Ten four on the vibrations. I had a cheap gauge mounted on the fuel rail beside the carb and the 2 screws backed out of the gauge that holds the face on. I have to buy a new gauge because I can’t find matching screws to fix it. They’re very small, approximately 2 mm. Next one I buy. I’ll use red thread locker on those 2 screws, if it has them.
IMO....I concur.....filling the gauge case with glycerin helps to dampen the pressure pulses, from a positive displacement fuel pump. There are other methods to dampen the pressure pulses. The most common type is an inline dampener that the gauge is screwed into and inturn screwed into the supply line. This dampener device has a small internal orifice, that reduces the reaction time but not the accuracy. The pulsation can also be controlled by using a diaphragm isolator to dampen the pulsation. There are other more expensive methods....electronically. But the simplest was described is just to remove the gauge after the pressure is set.
So do you sit the pressure under load or at idle. Guessing this would depend on the type pump and regulator being used.
It depends on the pressure suggested by the specific carburetor manufacturer. For example, my Edlebrock is suggested to run off 6.5 pds. If it’s too little or too much the carb doesn’t spray fuel efficiently. To answer your idle question. A regulator sets the same pressure at idle or throttle input. You can add a vacuum supply line to a regulator which will allow the pressure to increase as throttle is increased. Setting it at 3.5 at idle it will increase to fuel pressure suggested as throttle is increased. But, it’s not necessary. I just set my pressure at 6.5 at idle and that is suffice. It always remains at 6.5 when no vacuum is applied. Regardless of idle or throttle input.
It would most definitely help if you mounted it somewhere more stable. But, you have a another problem. You most likely have a return fuel line to your tank. This creates erratic pressure or erratic needle movement because of your return line you most likely have. If you temporarily disconnect the return line. The needle on the gauge should be steady. You’re losing consistent fuel pressure back to your tank. It builds pressure at the regulator, then that pressure is not constant because the pressure has too far to travel and your tank is vented. That would be the case if you have a return line. I had the same problem when I added a return line. I just increased pressure about 3-4 pds more than recommended to compensate. My engine runs great and my vapor lock is cured. But, the needle will always bounce a lot. Nothing you can do about that. Unless you remove return line or install return line after gauge. But, if it’s after gauge you’re still going to have pulsating pressure to the actual carburetor.
An aftermarket 4 barrel carburetor is designed to operate properly at a specified fuel pressure rating per the manufacturer’s suggestion based on the design of that specific 4 barrel carb. The fuel pressure has to meet that suggested pressure or the fuel doesn’t burn efficiently. Most 4 barrel carburetors have a manufacturer suggested fuel pressure ranging between 5.5 to 8.5 pds. If it’s too high the fuel blows past the venturies and doesn’t burn as efficiently as it should. If the pressure is too low. The engine starves fuel. This doesn’t apply to original 2 barrel, single barrel or original 4 barrel carbs because those carburetors were designed to run on the output of that specific factory fuel pump and it’s designed fuel output. This is why you need a gauge and regulator. If you have an aftermarket 4 barrel. A gauge can also be used to monitor the condition of a mechanical / electric pump and fuel filter. Once the pressure is set.
Thank you, bud. That’s what it’s all about. Helping each other
That too!
On an original carb and original pump, yes. But, the design of an aftermarket carburetor has different flow characteristics compared to the original carb and original pump combined. The venturies change from carb to carb. If the aftermarket carb has better flowing venturies. The fuel pressure has to meet that new designed flow and design of different venturies.
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