A few Holley Questions.
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 3,341
Likes: 7
From: Connecticut
A few Holley Questions.
Street Avenger 670
I have this carb on my ZZ4 and am having problems getting it dialed in. It had a rough idle and rough cruise.
I increased the main jets three sizes from 65's to 68's per Lars thread addressing these carbs which helped quite a bit on the cruise and a little on the idle but now it's running rich. I can smell it and see it out the exhaust.
My questions are, does the primary float adjustment effect the idle and or cruise? And does the secondary circuit have any effect on the primary side?
I had been trying to find some answers on the web and did read that the secondary circuit can have a very slight effect on the idle and part throttle.
One last thing I can add is that sometimes when I brake hard to a stop, the engine will drop in RPM and just about stall for a second or two and then it comes back up to normal.
Thanks for any replys.
I have this carb on my ZZ4 and am having problems getting it dialed in. It had a rough idle and rough cruise.
I increased the main jets three sizes from 65's to 68's per Lars thread addressing these carbs which helped quite a bit on the cruise and a little on the idle but now it's running rich. I can smell it and see it out the exhaust.
My questions are, does the primary float adjustment effect the idle and or cruise? And does the secondary circuit have any effect on the primary side?
I had been trying to find some answers on the web and did read that the secondary circuit can have a very slight effect on the idle and part throttle.
One last thing I can add is that sometimes when I brake hard to a stop, the engine will drop in RPM and just about stall for a second or two and then it comes back up to normal.
Thanks for any replys.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
How does changing the jets help cruise and idle. The idle circuit has nothing nothing to do with the main jets.
At cruise under light loads and say under 2500-3000 rpm the main circuit again has nothing to do with the cruise mixture.
You cruise on the idle circuit. The idle circuit is usually tuned rich, our motors like to idle rich. After you open the throttle this same idle mixture becomes your cruise mixture by way of the transfer slots so if you set say 12-1 for idle that is your cruise mixture and unless you drop down a gear, bring the revs to over 3000 to get onto the main jets you are only playing with the idle circuit.
Pull all the jetting changes you want and it will not help the idle or the low rpm cruise mode.
At cruise under light loads and say under 2500-3000 rpm the main circuit again has nothing to do with the cruise mixture.
You cruise on the idle circuit. The idle circuit is usually tuned rich, our motors like to idle rich. After you open the throttle this same idle mixture becomes your cruise mixture by way of the transfer slots so if you set say 12-1 for idle that is your cruise mixture and unless you drop down a gear, bring the revs to over 3000 to get onto the main jets you are only playing with the idle circuit.
Pull all the jetting changes you want and it will not help the idle or the low rpm cruise mode.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
On a side note even if the power valve is wide open at idle it still doesn;t affect the idle mixture. A ruptured diagraghm will flood the motor but not the wrong size of power valve.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I have a habit of turning my fuel pumps off about a block and one half from home so the carb float bowls are close to empty when I shut down and my car idles the same right up till the last minute before it dies so it appears float level doesn't affect it at idle.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Are you running a vacuum advance??? If not that really affects a good idling and running/cuise motor. If you want to run lean you need vacuum advance and I jet my transfer slots so I can have the rich idle and at the same time a lean cruise. I increased my gas mileage range by at least 50% by jetting the transfer slots.
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
I don't mess with the secondary circuit other then jet changes since I don't cruise on it and only call on it for WOT where I want it rich.
Rich /lean only applies to WOT. What we call lean is not lean at cruise and again only at WOT can you burn up an engine by running too lean.
Run them as lean as you want at light cruise loads and you can't hurt them. MY plugs are snow white under cruise conditions but after years in the car they still look new. I run 16-17 to 1 under cruise conditions. Idle at 12.5-13 and under blower power in the 10-11's to prevent detontion.
You onlye run rich at WOT to help prevent detonation. A motor makes maximum power around 13.2 but that is considered lean under WOT since detonation can suddenly happen and that is a NO NO.
Rich /lean only applies to WOT. What we call lean is not lean at cruise and again only at WOT can you burn up an engine by running too lean.
Run them as lean as you want at light cruise loads and you can't hurt them. MY plugs are snow white under cruise conditions but after years in the car they still look new. I run 16-17 to 1 under cruise conditions. Idle at 12.5-13 and under blower power in the 10-11's to prevent detontion.
You onlye run rich at WOT to help prevent detonation. A motor makes maximum power around 13.2 but that is considered lean under WOT since detonation can suddenly happen and that is a NO NO.
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 3,341
Likes: 7
From: Connecticut
I know nothing about Holley carbs but I do know that when I raised the primary jets up 3 sizes, the cruise (from off idle to 2,500 RPM or so) got much smoother and the idle got a tiny bit smoother.
