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Old 02-13-2017, 12:12 AM
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383 stroker acts like fuel starvation at WOT

Hi,
I have a fairly new build carbureted 383 stroker that's pushing close to 600 hp on 93 octane, .that is starting to flutter/sputter at WOT and will actually shut down due to lack of fuel and I have to wait until the pump pressurizes and I pump the throttle and then starts right back up. does this hot or cold.
Its like the engine demand is sucking the carb. dry!???

I am running an Edelbrock 650 single line with a Holley 150 fuel pump and regulator that is brand new and is holding 8lbs of pressure at switch on and then maintains 4lbs at engine idle to 3000 rpms.

I recently cleaned all fuel lines and changed both fuel filters and their seems to be great flow.
I did find some fuel cell sponge residue in the fuel and then pulled and replaced the cell sponge after flushing the fuel lines.

air flow mixture is relatively stable sustaining 12.2 - 13.4 ratio.

it appears that all the vacuum hoses are fitted properly and not leaking and the timing appears to advance etc.. while accelerating.

I know this is a long post, but we are now totally lost as where to find the problem. Any Ideas???
Any help or recommendations would be appreciated
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Old 02-13-2017, 12:43 AM
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Is that Holley 150 pump electric or mechanical?? My guess is Electrical since I don't believe Holley makes a 150 mechanical, but I don't know for sure.

What does the fuel pressure gauge say when the engine is sputtering at WOT??

What size fuel line is exiting the fuel tank or fuel cell??

You say you have two filters, what micron rating is each and where is each located in the fuel system??
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Old 02-13-2017, 01:08 AM
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383 stroker acts like fuel starvation at wot

hi,
it is a Holley 150 electric fuel pump and regulator, (brand new)
I am running 3/8 steel braided fuel line front to rear.
the fuel pressure guage is at the carb, but on throttle rap test the pressure stays at a consistant 3 lbs.
I cannot duplicate the problem in the garage, only under a load while driving.
I can start out on a roll and rotate into the throttle to full and 1st gear is okay then quick shift into 2nd then act like no more fuel at about 38-4000 rpms and the car will shut off. I set and wait for the fuel line to re-prime and pump the throttle while starting and will come back, coughing and spitting until I clear it out.
the car runs ok at idle and as long as I don't ask much of it, like interstate driving. (no quick throttle oscillation)

filters, I cant remember what holley prescribed but whatever holley they said is, that is how it was set up. I think 100 pre-pump and 40 after pump
thanks
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Old 02-13-2017, 01:49 AM
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Seems to me that a 383 pushing 600 HP needs a bigger carb than a 650, if you do a carb calculation that carb supports somewhere between 350 to 450 HP, your electric fuel pump is a 150 gph an at best it pushing 8 psi , seems low, should be 10-12 psi at no run ! Line size seems OK !! Just my thoughts !
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Old 02-13-2017, 03:50 AM
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So you don't actually know what the fuel pressure is at WOT just as the engine dies out??


From your description it sounds just like a lack of fuel delivery....what the gauge reads at idle and revved in the garage is almost meaningless, you need to know what the pressure is doing right at the point the problem begins.

If necessary, hook up a temporary fuel pressure gauge(such as a vacuum/pressure test gauge) on a rubber line and duct tape it to the windshield so you can see exactly what happens when the engine dies out.

If you have to wait for the pump to catch up when the engine dies, then the feed into the pump is restricted somehow...could be too small of line, could be clogged sock on the end of the stock pick-up line, or could be lack of a vent on the tank.

Is the tank or cell vented well??

The pump you have is a good one, and should have no trouble feeding 500+ HP.

Where is the pump located in relation to the fuel cell??
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Old 02-13-2017, 05:02 AM
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The electric fuel pump your using is a 150 gph free flow, what is the max it push's under pressure? I under stand you said 8 psi at no run, but what was the max specs from manufacturer ? Just because it says 150 gph doesn't mean it will push that under pressure. I have a 180 gph free flow that pumps 85 psi max and l have a 35 gph free flow that pumps 12 psi max. 2 totally different beast ! An the smaller system runs both a 502 an a 468 .

Thing about this a Chevy mechanical pump is normally pushing 7 psi .
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Old 02-13-2017, 06:31 AM
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383 stroker acts like fuel starvation at WOT

I have the same pump on my Camaro with a big block engine pushing 600+ hp. So if you have everything installed like the diagram that Holley provides then most likely your wimpy 650 Eddy carburetor is the problem. In the first place you can't run but 5 psi or less fuel to the carburetor. Opening the carb to wot, it is probably is emptying the bowl faster than the 5 psi can refill it. If you know someone that has a 750 Holley or a 850 Holley that you could use for testing would be great. I wouldn't say the lines are to small because Chevy ran 3/8 metal lines on big blocks for years with no problems. With the braided stainless steel I don't know. I have 10 AN stainless steel braided line from my tank to regulator. Then I run 8 AN to the 850 Holley carburetor. I have had no problems with gas flow.
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Old 02-13-2017, 08:04 AM
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Was the 600 hp measured on a dyno? If so, what carb was used? The Edelbrock 650 (I assume Thunder AVS) may not be the best choice for the engine combo, but its CFM rating is NOT causing the engine to fuel starve at 3800-4000 RPM.

