Engine problems: Any advice?

[timsullivan]

When accelerating at partial throttle the engine runs just fine and has plenty of power but as soon as I really kick it the engine falls flat on its face kicking, spitting and refuses to run right until I get back off the throttle partially, where it continues to run just fine.


Here are the specs on my Ford small block:

408” 351W based stroker motor
Late model 351W factory roller cam block.
Crank: Eagle 4.0” Stroke Rods: Eagle 6.200” Pistons: Probe Industries Forged Aluminum SRS 4.030” bore, Reverse Dome 22cc (Compression ratio should be about 10.09:1 with these pistons and the Edelbrock heads with 60cc chamber volumes)

Cylinder Heads: Edelbrock Performer RPM 2.02” Intake Valves, 60cc chambers

Intake manifold: Edelbrock RPM Air Gap 351W

Carb: Holley Model 4160, 750 CFM, manual choke, vacuum secondary’s #0-3310C

Fuel pump: Summit Mechanical 110 GPH

Camshaft: Mike Forte Custom Grind 510/534 Lift, 222/232 duration at .050, 114 LC

Camshaft Hydraulic Roller Lifters: Ford M-6500 R302

Roller Rocker Arms: Competition Cams #1131-8
Hydraulic Roller Lifter Retainer and Spiders: Ford factory

Crankshaft Damper: Ford Racing Nodular Iron, external balance #M-6311-K351

Oil Pan: Milodon 8 quart

Timing Chain Set: Edelbrock #7811 Performer-Link True Roller chain set

Distributor: MSD Pro Billet Small Diameter, Magnetic Trigger #8478, with vacuum advance

Distributor shaft Steel Gear (#85834) and installation by MSD factory.

Superformance stock Ford Dura Spark ignition module coil

Spark Plug Wires: Ford Racing black 9 MM

Spark Plugs: Champion RC12YC (Recommended by Edelbrock for use with their alum heads). Spark plug gap: 036”

Ignition timing is about 15 degrees initial, 21 mechanical for a total of 36 degrees all in at about 3,100 RPM

When accelerating at partial throttle the engine runs just fine and has plenty of power but as soon as I really kick it the engine falls flat on its face kicking, spitting and refuses to run right until I get back off the throttle partially, where it continues to run just fine. I replaced the coil which made no difference.

The vacuum secondary’s are running the Holley stock Black spring which I understand is the heaviest spring available and I know, given the light weight of my car, I need a much lighter spring. Could this be the problem with my car?

Thanks for any advice or feedback you can give me here.
-Tim

[Bartruff1]

I would start with the most simple solution...if the car has been in storage as mine has for 6 months...there could be water in the gas, especially if it was parked with a ethanol blend ....try some additive to dry the gas...next check the fuel filters...assuming that doesn't solve it...I would supect a electrical problem, starting with the spark plugs and wires...and that is the limit of my expertise...!!!

[MOTORHEAD]

Try a lighter spring, then bigger acc pump nozzel. How old is this carb, and does it have a blue dot on the front bowl?
Sounds like your ignition is fine.

[john chesnut]

I believe the problem is with the carbs secondary circuit too.

[timsullivan]

Motorhead: Its is a brand new carb that I purchased from Summit Auto. It does not have a blue dot on the front fuel bowl.

[MOTORHEAD]

OK, no blue dot is good. Check your plugs to see what your F/A mixture is running and check/set fuel bowl levels. If all ok, ck acc pump operation, should shoot fuel as soon as linkage starts, no hesitation. You should have an instruction sheet that came with the carb which covers these points and more on how to dial the carb in to your engine. If not, go to holleys website for detailed info.

[Barnsnake]

Since your description doesn't sound like a momentary bog, I'd pull the secondary float bowl and check for debris in the jets or an obstruction in the fuel inlet.

You might also want to try it once with the vacuum advance disconnected. If the vacuum advance is not backing off immediately at low vacuum you would have wildly excessive timing advance.

[Rick Parker]

You may find there is no fuel in the secondary float bowl. Have you verified the fuel level in both bowls? It sounds like when the secondaries are pulled open there is a huge lean spot created :no fuel.

[jhv48]

Tim, you left out one detail that you included in your SCOF thread. The vacuum secondaries in your carb have the stiffest spring (black) that Holley makes. With these light cars, they need a mid pack spring at least, as they are so light.

Before you mess with anything else, get the mid tension spring and see what happens. Your symptoms are that of a car whose secondaries are not opening.

[Gaz64]

Originally Posted by jhv48

Tim, you left out one detail that you included in your SCOF thread. The vacuum secondaries in your carb have the stiffest spring (black) that Holley makes. With these light cars, they need a mid pack spring at least, as they are so light.

Before you mess with anything else, get the mid tension spring and see what happens. Your symptoms are that of a car whose secondaries are not opening.

Secondaries not operating would make the engine lay over but not spit and cough etc as described.
Effectively you have a 390 2 barrel (half of 780 cfm).

Check the float levels, I'd bet on a stuck secondary needle and seat.

By all means change that spring to a green, red, or a long yellow.

[RICK LAKE]

timsullivan Rick Parker beat me to the issue. No fuel in the second bowl. Pull the carb off the motor. DON'T TIP IT. Get on flat surface and pull the plug for the second fuel bowl level sight hole. Do you have gas leaking out? If yes, we are going to drain the carb and pull the second side tank and start checking for the problem. If no gas is in the tank we have a clogged tube or port to supply it. Again need to drain the carb and pull it apart and check. You may want to get a set of bowl gaskets before you start this. Papaer are ok but the Green ones are better with the methonal in the gas now. You also need to check the fuel filter for ANY little black spec's. If the car has any fuel line in rubber this could also be partially the failure and messing up the carb. You may have to replace the fuel lines and go with SS lines. After we find the issue with the carb, drop down to the spring in the middle for the secondarys to open up. We need to test 1 part at a time until with find out what makes the motor happy. Take your time with the carb, couple large cans of cleaner, a quiet place in your man cave with the door locked to work on this. If you need some help call in the evening 732-254-3536 I am 3 hours ahead of you. Rick L.

[FWB]

while all of the above is good advise.......one thing stands out in my mind when i read the post.
champion plugs......
whenever i see champion plugs i start there....put in a set of comparable autolites as the first plan of attack

[timsullivan]

Thank for the advice guys. Good thoughts to be sure. I previously set both float levels such that fuel was right at the very bottom of the site plugs. Fuel mixtures screws at maximum idle vacuum readings. Definitely have fuel in the secondary bowl.

I have sent away for the lighter spring and will disassemble the secondary bowl and check it out when I replace the vacuum module spring to make sure I don't have anything in there blocking the circuits. I think the core problem is the secondary circuit but will also check the vacuum advance to ensure that it is not adding to the problem.

Please keep those ideas coming.

-Tim

[Rick Parker]

Try this: with the car idling, gently pull up on the secondary arm that's attached to the diaphram. If the circuit is functioning the speed will increase, if not start chasing fuel gremlins in the secondary passages.