Maybe there is something internally wrong with this carb which is causing a jet change to effect a circuit that it shouldn't, but I am only telling you exactly what I did and exactly what the results were.
Yes I am running a vacuum advance.
Last edited by Bob Onit; Sep 24, 2007 at 02:20 PM.
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Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I don't know a fraction of what Lars knows but I do know how to get my holleys running well and I find that out of the box they are all too rich. I lean then out,drill and tap passages and add jets where holley never put them.
Buy the top of the line holley carb or metering blocks and in the primary side alone there are about 20 TWENTY jets that can be changed.
It is not a simple matter of changing the main jets and tweaking the idle mixture screws anymore.
Done properly I feel the new modern holleys can be tuning like fuel injection to give good mixtures under most conditions.
A complete set of jets for the new holley's can run $300.
I will try and post a picture tomorrow of the new metering blocks and some of the jets that are changable
Buy the top of the line holley carb or metering blocks and in the primary side alone there are about 20 TWENTY jets that can be changed.
It is not a simple matter of changing the main jets and tweaking the idle mixture screws anymore.
Done properly I feel the new modern holleys can be tuning like fuel injection to give good mixtures under most conditions.
A complete set of jets for the new holley's can run $300.
I will try and post a picture tomorrow of the new metering blocks and some of the jets that are changable
Race Director
Joined: Oct 2000
Posts: 14,945
Likes: 79
From: central FL, near the beach.
Street Avenger 670
I have this carb on my ZZ4 and am having problems getting it dialed in. It had a rough idle and rough cruise.
I increased the main jets three sizes from 65's to 68's per Lars thread addressing these carbs which helped quite a bit on the cruise and a little on the idle but now it's running rich. I can smell it and see it out the exhaust.
My questions are, does the primary float adjustment effect the idle and or cruise? And does the secondary circuit have any effect on the primary side?
I had been trying to find some answers on the web and did read that the secondary circuit can have a very slight effect on the idle and part throttle.
One last thing I can add is that sometimes when I brake hard to a stop, the engine will drop in RPM and just about stall for a second or two and then it comes back up to normal.
Thanks for any replys.
I have this carb on my ZZ4 and am having problems getting it dialed in. It had a rough idle and rough cruise.
I increased the main jets three sizes from 65's to 68's per Lars thread addressing these carbs which helped quite a bit on the cruise and a little on the idle but now it's running rich. I can smell it and see it out the exhaust.
My questions are, does the primary float adjustment effect the idle and or cruise? And does the secondary circuit have any effect on the primary side?
I had been trying to find some answers on the web and did read that the secondary circuit can have a very slight effect on the idle and part throttle.
One last thing I can add is that sometimes when I brake hard to a stop, the engine will drop in RPM and just about stall for a second or two and then it comes back up to normal.
Thanks for any replys.
a well matched tune(to the car/engine) runs on the main at cruise 40 mph or less.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
I don't know if you saw this thread but you may want to take a look.
http://forums.corvetteforum.com/show....php?t=1759376
As far as the stalling on hard breaking goes, it could be the secondary float level. If it is too high it can spew fuel out the vent and down into the engine. Lower it just a bit and see what happens.
If this carb has four corner idle circuits they need to be set equally. A ragged idle generally means it's lean. The ways to richen the idle circuit are (easiest to hardest) 1) open the idle mixture screws (both primary and secondary evenly), 2) close down on the idle speed screws (both primary and secondary evenly) 3) if it has replaceable idle air bleeds, go to a smaller breed.
There is also the idle channel restriction but you shouldn't need to go inside the carburetor to fix this problem.
All this being said I have to ask, why not a 'Jet?
BigBlockk
Later.....
http://forums.corvetteforum.com/show....php?t=1759376
As far as the stalling on hard breaking goes, it could be the secondary float level. If it is too high it can spew fuel out the vent and down into the engine. Lower it just a bit and see what happens.
If this carb has four corner idle circuits they need to be set equally. A ragged idle generally means it's lean. The ways to richen the idle circuit are (easiest to hardest) 1) open the idle mixture screws (both primary and secondary evenly), 2) close down on the idle speed screws (both primary and secondary evenly) 3) if it has replaceable idle air bleeds, go to a smaller breed.
There is also the idle channel restriction but you shouldn't need to go inside the carburetor to fix this problem.
All this being said I have to ask, why not a 'Jet?
BigBlockk
Later.....
Last edited by BigBlockk; Sep 27, 2007 at 11:42 PM.
