Diagnosing a Potential Fuel Problem

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MuuMuu101

MuuMuu101

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So, my Dart has been having a wide variety of fuel problems in my opinion and I think I'm getting to the root cause. I just want to make sure I'm going along the right path. The car has a 408ci engine, stock fuel tank, holley blue electric fuel pump that feeds into a pressure regulator, and a holley 850 dp carb.

Here are a couple of my problems. Depending on how the car feels that day will depend on whether or not it wants to start up. On some days, I can start it up on the first or second try (second try because I'm still learning it). These are usually colder mornings (40-60F). Other times, I have to try 3-5 times. I'll turn the key to prime the pump, wait awhile, put my foot on a little past half throttle and turn the key letting my foot off the gas. 75% of the time, the car will run for about 5 seconds and then die out. Half the time when I give the throttle just a little tap after it starts up it will shut off and the other half it will start singing a new tune and then properly warm up. The car does not like to run until water temp reaches about 150F. My other problem was that the car got about 6.7 mpg. Granted, I did drive it 80% of the time on the streets and having fun, but that seems a little low for a car that has a T56 and no autocrossing, yet. Lastly, at my last autocross, during 2 of my 4 runs, on the first corner the car would die out. Now this corner was tight, slightly uphill off camberish, and not very high speeds. But this caused me to DNF and that's no fun. After the car died out, it took another minute of multiple attempts to start the car. Pretty embarrassing.

So, first off, the car was smelling of fuel pretty bad around the gas cap. I took a look at the gas cap and sure enough, the gasket had cracks along the end and some evidence of drizzling fuel. So, I bought a new locking gas cap which may help with my fuel mileage issue as this gasket has a much larger gasket. Plus now I have added security with the locking feature. In the past day or two, the car doesn't smell like fuel anymore; however, I won't have an opportunity to drive it till tomorrow to see if it will leak.

Second, I've been watching videos on how to tune a Holley Carb on Youtube. It's been super helpful and here are two things I think I may have to adjust; however, I feel that one may fix the problem. A common theme in these videos is that the Holley carb generally likes to run at about 6psi of fuel pressure at idle and that 7psi is it's max and it doesn't like it there. I turned on my key and checked my gauge, prior to letting my car run. For the first 30 seconds the gauge reads 7 psi, the next 30 seconds it climbs to 8 psi, after that it drops down and flickers back and forth between 6.5-7 psi. So, my guess is I need to tune the regulator down so that the carb is getting 6psi of fuel pressure and my backup option would be adjusting the floats.

I know that was long, but do you guys think I'm on the right path?
 
The 850 is too big, the double pumper is wrong for the street.
 
Sounds like you need a working and properly adjusted choke for your cold start issues. Along with that you should get fast idle. Your autocross issue sounds like a fuel starvation issue. Could be the fuel level was too low in the tank to fuel sloshing in the float bowls. You may have to do some mods to be able to autocross.
 
for me, with a carb and a properly adjusted choke, 2 full pumps then hit the key. The first pump allows the choke to close.
 
