Engine Carbed Mustang Acting Up

rdoc86GT

New Member
Jun 14, 2019
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Hello all,

Backstory, I was cruising along and the car backfired, rpms dropped to 0 then back up to 2k, back to zero, back up and then finally died on me. Car started right back up after a minute but did the same thing 4 or 5 times on the way home. Now for the past two weeks, I have been able to start the car with no backfires, but it will die after a minute like I turned the key off.

Today I had the same results (run for a min and die), but I got it to run for a good ten minutes and I turned it off myself, problem is it is idling too high (900 to 1000rpm). I try to adjust the idle screw, it will die. Adjust the mixer screws to more of a lean mix, it will die. It only wants to run at 1000rpm and rich. I think my brand new carb is giving me a fuss, but not a 100%. Don't have a extra carb to test out my theory. Hoping someone out there more versed in carbs could give me their thoughts.

video of it acting up. 45second to 49 second mark is where it dies, but the whole video shows it will run and rev to 3k rpms with no issues. View: https://www.youtube.com/watch?v=Bb1CTmKXHCE&feature=youtu.be
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Can't see the video. Anyway need to know what year it is and if it is a efi to carb swap, did you do the swap and how it was done.
 

rdoc86GT

New Member
Jun 14, 2019
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Macomb
Can't see the video. Anyway need to know what year it is and if it is a efi to carb swap, did you do the swap and how it was done.

Hello karthief,

Thank you for looking at my post. I made the YT video public, sorry about that. could you please let me know if you can see it now? it is a 1986 GT and I got it as a roller. the people I bought it from had a carbed 351 in it. I already had a carbed motor so I just dropped it in. I am not using any of the factory wiring because I am using MSD all around, distributur, box, and coil. I failed to mention in my original post, it is timed at 10 degrees. If there is anything else you are looking for please let me know.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
17,928
5,842
193
polk county florida
Watched the video, when it shuts down look into the top of the carb and pump the accelerator a couple times if it squirts fuel then it would likely be ignition.
 

rdoc86GT

New Member
Jun 14, 2019
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Macomb
Watched the video, when it shuts down look into the top of the carb and pump the accelerator a couple times if it squirts fuel then it would likely be ignition.

Thanks karthief! Awhile back, I replaced the ignition switch, maybe something came loose. I was trying to eliminate the carb first since it seemed to me to be causing the issue. I will let you know the results! Thanks again.
 

jrichker

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@rdoc86GT

@rdoc86GT

Backfiring on Carburetor equipped cars
Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen.

Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches. See the chart below for additional help.

Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
It is time to beg, borrow or buy a vacuum gauge to troubleshoot the problem. Most auto parts stores will rent or load one if you have a credit card.
Vacuum Gauge readings


B.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring.
Look for low pressure or fluctuating pressure. Standard pressure is 4-6 PSI at idle for a carburetor equipped car.

C.) Wrong firing order
The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8


Vacuum leak due to slipped lower intake manifold gasket...

Ask Nicoleb3x3 about the intake gasket that slipped out of place and caused idle and vacuum leak problems that could not be seen or found by external examination. I don't care what you spray with, you won't find the leak when it is sucking air from the lifter valley. It simply isn't possible to spray anything in there with the lower manifold bolted in place.


End of Finding vacuum leaks

EFI to CARB swap warnings
1. Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. If the add on pressure regulator fails, you will flood the engine with gas and wash all the oil off the cylinder walls. That will cost you big time $$$. Either go full EFI or use a tank/fuel pump/fuel lines out of an 85 or earlier Stang. The in tank electric fuel pump from an 85 5.0 Stang can be used since it is only 10 PSI and not 40PSI+ output pressure that an EFI pump delivers.. Fabricating your own setup is possible but there are some snags to overcome.

2. Do not attempt to leave the EFI computer in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.

3. If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.

4. You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. The external pump will have to be mounted below the bottom of the tank to get the siphon effect needed to keep the pump fed sufficiently. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump. Do not try to wire the fuel pump without the relay. The 15-20 amps the pump pulls will overload the circuit. This will take power away from other items on the same circuit or cause the fuse or fuse link to blow.

5.
fuel-pump-relay-for-carbd-cars-gif.gif


6. You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.

7. For some help fabricating your own stainless steel hose assemblies, see
8. http://www.turbinefun.com/Stainless_Braided_Hose_Assembly.asp

9. For stainless steel braided hose and fittings for automotive use:

10. See http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1
11. http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1

12. http://www.jegs.com/webapp/wcs/stor...hall&searchTerm=stainless+steel+hose&x=18&y=4

13. See http://www.eaton.com/Eaton/Product...rformanceProducts/FittingsProducts/index.htm for more information on High performance automotive hose products

14. AN fittings require a 37 degree flaring tool. A standard automotive or household plumbing tool is 45 degrees and cannot be used with AN flare fittings. If you do, the flare is subjected to too much stress when the fitting is tightened, and is likely to fail or leak.

15. See http://www.mscdirect.com/ , http://www.mcmaster.com/ or for the flaring tool you will need . Prices start at $85 and go up

16. http://www1.mscdirect.com/CGI/N2DRVSH?PACACHE=000000013509163
17.
7478363-11.jpg


18. http://www.mcmaster.com/#flaring-tools/=b4fxc3
19.


20. Last time I was in Summit racing, they had a 37 degree flaring tool for less than $40. It may or may not be a catalog item.

21. While you are at the electrical part, you'll need a Duraspark or similar ignition system. The 85 Mustang GT 5 speed has a suitable Duraspark distributor with a steel gear compatible with the roller camshaft. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Duraspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information. Cost is about $400, which makes the 85 Mustang reman units look really appealing.


Duraspark II ignition diagram:

Diagram courtesy of /www.billwrigley.com

See http://webpages.charter.net/1bad6t/duraspark.html for more help.
Note the ballast resistor shown in the diagram: you’ll need that too
If you use a coil from a 78 or later Mustang, you don't need the ballast resistor. The stock 89 Ford/Mustang ignition coil does not need a ballast resistor


A simpler HEI ignition that uses the same distributor and fewer parts can be found here. This is an excellent resource, and I suggest that you add it to your Internet Favorites
 

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