BJ/BK Carbs Will Not Idle Down

[JWH]

After installing freshly rebuilt engine, I could not get the BJ/BK carbs to idle below 1,400 rpm even with the choke wide open, the fast idle cam off and both the Primary and Secondary idle screws backed all the way out on both carbs. 
      I pulled the BJ/BK carbs off and replaced with another set of Holleys I have and they idle perfectly at 700 all day long. So I am confident the problem is in the carburetors. What would be some things to check on the BJ/BKs that would cause this idle problem?
Thanks in advance for any suggestions.
Jeff

[Royce Peterson]

There is an idle stop screw on the secondaries of each carburetor. I would flip the carbs upside down and see if they are wider than they should be. There's a specification for how much the secondaries should be open at idle, from memory it is something like .005". Basically enough to see a sliver of light if you look at the closed butterfly.

[The Going Thing]

The plastic fast idle cam would not release on my BJ-BKs. I could flip if off of fast idle with the choke open and it would idle normally. 900 RPM in my case.
If reaching behind the choke body and flipping the plasctic arm allows it to return to normal then the choke is the issue. Drew here can give you a hand with this.
Here is his facebook page and he is here often.
https://www.facebook.com/AirFuelSParkTech/

[shelbydoug]

Yes, verify the secondaries are as closed as you can get them.

If you are certain that when the choke is fully open, and that the choke idle screw is not holding the primaries open, then there are two other things that you can try.

The throttle plates may need to be played with, i.e., loosened them, the throttle firmly closed and re-tightened the retaining screws. I had this issue with them just back from rebuild. This procedure alone brought the idle down from about 1,400.

The second thing to try is to set the idle mixture screws at 1-1/8 turns out instead of 1-1/2. This had the effect of finally bringing the idle right down between 850 and 875 AND yielded a 13-14 inch vacuum. I was surprised that it had so much effect.


Just as a footnote, carbs with smaller throttle plates will idle lower on this set up.


I always use a vacuum gauge to help give me a clue about what is going on. At idle, 870 rpm, I have 13-14 inches of vacuum.

At 1,400 (fast idle) I have 17.


In my case the non-stock camshaft profile (236 @ 50) and the idle characteristics of the T/A manifold is basically causing the lower idle vacuum.
Also of note, I switched to a 160 thermostat. The engine runs 20 degrees cooler and idles lower then with a 192. I did not try a 180 but would guess that the higher operating temperature would idle it up higher. Somewhere in between.


You also need to be certain that the distributor is at 12 degrees initial and that IF you are using a distributor with a vacuum advance that there is no vacuum advance at idle.


850 to 900 rpm is about as low as you are going to get it to idle with those carbs.


I'm using the stock 67 GT500 throttle linkage which mounts the carbs backwards like on the production 427 cars. That linkage NEEDS to be centered properly otherwise it will hold the carbs open too much at idle. It's an innocent looking linkage but it isn't child's play at all.

[Shelbypat]

Retight your intake hot. It can suck by underneath.
Patrick

[The Going Thing]

It's not the intake. He said the other carbs work fine. Drew set my carbs up so the idle adjustment is via the secondary plates. It keeps the car from running rich.

[shelbydoug]

It's not the intake. He said the other carbs work fine. Drew set my carbs up so the idle adjustment is via the secondary plates. It keeps the car from running rich.

Are you sure that he didn't mean that the idle adjustment is done on the primaries of the secondary carb?

How are the secondaries adjustable at idle? Those should be fully closed, no?

[Drew Pojedinec]

I toss the stock screws for secondary venturi. Replace with 8-32 or 10-32 set screw so it can be adjusted with carbs installed.


Dry setting:

Open primary venturi both carbs until t slot is visible. Close slowly while holding baseplate up to light. Stop closing when t slot is not visible but you can see it's location via the light.
Do this both carbs.

Secondaries, open until you can view t slot. Close to hide t slot. Do this both carbs.

This will result in a 900-950rpm no load on almost all engines.
If cam is mild and you prefer a slower rpm, close secondary venturi on both carbs.
If cam is large and you prefer a faster idle, open the primary venturi on the primary carb.

I prefer to not expose slot on secondary carb, here is my reason:
With moderate cam in the 240-250 @.050 kinda duration that is common with performance engines you see 8-10 inch of vac at idle.
If idle settings are adding fuel to keep proper a/f no load they will provide excessive richness at cruise when vac is high.
Yes you can tune around it, but better to keep it simple and bot have to chase your tail.

I'm sure there are several methods to reach the same endgoal, this is just mine.

[Royce Peterson]

No, a certain amount of airflow is needed through the secondaries for various reasons. One reason is so the fuel doesn't go stale in the secondary float bowls if a person drives the car without ever or nearly never stepping on the throttle enough to open them. Second reason is so the butterflies don't bind in the bores. Third reason is so that the primary throttle blades can be closed more in order that the idle mixture transfer slots are usable.

