Bowtie T
Active Member
I may be wrong, but I think what you are seeing is the stagger in the heads? Mine from speedway were the same. You probably measured from the collector
to the back tires? Anyways, you car is looking great
The Bucket List
- Thread starter Intrepid
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to the back tires? Anyways, you car is looking great
Indycars
Well-Known Member
Just curious, what did you base your decisions on?
BTW, you can make your own metering orifices with brass set screws and then drill them. Brass is very easy to drill.
McMaster-Carr
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tfeverfred
Well-Known Member
I'm assuming that's "centigrade"?
2old2fast
Active Member
IMO , you've gone the wrong way w/the PV... a 6.5-8.5 is probably a better choice [unless you're way past 235* duration @ .050....1 choke is all ou need w/2x4 TR....changing jet sizes[IFR as well ] w/o a baseline from either driving or a dyno session or o2 sensor data is abject futility...
Intrepid
Active Member
Fletch - Decisions on the mods to the carbs are just based on research so far. I have read plenty about guys with dual 4's putting wire in the IFR and I thought drilling for a jet would be more accurate, and I can just change the jet up or down as needed. The idle/transition circuit seems to be the biggest PITA for guys running two 4s, and it seems logical I would need to jet down a bit running 2 carbs.
Fred - ya that's centigrade.
Indy - I was going to just buy the brass set screws and drill them but I thought it would be more accurate to just buy the emulsion jets for $3 a pair.
2Old - I have never had this engine started yet so I don't have a base line, I thought this would be a good place to start, I did buy extra jets, and I do have a vacuum gauge. So far I can only assume that I will be making somewhat less vacuum than normal, doubling the amount of idle and transition slots will make those two circuits a bit rich, and the same goes for the main jets.
I don't have room to add the second metering blocks and convert the carbs to 4150's or I would do that.
I am sure I will be playing and tuning for a while once the cam is broke in.
Fred - ya that's centigrade.
Indy - I was going to just buy the brass set screws and drill them but I thought it would be more accurate to just buy the emulsion jets for $3 a pair.
2Old - I have never had this engine started yet so I don't have a base line, I thought this would be a good place to start, I did buy extra jets, and I do have a vacuum gauge. So far I can only assume that I will be making somewhat less vacuum than normal, doubling the amount of idle and transition slots will make those two circuits a bit rich, and the same goes for the main jets.
I don't have room to add the second metering blocks and convert the carbs to 4150's or I would do that.
I am sure I will be playing and tuning for a while once the cam is broke in.
Intrepid
Active Member
LOL .. so everywhere eh ?
I wish I had carbs that could do all of that but I am a bit restricted with the 1850-2's.
What I would really like to do is 3D print some metering blocks half the size with all the adjustable jets like the Quick Fuel ones so I could fit both carbs on the intake and still play with everything.
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Indycars
Well-Known Member
Pretty much, but I didn't buy a carburetor with those adjustments, I drilled and tapped the holes by hand
mostly, but some were done on a drill press. I did start with a new SpeedDemon 750cfm carburetor.
The first thing I did was measure all the orifices so I would have a starting point.
Indycars
Well-Known Member
Yes, you made a good point!
Intrepid
Active Member
Nice work Indy.
I decided to add IFR's to the top of the circuit closer to the air input because it was easier to tap - its already to go for 6/32 tap no drilling required.
I am down sizing that circuit, but if I need to I can just take them out and I am back to stock, or I can drill out the original IFR's and upsize.
I don't think I have the meat on the body to drill out the air bleeds but I will check.
I should get a pin gauge set and measure all the orifices before I start just to make sure no one has already messed with them.
I decided to add IFR's to the top of the circuit closer to the air input because it was easier to tap - its already to go for 6/32 tap no drilling required.
I am down sizing that circuit, but if I need to I can just take them out and I am back to stock, or I can drill out the original IFR's and upsize.
I don't think I have the meat on the body to drill out the air bleeds but I will check.
I should get a pin gauge set and measure all the orifices before I start just to make sure no one has already messed with them.
Indycars
Well-Known Member
Thanks for the compliment!
I'm confused about putting the IFR at the top. Are you referring to the Siphon Break
or Emulsion Hole maybe?
I bought the numbered size drills [1-80] and used them to measure all the orifices. They
were very blunt on the end, so I used some 1000 grit wet-or-dry paper and WD40 to
knock the sharp edge off the drill bit before using them to size the holes.
