mrg

From the Holley website:


10 Micron filters are recommended for use as a post filter in EFI systems

40 Micron filters are recommended for use as a post filter in carbureted systems

100 Micron filters are recommended for use as a pre filter in carbureted and EFI systems

As a point of information:
While it wouldn't seem so, is using a 10 micron rated fuel filter not a good idea on carbureted engines?

Plasticman

I have been using only a 100 micron (screen type) filter on my dual AFBs for several years (per the recommendation of a fuel plumbing supplier).

Filter did start to clog up when my gas tank fuel sock (plastic) went belly-up from the ethanol fuel we started using after Katrina. I cleaned out the filter, replaced the sock, then openup the carbs. Both carbs were just fine!

What was left of the sock.


This came out of the 100 micron screen filter.


Plasticman

Mike Ward

What problem are you trying to avoid or fix?

Westlotorn

The reason Fuel injection needs the 10 micron filter is to avoid plugging the injectors which need very clean fuel. A jet in a carb can pass much larger particles with no issue so the specs are more relaxed. More aggressive filtering can produce drag in your fuel delivery which is not an issue with a Electric pusher pump feeding fuel under high pressure but may be a big issue with a mechanical puller pump that is pulling fuel from your tank before it pressurizes it to the 6-7 lbs needed.

mrg

Mike ..
What Wes says in the above is exactly what I was concerned about.

The pump to carb fuel line in my car utilizes the all metal Fram 3727 filter. Napa, Wix, Purolator, and AC also carry this same filter in their lineup. All, including the Fram are 10 micron rated filters.

Now I'm wondering if using a 10 micron rated filter might be too 'tight', with respect to fuel flow resistance through the filtering media and using a puller fuel pump. With the exception of a recent bog/shutdown problem the engine runs fine, otherwise. A recent fuel pump pressure test with engine running showed 5.25 PSI, the minimum spec. .. . The fuel volume/time test as shown in the CSM wasn't done. I need to do that.

The top of the AFB was taken off to have a look inside. Interestingly, there were some rust particles resting on the bottom in both the primary and secondary fuel bowls. The carb has been rebuilt recently and was clean as a whistle inside, afterwards . It hasn't seen many road miles since being rebuilt. Seems a 10 micron rated filter should have trapped those rust particles.

John ..
Interesting that the 100 micron filter media you used worked just fine in keeping the AFB's clean.

Well, now what?. .. Might have to redo a new fuel line using a 40 rated filter.

Thanks, guys.

Westlotorn

John ..
Interesting that the 100 micron filter media you used worked just fine in keeping the AFB's clean.

Maybe John has a cleaner tank, buys fuel from a station with a cleaner supply. Gas pumps today do have filters on them but that does not mean they are serviced properly.

I have not seen any print information showing the reduction caused by the 10 micron filter maybe there is info out there that shows a old mechanical pump can pull through a 10 micron filter. It is worth a look. I have been through the Carter fuel training school a 5 day course but that was almost 20 years back so my info is dated.

Plasticman

After I did the fuel sock replacement, cleaned out the filter, and checked the AFBs, I did a full throttle fuel pressure test at about 110 mph in 3rd gear (my 3rd gear is 1:1). Fuel pressure was still at 5 psi (which I thought to be great). This is with an aftermarket Carter Street Super mechanical fuel pump that at idle holds 6 psi. Too bad Carter does not offer that pump (for Chevy) any more.

John