Car stumbles on Hard Acceleration
03-03-2013, 12:36 PM
#1
Thread Starter
Join Date: Mar 2013
Location: California
Posts: 13
Car stumbles on Hard Acceleration
Hi, I'm new to the forums and i dont actually have a mustang. I have a Mercury Comet GT from 1974, but it's so hard to find classic forums and tech support so i figured i'd give it a shot here.
I recently replaced the distributor on my car (Has a 302) because the original distributor's vacuum advance would kill the car when plugged in. (I still don't understand the reason it did that) So i got a single diaphragm vacuum advance that uses the constant vacuum port on my Holley 600cfm Vacuum Secondaries Carb. Upon putting it in, i noticed that for reasons unknown the car will actually idle and accelerate smooth as silk now, but will not start well and does not take a hard acceleration well like it used to. It will bog down to the point of dying at about 60% throttle increase unless it is done slowly.
Also when i turn on the car the starter bogs down extremely bad as if the engine were advanced too far. The only problem is, if i retard the timing, the car refuses to start at all, and even still it bogs down the starter. I never used to have that issue before. I replaced the jets on the carburetor hoping that it would solve the accelerating issue but the issue still stands and if i move the distributor 1 tooth in any direction the car will refuse to start as well..
(I don''t believe to be 180 degrees out because i put the engine on TDC on the compression stroke when i put the distributor in and that's the only place it will run but i could be wrong)
Any ideas or suggestions? I'm extremely puzzled at this point. Is my carburetor's float too high? (It seems like gas is seeping out of the throttle plates and the top of the carburetor now)
I'm only a 17 year old DIY mechanic with the knowlege of my (late) dad. So any help is greatly appreciated.
Thanks!
I recently replaced the distributor on my car (Has a 302) because the original distributor's vacuum advance would kill the car when plugged in. (I still don't understand the reason it did that) So i got a single diaphragm vacuum advance that uses the constant vacuum port on my Holley 600cfm Vacuum Secondaries Carb. Upon putting it in, i noticed that for reasons unknown the car will actually idle and accelerate smooth as silk now, but will not start well and does not take a hard acceleration well like it used to. It will bog down to the point of dying at about 60% throttle increase unless it is done slowly.
Also when i turn on the car the starter bogs down extremely bad as if the engine were advanced too far. The only problem is, if i retard the timing, the car refuses to start at all, and even still it bogs down the starter. I never used to have that issue before. I replaced the jets on the carburetor hoping that it would solve the accelerating issue but the issue still stands and if i move the distributor 1 tooth in any direction the car will refuse to start as well..
(I don''t believe to be 180 degrees out because i put the engine on TDC on the compression stroke when i put the distributor in and that's the only place it will run but i could be wrong)
Any ideas or suggestions? I'm extremely puzzled at this point. Is my carburetor's float too high? (It seems like gas is seeping out of the throttle plates and the top of the carburetor now)
I'm only a 17 year old DIY mechanic with the knowlege of my (late) dad. So any help is greatly appreciated.
Thanks!
03-04-2013, 09:11 AM
#3
Thread Starter
Join Date: Mar 2013
Location: California
Posts: 13
Uhm, no. I'm not too sure how the battery is holding up. It looks old and crusty though, and perhaps it's a little small for the car, but it used to turn over perfectly. Do you think it may be a battery issue?
And It has electronic ignition. It's an A1 Cardone rebuilt distributer (I don't have the funds yet for Mallory ignition haha)
And It has electronic ignition. It's an A1 Cardone rebuilt distributer (I don't have the funds yet for Mallory ignition haha)
03-06-2013, 10:45 PM
#6
Thread Starter
Join Date: Mar 2013
Location: California
Posts: 13
Well okay then. Just put in a new battery and the car seems to crank over well now. It even started for me! 
But as of now the car still bogs down badly on a hard acceleration. I mean it really seems to stumble hard.If i accelerate slowly enough, it will gain speed, but it still seems very sluggish. If I give it too much gas as one time the car will bog down, and then suddenly with a burst of energy come to life. Could that maybe be a timing issue? Accelerator Pump? (I've already tried adjusting that) Float Level? (Not too good at getting it *just* right)
Any ideas?
But as of now the car still bogs down badly on a hard acceleration. I mean it really seems to stumble hard.If i accelerate slowly enough, it will gain speed, but it still seems very sluggish. If I give it too much gas as one time the car will bog down, and then suddenly with a burst of energy come to life. Could that maybe be a timing issue? Accelerator Pump? (I've already tried adjusting that) Float Level? (Not too good at getting it *just* right)
Any ideas?
03-06-2013, 11:26 PM
#7
Moderator
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
Next we must determine if incoming fuel supply is greater than fuel consumption.
Battery is first now this is second.
Without first verifying adequate fuel pressure + volume you're jerking off as fastback so eloquently put it.