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 3,341
Likes: 7
From: Connecticut
Ok,now I'm still not sure as to whether or not the main jets effect the cruise... If I read the replys correctly, Norval says no and Matt says yes... Please excuse me if I interpreted your posts wrong. 
Well, I honestly don't have the proper jets and metering rods for the Q-jets to match the new engine.
Plus, I kinda want to learn how to tune my Holley
Well, I honestly don't have the proper jets and metering rods for the Q-jets to match the new engine.
Plus, I kinda want to learn how to tune my Holley
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Yes I have 2 850 double pumpers. So??
I hang around a tuning forum alot. The guy called Tuner knows everything about carbs, he is my idol. I read everything he has to say. I spent months on that forum learning, trying and finally after about 40 plus years of tuning I finally understand alot more about the holley carb. I also run a wide band oxygen sensor and 4 exhaust gas temperature probes so I monitor the motor pretty closely.
I am just giving my opinion, it is not gospel and most of it is just reguritated from what tuner has drummed into me.
I am not the expert but I remember what others say and again I just repeat it.
Make up your own mind but I say at 60 or 70 mph you are on your cruise circuit, not the main jets so if the idle is rich and it should be the cruise is also rich and no jet helps the idle circuit. NOne.
The main idle feed restrictions are about .033-.039 and the idle air bleed should be .070-.075 with a main air bleed of .026-.028.
Just to throw numbers out there.
I hang around a tuning forum alot. The guy called Tuner knows everything about carbs, he is my idol. I read everything he has to say. I spent months on that forum learning, trying and finally after about 40 plus years of tuning I finally understand alot more about the holley carb. I also run a wide band oxygen sensor and 4 exhaust gas temperature probes so I monitor the motor pretty closely.
I am just giving my opinion, it is not gospel and most of it is just reguritated from what tuner has drummed into me.
I am not the expert but I remember what others say and again I just repeat it.
Make up your own mind but I say at 60 or 70 mph you are on your cruise circuit, not the main jets so if the idle is rich and it should be the cruise is also rich and no jet helps the idle circuit. NOne.
The main idle feed restrictions are about .033-.039 and the idle air bleed should be .070-.075 with a main air bleed of .026-.028.
Just to throw numbers out there.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Try your own experiment. Jet the mains about 10 times too rich, way too big. You have what 68? Try 80's and then go for a run. When the carb goes onto the main circuit it should suddenly go extremely rich. If you can run at say 2500 and it still runs fine you are not on the main jets.
How about jetting the other way, extremely lean, smallest jets you have. Take it for a run, cruise slowly and lean slowly into it building speed until the motor falls on it's face. This is when the main curcuit kicks in.
With a wide band oxygen sensor the correct way is jetting way too rich, take it to 4000 and then drop 200 rpm, take readings and it will read 11 or 12, drop another 200, take a reading, again rich. Keep dropping until suddenly the mixtures head lean and you have the crossover point.
Mine takes over 3000
How about jetting the other way, extremely lean, smallest jets you have. Take it for a run, cruise slowly and lean slowly into it building speed until the motor falls on it's face. This is when the main curcuit kicks in.
With a wide band oxygen sensor the correct way is jetting way too rich, take it to 4000 and then drop 200 rpm, take readings and it will read 11 or 12, drop another 200, take a reading, again rich. Keep dropping until suddenly the mixtures head lean and you have the crossover point.
Mine takes over 3000
Racer
Joined: May 2006
Posts: 264
Likes: 0
From: Fort Myers, Fl / St. Paul, Mn
I also have a Holley SA and had the same problems.
If you lower the secondary float level to 1/2 turn below the bottom of the sight hole that will solve the flooding out on a hard stop - it also helps a lot with bowl percolation in hot weather. I also run the primary float lower - 1/4 turn - again because of percolation.
If you have the idle screws too far in you will get lurching at slow cruise - 30-35 mph. I have mine set at 1-5/8 turns out from a soft stop. The difference between rich and lean is only about 1/8 turn. I run mine as lean as I can without lurching.
You also need your timing right on. For a better idle I use manifold vacuum instead of ported vacuum.
Guys like Norval are all-out power guys and may not agree with my ideas but they work real good for me.
If you lower the secondary float level to 1/2 turn below the bottom of the sight hole that will solve the flooding out on a hard stop - it also helps a lot with bowl percolation in hot weather. I also run the primary float lower - 1/4 turn - again because of percolation.
If you have the idle screws too far in you will get lurching at slow cruise - 30-35 mph. I have mine set at 1-5/8 turns out from a soft stop. The difference between rich and lean is only about 1/8 turn. I run mine as lean as I can without lurching.
You also need your timing right on. For a better idle I use manifold vacuum instead of ported vacuum.
