Thread: SBC shut down while accelerating?

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Originally posted by C9x
You can get a flat spot with the Edelbrocks when making an abrupt transition from primaries to secondaries opening.
Abrupt meaning tromping on the throttle as vs rolling it smoothly in.

Running at a higher altitude than you usually do can make the flat spot worse.

It is a flat spot though and it doesn't take long for fuel to start flowing in the secondary circuits and it's more of a bother than a giant pain in the backside.

Many of the Edelbrocks come stock with the orange metering rod spring.
Changing to a pink spring cured the stumble in my 750 Edelbrock.

It helped as well that I jetted the carb - jets and metering rods - leaner for the altitude I'd moved to.
3300' vs 350'.

It does sound like your engine is simply running out of gas and for that reason I'd make a point to check the fuel pressure under load.

Make sure as well you don't have a kinked fuel line.
Rubber and hard line....

I tried the roll vs. tromp on the throttle and it makes no difference. Now.... with the trans manually in 2nd gear, I can get 5500 rpm with secondaries but in high shut down at 4000??? Dont know what that is all about. Must be fuel related. Worked late. Going out to lift the hood and start checking floats, cleanliness, and general condition of carb. Still need some instruction on fuel pressure check while vehicle under a load?

Sure sounds like it's a fuel pressure problem.

Install a fuel pressure gauge, run it through the gears and see where the pressure goes.
If it drops off below 2# or less more than likely that's your problem.

I'm betting you'll see 1/2# or less when the engine starts running bad.

Originally posted by s10streeter
How do I perform fuel pressure check with load?

Yea, just like what C9x said, install a pressure guage.

My old handheld vacum guage slid off the fender for the last time, and I had to get a new one. My new one will do moderate pressure as well. It even came with fittings to hook it up as a fuel pressure guage. I think it was $29 or so at O'reily.

Well, after removing the airhorn assembly and measuring the floats per edelbrocks instructions I made a fraction of adjustment to both floats. The measurments were fine with the floats at rest, the adjustment was made at the back to change the level when at the bottom(hanging). I mean these were just hairline adjustments so I dont think this will change anything. The carb overall looked fine. A little varnish here and there. Removed the remaining assembly from the intake and used gunk carb cleaner top to bottom and all places in between. Learned a little bit about the anatomy of a carb. Not as complicated as I thought. But this is a Edelbrock and I have seen mechanics with Quadra-jets dissasembled and that was a mess! To make a long story short, the truck is back on the road. Havent had a chance to test yet ( too much holiday traffic). Will have to get a gauge after the holiday if things havent improved. Still need to check for fuel line restrictions. Took all free time I had to do the carb and head to work. Have a great holiday everyone and I'll post again next week.

I'm not sure if I understand how you are adjusting the floats.

Float level is set with the airhorn upside down with the float tang resting on the needle.
That is what controls the depth of fuel in the float bowl.

The other adjustment is float drop which is done with the airhorn right side up.
This one's done to keep the float from going too far down.

If the float is allowed to hang down too far, the needle drops too low, the float tang presses sideways against the needle instead of upward and the float will remain open with fuel under pressure flooding the engine and overflowing the carb.

Color me confused, but it looks like maybe you adjusted the float level with the airhorn right side up and somewhere along the line got the float adjustment way low and it's shutting off fuel flow before the fuel can fill the float bowl.

Probably just me mis-interpreting what you wrote, but if you got the float drop and height backwards . . . maybe....

Heres a link to the float adjustment from Edelbrock. The adjustment I made was with the floats hanging. They measured about 1 3\8" from the gasket surface so I adjusted about 1\8". Would this small of an adjustment possibly correct the fuel starvation at the secondaries at high rpm? Hopefully I'll know more after the drive home tonight. Need to be careful though. Dont need a ticket this weekend. But I dont own a speedway either. Seen alot of fuzz already.

EPS carb manual

With the floats hanging you adjusted float drop and it looks like you're right on the money.

You shouldn't see a change in how the car runs with this adjustment - unless it was so far out it was creating a flooding problem which you don't seem to have.

Take note of Edelbrock's float height setting of 7/16" and note as well it's measured with gasket in place.

As far as the fuel lines go, if you turn a very tight corner with a rubber line it can kink or nearly kink and stop or restrict flow.

You may want to check out the hard fuel line as well.
Start at the tank and see if the line is smashed flat due to a rock hitting it, a jack inadvertently catching it etc.

I think the fuel pressure test will tell you a lot.

Like I said above, use an isolater or an electric fuel pressure gauge.
You do not want a pressurized fuel line inside the cockpit.

Thought I'd point out as well that the usual culprit in the kinked fuel line bit is the rubber line between frame and pump.
It's under suction and if you used the wrong type line the fuel pump will suck it flat cutting off fuel flow.