Are you setting the transition slot so it looks like a square or about .020" opening? You
will want it to idle with the transition slot looking like a square.
Intrepid
Active Member
When I say the top of the circuit I think its the emulsion hole opposite from where the air inlet is from the air bleed.
like this guy
The gauge pins I want are these HFS Steel Pin Gauge Set - 50pcs M0 .011-.060" - Class ZZ | eBay
And yes I should be between .020 and .040 on the transfer so it looks square.
like this guy
And yes I should be between .020 and .040 on the transfer so it looks square.
Indycars
Well-Known Member
Ok, I see what you are doing now. If you do have the room, drilling the air bleeds will
make it adjustable without pulling the fuel bowl and the mess that comes with it.
The down side is if you drop a jet down the venturi, then you have another problem.
I used rags in the venturi to catch the jet if I dropped one. The allen wrench usually
had a pretty good grip so the jet came out with the wrench.
Thanks ..... I learned something today!
make it adjustable without pulling the fuel bowl and the mess that comes with it.
The down side is if you drop a jet down the venturi, then you have another problem.
I used rags in the venturi to catch the jet if I dropped one. The allen wrench usually
had a pretty good grip so the jet came out with the wrench.
Thanks ..... I learned something today!
Intrepid
Active Member
Indy do you set the secondarys at the same spot, say 20-40 thow on the transfers as a base starting point?
I have done allot of research and read the David Vizard's SuperTune and modify but it really doesn't cover setting up the secondary's for starting off with a blank canvas.
I have done allot of research and read the David Vizard's SuperTune and modify but it really doesn't cover setting up the secondary's for starting off with a blank canvas.
Indycars
Well-Known Member
Your carb doesn't have 4 corner idle AFR adjustments screws. It does have the transition slot for moving slight amounts of fuel thru the secondary bowl to keep it from getting stale. Some people never open the throttle enough to use the secondaries. Read thru the following, I want to give credit to the authors, in the link provided.
Carburetor Tuning the Scientific Way
Idle
The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. If you have a bit of a stumble in very light, low speed operation, sometimes it helps to richen it up by another 1/4 turn.
If you are starting your adjustments fresh, begin at about 2 turns out. Depending upon if you have a regular carb or a smog carb, your adjustment can be lean when screwing in (normal) or rich going in (smog style). The way to tell the difference is the smog carb will have a little sticker on the metering block telling you it goes opposite of normal, and the smog carb will have blunt screws rather than the pointed ones on a regular carb. If you have a carb with a normal system where the mixture leans as you turn the screws in, then when you screw them in almost to a light seating, the engine should die.
On a regular, standard idle circuit Holley, turning the idle mixture screws all the way in should kill the engine. If your idle mixture screws do not respond to adjustments, you may have several different problems. The most common is using the wrong carburetor for the application. Smog carbs with reverse mixture screws (these are the ones with the little decals, telling you to turn the screws in for richer mixtures) only have a small band of adjustment built in. Smog carbs work well on stock engines only, and you can't expect them to work well on a modified engine, especially one with a lopey cam.
Another common cause of non-responsive idle mixture screws is having too much (more than .040 inch) of the idle transfer circuit exposed. The idle circuit allows a very small amount of finely metered fuel into the engine. By exposing the transfer circuit too much, the gross feed of fuel coming out of the transfer circuit overpowers the fine amount coming out of the idle ports. This is akin to adding a squirt gun's flow into a garden hose's flow...the fine amount of the squirt gun is so insignificant compared to the garden hose, that there is no way that adjusting the flow of the squirt gun will make any difference. There are several ways to fix this problem:
1. If your engine is worn, or has a big vacuum leak, you should fix those problems before trying to crutch your carb. Sometimes, with worn engines or one with a vacuum leak, the carb must be opened quite a bit just to get the engine to run.
2. Buy the right sized carb! If you're trying to use a 600 cfm carb on a lopey-cammed 460, then you must open the primaries too far into the transfer slots just to get enough air into the engine to get it to idle. A larger carb on this example would have a larger throttle plate, which would need to opened less to allow the engine to idle.
3. Open the secondaries a bit, and close the primaries a like amount. This will allow more air in, without exposing quite so much of either primary or secondary transfer slots.
