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Discussion Starter · #1 ·
First of all I want to apologize for my ignorance. I always wanted to have a carb motor but I have limited knowlae about them

so I bought this 1987 Chevy with a recently rebuild motor and manual tranny. It was working fine until it didn’t after a few hundred miles

it works perfectly fine until it reaches 2000rpm. It came with a new elderbrook AVS2. Also a MDS dist with centrifugal vacuum so the only vacuum that it has is for my ac controls. No direct advance or pvc valve

I have changed wires and spark plugs I have a new fuel pump at 6 psi. I didn’t buy the carb do I don’t have the different Needle springs that come when you buy a new carb so have not change the spring

many help will be really appreciated
 

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There are many factors that can cause running issues. Do you know all the specs of your motor such as cam size and cylinder heads and compression ratio etc. Also your carb is it cruddy looking and perhaps of needing rebuilt? Also on your Edelbrock 6 psi is a little high on the fuel pressure side as in most cases from what I have read the Edelbrock carbs like only no more then about 5 psi and its always good to run a fuel pressure regulator with it and also they are really bad for heat soak and the fuel boiling in the carb and after shutoff it will boil over the side of the carb to inside the intake.

Also you want to make sure your timing is set up correctly as that can effect a lot of things. If you have a flat tappet cam if you have a lobe going down it can cause a lot of issues as well or if you have valvetrain adjustment problems as well. Many things can cause issues and you need to do a checklist of the minor things first then go from there. Here a few videos you might want to look over.




 

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As the old saying goes “most carburetor problems are electrical”. Meaning that usually problems thought to be carburetor or fuel supply turn out to be ignition or electricity supply.

I’m presuming the MSD distributor is the HEI type, the most common failure with MSD is their module. Suddenly it won’t start, or runs like crap, or is RPM limited are common indicators that the module is crapping out. Another chronic if using vacuum advance is either hose or diaphragm failure that allows a vacuum leak, however, this usually is not so large as to affect an RPM limitation.

For Edelbrock carburetor issues running rich, hard to start, and RPM problems relate to the choke stuck or otherwise not opening or floats filling with fuel and sinking. These are conditions that also lead to fouled spark plugs and you will find that these peanut plugs once fuel fouled must be replaced. Back at the carb once the engine is cold started check for the choke opening. The choke on these are either mechanically controlled by the driver in which case you need to see that moving the handle in the cockpit also moves the choke blade. If electric then does it have voltage on the heater coil and or does the coil actually get hot. Then if it does will it move the linkage. Probably the biggest PIA with carburetors is the external choke linkage which gets dirty, corroded and lube dried in service often leading to issues with either getting the choke blade open or closed and getting the fast idle cam stuck somewhere in its motion. The other big pain of the Edelbrock is the brass floats inside, they are often cracked by careless level setting mechanics that don’t follow the instructions and that leads to stressing the float when the tang is set using improper tools and procedure. This leads to cracking the float’s hull allowing fuel inside then they get heavy and sink allowing too much fuel into the bowls. I highly recommend getting the Edelbrock instruction sheets, they are on line and come in the rebuild kit. Don’t expect to read them once and be an expert, they are more complicated than they seem. If you live in a town with a parts store you will find that most parts stores can access Edelbrock parts within a day, if not in stock.

Service problems with non computerized ignitions and carburetors rather than EFI are usually pretty simple to diagnose and repair with some thought of how they operate and hand tools to execute repairs. There is no mysterious programming inside a box, very little wiring and the operating device is also the sensor.

Its useful to lay out a plan, to minimize doing too many things at once, to not jump to the complex solution up front, Holley guys are great at ascribing every Holley problem to air correction jets or power valve jets accelerating pump stroke and or jets. Before they know it the carb is so far off there is no logical return path left. So start simple with the Edelbrock suffering a sudden problem it probably isn't metering rods and their control springs. Although the metering rods are easily damaged by clunky diss and re-assembly techniques. An example is don’t take off the top cover then try to replace it with the metering rods in it, the chances of missing the rods into their jets and thusly damaging if not destroying the rods is off the high side of the scale of likelyhood.

Bogie
 

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As the old saying goes “most carburetor problems are electrical”. Meaning that usually problems thought to be carburetor or fuel supply turn out to be ignition or electricity supply.
That is a 5-star quote!!!! Makes me long for an old Sun Scope! Now there's a useful piece of equipment no one has anymore (if you know how to read them).
 

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Discussion Starter · #7 ·
Flat tappet or roller lifter can ?
So you think it’s a interior issue instead of gas or something like that?
As the old saying goes “most carburetor problems are electrical”. Meaning that usually problems thought to be carburetor or fuel supply turn out to be ignition or electricity supply.

I’m presuming the MSD distributor is the HEI type, the most common failure with MSD is their module. Suddenly it won’t start, or runs like crap, or is RPM limited are common indicators that the module is crapping out. Another chronic if using vacuum advance is either hose or diaphragm failure that allows a vacuum leak, however, this usually is not so large as to affect an RPM limitation.