If you're not sure what you have, go to a 'real' parts store - NAPA's are usually very good - and get "Fuel Line."

Originally posted by C9x
Thought I'd point out as well that the usual culprit in the kinked fuel line bit is the rubber line between frame and pump.
It's under suction and if you used the wrong type line the fuel pump will suck it flat cutting off fuel flow.

If you're not sure what you have, go to a 'real' parts store - NAPA's are usually very good - and get "Fuel Line."

The rubber line that Cx9 suggested from frame to pump is very old and cracked. Cant read any markings such as specifying that it is in deed a "fuel line" but it does feel very spongy when pinched. Think I will replace this one and hope for the best.


Heres a new question off of the subject: How acurate is the "vacuum gauge" method of setting at max Hg. to time initial ignition spark?

Hope everyone had a nice holiday weekend.

After inspection of fuel lines, all of the steel lines from the tank up to the rubber connections looked fine. The were some lengths that were not visible because they run inside the frame but from what I could see they all looked o.k. The rubber line going to the pump looked cracked and felt spongy so I replaced it. The problem still existed so I purchased a fuel pressure\vacuum gauge and tested the pump at idle only because I'm not sure how to test fuel pressure while vehicle is moving. There are no instructions with this gauge except for pump at idle and volume tests. The pressure at idle shows 4 to 4.5 psi. Unless I am mistaken I remember reading on the Edelbrock website that these carbs need 6 to 8 psi. Would this warrant replacement? Could this be the problem. I would like more detailed instruction for pressure at highway speed tests if anyone could help. I really dont look forward to dropping the tank and checking for restrictions but that may be what I have to do. Any suggestions?

Also, TECHINSPECTOR had mentioned valve springs? How do I rule out that possibility?

Originally posted by s10streeter
Hope everyone had a nice holiday weekend.

After inspection of fuel lines, all of the steel lines from the tank up to the rubber connections looked fine. The were some lengths that were not visible because they run inside the frame but from what I could see they all looked o.k. The rubber line going to the pump looked cracked and felt spongy so I replaced it. The problem still existed so I purchased a fuel pressure\vacuum gauge and tested the pump at idle only because I'm not sure how to test fuel pressure while vehicle is moving. There are no instructions with this gauge except for pump at idle and volume tests. The pressure at idle shows 4 to 4.5 psi. Unless I am mistaken I remember reading on the Edelbrock website that these carbs need 6 to 8 psi. Would this warrant replacement? Could this be the problem. I would like more detailed instruction for pressure at highway speed tests if anyone could help. I really dont look forward to dropping the tank and checking for restrictions but that may be what I have to do. Any suggestions?

Also, TECHINSPECTOR had mentioned valve springs? How do I rule out that possibility?

that pressure is on the low side and if it drops much more then that is the problen. tee you gauge into the fuel line going from the furl pump to the carb. have the hose long so you can run it out from under the hood, and lay it on the windshild wiper so you can read it going down the road. crank the car got out on the road and watch the gauge normal driving and at WOT, see how low it gets at WOT. anything below 3 lbs. will give you a problem. tthats not really a speed test because speed dont have anything to do with it. itasa WOT test or rpm test.

OK, got the tee and extra long hose to do the pressure test. Will have to wait till tomorrow to test. Will keep yall updated. Thanx for all the replies. This is a great forum. Glad to be a member.

Just a thought, is there a filter inside your carb, just where the fuel line enters . it may have a small paper or screen filter that could be clogged carlg

Thanx orange crush, I will check for that.

Originally posted by C9x
Sure sounds like it's a fuel pressure problem.

Install a fuel pressure gauge, run it through the gears and see where the pressure goes.
If it drops off below 2# or less more than likely that's your problem.

I'm betting you'll see 1/2# or less when the engine starts running bad.

Troubleshoot update-- Some good news and some bad news.

During the pressure test the pump showed 3 to 5 psi at idle (wide fluctuation). Pressure became steady with throttle to 3psi. During acceleration test the pressure dropped to barley enough to read. Then when decel., the pressure came back to 3 psi. Evaluating this, I purchaced a new pump.

The good news: I have a new pump.

The bad news: cant tell by the pressure gauge, still the same drop and fluctuation.

Looks like I'm going to be pulling the tank to check the sock that Lt1 mentioned.

This pump is showing more pressure at idle, 4 to 6 with wide fluctuation. Its rated 7 to 9psi. It drops off to less than 1\2psi during accel.

The rubber fuel lines have all been replaced with NAPA brand 50 psi fuel hose. The steel lines have been inspected, (what I can see) and appear kink and pinch free. Must be at the tank?