>The cold-start is probably a combination of choke adjustments, a lean low-speed circuit,lazy timing, and/or operator error.
>The engine not liking to run until the temp comes up, is either a lean AFR, or lazy timing or a combination. I have noticed that aluminum heads and the AirGap do take a bit of warm-up time, but a fat low-speed circuit solved it for me.A direct drive fan may aggravate the warm-up time.The cold engine likes a ton of advance. I give it that thru the vacuum advance can,using ported vacuum, and the fast-idle cam to activate the circuit.
>The stall on the corner sounds like fuel slosh, and the long crank time kindof proves it.If the fuel ends up in a corner of the bowl, and the float drops, BAM!, the electric pump will over-fill the bowl in a heartbeat.
>6.7mpg! You actually checked it?! Wow, that does seem excessive. First I would examine the entire supply line for leaks.Then I would pull the dipstick and make sure the fuel is not ending up in the pan. If no leaks are found, you have two choices;1) get an AFR gauge, or 2) empiracle testing. The first circuit to undergo testing is the one you spend the most time on. But in all likelyhood, fuel consumption will settle down, as the novelty of the mighty stroker wears off,lol.
> as to carb size; Performance sucked on my 367 with a 600 vac carb. It was better with a 750 vac carb. It perked up quite a bit with a 750DP. It is 100% street driven.I really liked the TQ, and the TQ really liked the 367. But I wanted the AG, and I had accumulated all these carbs, so I went on a testing spree. I must admit, the 600 can make amazing point to point mileage. Someday, I'd like to test an 850DP!
>The CFM formula says a 750 is right for my 367 to 7000rpm. The formula says in a stroker,a 750 is good to 6200,and 850 is good to 7100.
That same formula says a 600 is good to about 5600 in my 367. I don't think so Tim. That 600 was good for fuel-mileage and banging around town and nothing else. The 750 is plenty for me,I guess,lol.
> I'm not a big fan of electric pumps.
The engine doesn't care how much pressure the fuel comes in at, as long as the pump does not overpower the float valves.The float level is only slightly affected by fuel pressure in the normal range,so long as the pressure does not exceed the valves ability to regulate.The low-speed circuit is the one that is most affected by a fluctuating fuel level.But even then it is a minor thing.
You can see this in action, by killing the pump on a warm engine, at idle, and waiting. One of three things will happen;1) if the fuel level is just right, it will idle normally for maybe 15 seconds, then begin to slow down,labor,and eventually stall,or 2) If the fuel level is too low, the engine will immediately lose rpm,labor, and stall,or 3) if the fuel level is too high, then the idle speed will slowly rise, level off, then begin to drop,labor and stall.
> personal opinion, but I think that fuel system is wanting a fuel-return.
 
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First things first. What type of ignition are you running? Do you have it wired through a ballast resistor? What do you have your initial and total timing set at? How much voltage is going to your coil when cranking? You should have full voltage at the coil while cranking the motor, 12V+.

Have you checked for vacuum leaks and confirmed that you have absolutely none going on?

Holley needle and seats are pretty hit and miss. On average they work pretty well, but if you get 10 sets, there will be about 2-3 pairs that will control fuel pressure much better than the rest, sometimes in excess of 11 psi and some can barely control 6 psi.

Confirm you are running a deadhead regulator. Where do you have your float levels adjusted to? How is your fuel system plumbed? Is the pump above the fuel tank? Do you have a fuel filter before the fuel pump? How long does the fuel system take take to fill up a gallon container? Is your fuel tank vented? Has the choke system been removed from the car?
 
