Are these bronze inlet filters a restriction of fuel flow on a mild performance small block? Is a paper filter better?
Depends on how fast the engine revs up, look into boat Q-jets, they used a screen instead of paper or bronze. Its easy enough to test it, make a run with and with out.
You can use the paper one and pull the little rubber valve out which will remove all the restriction or leave the filter out all together and put a filter down at the pump then you won't have to take it loose at the carb any more risking stripped threads. The rubber valve in the paper filters is there to help stop drain back, I have never noticed any issues removing it.
Black gasket end goes against inlet fitting. These also have a check valve that prevents fuel back tracking from carb.
Early 70’s we pulled those out an put a inline fuel filter on it. Regular changes at the carb inlet the threads started to give away.
Much like an oil filter, the qjet filters either bronze or paper have a built in bypass, if they become a restriction the fuel pump pushes the filter against the spring and fuel now goes around. I don't believe one is more restrictive than the other.
Been involved with many qjets since 1967 , NEVER had a fuel delivery problem with either the bronze OE paper inlet filters ,long or short . This reminds of carbureted smkv era engines , the folks that didn't want to learn what the factory intended used to remove/ disable any smog stuf , usually the engine ran worse & got worse gas mileage plus they made the car pollute more than one produced without the controls , lose/lose ..
New they dont have a restriction, but I've seen people neglect them long enough they would get clogged and cause problems trying to run WOT. I always threw them away and either ran paper or nothing but an inline filter. Highway use is not really much of a problem, we were mostly using them on dirt tracks, on very old systems. Good Luck
We always referred to those brass looking filters as "sintered brass". I've never had an issue with either the brass or the paper elements (with or without the little flowback valve). I've seen guys pull that flowback valve out as a matter of course. I've done it myself at times. Now-a-says I tend to leave them in. I doubt it would cause much of a restriction. I have see old quadrajets where people had stripped the threads out while trying to change a filter. I never understood that. I guess some folks are a little ham handed. As Joe H stated, make a few runs with and without the filter and see if you see a difference. If you have other filters in the line somewhere then you could definitely do without it.
A few thoughts on this issue: (1) The sintered brass filter will have no more restriction than the paper ones. Rochester went to paper because they were cheaper. (2) As mentioned in this thread, the Q-Jet is designed with a bypass (spring) on the filter. If either the sintered brass or the paper one were to stop up, the spring would compress, and unfiltered fuel would flow into the carburetor. No restriction. (3) I would HIGHLY suggest just removing the internal filter and replacing it with an inline UNLESS the vehicle is a numbers-matching show vehicle. 40 years ago, we could still get Rochester replacement bowls. For testing, I took a new old stock bowl, and fixed it in a vice. I then pulled a new old stock fuel inlet nut off the shelf. Now, armed with a torque wrench, I proceded to "change the filter" several times. The 12th time, the inlet threads were so bad, the fitting would NOT hold the specified torque! (4) If a fuel restriction exists, it is the fuel valve and/or the early placement of the float pin. Many Q-Jets came with the 0.125 inch orifice fuel valve. Some came with the 0.135 orifice. For racing, one can now order a 0.149 valve. Apologies to the moderators for some specific newer information, but some may elect to use these on their hot rods, and this is important. When still restoring carbs, I used to discuss this issue with customers, as the 0.135, under certain conditions on a STOCK vehicle can leak when used for street use. I always recommended the 0.125 valve. One really good customer had access to a dyno, and checked a 1968 Pontiac RA-II with both the 0.125 valve, and the 0.135 valve - NO DIFFERENCE! I did 7 restorations for him, all using the 0.125 valve. Don't even think about the 0.149 valve except for a trailered race car. (5) After the float pin placement change (overlap on models in 1969 and 1970), Rochester used a "windowed" valve seat to improve fuel flow. Do not use the windowed seat on the early pin placement, as the flow of fuel from the window will cause the float to NOT perform properly. (6) These are excellent carburetors to run on newer engines (or any engine for which an intake exists) in hot rods. Just learn the nuances of the Q-Jet. Cliff Ruggles (Mr. Q-Jet) had a professionally modified 800 Q-Jet tested against a professionally modified 880 Holley in back to back dyno runs on a built 455 Pontiac; the Q-Jet won, by roughly 3 percent, over the Holley! (7) If you choose to ignore my suggestion on the inline filter........................... Jon
IIRC, Cadillac used a paper filter that was double the length of the one pictured above. It used a fuel inlet nut that was twice as deep.
Not just Cadillac, others as well. We sell about 4 kits with the long filter to 1 kit with the short filter. Jon
I do the same thing, but learned that inlet repair kits exist. I had one that the previous owner buggered up.
Jon, your encyclopedic knowledge of all things carburetor related is amazing. We are fortunate to have you on the HAMB.
For safety sake, if you do remove factory filter and install an inline, make sure to bubble the ends of the hard line so any clamp you use has no chance of coming off. Do not wish an inferno on anyone.
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