. LOL
Somehow? The Venturi lowers the pressure by increasing the speed of the air compared to the surrounding air, therefore decompression. Just opposite of compression, that heats... decompression cools. Thats how air conditioners work and carburetors ice. Bones
That stands to reason. Vapor lock is a myth? Keep in mind simply because you personally haven't experienced some thing, that doesn't mean that it doesn't exist. I'm confident both carburetor icing and vapor lock are well established.
Can personally attest to both, vapor lock on a 53 Flathead about 1958 and icing on a 10 hp Briggs and Stratton powered generator in 2000. Of course the vapor lock on the Flathead was due to the fuel pump location, not the carburetor. That’s why on later V8s you almost always see the fuel pump on the lower front of the engine. It’s cooler there. Bones
I was running one of those spider intakes on my airvair, with a Holley on it it would turn into a big chunk of ice. Changed it to a AFB and no more icing. This was in the heat of summer, and it gets hot here.
One huge problem with running an engine with a too rich mixture is gasoline washing the oil from the cylinder walls (metal to metal) and washing carbon into the crankcase which finds it's way to rod and crank bearings making them tend to want to spin. If float levels are not ideal then jetting is going to be messed up. Some carbs need float levels different from manufacture specs. You might lower your floats by a millimeter or two and see if your plugs return to light tan condition.
Once I installed a gas carb on a Farm tractor that was a LP . It had a unheated intake manifold. and would ice in a minute of running. Impossible to keep it from icing couldn't use it. Changed to a heated manifold and no problems. My Hercules flathead 6 powered linclon welder was icing up and I ran a copper line from the exhaust and wrapped it around the intake above the carb mount and cured it. The OP's intake might benefit from a balance tube with heat from the water jacket or exhaust routed thru it?
Ok I went and took pictures. On the welder I ran a copper tube from the exhaust manifold and wrapped it around the intake neck just above the carb leaving the end open. the Third picture is of a LP carb & manifold.That setup the regulator has engine coolant running thru it. the fourth picture is of a H power unit that has the factory LP intake. I took the carb off a excellent running factory Gas H power unit he same size and put on the LP intake. Instant carb icing & black exhaust smoke you had to close the choke two thirds to keep it running. The fifth picture is the H carb on the factory gas intake and it runs perfect . I cant see any logical reason to not run a heated intake on a street driven engine. I had to notch one of the mounting ears on the gas carb to fit it on the LP intake.
This is all interesting, but has nothing to do with the problems I was having Sent from my iPhone using The H.A.M.B. mobile app
The small air cleaners I was running restricted the air flow to the carbs which was flooding them out , there running just a smudge rich still, but much better, Sent from my iPhone using The H.A.M.B. mobile app
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