AJ/FormS said:
>The cold-start is probably a combination of choke adjustments, a lean low-speed circuit,lazy timing, and/or operator error.
>The engine not liking to run until the temp comes up, is either a lean AFR, or lazy timing or a combination. I have noticed that aluminum heads and the AirGap do take a bit of warm-up time, but a fat low-speed circuit solved it for me.A direct drive fan may aggravate the warm-up time.The cold engine likes a ton of advance. I give it that thru the vacuum advance can,using ported vacuum, and the fast-idle cam to activate the circuit.
>The stall on the corner sounds like fuel slosh, and the long crank time kindof proves it.If the fuel ends up in a corner of the bowl, and the float drops, BAM!, the electric pump will over-fill the bowl in a heartbeat.
>6.7mpg! You actually checked it?! Wow, that does seem excessive. First I would examine the entire supply line for leaks.Then I would pull the dipstick and make sure the fuel is not ending up in the pan. If no leaks are found, you have two choices;1) get an AFR gauge, or 2) empiracle testing. The first circuit to undergo testing is the one you spend the most time on. But in all likelyhood, fuel consumption will settle down, as the novelty of the mighty stroker wears off,lol.
> as to carb size; Performance sucked on my 367 with a 600 vac carb. It was better with a 750 vac carb. It perked up quite a bit with a 750DP. It is 100% street driven.I really liked the TQ, and the TQ really liked the 367. But I wanted the AG, and I had accumulated all these carbs, so I went on a testing spree. I must admit, the 600 can make amazing point to point mileage. Someday, I'd like to test an 850DP!
>The CFM formula says a 750 is right for my 367 to 7000rpm. The formula says in a stroker,a 750 is good to 6200,and 850 is good to 7100.
That same formula says a 600 is good to about 5600 in my 367. I don't think so Tim. That 600 was good for fuel-mileage and banging around town and nothing else. The 750 is plenty for me,I guess,lol.
> I'm not a big fan of electric pumps.
The engine doesn't care how much pressure the fuel comes in at, as long as the pump does not overpower the float valves.The float level is only slightly affected by fuel pressure in the normal range,so long as the pressure does not exceed the valves ability to regulate.The low-speed circuit is the one that is most affected by a fluctuating fuel level.But even then it is a minor thing.
You can see this in action, by killing the pump on a warm engine, at idle, and waiting. One of three things will happen;1) if the fuel level is just right, it will idle normally for maybe 15 seconds, then begin to slow down,labor,and eventually stall,or 2) If the fuel level is too low, the engine will immediately lose rpm,labor, and stall,or 3) if the fuel level is too high, then the idle speed will slowly rise, level off, then begin to drop,labor and stall.
> personal opinion, but I think that fuel system is wanting a fuel-return.
Click to expand...

Let me try to address everything so you guys have more information.

>I'm assuming that 50-75% of the cold start issue could be due to operator error. I've tried a variety of different methods and it's really hit or miss as to what worked. At first it was the 2 quick pumps, turn the key and let it go. Then it was hold at half throttle and let it off.
>The car is running 34 degrees of total timing and has an MSD Ready-to-Run distributor on it with the vacuum advance disconnected. We had problems with the vacuum advance as the engine doesn't provide enough vacuum and it was causing the engine to misfire and throw timing around like crazy. IMM, who built the engine also recommended not to connect it. The engine has EQ (iron) heads and a port matched LD4B on it. Generally, iron takes more time to heat up than aluminum.
>Totally makes sense with the fuel slosh in the carburetor, that's what I was figuring was happening. Just too much fuel was getting into the boals. I filled the car up with a full tank of gas prior to my autocross event.
>Yes, I measured my mpg. I like numbers. Lol. I'll check the dipstick today, but as far as I can tell, I do not have a fuel leak. I'm not noticing any puddling.
>The carb is what I have and that's what IMM spec'ed out for me. I'd like to keep it as I really don't want to put any more money than I should into this. The rev limiter is set to 6500 on this engine and it really drops off in power at about 6000 rpm.
>I am not a fan of electric fuel pumps either. They're not as reliable and annoyingly loud. For whatever reason, I can't remember, the shop that put my car together got rid of the mechanical pump for an electric one.
 
Set the fuel pressure regulator to 6 psi, re-set the floats to spec and then see what happens.

I bet the engine is too lean after start because the choke probably doesn't work correctly if there even is one.

Anything beyond that is tough to do remotely without some readings from something like a wideband.

When I had a holley it would take one quick pump and then immediately fire, but then again my choke worked. Sometimes you have to feather it slightly to keep it running if it's really cold but really anything without an exhaust crossover will be a little bit cold blooded.
 