In fact, I ran a 600 CFM Edelbrock 1406 and low rise Performer EPS intake on a mild 383 (210/210, .440"/.440" cam, 180 heads, 1.5" headers tubes) that would rev to >5000 RPM. Doing nothing but going to a Performer RPM intake got me another 400-500 RPM, but the thing simply hit an RPM wall. It never ran out of fuel, even with a stock fuel pump and 5/16 fuel line!

Also a friend of mine ran the 650 Thunder AVS carb on a 383 with a 230/235 cam and Performer RPM intake. It would rev to >6000 with no fuel starvation. So, I'd suspect that whatever your problem is, excepting float level or some other internal issue, it would still be present with ANY carb.

Edelbrock says fuel pressure should not exceed 6.5 psi. I'm not saying that's where you should be, but I'd certainly want 5 psi. Also, have you checked the float levels? I have seen them all over the place right out of the box.
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Old 02-13-2017, 08:25 PM
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Hey guys,
thank for all of the response!!* Very helpful!!

We took the fuel lines apart today and found particles of the fuel cell sponge in the filters. so we removed the sponge material from the cell completely.

Next we took the carb apart and found that the floats were only allowing the bowls* to accumulate a little less that half the capacity of the bowls which we are now adjusting to allow full capacity.

We also found a little fuel cell sponge material in the carb screens as well.

We will have the carb back together late this evening and will post an update as soon as possible.

I understand about some concern with the Edelbrock 650 with the relationship to engine H.P but this fuel delivery issue just came about in the last 50-60 driving miles and prior to that, this motor was crazy fast, and launched like it was on alcohol.

Prior to this issue, a bigger carb wasn't even on the radar.

I purchased the car with a verified dyno sheet which was at or above the range I mentioned in my post.

I, like you, felt like there wasn't enough carb but it "was" working efficiently.

I also rechecked the iridium plugs (new last week) and the visual verified a little fat, which makes me think that if the carb gets the opportunity to dish it out,....

having said that, if the floats aren't the issue, I might be looking for a holley or demon 800.
if someone has a like new one setting on their shelf for sale, let me know!

Thanks for all of your advice and input!!

More tomorrow!
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Old 02-13-2017, 09:32 PM
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I agree with the previous Gentleman, a 650 CFM carb doesn't have the capacity to feed enough air into a 383 600 HP ! Referring to your dyno sheet was it using the same carb an fuel system ? A dyno sheet states what it is capable with certain parts but maybe you have a variable ?

You say you car use to take right off, well it is a light car an 600 HP should but you back in the seat looking at the sky if she hooks.

Yes your floats need to be adjust up more than you stated.You also stated that your plugs are looking fat, assuming that means rich, ofcourse it's rich it's not getting enough air/CFM !

Once again just some thoughts to think about !
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Old 02-13-2017, 11:44 PM
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you need an 85p cfm carb to make 600 hp.
The fuel is drawn through the jets by the air volume and speed. If its not enough air to make power up top the gas flow will not increase on its own,
The engine should rev to redline at light throttle. If you are at wfo the fuel can drain faster if the engine needs more fuel.

when the engine quits, will it come back to life if do are slowing down with the throttle linkage at the idle position? Or, can you feel the power shrinking while at a stead rpm on the highway? Has this happened before? Where are you located? Have only had it happen to me one in a life time, carb icing? Can you feed warm air to the carb?
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Old 02-14-2017, 12:17 AM
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A temporary fuel pressure gauge is a must at this point to confirm the fuel pressure when the issue develops.

The sponge particles found in the carb bowls would have me reconsidering the filters. They should not be making it there.

Where is the pump located and have you checked your pump ground and power supply?
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Old 02-14-2017, 01:06 AM
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383 stroker acts like fuel starvation at WOT

Do you have a 100 Micron filter in the line leaving the fuel cell? Also you need another 40 Micron filter in the line near the carburetor? Look at Figure 1 and Figure 2A. http://documents.holley.com/199r10367rev1.pdf
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Old 02-14-2017, 09:15 AM
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I wouldn't mind seeing this dyno sheet. Dyno's are often adjusted to make it say what the operator wants.
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Old 02-14-2017, 09:54 AM
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Simply plugging in bogus specific gravity and air density can change things greatly.
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