Not a a huge problem, just a little tuning question. So i take the 70 out tonight to test the carb, I set the float levels and checked fuel pressure before heading out. I didn't make any adjustments to anything else, just like it came out of the box. My timing is dead on, new plugs, wires and everything else is in good order. If i try to get into it she is leaning out. I stopped turned the 4 corner idle screws in one turn each, it gets a little better. Stop again, turn the screws in all the way, and back them off one and a half turns, it gets better but still leaning out of idle. It doesn't stink at all, not blowing black smoke, and the plugs look better than they ever have. The jetting is 94 squared, so think I need to go up a jet size or 2?? It idles perfect @ 850 rpms too, which is a first since i've owned the car. :hurray:
ProSystems SV-1 Carb issues
seabees72ss
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I'll take those cheap Dominators all day long (not that I need any more, 1-1050, 2-1150's, and a 1250). If you know what to do a Dominator works just fine. And yes the factory calibrations suck on most of them. As far as richening the idle feed, what you have to realize is that the idle feed and idle air bleed supply fuel for the transition circuit even in the SV1, you have to adjust them to get the transition fuel mixture and the duration of the transition circuit is active correct. Since idle won't need as much fuel as you are under a heavier load with the transition circuit, you have mixture screws to lean it out. Richer idle jets help fill the lean in the transition circuit, ll you do after is readjust your mixture screws for best idle. If the transition wasn't staying active long enough to get into the mains, you would go down in the idle air bleed.
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101 Posts
Hi Folks,
Heard about the post..sorry I haven't been in here in awhile.
The SV1 is different. Think of that idle feed like an idle air bleed. You need to make a move on it to notice anything.
The nice thing about that is it can get partially coated etc...with gunk and the SV1 still runs good. Why is that you ask?
Most idle feeds you only move .002-.003 at a time BUT you move triple that on an SV1. This is done on purpose.
Have you ever raced with carbs that are very sensitive to minor changes in tuneups and weather?
Thats because the base idle metering bleeds are waaay to responsive. So as the bleed cools off it shrinks and this changes the tuneup..then the carb heats up from engine heat soak after shut down and the bleed expands and the idle quality and the engine loads up a little or leans out a little at the starting line or the stop light as an over sensitive bleed design effectively constantly changes the tuneup as the carb body and bleeds heat up and cool down. So the car is inconsistent.
The SV1 design requires real moves on these circuits to effect it. It also allows you to fine tune them better and thats why the SV1 is just amazingly consistent as a result. Its by design.
The idle metering system is very critical to changing your tuneup from run to run...before the run has even started.
The main jetting I kept very simple as well. That system maintains the stock ratio climb. BUT the nice thing is every SV1 will stay moving fuel to a Holley 109 jet (.165 range). So Q16 fuel is just a jet change away...no air bleed changes needed.
So the things you see that seem different are very different, but no need for alarm. They are better.
Some of these numbers you have seen before. But be aware, we have gasoline carbs that use .076 idle feeds ...yes you read that right and we have E85 designs that use .048 idle feeds...yes that seems wrong to the systems you are used to seeing. But its a new world.
But not too new.
On some SV1's we have had to add intermediate circuits to them as some folks were just to lean at part throttle without them.
Yet, on some SV1's we have had to go the opposite direction. We needed to lean them down at part throttle. Its the same stuff we have all been encountering in four barrel carbs for 15 years now.
Since the SV1's release in late October we have encountered many different situations that we did not see after about a year of testing on multiple combinations prior to release. Fortunately we have been able to find the tuneup the customer required in usually just a call or two.
BUT, not always. There are a few out there that we haven't figured out yet...we put those combos on the to-do list. Then you take care of the customer. You set the customer up with a conventional four barrel carb that we have years worth of records on and be sure everyones happy in the end.
We're not the only one that does this, other talented and successful carb shops practice this same philosophy. If they miss it (and we all miss it), just take care of the customer. If you take care of the customer, you get to keep that customer and its easier to keep one than get a new one.
Thanks for reading.
Patrick James
PRO SYSTEMS
Heard about the post..sorry I haven't been in here in awhile.
The SV1 is different. Think of that idle feed like an idle air bleed. You need to make a move on it to notice anything.
The nice thing about that is it can get partially coated etc...with gunk and the SV1 still runs good. Why is that you ask?
Most idle feeds you only move .002-.003 at a time BUT you move triple that on an SV1. This is done on purpose.
Have you ever raced with carbs that are very sensitive to minor changes in tuneups and weather?
Thats because the base idle metering bleeds are waaay to responsive. So as the bleed cools off it shrinks and this changes the tuneup..then the carb heats up from engine heat soak after shut down and the bleed expands and the idle quality and the engine loads up a little or leans out a little at the starting line or the stop light as an over sensitive bleed design effectively constantly changes the tuneup as the carb body and bleeds heat up and cool down. So the car is inconsistent.