click to expand
MuuMuu101 said:
Let me try to address everything so you guys have more information.
What are your cam specs? And how much vacuum at 1200 rpm?
>I'm assuming that 50-75% of the cold start issue could be due to operator error. Probably not nearly that high I've tried a variety of different methods and it's really hit or miss as to what worked. At first it was the 2 quick pumps, turn the key and let it go. Then it was hold at half throttle and let it off. Does this unit have a working choke?
>The car is running 34 degrees of total timing What is the idle-timing?and has an MSD Ready-to-Run distributor on it with the vacuum advance disconnected.IMO a bad plan We had problems with the vacuum advance as the engine doesn't provide enough vacuum and it was causing the engine to misfire and throw timing around like crazy.Fix the rotor phasing, then reconnect the can. Like I said the cold engine wants a ton of advance, and the only way to get it is with the Vcan. IMM, who built the engine also recommended not to connect it. The engine has EQ (iron) heads and a port matched LD4B on it. Generally, iron takes more time to heat up than aluminum.From dead-cold,I disagree
>Totally makes sense with the fuel slosh in the carburetor, that's what I was figuring was happening.I'm not saying it was slosh. Does she have the extended pick-ups in the bowl and baffles Just too much fuel was getting into the bowls. I filled the car up with a full tank of gas prior to my autocross event.Tank slosh doesn't count,unless the pick-up gets uncovered, which is hardly likely with a full tank.
>Yes, I measured my mpg. I like numbers. Lol.Me too I'll check the dipstick today, but as far as I can tell, I do not have a fuel leak. I'm not noticing any puddling.Look for seepage, especially at all interconnections.
>The carb is what I have and that's what IMM spec'ed out for me. I'd like to keep it as I really don't want to put any more money than I should into this. The rev limiter is set to 6500 on this engine and it really drops off in power at about 6000 rpm.the carb will work
>I am not a fan of electric fuel pumps either. They're not as reliable and annoyingly loud.I agree For whatever reason, I can't remember, the shop that put my car together got rid of the mechanical pump for an electric one.Does it have a return to tank system or is it deadheaded at the regulator?
Click to expand...
 
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>Cam specs: Unfortunately, IMM forgot to give me my cam spec sheet. It's a custom grind. It's either 238/242 or 242/246 at 0.050".
>When I go for my drive today, I'm going to take a look at the choke. The Holley and Jegs videos are saying if you have problem with cold start up, to dial it back one notch.
>Timing: I don't have a timing light on me to measure initial timing. Like I said, I took it to an engine/dyno shop to take a look at it when I had the misfiring issues with the shop that was building the car. I don't recall what he measured for initial timing. How do I fix rotor phasing?
>Fuel: How would I know if I have extended pick ups in the bowls? Do they vary per model or am I going to have to take the carb apart? I just mentioned a full tank to eliminate the pickup idea. I'll take a look at all of the lines before I go for a drive today. I'm pretty sure this is a returnless system, but will verify.
 
I think you are gonna need a friend,lol. Someone with tools, time and expertise.
Or you are gonna need some books. Or this is gonna be a long process.

Here are the tools you are gonna need; a timing light. Preferably one with a tachometer in it, and a dial-back feature. If you are running a CDI, you will need a special lite or more tools. CDI systems do not like DB lites and lose their place. This may be what happened to your tuner. If you get a standard lite, it may work with the CDI, but then you will need to calibrate your balancer. And you will still need a tach at or near the timing lite.
Also you will need a Vacuum gauge.
These are minimum requirements to procede.
One more time, a cold engine, especially one with a big cam,like yours, wants a ton of timing during the warm up period. This has nothing to do with starting, only to keep it running. The fuel mixture needs to be very rich, and the timing needs to be almost excessive. It is the job of the choke to control the cold/warm-up mixture. It is up to you or your tuner to give the engine the timing it is craving. I think 40* at 1200 to 1400 is not excessive during the first few minutes. This requires about 16 minimum idle-timing. 6 more in the centrifugal and hopefully 18 in the Vcan. This period only needs to last a minute or so, and then you can tap the fast-idle down, at which time the vacuum advance should also drop out. Then the engine will be running on the idle timing plus whatever the centrifugal is commanding; perhaps 2 to 4. If you don't have at least close to these amounts, nothing you do will help much.I think as a minimum 30* might work.
 
