(INTAKE) Carburetor Troubleshooting- Acceleration Problems
11-02-03, 02:49 PM
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Nikki-Modder Rex-Rodder
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(INTAKE) Carburetor Troubleshooting- Acceleration Problems
This is my take on the usual acceleration problems that many Rx-7 owners will experience at some point while enjoying these fine cars.
The following is a list of the probable causes and fixes.
If I've left something out, please add to it.
Sterling
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ACCELERATION PROBLEMS
Acceleration response problems are attributed to just a handful of things. It could be a clogged exhaust system or an ignition issue, but that's not my forte.
Regarding carburetion, there are really only a few things it could be. Usually fuel starvation will only demonstrate an acceleration problem at very high RPMs, but the acceleration problem is very much overshadowed by the lack of high end power to begin with.
Flooding issues will cause poor acceleration because the engine is being overdosed with fuel even under the load of normal acceleration.
But the most obvious cause is that your accelerator pump is operating poorly or not at all.
Test the accelerator pump by visually inspecting the strength of the stream as you operate the primary linkage by hand. It should have a strong, even stream that's the same on both sides. If the shot dribbles, seems too little, or isn't there at all, the accelerator pump needs attention.
Simply remove the air fliter top and peek down into the carb. There is a nozzel with two jets drilled into it mounted right between the smaller bores. Operate the linkage by hand to observe the pump shot.
When testing the pump shot, keep in mind that the fuel for the shot is being drawn from the firewall side fuel bowl. Though the inlet hole behind the pump housing is down fairly low in the bowl, the float does displace a bit of volume of fuel. You will quickly run out of fuel if you continue to test the accelerator pump unless the bowl is replenished by turning on the ignition.
A poor accelerator pump shot is due to incorrect adjustment, one or both of the checkballs being stuck due to varnish accumulation, a dried out or torn diaphragm due to age or sitting dry for too long, or a clogged accelerator pump circuit or orifices.
These are listed in the order that they should be checked.
Adjust the accelerator pump by turning the nut on the threaded rod that protrudes through the hole in the accelerator pump lever. I set my accelerator pumps at the point where the vertical part of the lever that sits in the pivot slot in the accelerator pump housing is parallel with the edges of the slot. Increases should be made in clockwise turns, no more than 1/2 turn at a time when driving. However, visually, a significant shot should be observed at that setting. If it is not, then there is another problem.
If ensuring proper adjustment does not fix the problem, then the nozzle should be removed and inspected. Chances are it is clean and free from debris. Inspect the brass banjo bolt orifices. A steel guitar string is a great tool for cleaning these.
Chances are the checkball at the bottom is partially stuck or coated in varnish. You can see if it is stuck simply enough, but please READ THIS WARNING!:
--Most long sharp tweezers can grab the brass weight over the checkball. If you operate the linkage without the nozzle and banjo bolt in place, there is a GREAT chance that you will lose that checkball. It can shoot out with great force. It may even land in your carburetor!
BE CAREFUL!
Clean off the checkball and replace it.
If this does not cure the problem, then you are basically down to two other choices; both of which require opening the carb to some degree.
The next suspect is the accelerator pump diaphragm. The pump housing must come off, and the diaphragm needs to be inspected. There is a spring between the diaphragm and the carb body. If the gasket is anything other than supple with a good amount of mobility in and out, replace it. It is at this point that I suggest that the carburetor be rebuilt with all new gaskets for three reasons:
-It's a PITA to change the accelerator pump diaphragm when it's on the car.
-The diaphragm by itself costs as much as $16, and you can get an entire rebuild (which includes that gasket) for only 4-6 dollars more.
-Chances are if your accelerator pump diaphragm is shot, then the other gaskets and rubber needle tips are shot, too.
If you choose to replace only the diaphragm, and still your problem is not fixed, then there maybe sediment blocking the accelerator pump circuit. In order to find out, you'll have to remove the top of the carburetor (air horn) and look into the fuel bowls to see if there is an accumulation of red-brown sediment. At this point you will have to decide if you want to rebuild it.
