Author Topic: 427 popping through the carburetors during acceleration and no power above 3500  (Read 3560 times)

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Robin Hood

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I own a 1964 Thunderbolt Tribute car that I can’t get to run strong, pops through the carbs or starts to cut out when accelerating.
12.7 compression, 20 degrees initial timing, 110 octane. Installing fuel pressure gage to determine if I’m starving it for fuel?
It has glimpses of unreal power but then starts cutting out and sometimes popping through the carbs.
Any help would be appreciated

GerryP

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Sort out the timing first.  Back your total down to around 35 total, which generally is going to put your initial at around 15.  Your symptoms point to timing too far advanced.  The popping would be out the exhaust.  Though that can be hard to distinguish from intake popping.  If you have access to an ignition oscilloscope, you want to use that and see how sturdy your ignition system is.  But the easiest thing to do is to dial back your timing since that is an instant A-B comparison and you can move on from there.

It's wise to also baseline your fuel system.

One other thing that causes what you're describing are failing valve springs.  Once the valves float, the engine seems as though it has a rev limiter on it.  Rule out the simple stuff first.  Again, start with the ignition. 

Falcon67

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Typically - not always, but typically - backfire in the intake is a lean condition or some condition with valves/springs.  Hitting a "wall" at 3500 could be both a weak spring issue and/or fuel delivery problem. 110 is right on the edge for 12.7 IMHO and per VP.  Like Gerry says, check your max advance with the 20 initial.  You can run as much initial as you can stand, it's the max that causes issues. 

Exhaust pops are lean conditions in the exhaust - gasket leak, loose bolts, etc.  Especially if it pops on decell, like off the throttle in the traps.  If you lift off and it pops through the exhaust it's almost guaranteed that's an air leak in the exhaust, usually at the header flange.

Robin Hood

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Thank you for your advice i do appreciate everyones input as i sort this out.
When I have the initial timing set to 16 it runs smoother at middle range but it still hits a wall around 4,000rpm, starts to cut out and backfire.
I am going to install two fuel pressure gages to see what the pressure is. Not sure what is recommended for this setup but at least i will have a base line to go from.
It almost seams as though it is starving for fuel during WOT. Any thoughts on what fuel pressure the feed rail should be set to?
Thanks for your help.
 

GerryP

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For Holley carbs, limit your pressure to six PSI max.  Over that will blow the needle off the seat or push past the o-rings.

Stangman

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Mechanical fuel pump or electric? I had a mechanical pump do a lot of what your saying. I could drive anywhere at normal operation but getting on it it would buck and fall on its face. Seemed like ignition and because it ran good around town I wasn’t thinking fuel pump.

Robin Hood

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Thank you for the info on the fuel pressure, I will check is my once my new gage comes in the mail and let you know what it is.

Also, it is a mechanical fuel pump with an electric pump pushing to it from the tank. It is a factory fuel pump that runs into a large fuel filter canister. You can see it in the attached photo

Robin Hood

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Can someone tell me what the fuel
Pressure should be for my car? I installed an in-line fuel pressure gage between the fuel rail and the front carburetor and it is 3.5 psi. Seams like it should be higher for my car.
Thank you in advance

Stangman

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Between 5.5 and 6.5 psi is good

frnkeore

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The spec, I grew up with, for Holley 4150/4160's, was always max 6lb, min 3 lb. At WOT, the pressure can drop but, shouldn't go below 3 lb.

But, that assumes a good needle & seat as well as float.
Frank

My427stang

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What are you running for ignition?

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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

Robin Hood

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Thank you!
I am running OEM coil and cap and rotor I believe.
When the motor was built 20 years ago it was done to be factory for authentication.
I want the vehicle to represent the intention of factory however, I would like it to run like it should.
Driving it into a car show it acts just fine, but put your foot in it and it struggles to make any real power.
Dyno at the real wheels was 350hp at 4,000. Above 4,000 and it wants to cut out and falls on its self.

My427stang

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I had a Pertonix 3 do that on a dyno. Regardless of the trigger I would look and see what the timing is doing when it breaks down, also consider unhooking the tach to see if it changes

Additionally, I have seen point pigtails go brittle, dist grounds straps fail or go missing and condensers fail, all of which could to what you are seeing

Last look very close at the underside of the cap for carbon tracking and keep plug gaps at .035 or so, wider makes it harder for the secondary ignition
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

rockhouse66

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It would be really handy to have another distributor to stick in there for testing purposes.  I have a Mallory dual point I use when I want to eliminate issues with whatever car I am having concerns about.  Do you have another or can borrow one nearby?  And also try another coil to eliminate a weak spark.
Jim

Robin Hood

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So today I did the following.
New Holley Fuel Pump and Pressure Regulator- set at 5.5psi at the fuel supply line to front carburetor
New MSD Coil
New Autolite Spark Plugs gapped to .035
Set initial timing at 18-BTDC
Did not run well, popping through the exhaust on acceleration and same rev limiting
Reset initial timing to 26-BTDC, no popping on acceleration and shows glimpses of starting to get after it, pulls harder up to about 5,000 with some hesitation but does run better.
 It like the larger gap in the spark plugs and the advanced timing at 26. That just seams to far advanced though…..