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Just got back from the garage. First thing I checked was the float levels. Turned the key twice at 2 second intervals each, unscrewed the front bowl site plug, shook the car a bit and fuel was gushing out. I backed the pressure regulator a little bit and reconducted the test. The fuel was barely trickling which should be good (or better). Kept the key ON and checked fuel pressure again and now I'm riding at about 6-6.5 psi. I am still practicing my start ups, but it seemed to start up a bit better.

This carb does not have an electric choke. Is it still considered a manual choke if you don't have the lever to open and close the throttle blades? Or is this considered choke-less? This is my carb when I took my air cleaner assembly off.

Sorry, working on engines and carbs (or cars in general) is still new to me. I have a friend who can help me, but it may take some time as he's busy at the moment.

Carb.jpg
 
Your choke is blocked open. The carb is a manual choke carb that uses a cable to operate it from the drivers seat. No wonder you are having issues. Holley may have a electric choke kit available. I don't know for sure. It's been 40 years .
 
fRONT OF THE AIR HORN iT SAYS "list" AND A 4 DIGIT NUMBER

List 4779?
 
Oh look!
It is possible to start the engine down to about freezing without a working choke. I have no choke. But the engine really does need the timing, which I have given mine. But it takes a certain amount of familiarity with the combo, and once running it takes quite a bit of babysitting, during the warm-up. Even at 50 or 60 degreesF, it takes a minute or two, with an aluminum intake, and no crossover. Carb-icing is a constant threat as temps get cooler towards freezing.
 
AJ/FormS said:
Oh look!
It is possible to start the engine down to about freezing without a working choke. I have no choke. But the engine really does need the timing, which I have given mine. But it takes a certain amount of familiarity with the combo, and once running it takes quite a bit of babysitting, during the warm-up. Even at 50 or 60 degreesF, it takes a minute or two, with an aluminum intake, and no crossover. Carb-icing is a constant threat as temps get cooler towards freezing.
Click to expand...

Well, in California, it rarely gets that cold and even if it does, odds are I won't be driving the Dart. Lol.
 
I just thought of something; I modded my carb to bring the vacuum advance in early. If you rev yours up to 1200 and find no signal at the sparkport, then the Vcan will not help you,during the warm-up. I find more than 1200 to be annoyingly fast, but see if you can get signal at 1400. Still no signal means the Vcan will not help the warm-up on your combo. Sorry, I forgot about that.
In this case, you only have the idle-timing and the centrifugal to work with, and you can only go so far with those, before it's too much.
Your cam is pretty big. This is a case where manifold vacuum could be made to work for you.
Here is what I would try; I would route full manifold vacuum to the Vcan. But I would route it through one of those Ford thermo-valves. The thermo-valve sits in the water jacket wherever is convenient. There are two vacuum sources sent to it;namely manifold vacuum, and ported vacuum. And it has one outlet to the Vcan. When the coolant is cold it sends full manifold vacuum to the can,and the engine receives whatever boost in timing that the can is able to give. When the engine is up to temp, the thermo-switch changes to ported vacuum, and the engine receives no additional timing at idle,at all. The switch point is not adjustable, but there are several set-points to choose from. I have used these from time to time. This system works well with engines that are able to generate a good vacuum at 1200 to 1400rpm, and with Vcans that can work with whatever signal the engine is generating. So some testing has to take place to find out if it will work for you.
It would work just fine on my 367 with a 230/237/110 cam,which generates plenty of manifold vacuum in the 1200 to 1400 zone.I was going to use this system on my chokeless 750 but I don't drive it at those low temps anymore, and I bought a dash-mounted dial-back,timing device instead. It has a range of 15*, and by setting it close to the center, before base-lining the timing, I can add 7 to 10 degrees from the driver's seat,during the warm-up. This has been sufficient with the way that the current timings are interfacing.
Again, more mumbo-jumbo,I know. But when it all works, that is the BIG pay-off. When you come out of the bar at two-am, stab the throttle two times hit the key, wait 30 seconds and drive it away; that makes my day! Oh wait, I quit drinking in 94, so maybe substitute some other venue,lol.
 
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