Guys like Norval are all-out power guys and may not agree with my ideas but they work real good for me.
Race Director
Joined: Oct 2000
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From: central FL, near the beach.
norval
i'm glad that you report your experiences! Often very helpful and interesting
i did similar experiments years ago and confirmed a 1400-1600 crossover to the main jets. also confirmed it with my o2 sensor. it goes way lean 16:1 on main in my case as my 4165 street legal 1970 carb is operating properly. But all Bob has to do is look down the throat and slowly rev it while sombody reads the tach. So how about it Bob? All Holleys are not alike! a 670 SA will likely be different than mine or 850's.
i'm glad that you report your experiences! Often very helpful and interesting
i did similar experiments years ago and confirmed a 1400-1600 crossover to the main jets. also confirmed it with my o2 sensor. it goes way lean 16:1 on main in my case as my 4165 street legal 1970 carb is operating properly. But all Bob has to do is look down the throat and slowly rev it while sombody reads the tach. So how about it Bob? All Holleys are not alike! a 670 SA will likely be different than mine or 850's.
Last edited by Matt Gruber; Sep 25, 2007 at 05:23 AM.
Race Director
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From: Waterloo ontario Canada
I grabbed this from a tuners forum. It is a paper put out for tuning carbs. It is long and requires a wide band oxygen sensor to do the tuning.
This is a small part that is expanded upon later for using the LM-1.
Remember this is copied. It is not mine
7. Cruise Tuning: Many tuners think that main jets control most of the fuel flow during cruise RPM – 2100 to 3400, depending on gearing. The reality is that the idle circuit on most carburetors can control most of the Air/Fuel Ratio during steady-state cruise, yielding better fuel economy. Using the Innovate LogWorks software, you can find the transition period between the idle circuits and the mains fairly easily, and then optimize the idle circuit as an “idle/cruise” circuit and let the mains & power valve specialize on high load, wide-open-throttle situations. A dyno is the safest and most repeatable place to do this type of tuning, but you could drive your car on a long, flat stretch of road to capture the data as well.
This is a small part that is expanded upon later for using the LM-1.
Remember this is copied. It is not mine
7. Cruise Tuning: Many tuners think that main jets control most of the fuel flow during cruise RPM – 2100 to 3400, depending on gearing. The reality is that the idle circuit on most carburetors can control most of the Air/Fuel Ratio during steady-state cruise, yielding better fuel economy. Using the Innovate LogWorks software, you can find the transition period between the idle circuits and the mains fairly easily, and then optimize the idle circuit as an “idle/cruise” circuit and let the mains & power valve specialize on high load, wide-open-throttle situations. A dyno is the safest and most repeatable place to do this type of tuning, but you could drive your car on a long, flat stretch of road to capture the data as well.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Matt you are lucky that you can get your car to cruise on the main jets at those low 1400-1600 rpm. Makes cruising tuning alot easier.
I have drilled my main body and installed jets in the transfer slots.
I also did at least 10 jetting changes in these transfer slots to get where I am today.
Another thing that most of us should do is enlarge the power valve restrictions in the meter block from about .060 to .070 for starters.
I have drilled my main body and installed jets in the transfer slots.
I also did at least 10 jetting changes in these transfer slots to get where I am today.
Another thing that most of us should do is enlarge the power valve restrictions in the meter block from about .060 to .070 for starters.
Race Director
Joined: Oct 2000
Posts: 14,945
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From: central FL, near the beach.
.Norval, thanks for your replys. I don't doubt most guys have tuning problems as they scoff at the 4165, why i have no idea, and then custom tune their pick. In 1975 tuner Al Kirchner told me to avoid the whole series of DP's as they are not street carbs. He told me to get a 4165, so i have him to thank for his expertise. no luck on my part, except knowing him, asking, and taking his advice.
Back to Bob's Q:
Thinpockets offers good SA 670 tips.
.
Guys, "cruise" is very vague.
slow cruise, what is that? We need specifics, MPH+ RPM & level ground. My 72 is TH400, doesnt shift into 3rd until 30mph, min rpm ~1500.
when do u downshift? very important!
.
Bob, are u going to look down the throat or r u a poser?
Back to Bob's Q:
Thinpockets offers good SA 670 tips.
.
Guys, "cruise" is very vague.
slow cruise, what is that? We need specifics, MPH+ RPM & level ground. My 72 is TH400, doesnt shift into 3rd until 30mph, min rpm ~1500.
when do u downshift? very important!
.
Bob, are u going to look down the throat or r u a poser?
Last edited by Matt Gruber; Sep 25, 2007 at 10:09 AM.