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The following is a list of the probable causes and fixes.
If I've left something out, please add to it.
Sterling
----------------------------------------------------------------------------------------------------
ACCELERATION PROBLEMS
Acceleration response problems are attributed to just a handful of things. It could be a clogged exhaust system or an ignition issue, but that's not my forte.
Regarding carburetion, there are really only a few things it could be. Usually fuel starvation will only demonstrate an acceleration problem at very high RPMs, but the acceleration problem is very much overshadowed by the lack of high end power to begin with.
Flooding issues will cause poor acceleration because the engine is being overdosed with fuel even under the load of normal acceleration.
But the most obvious cause is that your accelerator pump is operating poorly or not at all.
Test the accelerator pump by visually inspecting the strength of the stream as you operate the primary linkage by hand. It should have a strong, even stream that's the same on both sides. If the shot dribbles, seems too little, or isn't there at all, the accelerator pump needs attention.
Simply remove the air fliter top and peek down into the carb. There is a nozzel with two jets drilled into it mounted right between the smaller bores. Operate the linkage by hand to observe the pump shot.
When testing the pump shot, keep in mind that the fuel for the shot is being drawn from the firewall side fuel bowl. Though the inlet hole behind the pump housing is down fairly low in the bowl, the float does displace a bit of volume of fuel. You will quickly run out of fuel if you continue to test the accelerator pump unless the bowl is replenished by turning on the ignition.
A poor accelerator pump shot is due to incorrect adjustment, one or both of the checkballs being stuck due to varnish accumulation, a dried out or torn diaphragm due to age or sitting dry for too long, or a clogged accelerator pump circuit or orifices.
These are listed in the order that they should be checked.
Adjust the accelerator pump by turning the nut on the threaded rod that protrudes through the hole in the accelerator pump lever. I set my accelerator pumps at the point where the vertical part of the lever that sits in the pivot slot in the accelerator pump housing is parallel with the edges of the slot. Increases should be made in clockwise turns, no more than 1/2 turn at a time when driving. However, visually, a significant shot should be observed at that setting. If it is not, then there is another problem.
If ensuring proper adjustment does not fix the problem, then the nozzle should be removed and inspected. Chances are it is clean and free from debris. Inspect the brass banjo bolt orifices. A steel guitar string is a great tool for cleaning these.
Chances are the checkball at the bottom is partially stuck or coated in varnish. You can see if it is stuck simply enough, but please READ THIS WARNING!:
--Most long sharp tweezers can grab the brass weight over the checkball. If you operate the linkage without the nozzle and banjo bolt in place, there is a GREAT chance that you will lose that checkball. It can shoot out with great force. It may even land in your carburetor!
BE CAREFUL!
Clean off the checkball and replace it.
If this does not cure the problem, then you are basically down to two other choices; both of which require opening the carb to some degree.
The next suspect is the accelerator pump diaphragm. The pump housing must come off, and the diaphragm needs to be inspected. There is a spring between the diaphragm and the carb body. If the gasket is anything other than supple with a good amount of mobility in and out, replace it. It is at this point that I suggest that the carburetor be rebuilt with all new gaskets for three reasons:
-It's a PITA to change the accelerator pump diaphragm when it's on the car.
-The diaphragm by itself costs as much as $16, and you can get an entire rebuild (which includes that gasket) for only 4-6 dollars more.
-Chances are if your accelerator pump diaphragm is shot, then the other gaskets and rubber needle tips are shot, too.
If you choose to replace only the diaphragm, and still your problem is not fixed, then there maybe sediment blocking the accelerator pump circuit. In order to find out, you'll have to remove the top of the carburetor (air horn) and look into the fuel bowls to see if there is an accumulation of red-brown sediment. At this point you will have to decide if you want to rebuild it.
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