jpc647

So I've been trying to chase down carburetor problems so I decided to check the fuel pressure today. It checks out at 5.2psi at idle/cranking, and it moves up the slightest amount, 5.3/5.4psi at WOT. This seems to be right, at least for what Edelbrock recommends.

A member on here (Tedd Thompson) recommended to another member to unlook the line and crank the engine over for 8-10 seconds. It should approx half fill up a soda bottle. So I did this a few times today and then measured how much gas was pumped out.

With Current Fuel Filter, 255ml, or a drop over 1 cup.

With a Brand New Fram G3 fuel filter 260ml.

With the Brand New Edelbrock Fuel Filter 255ml.

Without a Fuel Filter, 480Ml, or Approx half of the soda bottle(a little more).

Now I don't know how much the bowls in the Edelbrock Hold, but it seems like I'm running out of fuel at WOT. The car roars, then feels like I let off the gas, then comes back to like a second later.

Does anyone make a "high-Flow" fuel filter? What do you guys use? How long do you guys go in between replacing them. The one on there is only from the begining of this season, May 15 to be exact and probably only has 1500 miles on it. Even for a $4 filter, it should last longer than that, right?

Mine is between the fuel pump and the carburetor. When it was before the pump with a different carb, the car was running really lean and when I cut the filter open it was pulled apart and stretched as if it had been sucked dry.

Fun71

That sounds weird. Many people run a G3 style inline filter before the fuel pump and I haven't heard of anyone having that - or any - issue. Perhaps it was just a bad filter?

Tedd Thompson

Have you tried bypassing the filter altogether and see if the problem persists? Unless your engine is a fuel monster (and some are) and require more than 8 oz of fuel in 8 seconds that amount will usually run your average grocery getter with no problems. Race drag types not so much. Another random thought and I know nothing about Edelbrocks but do they have a carb filter at the carb like a q jet and could it be plug or causing restriction? ..Just a thought ..Tedd

jpc647

I know, hence my question. I had replaced that filter a couple of times and I still had the problem. One day at a car show an old hot rodder came up to me(He owns a 70 w30 he's had since 71) and we were talking. I told him about my hesitation, and he told me to swap my fuel filter to after the pump, and it was a night and day difference. Maybe this is pointing to another problem?

The fuel pump checks out okay otherwise, pressure is fine, flow without a filter is fine.


I haven't. Its monsooning here in Massachusetts, so I can't take the car out, but that's the plan. I'll run it for a couple of miles without a filter and see. The Edelbrock's do not have the inboard fitler like the Q-Jets. You're right, 8oz of fuel would be enough, but from my test, I'm getting about half that. At WOT, maybe that isn't enough.

Even so, it's amazing that a standard filter will reduce that much flow. How often should a standard G2/g3 filter be replaced. I know they're only a few bucks, but they shouldn't have to be replaced at every oil change.

oldcutlass

I change my filter once every year. Have you checked your rubber lines at the tank and before the fuel pump to see if they were sucking air?

Tedd Thompson

I have had one on my 324 for about 10 years and 30 thousand miles with no problem. Which reminds me I probably should switch it out next time I'm down there....Tedd

442craig

I am having the same problem with my '68 400 with a q-jet. Everything was rebuilt and blueprinted. The car cuts out at WOT just like yours. I have an inline filter, before the pump, as well as the stock filter in the carb inlet. Another consideration is the float level is off. I'm actually taking mine to the carb rebuilder on Tuesday. I'll report back with his findings! Good luck!

jpc647

Yup, all the lines look okay. The lines between the pump and the metal lines at the frame are only a year old too. Is there a better way to check them besides visual inspection?



A cheap g3 or similar filter has been in your car that long? Wow, no problems at all?


For the hell of it, before you send it out, try eliminating the filter. It'd be curious if it stops cutting out.

I'm just waiting for the rain to clear before I try. Cant go WOT in a downpour.

My float level is at 7/16", which is what Edelbrock says is the target. But please report back when you find a solution to your problem.

442craig

Yeah, been meaning to try that, I'll try it this weekend and let you know. I did have a crack in the hard line above the rear spring. Loads of fun to replace.

oldcutlass

With engine off, have someone push the gas pedal to the floor and look down into the carb see if your bottom butterflies are opening all the way.

