Need help with Rotary Shack Weber
05-03-17, 09:49 PM
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Need help with Rotary Shack Weber
Hey guys, so I have a freshly rebuilt 12A on my 80 and was wondering if anything can be done about starting issue. The system is a Rotary Shack Weber 48 without choke. I have a Mallory pumps with Mallory regulator. Some issues I have:
1. The fuel pressure is not consistent. Sometimes runs 2.5 psi, sometimes goes to 4, etc... I keep adjusting it but fluctuates.
2. The engine is really hard to start, I have to pump the gas 10-20 times and sometimes takes many times to start. Once it starts I have to keep it at 3000 RPM+ until it really warms up.
I gave Rob at RS the specs, it's a 12A half brigde and he put the internals in the carb. Not sure what's in it.
I have not tested compression but the engine was rebuilt with new parts. It was my first engine so I am not saying it was done perfectly but it was done. The car runs hard if launched at 3k rpm but it is a hog from 1200-3000 RPM. It will die if the gas pedal is slammed.
Any help would be appreciated.
Thanks
1. The fuel pressure is not consistent. Sometimes runs 2.5 psi, sometimes goes to 4, etc... I keep adjusting it but fluctuates.
2. The engine is really hard to start, I have to pump the gas 10-20 times and sometimes takes many times to start. Once it starts I have to keep it at 3000 RPM+ until it really warms up.
I gave Rob at RS the specs, it's a 12A half brigde and he put the internals in the carb. Not sure what's in it.
I have not tested compression but the engine was rebuilt with new parts. It was my first engine so I am not saying it was done perfectly but it was done. The car runs hard if launched at 3k rpm but it is a hog from 1200-3000 RPM. It will die if the gas pedal is slammed.
Any help would be appreciated.
Thanks
05-04-17, 06:37 AM
#2
carb whisperer
Hey guys, so I have a freshly rebuilt 12A on my 80 and was wondering if anything can be done about starting issue. The system is a Rotary Shack Weber 48 without choke. I have a Mallory pumps with Mallory regulator. Some issues I have:
1. The fuel pressure is not consistent. Sometimes runs 2.5 psi, sometimes goes to 4, etc... I keep adjusting it but fluctuates.
2. The engine is really hard to start, I have to pump the gas 10-20 times and sometimes takes many times to start. Once it starts I have to keep it at 3000 RPM+ until it really warms up.
I gave Rob at RS the specs, it's a 12A half brigde and he put the internals in the carb. Not sure what's in it.
I have not tested compression but the engine was rebuilt with new parts. It was my first engine so I am not saying it was done perfectly but it was done. The car runs hard if launched at 3k rpm but it is a hog from 1200-3000 RPM. It will die if the gas pedal is slammed.
Any help would be appreciated.
Thanks
1. The fuel pressure is not consistent. Sometimes runs 2.5 psi, sometimes goes to 4, etc... I keep adjusting it but fluctuates.
2. The engine is really hard to start, I have to pump the gas 10-20 times and sometimes takes many times to start. Once it starts I have to keep it at 3000 RPM+ until it really warms up.
I gave Rob at RS the specs, it's a 12A half brigde and he put the internals in the carb. Not sure what's in it.
I have not tested compression but the engine was rebuilt with new parts. It was my first engine so I am not saying it was done perfectly but it was done. The car runs hard if launched at 3k rpm but it is a hog from 1200-3000 RPM. It will die if the gas pedal is slammed.
Any help would be appreciated.
Thanks
fuel pressure problem is most likely too large of a fuel pump, and no return line (or too small of a return)
Carb running issues are probably just the quality of "tune" you got from your vendor, and congrats on actually getting a product from there that you paid for!
now, start with the basics.
First, warm the engine to running temp. This can take 3-5 minutes AFTER it starts to idle on its own.
When it starts to idle, does it respond to idle adjustments? Can you tune a full range of varying idle speed or lean it out, richen it, etc.
Verify vacuum at idle. Use a gauge. Report back with this.
use carb cleaner and spray around your intake manifold to engine flange and listen for rises in RPM. repeat same process with the carb to intake flange.
verify choke size in carb. Sounds like it might be too big.
try to get an idea of the rest of the layout (jeys, etubes, air bleeds)
report back to me!
