Hotrod66

I had my 427 rebuilt to 462 ci a couple of years ago.
I am using the original Holley 780
It does not fire up easily and seems to be starved for fuel
If I pour gas striaght down the carb it fires up instantly
Under hard acceleration and in about 3rd gear it has cut out on me twice, again I think it simply runs out of fuel
I thought I would start at the fuel tank and pull the screen from inside the tank.
Did that today and the tank is very clean inside, no evidence of debris however when I pulled the flex fuel line off the tank end to drain the tank no fuel came out although the tank was half full.
When I got the tank completely out I managed to get it flowing.
The screen was brittle but looked okay otherwise and there was no debris that I could see causing any blockage. (could it have been a vapour lock??) I'll replace the screen.
I have a few questions. Why no fuel flow when the tank is half full?
Is a 780cfm big enough and simply requires bigger nozzles??
Is a stock fuel pump enough or should I be installing a high flow electric.
The hard starting is the worst as there is simply not enough fuel being delivered.
Wondering if anyone has seen this or experienced this before.
Thanks for any advice

ghostrider20

I think the carb size is just fine. Check the jet size referenced to the OEM size. The squirter can be checked for operation by moving the throttle linkage, look down the carb and they should shoot a good stream out.

Check the fuel filter as well. If you cannot remember the last time you changed it, it may be time for a new one.

If there are any rubber lines in the system check to make sure they are not making any extreme bend or have any kinks in them. Rubber up stream of the fuel pump will collapse under heavy vacuum.

A vapor lock were air is concerned will migrate itÂ’s way out or be sucked out through the fuel system. Fuel vapor lock due to heated fuel is a different phenomenon.

Concerning cold starts, the ownerÂ’s manual recommends pushing the pedal all the way to the floor once.

This does 2 things, it give a pump shot to the squirters for a prime, and sets the choke.

If I cold crank my car with out this step it will crank longer then need be to start. Hot starts should no need this method.

Quote
"Is a stock fuel pump enough or should I be installing a high flow electric."

Stock is just fine, you can check the fuel pressure with a gauge or by a timing method and a coffe can. The details are outlined in the Shop Manual.
In every instance I have been involved with mechanical fuel pump failure the pump failed noticably. Or was leaking oil beyond an acceptable amount. Electrics are a PITA. They will give you far more trouble then a Mech. pump will. Most requier a pressure regulator and they can cost as much as the pump for a good one.

Good luck and welcome to the forum

Mark


[Modified by ghostrider20, 11:08 PM 2/21/2004]


[Modified by ghostrider20, 11:13 PM 2/21/2004]

Hotrod66

thanks for the reply
the fuel filters are new
seems like there should be enough fuel when I pull the throttle, squirts a decent amount of fuel but maybe they should be changed to a bigger size
i had thought about replacing the flex hose upstream of the pump with a solid connection so with your comments about excessive vacuum maybe its a good idea
thanks again

ghostrider20

The rubber hose ahead, or, “from the pump to the carb” should be OK. This is the pressure side and therefore no vacuum. The vacuum would be from the pump to the tank, or the suction side.

The squirters main function is to “cover up a dead spot” created when the throttle plates are opened. The vacuum inside the manifold momentarily drops, or in the case of WOT goes to atmospheric pressure. This causes the fuel to condense on the walls of the manifold, thus starving the engine. The squirter or “pump shot” covers this up. If you disabled the squirter the engine would perform fine at one throttle setting but any change will produce a stumble. So even getting the car going would be a problem. I had the arm bend and slip off the pump lever and it rendered the car virtually undriveable in traffic.

Tuning the squirter or “pump shot” can be timely. It is a matter of selecting one of the many pump cams, and then, their many positions. I would start with what the factory recomends. The cams are colored so you can identify them. One note, you want to adjust the squirter assembly so that it actively starts to shoot when you move the throttle. Many times this is overlooked and can cause a slight delay in WOT revs. I am not sure what mods you have done to your car so tuning around those may be a consideration as well. I installed 4:11’s in my vette so I discovered through trial and error that a larger squirter with a more aggressive pump cam produced better throttle response.

