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Sputtering, Stalling, and Backfiring

1052 Views 7 Replies 2 Participants Last post by  Print Dad

I have been having problems with my ’70 vert. It started one day when I had a hard time getting it started after it had been running a while. When I finally got it started, I put it in gear and went to accelerate and it sputtered before stalling. This went on for a while.

Thinking that the 2bbl carb was part of the problem, I took this opportunity to replace it with a new intake and 4bbl carb. I had a buddy of mine do all the work. We also replaced the ignition with a Flame Thrower II coil and the Ignitor II. After all that work the car is still doing the same thing. We checked all the electrical volt readings and connections and adjusted the timing and nothing works.

We are now going to replace the fuel pump in the hopes that this works. Does anyone have any idea of what could be causing this problem?
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Hello BigSecz,
My first thought was the fuel pump but what I would do is
Carefully, disconnect the fuel line from the pump and put it into a clear tonic bottle. Pull the coil wire and crqnk the motor.

The pump should push a fair amount of fuel in about 20 secs.

This is not the best way to check fuel pump but unless you have pressure gauges it is a start. You can tell if the fuel pump is just spiting and this is an indication of a bad pump.

I think you will find this to be the trouble but always try to isolate the problem so you don't just replace things. It get expensive.

Good Luck.........Print Dad
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Thanks. I'm hoping this is the problem. We did install a clear glass fuel filter in line before the carb. We noticed that there wasn't as much fuel being held in the filter as there should be. We also noticed that there was some debris in the line that was being filtered out. So our next plan of attack while we replace the pump is to install another filter in line between the tank and the pump just incase any debris from the tank is being pushed to the pump.

I was just wondering if there were any other possilbe causes for this. The odd thing is that when it's in park and you press the accelerator it sounds ok. As so as you put it in gear and got to take off is when there are problems.
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Hello BigSecz,
What type of carb did you use? If it is a Holley have you checked the bowl height? There are sight screw on the pass side. With the car off, remove the brass screw on the side of the bowl. The fuel should be at the bottom of the hole. Give the cara bit of a shake and the gas should trickle out.

Now for the particles in the filter. First, a filter before the pump is a good idea. You could also pull the line from where it feeds from the gas tank and disconnect it before the fuel pump. Blow compressed air from the tank end towards the fuel pump. Don't use much pressure. I know this requires a compressor but it sounds like trouble in the lines or tank.
Also you could replace the rubber (neoprene) line that attaches near the front driver tire. Sometimes the hoses collapse or break down inside.

If you keep seeing debris, it may be time to look at the tank. I just replace mine on my 70 Mach but that was because the tank had sat for 20 years. But if you do notice too much debris, after blowing out the lines I I would just replace and not have it dipped. The cost for a new one with a drain is about they charge for a clean out.

Don't go for the tank yet....try the easy little things first.

post back.........Print Dad
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Thanks for the advice. I spoke to my buddy this morning and he said the new fuel pump did the trick. He tweaked the timing a little and he said it's running great. That's the good news. Bad news, like with so many projects like this you find even more problems somewhere else. Looks like my next project is going to be a new oil pan and a trip to a trans shop for service.
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Well I'm now having a problem getting her to run cool. It starts great cold but then after driving it for about 30 minutes in noticed the temp was creeping above the half way mark. Then after stopping at a stop light it continued to creep. I shut it off for about 15 minutes went back and she wouldn't start at all. I noticed then the temp was maxed. I waited a little while and she started to cool a little and then I was able to get her started. We replaced the thermostat when we installed the new intake so I'm sure that isn't the problem. My buddy told me the radiator is small for that car so that may be one of the problems. Another problem was he was unable to hook up the vacuum advance due to an issue with the plate in the distributor.
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Hello Big Secz,
Good to hear part of the trouble is fixed. As far as the trani - - what's up?
Check the area around the modulator and see if you see any fluid. If you do...replace the modulator.
Look on these forums for tranni help. Guys like PaulS seem to work on them for a living. A bad modulator will cause a bunch of headaches I would check this out before replacing radiator.........Print Dad
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Hello, Check out this link where PaulS speaks about lower radiator hose.
Try the simple easy stuff first before changing radiator.....Print Dad
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