Fun71

I would guess that a visual inspection won't detect a hairline crack, or even a huge crack on the top of the line below the floorboard or frame where you can't see. Mine had a hole in the metal line at the top of the bend coming out of the fuel tank, where the line rubbed against something metal (floorboard? it's been 25 years so I can't remember the exact details) so I slipped a 4" length of fuel hose over it and clamped it on both ends. I detected that leak by seeing fuel seeping along the line and not actually seeing the hole.

The most positive method of checking for leaks would be to disconnect the rubber lines at the tank end and at the fuel pump end, plug the end of one hose, pressurize the other end, and check for leakdown.

jpc647

Looking forward to your results. Could you visually see the crack in the line, was there a leak?


Just did this. They appear to be opening all the way. I used a thing metal rod to gently push them and it didn't move any further. I also made sure the pedal to the floor is wide open on the carb, meaning the linkage 'bottomed out' and it did.


Okay, thanks. When the rain stops, I'll crawl under the car use my small handheld pressure tester kit to add a coupe psi to the lines and check.

But a question. How does possibly having a crack explain how when I add the filter, flow rate drops?

442craig

I could smell gas and the paint was coming off of the frame where it was leaking. I kinda man handled it out of the car when I replaced it so didn't get a good forensic look at it.

Craig

hookem horns

Instead of a cut out, any chance this is a bog due to the secondaries opening too fast? I don't know Edelbrocks or if you are running a vacuum or mechanical carb, but slightly tighening the secondary spring on my quadrajet made a world of difference.

442craig

I took out the in line filter and the pressure gauge and ran it with just the hose. Still a major bog at WOT. I am taking it to the guy who rebuilt the carb on Tuesday I will let you know

Craig

Ozzie

It sounds like a fuel starvation problem. Try to verify the performance of each component in the fuel supply. Is the tank filter clear? Is the tank vent clear? I can't imagine that a LARGE fuel filter would cause such a problem unless it was congested. If somehow the filter was the problem, you could always use two in parallel. Also be sure that the air supply is sufficient.

stan 65 cutlass

fuel sock in the tank?

brown7373

What rpm is it cutting out? Could the ignition be cutting out?

442craig

Well, spent a day at C & J engineering in Southern Cal. They did a remarkable job rebuilding my Q-jet. One of the last great carburetor (and much more) guys! Anyways. My car runs awesome now. His shop is 60 miles from me so it was a good test run. (the longest drive yet on the new engine) Turns out my bogging problem was the fuel pump. I have a stock high flow pump and it dropped from 6psi to 2 psi when it warmed up and was at WOT. They bypassed the return line to give it more kick and that did the trick. She's galloping on all horses now!

Craig

jpc647

I'm sorry, a stock high flow pump??? That sounds like an oxymoron to me.

442craig

Stock meaning, fits like a stock pump and not and electric. Sorry for the confusion!

jpc647

Thanks for the clarification. I wasn't sure.

Glad you got it figured out.

droldsmorland

Mine did this as well for many(10-15) years. Built in rev limiter. Probably a good thing as I was a 20 year old kid when I got the car you see in my avatar and was used to driving Chevy small blocks. Under full throttle it would fall on its azz towards the top end of a good run say ~4500rpm at ~65-70mph. Original 400 rebuilt to old school W30 specs but with 11:1s. Original fuel system and lines with in-line filter in the QJet air horn. Original A/C car running all of that original stuff. Eventually older and smarter(?) I decided to look for the problem now that my trouble shooting skills were well honed. What I finally found was...get this...rip that black rubber check valve out of the end of the dam filter. Then road test it and get back to us...

442craig

I spent big bucks to make it factory original (at least looking) I didn't want to mess with it. Carbs and I never got along! (short attention span) Like I said before It rocks now! The pump couldn't handle the 1/4" return line. It is blocked off and runs strong now!

Craig

jpc647

You're talking about the return line that ultimately connects to the charcoal canister thing? Sorry if thats a dumb question, I don't have a Q-Jet on my car...

RetroRanger

Some fuel pumps (BBO w AC IIRC) have a third line on the fuel pump that returns fuel to the tank your SBO probably doesn't have one

442craig

Yes, the 68 has a vapor return line on it. It doesn't have a charcoal canister like the later models