A high RPM cut-out would more likely be a jetting issue. The jets are located in the main metering block. So you will have to take the float bowl off to inspect them, and note there size. I am not sure about the model or type holley you have, so some general rules that my catchall.

-Increase the jet size by one number at a time.
–Do the same for the back, if it has jets in the back.

In any experimentation try to control the variable’s the best you can. EG. Don’t change more then on thing at a time if you can help it. This will allow you to note the gain/loss from your work and apply it to the correct variable.

Lastly, check the fuel level in the float bowls. There is a sight window for this. Unscrew the screw and you should not have fuel running out the hole. It should be just level with the bottom of the whole. I raise the level until the gas just wants to come out. You can take your leg and rock the car a tad and a little gas should trickle out. If it pours out the float is set way too high.

Mark

aworks

when the car is cold look down the carb and see if it is getting fuel when you pump the throttle. if it is not, the needle and seats are leaking down after the car is shut off. after a drive shut the car off and pull the air cleaner lid see if there is any smoke coming from inside the carb. that is a sign that the carb is leaking down. when the seats leak it slowly drains the bowls and when you try to start it, the motor has to crank to pump fuel to the bowls so you can pump the gas all you want but untill the bowls fill up there is no fuel to pump. as far as the car running out of fuel when driving or putting a load on the car, you may not have the right volume pump. large cubic inch motors need more volume than a stock pump can handle. you can go elec. with a regulator. or try a new high volume pump from edelbrock or carter. dont keep driving the car if it is staving for fuel a lean cond. is a very bad thing, i wont go in to the damage that could do. sounds to me like you need to find a guy that is good at tuning holleys. if you dont know anyone go to wherever. gearheads hang around or a drag strip. carb tuning comes from experience.

jimgessner

"Aworks" has some very good suggestions.

The 'POWER VALVE' in a Holly can be blown out with one backfire, which is very common in Holly carbs. This will lead to a lean fuel problem on acceleration.

No has talked about IGNITION system. Are you sure your ignition switch is working properly? Yes it turns over the starter, but are you getting spark to the plugs while cranking? I have seen swiches that are so worn that when the key is released from the crank position , the coil finally gets B+ voltage to ignite the cylinders.

Has anyone checked the advance system and timing of the distributor to the CAM that is installed in the engine? Basic timing and vacumn advance may be way off the factory specs. I have seen many 'hot rod' motor changes where no work was done on the distributor advance system, which resulted in over 100hp loss as well as surging and fuel starvation symptoms.

Over the years, mechanics tend to out engineer the engineers. BIGGER carburators, BIGGER camshafts, BIGGER headers........but very few look at the TOTAL ENGINE PACKAGE.

One must get back to basics. 14 parts air to 1 part fuel is the perfect combustion of ALL ENGINES.

It is now that a modern tech who is completly trained with modern test gear can take your old beast, put a four gas analyzer probe up its tailpipe and power check the cars ignition, carburation and full timing ( on a dyno preferably) and make the proper corrections or recomendations for you to do. And yes, there is lots of great knowledge at the drag strip........race course.......cruise in.

But my best advice is find a pro that you can feel comfortable with who will give you your monies worth for service received. It usually is the guy who has been in business for some time, has a 'good' reputation in town and who has stayed up with the new tech of todays cars and emission systems


[Modified by jimgessner, 5:08 AM 2/22/2004]

Hotrod66

lots of good advice here but I'm a novice gear head wannabe so you'll have to be patient with me.
I'll have to approach this bit by bit
the engine was built by very reputable engine shop here in Mississauga, they are drag racers themselves and build many race engines. They took my 427 block and built up to 462 with 454 internally balanced forged steek crank, Keith Black pistons, Crane roller rockers , solid lifters and a Comp Camshaft with specs as follows as per the spec card (part number is 11-218-4):

valve adjustment intake .022, exhaust .022;
gross valve lift intake .56, exhaust .561;
duration at .015 tappet lift 282
valve timing at .015 intake open (35 btdc), close (67 abdc)
exhaust open (75 bbdc), close (27 atdc)
specs are for cam installed at 106 intake center line
duration at .050 intake 236, exhaust 236
lobe lift intake .3300, exhasut .3300
lobe separation 110

I replaced the stock distributor with an MSD unit, coil and ignition control box and replaced the ignition wires from Taylor, probably has about 50 miles on from last summer so it is getting plenty of spark.

