weird fuel pressure fluctuation

[chris71]

input needed guys,

the problem, my new 1406 edlebrock carb loads up and stumbles from off-idle acceleration, i have adjusted the accelerator pump to the lowest setting, and problem still exists, checked the fuel pressure at idle, she flucuates from 3 to 10 psi, and hangs around 6-7 psi as middle of the fluctuation, the fluctuation is very fast. spin the motor up to 1000 to 1500 rpm and she is in the 5-8 to 6-7 range. the fuel pump is 2 yrs old, stock replacement from napa for the 1982 305. sounds like the fuel pump is bad? would a pressure regulator fix this since 10 psi is way to high? my buddy was saying the the lobe on the cam may be screwed up, would this be a possible cause for my problem?

Thanks in advance.

[68gmsee]

Why do you suspect the fuel pump? If it's a mechanical one it goes up and down with engine rpms.

If you haven't already, I'd check carb, distributor mechanical vacuum advance, or maybe vacuum leaks first.

The Edelbrock site has some tips you may want to try..

http://edelbrock.com/automotive_new/...ech_vids.shtml

[dznucks]

you are probably using a Mr gasket fuel pressure gage. mine did the same thing. the fluctuation you are seeing is the actual pulsing of the pump as it makes each pump stroke.

You need a regulator with an edelbrock carb. i have a holley regulator and i bought a glycerin filled gage from grainger. the glycerin filled gage stops the fluctuation of the needle. however when you use the regulator that stops the pulsing from the pump.

i attached a pic of my setup. i mounted the regulator on the fender.
Your engine problems might not be related to that fluctuation. however the high fuel pressure might be causing some of it. edelbrock says to go with 5.5psi, i dropped mine to 4.5 psi. your stock pump with no regulator will put out too much.

Make sure your floats are adjusted correctly, mine were both off out of the box.

What size engine are you running?

[chris71]

dznucks, yes i was thinking that the added fuel pressure at idle was giving me issues, making the carb load-up, the engine is a stock 1982 305. is the 600cfm of the 1406 way too much for my 305? i got the 600cfm thinking i was going to get a 350ci engine, but this old 305 is still running strong.

68gmsee, i was under the impression that the pump was to give a constant and steady pressure to the carb, so i just though that the pump was the culprit

[rwolf9653]

I had the same problem on a 350 sb with an edelbrock 600cfm, performer intake. I spent $30 on an adjustable fuel pressure regulator from Summit and it cleared up all of my problems once I set it to 5 psi.

[fdbdw]

If you are planning on sticking with that carb for a while, I would suggest putting in an edel fuel pump, they are made to support edel carbs and dont go over 6psi, it does cost a little more but very easy to install. I wasnt real happy about with the idea of mounting a regulator and running more fuel lines, ( in my mind its just another thing to go wrong at some point), so I installed an edel pump for my 1406 and its worked out great, looks good and you get a new pump out of the deal, just my opinion

[D.PASSMORE]

FYI, with my EDL, I had a similar problem with loading up and dumpimg fuel. I finally took the carb apart a discovered that my floats were way out of adjustment. Set back to SPEC and cured the problem.

[fdbdw]

I had the same issue right out of the box, Ive also heard that sometimes the welds can crack on the floats , so when your checking the float level its a good time to check the welds and put them is some water to make sure they arent taking in fluid

[ChevLoRay]

1405 (manual choke) is jetted for performance with .100 main jets. I think the others in that style are not so fat. In my case, I gave up and put an Edelbrock 1901 on it (Q-Jet) and never looked back. I like these AFB-style 1400-series carbs, though. They look good, especially if you have the ones with their Durashine finish.

[68gmsee]

I've never used Edelbrock carbs, but I sure find it hard to believe that they would make a carb that requires a regulator with a stock mechanical fuel pump. Seems to me that would be a design issue.

That being said, I agree with the comments about adjusting the floats properly. If they're adjusted properly and the needle valve is doing it's job and the fuel pump is the correct one and working properly, I don't see where that would make a carb surge unless something else was wrong.

But I could be wrong... I'll stick to quadrajets.

[mclairmo]

Buy a Holley carb. I have the 3310 and also have a Holley mechanical hi volume fuel pump and Summit pressure gauge and it reads 7-8 psi steady at idle (at 1,000 rpm) with very little fluctuation and the Holley carb can take the 8 psi with no problem. I have heard many times now that the Edelbrocks cant take 7-8 psi and need less, which seems like a design flaw to me, too, when most mechanical pumps are in the 7-8 psi range.

[chris71]

well, i got a summit edlebrock pump, part # SUM-EDL21, nice pump, nice price, even came in the edlebrock box, installed it, took the top of the carb off, re adjusted the floats, they were slighty off but not too bad. cleaned out the carb because there was some trash in there, steped down to the next leanest primary jet and metereing rod and put her back together. checked fuel pressure and she is steady at 6psi, no fluctuation, the motor runs good now, more power, less stumble off the line on moderate to heavy acceleration, although I may have to fine tune a little more, have a slight part throttle hesitation from time to time. I also took the pump push rod out and inspected it for signs of the cam lobe tearing up, everything checked out okay.

one thing worth noting here, I had to re-clock the fuel pump so the 'in' fitting wouldnt hit the frame mount tower, when i took the pump apart i noticed some dirt and metal shavings in there when they manufactured it, i cleaned her out real good, so FYI if you buy an edlebrock pump, it would be a good idea to tear apart and clean, some of the metal shavings were pretty big, big enough to clog the jets in the carb or possibly cause damage to the pump.

[chris71]

thanks for everyones help by the way

[fdbdw]

stumble could be due to the step up springs, the spring strength should be half your vacum reading at idle