For Edelbrock carburetor issues running rich, hard to start, and RPM problems relate to the choke stuck or otherwise not opening or floats filling with fuel and sinking. These are conditions that also lead to fouled spark plugs and you will find that these peanut plugs once fuel fouled must be replaced. Back at the carb once the engine is cold started check for the choke opening. The choke on these are either mechanically controlled by the driver in which case you need to see that moving the handle in the cockpit also moves the choke blade. If electric then does it have voltage on the heater coil and or does the coil actually get hot. Then if it does will it move the linkage. Probably the biggest PIA with carburetors is the external choke linkage which gets dirty, corroded and lube dried in service often leading to issues with either getting the choke blade open or closed and getting the fast idle cam stuck somewhere in its motion. The other big pain of the Edelbrock is the brass floats inside, they are often cracked by careless level setting mechanics that don’t follow the instructions and that leads to stressing the float when the tang is set using improper tools and procedure. This leads to cracking the float’s hull allowing fuel inside then they get heavy and sink allowing too much fuel into the bowls. I highly recommend getting the Edelbrock instruction sheets, they are on line and come in the rebuild kit. Don’t expect to read them once and be an expert, they are more complicated than they seem. If you live in a town with a parts store you will find that most parts stores can access Edelbrock parts within a day, if not in stock.

Service problems with non computerized ignitions and carburetors rather than EFI are usually pretty simple to diagnose and repair with some thought of how they operate and hand tools to execute repairs. There is no mysterious programming inside a box, very little wiring and the operating device is also the sensor.

Its useful to lay out a plan, to minimize doing too many things at once, to not jump to the complex solution up front, Holley guys are great at ascribing every Holley problem to air correction jets or power valve jets accelerating pump stroke and or jets. Before they know it the carb is so far off there is no logical return path left. So start simple with the Edelbrock suffering a sudden problem it probably isn't metering rods and their control springs. Although the metering rods are easily damaged by clunky diss and re-assembly techniques. An example is don’t take off the top cover then try to replace it with the metering rods in it, the chances of missing the rods into their jets and thusly damaging if not destroying the rods is off the high side of the scale of likelyhood.

Bogie
I also want to think that is an electronic issue because everything start happening right after I changed the tach/power plug for a new one. the electronic module is practivally new because I change it when I was not getting spark around 2 months ago. Now this truck I use it twice a month that’s why I say that is practically new
 

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You did not mention the tach/ plug in your initial description , complete , accurate information really helps
 

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So you think it’s a interior issue instead of gas or something like that?

I also want to think that is an electronic issue because everything start happening right after I changed the tach/power plug for a new one. the electronic module is practivally new because I change it when I was not getting spark around 2 months ago. Now this truck I use it twice a month that’s why I say that is practically new
And that statement now opens the door for it to be a issue with the recent module change.....there are a lot of cheap modules out there, and only a couple of good ones.

Your issue strikes me as a match for a common complaint for cheap modules...they work for a while than go wonky all the sudden like a built in rev-limiter, but it is actual a partial failure.
 

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One thing you want to be careful of is when you install a new control module you have to use the correct heat sink compound underneath it to help keep the module cool and from getting to hot and burn out. A lot of the modules does not come with anything and a lot of people put dielectric grease underneath it or lithium grease or forget to put anything and they will burn out in short order. I have had cheap modules last me for years and give no problems with the proper heat sink compound that will help keep them from burning up but I have also good quality modules just go bad in short order even with heat sink compound.

There are other things that can cause problems as well and I last year had a distributor that was not very old at all and had less then ten thousand miles on it and it started to give me a lot of issues and could not figure it out what was wronga and checked so many things it stumped and the only thing left was the magnetic pickup and lo and behold it was bad and I replaced the distributor and all was good again. Go figure as its rare for one of those to go bad but that is one of several things to check in your distributor along with other things.

Getting your module checked at the auto store might not be possible at least in my area, every single store no longer carries the tester to test them with and let you know if they are good or not since cars has not had any type of distributor for the most part in over twenty years. A good control module can be had by BWD from advance auto parts or a good quality one from Proform off of ebay. I get some good deals on the BWD ones for less then twenty bucks off of ebay and they are made in the USA the last I have seen or maybe Taiwan but not made in China and are not cheap quality for a decent module. That is if your using a large cap HEI MSD distributor. If your using a smaller one then I can't tell you what brand would have a good module since they are not in the smaller distributors and I don't know what all options are available for them.
 

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Haha, I squeezed by with using anti seize for thermal grease, haven’t run it long yet so that jury is still out. But since the OP has been playing with the wiring and between getting what goes where potentially messed up and at the risk of feeding the module power when the engine is not running, certainly puts the chase on finding if the operating smoke leaked out of the module. which is why I had to replace the module in my PCE 7000.

Bogie
 
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