05-04-17, 07:36 AM
#3
Waffles - hmmm good
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Anything put in there by the vendor for tuning the carb is just a guess. You will need to get a good book
on tuning webers and some jets and then work your way through the carbs stages to tune it.
The best book I have use is How to Build and Tune Weber and Dellorto carbs,
you can find a copy here Foxed.ca - Mazda RX-7 Manuals
on tuning webers and some jets and then work your way through the carbs stages to tune it.
The best book I have use is How to Build and Tune Weber and Dellorto carbs,
you can find a copy here Foxed.ca - Mazda RX-7 Manuals
05-04-17, 12:35 PM
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Thanks guys. Didn't realize RS was not a good place to shop. I talked to Rob and he seemed pretty knowledgeable. Had a few lengthy discussions after I bought the system and after a while he quit answering the phone and would not answer FB or Snapchat messages. It seems like he is always posting pictures of food on those sites.
Anyway, the fuel system has the Racing Beat recommended Mallory pump and regulator. Is that adequate? I did find that the return line was a bit kinked but not sure if that was enough to cause the varying PSI. I have ran a bigger return hose but once you get to the tank the fitting is a bit smaller than the hose. I assumed that was fine. The pump has the spacer and not the spring installed.
Once the car warms up, it has kind of a mind of its own. Sometimes it idles fine, sometimes it eventually dies. The idle speed will adjust on the single screw adjustment on the side of the carb. Now, if I try to adjust the individual adjustments for each side of the carb, I don't see any major changes.
I will take stuff apart and see what it has inside.
Thanks again
Anyway, the fuel system has the Racing Beat recommended Mallory pump and regulator. Is that adequate? I did find that the return line was a bit kinked but not sure if that was enough to cause the varying PSI. I have ran a bigger return hose but once you get to the tank the fitting is a bit smaller than the hose. I assumed that was fine. The pump has the spacer and not the spring installed.
Once the car warms up, it has kind of a mind of its own. Sometimes it idles fine, sometimes it eventually dies. The idle speed will adjust on the single screw adjustment on the side of the carb. Now, if I try to adjust the individual adjustments for each side of the carb, I don't see any major changes.
I will take stuff apart and see what it has inside.
Thanks again
05-04-17, 07:21 PM
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anything anyone says about what should be the carb is a guess, some are more educated than others. especially on a bridge, as a bridge can vary quite a bit.
for starters i would get the fuel pressure thing sorted, although it shouldn't really affect starting. it could be a bunch of things, so i'd remove the regulator, and see if that changes, and then just deadhead the pump, etc. chances are you will find a simple thing or two thats causing it, maybe even the gauge.
for the carb, we need to know ifs its a downdraft IDA or a DCOE or something else.
tuning the carb is a process. if you have a wide band oxygen sensor, it will speed the process up a bit, but its not required.
you start from the basic carb setup, and then work on the idle, and then wide open and then the transition.
for the basics, you need to set the throttle stop screw, mistakenly called the idle speed screw. if you're looking at the carb from the bottom, it should just uncover the idle hole, and not the transition hole(s). this is approximately 1/2 in from when the screw hits the throttle lever. you can then give it another 1/2 turn to adjust idle speed. if you give it another turn, the idle speed will go up, but it will uncover the transition hole, which is ok, but we have to tune around it. the transition hole is there to help it go from the idle jet to the main jet.
idle mixture screws should be lightly bottomed out (by hand is fine), and then backed out between 1/2 turn and a full turn.
if your idle jet is right, it should run ok, although probably idle low. if it does not run ok, you need an idle jet. on the P ports we've been running about a 65 jet, but yours could be +/-10. since its a bridge you will just have to run it, and see which one it likes the best, take notes
once you get that all straight, it should start ok, idle ok and be ok up to like 25% throttle or about 2500rpm, where the main circuit takes over.
for starters i would get the fuel pressure thing sorted, although it shouldn't really affect starting. it could be a bunch of things, so i'd remove the regulator, and see if that changes, and then just deadhead the pump, etc. chances are you will find a simple thing or two thats causing it, maybe even the gauge.
for the carb, we need to know ifs its a downdraft IDA or a DCOE or something else.
tuning the carb is a process. if you have a wide band oxygen sensor, it will speed the process up a bit, but its not required.
you start from the basic carb setup, and then work on the idle, and then wide open and then the transition.