This is why the Holley manual calls for a specific gap on the secondary throttle blades. I checked the 1967 Ford manual, it specifies secondary throttle stops set at 1/2 turn from closed. I checked my copy of the 1965 Ford shop manual which shows the BT - BU 8V carbs and it does not give any instructions as far as I can see.

Idle speed is set using the idle stop screws on the primary bores.

It's not the intake. He said the other carbs work fine. Drew set my carbs up so the idle adjustment is via the secondary plates. It keeps the car from running rich.

Are you sure that he didn't mean that the idle adjustment is done on the primaries of the secondary carb?

How are the secondaries adjustable at idle? Those should be fully closed, no?

[shelbydoug]

Royce. I think the point being made here is that all idle plates need to be closed down as much as possible to reduce the idle speeds? The transfer slots are just part of it.

The tolerances of the throttle plates to the bores create leaks and the leaks supply fuel mixture.

Instead of just 4 plates, there are 8 and twice as much leakage through the tolerances.


Also even on the 427's, the factory cams were much milder at idle and had better idle vacuum, which helps.



I'm working on two sets of carbs. I've got the 3300 and 3301 idling as I stated and packed away.


I'm working in another set right now, this time 1850's with the hope that they will be a little smoother and lower at idle.

So far I'm still working on getting the float levels right on those and having the usual issues with the float valves (brand new) sticking open. I think Drew just whacks the carbs with a rubber mallet. That's not enough for me. I want to use a "nuclear device" just for satisfaction I think? Man those valves suck.

The Holley dry method didn't work again and even using the stains on the floats as guides punked out. I could say Niagara Falls but you know what happens to Lou Costello when he says Niagara Fallls? 


I'm seeing about the same minimum idle speeds as Drew is and Keith is at 900 as well. Also at 1-1/8 turns on the idle mixture screws and similar vacuum as I have.


The allen socket set screws on the secondaries is a good idea. Thanks Drew. I'll try that. These have to come off again because of the float issue anyway. Ironic. The one bowl giving me issues is right off of another carb already set up. Must be a sticking inlet valve? Use a 40 pound sledge, right?

[Royce Peterson]

Well like anything else the designers / engineers did everything for a reason. It's best to start with what Holley intended and work from there, carefully documenting what improves your situation and what makes your situation worse. For sure if your cam develops less vacuum than the carbs were designed for then you will have issues to solve. The factory R code 427 cams were indeed very mild by today's standards. You can compensate somewhat by carefully choosing a good roller cam that compliments the use of dual fours.

I have no experience with any of Drew's carburetors but he seems to know his business. If he knew what the rest of the engine was going to be like I am sure he could build a carburetor or pair of carburetors to suit.

Royce. I think the point being made here is that all idle plates need to be closed down as much as possible to reduce the idle speeds? The transfer slots are just part of it.

The tolerances of the throttle plates to the bores create leaks and the leaks supply fuel mixture.

Instead of just 4 plates, there are 8 and twice as much leakage through the tolerances.


Also even on the 427's, the factory cams were much milder at idle and had better idle vacuum, which helps.



I'm working on two sets of carbs. I've got the 3300 and 3301 idling as I stated and packed away.


I'm working in another set right now, this time 1850's with the hope that they will be a little smoother and lower at idle.

So far I'm still working on getting the float levels right on those and having the usual issues with the float valves (brand new) sticking open. I think Drew just whacks the carbs with a rubber mallet. That's not enough for me. I want to use a "nuclear device" just for satisfaction I think? Man those valves suck.

The Holley dry method didn't work again and even using the stains on the floats as guides punked out. I could say Niagara Falls but you know what happens to Lou Costello when he says Niagara Fallls? 


I'm seeing about the same minimum idle speeds as Drew is and Keith is at 900 as well. Also at 1-1/8 turns on the idle mixture screws and similar vacuum as I have.


The allen socket set screws on the secondaries is a good idea. Thanks Drew. I'll try that. These have to come off again because of the float issue anyway. Ironic. The one bowl giving me issues is right off of another carb already set up. Must be a sticking inlet valve? Use a 40 pound sledge, right?

[The Going Thing]

If you're running a long duration cam Ford/Holley information for stock settings is useless. 11 inches at idle causes some interesting issues. I wound venture to guess many here did away with Ford's anemic cams and went to roller valve trains and long duration high lift cams.

Drew's extremely knowledgeable and solved many issues I was suffering.  One of the first issues brought to light was the issue so many were having with the Carter Fuel Pumps that were rated at 6 PSI that were actually closer to 9 PSI. Many were putting fuel pressure regulators on.  No place to hide them on a dual quad car. The needle valve size reduction from the .110 to the .090 window size and setting them to idle primarily from the secondary so the transition slots were not exposed to a point that caused extremely rich idling because of reduced signal from low idle vacuum.

Drew rebuilt my units and even found an issue that would have ran most seasoned carb people in circles.  He doesn't just throw a carb kit in them and make them look pretty.  It's why I will never use anyone else.