The carb is the original carb for the 427/425hp block. It is a Holley 4150 (list 3247). It was rebuilt about 4 years ago and should be rebuilt again I guess (i read about guys taking there carbs off the intake every winter to drain them and wrap them up, sounds like as another good idea).
I've checked the float levels before and they seem fine, fuel is at the bottom of the set screw on the carb. The squirters push fuel down the carb immediately on engaging the throttle (looks like a healthy squirt to me)

I understood what you meant by collapsing the fuel line I mispoke, the flex fuel line is hooked to the steel line from the tank and has a bend in it although it is not kinked and then attaches to the fuel pump (not upstream but downstream). If under heavy acceleration the vaccuum increases to the point where the flex hose starts to collapse then maybe simply the fuel pump can't "suck" enough gas? Sounds like a reasonable theory to me. It does not explain the cold start issue though. I'll make a "solid" connection and remove the flex hose to eliminate this problem if it exists.
A good friend of mine is knowledgeable in this area and he is convinced that the carb simply isn't big enough and that the engine simply needs to have a ton of fuel "dumped" into the throat. I'd like to keep the original Holley and use it so if it can be rejetted etc.... The power valve would have been set up to match the original 427/425hp motor when the carb was rebuilt. I don't know how much hp the new rebuilt motor creates but it sure must require a lot more air. Does it not make sense that a different power valve is required simply because it is a bigger engine? It has backfired before as well so maybe it did blow out the curent power valve. What would a carb rebuild shop need to know in order to get it set up so that it was close to being correct for this motor or is it something that needs tinkering with and a bit of trial and error.
Sorry for the length but thought I would proved as much info on the current engine as maybe this would help you guys try to diagnose.

I'll pull my Holley carb manual out and start reading again.... think I need a course in hotrodding.
sincerely appreciate the help, this can get frustrating

Dan

JohnZ

I'd start right here - when you pull off the rubber hose from the outlet pipe on the sender, fuel should POUR out of the pipe; you have a blockage or restriction somewhere in the sock or the sending unit plumbing. The sock may "look good", but it's a very fine mesh, and it's probably coated with varnish, dramatically reducing its flow capability - replace it.

Your carb is plenty big enough, and a stock fuel pump will work just fine - they didn't have any problem feeding an L-88. Fix the fuel feed problem first, then you can work on carb and ignition system tuning. :thumbs:

Hotrod66

i agree
the sock was dark and brittle (new one on order)
i have no idea whether it was ever replaced but if not it would be 38 years old!
cold starting is still an issue though....

ghostrider20

Quote
"A good friend of mine is knowledgeable in this area and he is convinced that the carb simply isn't big enough"

"The mech fuel pump is not supplying enough fuel"


The carb is plenty big. You can calculate the CFM flow of the engine at a certain rev. At 6500 RPM I would venture to guess it is around 700-725.

Remember that your engine only sees this RPM for a second, then you shift.

Over carbing is a common problem. This kills throttle response.

With the recent rebuild, you may need some more Fuel on the top end, this is where the jets come in.

The mech fuel pumps service all kinds of gas-guzzlers. My dad’s motor home has a 455 olds and that thing gets around 7 MPG. So that fuel pump sure pumps allot of fuel.

Holley’s tend to warp and leak and cause the problems Aworks described.

Mark

NVaVettes

John Z's advice rings true (again).

Sounds like you're looking for a nearly complete mal-function of something (under certain conditions) and not just a "subtle" tuning thing.

Fuel starvation (blockage) has given me these symptoms in the past, although in a completely different type of car. I "tuned" things until I was blue in the face. Finally fixed the blockage and viola', no more problems.