for the basics, you need to set the throttle stop screw, mistakenly called the idle speed screw. if you're looking at the carb from the bottom, it should just uncover the idle hole, and not the transition hole(s). this is approximately 1/2 in from when the screw hits the throttle lever. you can then give it another 1/2 turn to adjust idle speed. if you give it another turn, the idle speed will go up, but it will uncover the transition hole, which is ok, but we have to tune around it. the transition hole is there to help it go from the idle jet to the main jet.
idle mixture screws should be lightly bottomed out (by hand is fine), and then backed out between 1/2 turn and a full turn.
if your idle jet is right, it should run ok, although probably idle low. if it does not run ok, you need an idle jet. on the P ports we've been running about a 65 jet, but yours could be +/-10. since its a bridge you will just have to run it, and see which one it likes the best, take notes
once you get that all straight, it should start ok, idle ok and be ok up to like 25% throttle or about 2500rpm, where the main circuit takes over.
05-04-17, 08:32 PM
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anything anyone says about what should be the carb is a guess, some are more educated than others. especially on a bridge, as a bridge can vary quite a bit.
for starters i would get the fuel pressure thing sorted, although it shouldn't really affect starting. it could be a bunch of things, so i'd remove the regulator, and see if that changes, and then just deadhead the pump, etc. chances are you will find a simple thing or two thats causing it, maybe even the gauge.
for the carb, we need to know ifs its a downdraft IDA or a DCOE or something else.
tuning the carb is a process. if you have a wide band oxygen sensor, it will speed the process up a bit, but its not required.
you start from the basic carb setup, and then work on the idle, and then wide open and then the transition.
for the basics, you need to set the throttle stop screw, mistakenly called the idle speed screw. if you're looking at the carb from the bottom, it should just uncover the idle hole, and not the transition hole(s). this is approximately 1/2 in from when the screw hits the throttle lever. you can then give it another 1/2 turn to adjust idle speed. if you give it another turn, the idle speed will go up, but it will uncover the transition hole, which is ok, but we have to tune around it. the transition hole is there to help it go from the idle jet to the main jet.
idle mixture screws should be lightly bottomed out (by hand is fine), and then backed out between 1/2 turn and a full turn.
if your idle jet is right, it should run ok, although probably idle low. if it does not run ok, you need an idle jet. on the P ports we've been running about a 65 jet, but yours could be +/-10. since its a bridge you will just have to run it, and see which one it likes the best, take notes
once you get that all straight, it should start ok, idle ok and be ok up to like 25% throttle or about 2500rpm, where the main circuit takes over.
for starters i would get the fuel pressure thing sorted, although it shouldn't really affect starting. it could be a bunch of things, so i'd remove the regulator, and see if that changes, and then just deadhead the pump, etc. chances are you will find a simple thing or two thats causing it, maybe even the gauge.
for the carb, we need to know ifs its a downdraft IDA or a DCOE or something else.
tuning the carb is a process. if you have a wide band oxygen sensor, it will speed the process up a bit, but its not required.
you start from the basic carb setup, and then work on the idle, and then wide open and then the transition.
for the basics, you need to set the throttle stop screw, mistakenly called the idle speed screw. if you're looking at the carb from the bottom, it should just uncover the idle hole, and not the transition hole(s). this is approximately 1/2 in from when the screw hits the throttle lever. you can then give it another 1/2 turn to adjust idle speed. if you give it another turn, the idle speed will go up, but it will uncover the transition hole, which is ok, but we have to tune around it. the transition hole is there to help it go from the idle jet to the main jet.
idle mixture screws should be lightly bottomed out (by hand is fine), and then backed out between 1/2 turn and a full turn.
if your idle jet is right, it should run ok, although probably idle low. if it does not run ok, you need an idle jet. on the P ports we've been running about a 65 jet, but yours could be +/-10. since its a bridge you will just have to run it, and see which one it likes the best, take notes
once you get that all straight, it should start ok, idle ok and be ok up to like 25% throttle or about 2500rpm, where the main circuit takes over.
Carb is a side draft 48 no choke
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05-07-17, 09:38 PM
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Timing was set to the pulley marks. I did run it today and took some work to start but once held at 3k rpm it ran well. A bit of backfiring here and there though. I have yet to take things apart and look at jets and all that.
The car really bogs down and sometimes dies when floored from idle.
Also, if I get a wideband O2 sensor, can I set it in the muffler tail pipe or do I have to set it closer to the engine? I am currently not equipped with a bung and my headers are coated so I don't want to weld anything on them.