If the car has a mechanical fuel pump remove the fuel line from the carb and place it in a 1 qt glass jar and crank the engine over but try not to start it have some one observe the fuel line in the jar. Fuel should rush out from the line into the jar almost directly with in 3 seconds there should be quite a bit of fuel in the jar maybe a 1/2 cup or more it should almost splash out of the jar.
If you get lots of fuel in the jar then cover the line with a thumb and crank the engine it should develop 6 psi fuel pressure you should be able to feel this and spray it like a garden hose into the jar.
If you dont have good pressure or volume replace any fuel filters try again then replace pump
The fuel in the jar should be 100% clean no serpents or floaters.
if everything checks out then rebuild the carb.
Battery is first now this is second.
Without first verifying adequate fuel pressure + volume you're jerking off as fastback so eloquently put it.
If the car has a mechanical fuel pump remove the fuel line from the carb and place it in a 1 qt glass jar and crank the engine over but try not to start it have some one observe the fuel line in the jar. Fuel should rush out from the line into the jar almost directly with in 3 seconds there should be quite a bit of fuel in the jar maybe a 1/2 cup or more it should almost splash out of the jar.
If you get lots of fuel in the jar then cover the line with a thumb and crank the engine it should develop 6 psi fuel pressure you should be able to feel this and spray it like a garden hose into the jar.
If you dont have good pressure or volume replace any fuel filters try again then replace pump
The fuel in the jar should be 100% clean no serpents or floaters.
if everything checks out then rebuild the carb.
03-06-2013, 11:47 PM
#8
Thread Starter
Join Date: Mar 2013
Location: California
Posts: 13
Okay. I will definitely test the fuel flow. I actually have decided to replace the carburetor with a Holley Street Avenger 750 CFM carburetor to test and see if the carburetor is the issue but the same problem persists. So between both of the carbs I'm sure I could simply buy a rebuild kit and get at least one of them working well. The fuel pump had already been replaced a few months prior so I will definitely test it as soon as possible to make sure that its working correctly.
Do you think there is any sign at all that perhaps some sort of timing could be the issue? Maybe a poorly rebuilt distributor/vacuum advance? Or do you primarily think its the fuel delivery?
If there's too much fuel what do I do? Lower the float level significantly and try again?
P.S.
The distributor advance diaphragm is running off of the constant vacuum port in the carburetor. This is the only way I could get the car to idle well. Is that wrong?
Do you think there is any sign at all that perhaps some sort of timing could be the issue? Maybe a poorly rebuilt distributor/vacuum advance? Or do you primarily think its the fuel delivery?
If there's too much fuel what do I do? Lower the float level significantly and try again?
P.S.
The distributor advance diaphragm is running off of the constant vacuum port in the carburetor. This is the only way I could get the car to idle well. Is that wrong?
03-07-2013, 06:40 AM
#9
Foghorn Leghorn
Join Date: Dec 2006
Location: I reside in a near constant state of amazment.
Posts: 2,923
Cool beans. Keep chopping the legs off the elephant and you'll have it dicked here before long.
750 is a lot of carburetor for a stock 302. Your 600 is plenty. Is the 750 new or did you take off your old 600 and putting an old 750 in its place to test? That's not really telling you much.
Go ahead and check your fuel flow like Gun said to scratch that off your list but it's sounding to me like your Holley needs some loving. If the car has been sitting with old gas in the bowls for a while then it will turn bad in no time.
Go drip around youtube and check out the Holley Troubleshooting videos put out by Holley. They have some really good poop and you will be able to more accurately interpret what is going on with your setup. Here's a good one for checking your accelerator pump
You seem pretty concerned with your timing so here is how I set mine:
Set your timing to the power curve of your car. The way you do that is to keep advancing your timing a little bit at a time until it just starts to pings under WOT (driving, not parked!) then back it off just far enough to where it doesn't ping. (Advance on a SBF is rotating your distributor clockwise).
750 is a lot of carburetor for a stock 302. Your 600 is plenty. Is the 750 new or did you take off your old 600 and putting an old 750 in its place to test? That's not really telling you much.
Go ahead and check your fuel flow like Gun said to scratch that off your list but it's sounding to me like your Holley needs some loving. If the car has been sitting with old gas in the bowls for a while then it will turn bad in no time.
Go drip around youtube and check out the Holley Troubleshooting videos put out by Holley. They have some really good poop and you will be able to more accurately interpret what is going on with your setup. Here's a good one for checking your accelerator pump
You seem pretty concerned with your timing so here is how I set mine:
Set your timing to the power curve of your car. The way you do that is to keep advancing your timing a little bit at a time until it just starts to pings under WOT (driving, not parked!) then back it off just far enough to where it doesn't ping. (Advance on a SBF is rotating your distributor clockwise).