The SV1 design requires real moves on these circuits to effect it. It also allows you to fine tune them better and thats why the SV1 is just amazingly consistent as a result. Its by design.
The idle metering system is very critical to changing your tuneup from run to run...before the run has even started.
The main jetting I kept very simple as well. That system maintains the stock ratio climb. BUT the nice thing is every SV1 will stay moving fuel to a Holley 109 jet (.165 range). So Q16 fuel is just a jet change away...no air bleed changes needed.
So the things you see that seem different are very different, but no need for alarm. They are better.
Some of these numbers you have seen before. But be aware, we have gasoline carbs that use .076 idle feeds ...yes you read that right and we have E85 designs that use .048 idle feeds...yes that seems wrong to the systems you are used to seeing. But its a new world.
But not too new.
On some SV1's we have had to add intermediate circuits to them as some folks were just to lean at part throttle without them.
Yet, on some SV1's we have had to go the opposite direction. We needed to lean them down at part throttle. Its the same stuff we have all been encountering in four barrel carbs for 15 years now.
Since the SV1's release in late October we have encountered many different situations that we did not see after about a year of testing on multiple combinations prior to release. Fortunately we have been able to find the tuneup the customer required in usually just a call or two.
BUT, not always. There are a few out there that we haven't figured out yet...we put those combos on the to-do list. Then you take care of the customer. You set the customer up with a conventional four barrel carb that we have years worth of records on and be sure everyones happy in the end.
We're not the only one that does this, other talented and successful carb shops practice this same philosophy. If they miss it (and we all miss it), just take care of the customer. If you take care of the customer, you get to keep that customer and its easier to keep one than get a new one.
Thanks for reading.
Patrick James
PRO SYSTEMS
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3,884 Posts
for $1000+ that carb better be able to suck more than just air...
i agree though, changing jets is one thing, but have to drill anything on that carb is crazy for that money. i guess i'm just too used to working with a 150 dollar carb with a 125 dollar main body on it.
i agree though, changing jets is one thing, but have to drill anything on that carb is crazy for that money. i guess i'm just too used to working with a 150 dollar carb with a 125 dollar main body on it.
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673 Posts
OK, made the simple changes tonight, huge difference. I just thought of something I didn't do, that is probably causing the engine to break up when i try to get into the throttle. I forgot to double check the phase rotation on the rotor.... It's probably off and causing the spark to jump between 2 cylinders under load. I think I've been done this road before. I will check and adjust and then test it out again. I feel like such a turd for not checking it...
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535 Posts
oops!! just looked at my spec-sheet
went from .047 to .062 not quite as much of a jump LOL!!
went from .047 to .062 not quite as much of a jump LOL!!
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673 Posts
Wasn't the rotor phasing... Dang it! I changed some air bleeds as directed by Patrick tonight, but its still not allowing me to get into it. Getting closer... I was directed to go a little larger with the idle feed jets, from .055 to max of .063, so thats on the plate for the morning. I don't mind doing the tuning on it, because I'm learning about how these operate. It is a little different than the old King Demon. I just hope that I can get it locked in this weekend, next week is going to be super busy at work.OK, made the simple changes tonight, huge difference. I just thought of something I didn't do, that is probably causing the engine to break up when i try to get into the throttle. I forgot to double check the phase rotation on the rotor.... It's probably off and causing the spark to jump between 2 cylinders under load. I think I've been done this road before. I will check and adjust and then test it out again. I feel like such a turd for not checking it...
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535 Posts
tim,drilling out to .063 worked for me as I said,just make sure you bring a small screwdriver with you for the test ride
If you get a little carried away leaning the idle mixture screws after drilling the IFR's,the motor will still be lean at part throttle, trust me
and once again its not like I had to excessively richen them to help matters
a quarter turn on each did it for me,I noticed when I started to richen them I had a noticable rpm increase,so I knew I was on to something
for years I made the mistake of thinking idle mixture screws are just for idle
If you get a little carried away leaning the idle mixture screws after drilling the IFR's,the motor will still be lean at part throttle, trust me
and once again its not like I had to excessively richen them to help matters
a quarter turn on each did it for me,I noticed when I started to richen them I had a noticable rpm increase,so I knew I was on to something
for years I made the mistake of thinking idle mixture screws are just for idle
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673 Posts
I sent the carb back to have an intermediate circuit installed, that should cure it. Hope so, summer and racing are going by fast...
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673 Posts
sent it back to have an intermediate circuit installed.
^^^^Agreed. That thing better be able to suck a golf ball through a garden hose for that kind of cheddar.
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