4. If opening the secondaries doesn't work, then you may have to drill small holes (1 per plate) in the primary throttle plates to allow air in while the plates cover the transfer slots. This is a trial and error procedure, so start small, about 1/16 inch. You should not have to go much larger than 3/16 inch. Drill on the side opposite of the transfer slots, to help keep this added airflow away from the idle ports and transfer slots.
5. Check for a blown power valve. See the section on power valves below.
If you notice a lean surge or throttle tip-in stumble due to an excessively lean idle, and you can't get the idle richened up, you may have a clog in the primary OR secondary idle systems, or both. Most people don't know that there is an idle system on the secondary side of the four barrel Holley to prevent the fuel from getting stale. If the secondary idle system is clogged up, no amount of cleaning on the primaries will get the thing to idle correctly. You must clean BOTH the primary and secondary idle systems. And since those circuits are very small, small amounts of debris or even varnish from disuse will clog the tiny passages.
My carb has 4 corner AFR adjustment, so the transition slots were lower in the venturi. Therefore the slots were the same for both primary and secondary. I would open them about the same as the primaries, which may not uncover the slot like the primaries..
Carburetor Tuning the Scientific Way
Idle
The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. If you have a bit of a stumble in very light, low speed operation, sometimes it helps to richen it up by another 1/4 turn.
If you are starting your adjustments fresh, begin at about 2 turns out. Depending upon if you have a regular carb or a smog carb, your adjustment can be lean when screwing in (normal) or rich going in (smog style). The way to tell the difference is the smog carb will have a little sticker on the metering block telling you it goes opposite of normal, and the smog carb will have blunt screws rather than the pointed ones on a regular carb. If you have a carb with a normal system where the mixture leans as you turn the screws in, then when you screw them in almost to a light seating, the engine should die.
On a regular, standard idle circuit Holley, turning the idle mixture screws all the way in should kill the engine. If your idle mixture screws do not respond to adjustments, you may have several different problems. The most common is using the wrong carburetor for the application. Smog carbs with reverse mixture screws (these are the ones with the little decals, telling you to turn the screws in for richer mixtures) only have a small band of adjustment built in. Smog carbs work well on stock engines only, and you can't expect them to work well on a modified engine, especially one with a lopey cam.
Another common cause of non-responsive idle mixture screws is having too much (more than .040 inch) of the idle transfer circuit exposed. The idle circuit allows a very small amount of finely metered fuel into the engine. By exposing the transfer circuit too much, the gross feed of fuel coming out of the transfer circuit overpowers the fine amount coming out of the idle ports. This is akin to adding a squirt gun's flow into a garden hose's flow...the fine amount of the squirt gun is so insignificant compared to the garden hose, that there is no way that adjusting the flow of the squirt gun will make any difference. There are several ways to fix this problem:
1. If your engine is worn, or has a big vacuum leak, you should fix those problems before trying to crutch your carb. Sometimes, with worn engines or one with a vacuum leak, the carb must be opened quite a bit just to get the engine to run.
2. Buy the right sized carb! If you're trying to use a 600 cfm carb on a lopey-cammed 460, then you must open the primaries too far into the transfer slots just to get enough air into the engine to get it to idle. A larger carb on this example would have a larger throttle plate, which would need to opened less to allow the engine to idle.
3. Open the secondaries a bit, and close the primaries a like amount. This will allow more air in, without exposing quite so much of either primary or secondary transfer slots.
4. If opening the secondaries doesn't work, then you may have to drill small holes (1 per plate) in the primary throttle plates to allow air in while the plates cover the transfer slots. This is a trial and error procedure, so start small, about 1/16 inch. You should not have to go much larger than 3/16 inch. Drill on the side opposite of the transfer slots, to help keep this added airflow away from the idle ports and transfer slots.
5. Check for a blown power valve. See the section on power valves below.
If you notice a lean surge or throttle tip-in stumble due to an excessively lean idle, and you can't get the idle richened up, you may have a clog in the primary OR secondary idle systems, or both. Most people don't know that there is an idle system on the secondary side of the four barrel Holley to prevent the fuel from getting stale. If the secondary idle system is clogged up, no amount of cleaning on the primaries will get the thing to idle correctly. You must clean BOTH the primary and secondary idle systems. And since those circuits are very small, small amounts of debris or even varnish from disuse will clog the tiny passages.
My carb has 4 corner AFR adjustment, so the transition slots were lower in the venturi. Therefore the slots were the same for both primary and secondary. I would open them about the same as the primaries, which may not uncover the slot like the primaries..
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