[shelbydoug]

If you're running a long duration cam Ford/Holley information for stock settings is useless. 11 inches at idle causes some interesting issues. I wound venture to guess many here did away with Ford's anemic cams and went to roller valve trains and long duration high lift cams.

Drew's extremely knowledgeable and solved many issues I was suffering.  One of the first issues brought to light was the issue so many were having with the Carter Fuel Pumps that were rated at 6 PSI that were actually closer to 9 PSI. Many were putting fuel pressure regulators on.  No place to hide them on a dual quad car. The needle valve size reduction from the .110 to the .090 window size and setting them to idle primarily from the secondary so the transition slots were not exposed to a point that caused extremely rich idling because of reduced signal from low idle vacuum.

Drew rebuilt my units and even found an issue that would have ran most seasoned carb people in circles.  He doesn't just throw a carb kit in them and make them look pretty.  It's why I will never use anyone else.

Keith, I'm not arguing or calling out anyone on this. Apparently there are various ways to get the carbs to idle down.

My secondaries are set at stock. I didn't touch that adjustment, just reset the throttle plates (as Drew suggested to me). That was on the bigger 3300 and 3301's which are going to tend to want to idle higher because of the bigger throttle bore and greater leak through area's as a result.


Technically Royce is correct on the secondaries need freshening. In reality the secondaries already leak enough even at fully closed to refresh the fuel bowls.

My own caution on the secondaries is not to close them so much as they lock themselves in and won't open on demand.

Drew suggested to me that "often" the throttle plates need to be played with to get them just right. He's always reminding though about the transfer slots.

It's much simpler to do a single 4 application. The dual 4's just magnify the "considerations".


What's the point of dual four's with a stock cam?

[Drew Pojedinec]

Cuz it looks cool 😂

Personally for smaller engines I really think the 3x2's are more fun.
427+ and 2, 600's make a ton more sense.

Odd you have so many needle/seat issues. You claimed I use a mallet, but honestly I really just don't have a problem there.
I have two really good fuel filters and a high end regulator set at 5psi. No problems.

Royce is 100% correct about factory settings on factory engines.
Of course once you throw a 250@.050 cam at the car, you do whatcha gotta go to make it all work.
My car is pretty fussy if I asked it to idle below 800 in gear. You can get it tuned to do it, and I often do a "low idle check"  but it's a lit more forgiving with 100rpm more.

[shelbydoug]

Cuz it looks cool 😂

Personally for smaller engines I really think the 3x2's are more fun.
427+ and 2, 600's make a ton more sense.

Odd you have so many needle/seat issues. You claimed I use a mallet, but honestly I really just don't have a problem there.
I have two really good fuel filters and a high end regulator set at 5psi. No problems.

Royce is 100% correct about factory settings on factory engines.
Of course once you throw a 250@.050 cam at the car, you do whatcha gotta go to make it all work.
My car is pretty fussy if I asked it to idle below 800 in gear. You can get it tuned to do it, and I often do a "low idle check"  but it's a lit more forgiving with 100rpm more.

I've got'em on a small block so the two fours take up the whole engine! 

I had a neighbor stop and ask if his brother visiting from Florida (they come here to spread the virus and break quarantine) see my car (the '68 GT350 was out).  He has a 66 Mustang FB back in FL. He looked under the hood, swayed like he was going to faint, paused and said, "that's 500 hp!". I said, "yea, kinda'".



The carbs I am working on are on that engine. A 347.

I can't idle any lower then what I am at BUT I haven't tried Drew's secondary trick yet. It just gets too rough under 800. 870 is fine with me. It's like a marching band now at idle. Boom, boom, bada, bada, boom, boom. It's got a rythem to it.


Drew. As far as the sticking inlet valves, if I have fuel shooting out of the vent like a gyser, then likely THE VALVE IS STUCK OPEN. Do I need to look? No.

In all honesty, that's the bowl I just pulled off of another carb which had been sitting a month or so, and I should know better then not to verify it wasn't stuck from sitting?    Me bad.


Mallet. You posted a video on your Facebook of you whacking, ok, tapping a carb on a running engine with a gimpy valve. I only saw it and didn't create it. Some of us here do follow you there you know?


Fuel. I'm in NY, just north of NYC. Whatever is in the pumps is what I use. AMMACO 93 and sometimes SUNOCO 93, is in the cars but I've heard complaints from some of the street rodders about the ethanol. It's only 10%. Their cars sit sometimes a couple of weeks and that in my experience is over the limit with a Holley once it's had fuel in it.

My Webers are MUCH more forgiving since they have no gaskets in the bowls and the inlet valves are glass balls with no rubber parts in them but they can stick too.


You do 30 carbs a day. I may have done 30 Holleys in my life total. Plus some think I'm retarded anyway so maybe they are right? I'll get it right. It just takes me longer.

I do have the tendency of creating my own problems. My son says it's because I have too many parameters going at the same time.

It's like the guy spinning the plates on sticks on the old Ed Sullivan show. You have to keep them all spinning without breaking any. The wife counts the missing plates.