Last edited by 350xfire; 05-07-17 at 09:50 PM.
05-07-17, 10:15 PM
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Update:
I removed a trumpet and looked into the chokes and they are 42mm. Trumpets are 52mm at top and 48 at the bottom.
I removed the top cover and removed the idle jets and main jets.
Idle jets say 55F8
Emulsion tube is holding a part labeled F7 and a main jet labeled 175.
I removed a trumpet and looked into the chokes and they are 42mm. Trumpets are 52mm at top and 48 at the bottom.
I removed the top cover and removed the idle jets and main jets.
Idle jets say 55F8
Emulsion tube is holding a part labeled F7 and a main jet labeled 175.
Last edited by 350xfire; 05-07-17 at 11:16 PM.
05-08-17, 08:58 AM
#10
Update:
I removed a trumpet and looked into the chokes and they are 42mm. Trumpets are 52mm at top and 48 at the bottom.
I removed the top cover and removed the idle jets and main jets.
Idle jets say 55F8
Emulsion tube is holding a part labeled F7 and a main jet labeled 175.
I removed a trumpet and looked into the chokes and they are 42mm. Trumpets are 52mm at top and 48 at the bottom.
I removed the top cover and removed the idle jets and main jets.
Idle jets say 55F8
Emulsion tube is holding a part labeled F7 and a main jet labeled 175.
05-08-17, 10:32 PM
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42 venturies are good starting point. you can bump up the idle jet by drilling them out using an index drill bit one size larger til you find the right size. try f11. 175 is too small but you can increase that later and my rule of thumb, air jet should be at 150 max. also once its idling. open up the fuel regulator until its barely dripping inside the venturiies then back off 1/8 turnn. hows the plugs during hard starting? are they wet or dry?
Emulsion tube holder has 175 air corrector, F7 emulsion tube and unknown main jet
Idle jet holder has 55F8 idle jet
Accelerator pump is a 75
Is there any other info I need to get? How about needle valve size?
Looks like I need to order F1 emulsion tubes right?
Also, would a wide band O2 sensor work installed at the exhaust tip? I have no bung for one.
Thanks for all the help so far!!!
05-27-17, 06:33 PM
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Hey guys
I went ahead and ordered the racing beat recommended main, emulsion and air correctors. I auume starting is due to improper idle jets. Starting really sucks and takes many times with starting fluid and pumping the gas pedal 10-30 times, hoping it starts, once it starts need to keep RPM to between 3-4000 to keep running.
Question: Is the ide air jet what I need to focus on? Which do I start with? I have 55F8 now.
Thanks
I went ahead and ordered the racing beat recommended main, emulsion and air correctors. I auume starting is due to improper idle jets. Starting really sucks and takes many times with starting fluid and pumping the gas pedal 10-30 times, hoping it starts, once it starts need to keep RPM to between 3-4000 to keep running.
Question: Is the ide air jet what I need to focus on? Which do I start with? I have 55F8 now.
Thanks
05-27-17, 08:51 PM
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Starts pretty quick with starting fluid but I have to start pumping the gas in and out until it gets going to 3k rpm plus. Sometimes that works sometimes it doesn't. Once I get it started, I have to keep it over 3000 rpm or it dies... if kept over 3k it runs ok.
05-28-17, 08:40 AM
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I would say based on how much I have to pump the gas to get it to try to start, it is running very lean and it wants a bunch of fuel I order to start. That would be the job of the idle jet right?
05-28-17, 12:31 PM
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So I turned the engine with a wrench and when I see the flat spot of the flywheel through the inspection window, there are no pulley lines lined up... Timing could be the issue... How do I correct this?
Oh, btw, I have a pulley without rivets, which means it can go on 4 different ways. I assume I need to set the flywheel flat spot on the inspection window, then set the first mark on the pulley at the indicator?
Thanks
Oh, btw, I have a pulley without rivets, which means it can go on 4 different ways. I assume I need to set the flywheel flat spot on the inspection window, then set the first mark on the pulley at the indicator?
Thanks
Last edited by 350xfire; 05-28-17 at 12:35 PM.
05-28-17, 09:24 PM
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OK, so I was mistaken, the first timing mark on the pulley lines up with the front cover timing indicator while the flat spot on the flywheel is on the passenger side sight window. I believe this is correct right?