Jump to content

Airtex 8012s electric fuel pump on a 1972 240z with 3 screws su carbs


Recommended Posts

My mechanic left the airtex 8012s electric fuel pump on the on position without cranking the engine and now the fuel pressure at the carbs has lowered from 4.3 psi to 3.2. Question? Could the filter that is besides the pump be clogged and thus causing the decrease in psi or could the pump be partially damage due to his negligence on not craking the engine immediately.

Link to comment
  • Replies 8
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

It depends. If he left it on for a long time, say, all night. I could see that being a problem, but turning on the fuel pump before cranking the starter wouldn't hurt the pump.

 

Do you have an adjustable psi regulator? Does the pump still pump fluid? Why not just crank up the PSI and see what happens?

Link to comment

The SU's don't need a lot of pressure. Just over 3 is plenty. If worried about the filter, just change it. But don't expect a change.

 

The pump is self regulating and pumps only when needed as the pressure lowers from gas drawn into the carbs during use. 

 

If you have a fuel return line it would have chugged along all night... the same as if you drove all night on holiday. The return line has a restriction so that pressure will build on the carb side or else all the gas from the pump would just return to the tank. The restriction has a small pin hole in it so that cooler gas from the tank is constantly recirculated past the carb and warmed gas from under the hood is returned to the tank.

 

Here's the restriction and pin hole in the L20B return line...

 

11aMYIJ.jpg

  • Like 1
Link to comment

Well when the pump was new the pressure was 4.3 and i had no hesitation or backfire between 3000 to 4500 rpms going from 2nd to 3rd gear.

I can't help but think that the extra psi is masking a tuning issue....

Now that it's running good how do the plugs look?

 

I think Mike touched on the su carbs wanting 3psi... and a quick search say 1.5 to 3 psi....

With that said I run a single weber side draft... initially the recommended carter pump was outputting around 6 psi. That was causing a rich condition, it would foul my plugs and make it hard to start the next day...Once I added a regulator and lowered the psi to 3.5 my weber was much happier. And No more plug fouling...

Link to comment

Hard to believe 3.1 is an issue. Generally people have the opposite issue with pump pressure too high. If pump pressure is the issue, all I can speculate is that your fuel return is not circulating as much fuel, thus delivered gas temperatures will be higher. Perhaps when really pushing your engine this could cause an issue. Pretty speculative though

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.