How far open do you have the secondary idle stop set?

 

Admittedly, I am not sure what you mean on this. I have vacuum secondaries and there are no idle fuel mixture screws on the rear metering block.

I don't see another way to adjust anything else. Can you elaborate.

Dcubedus

 

1. Check the idle adjustment screws to see if they have bottomed out and left a round impression. This will render them useless.

2. There is a slot in the throttle body for your idle circuit. If the butterfly is open beyond this point, your idle screws won't do anything.

3. Don't drill the holes...it's not easy to un-drill them

Look up idle circuit adjustment and do it the right way

http://forums.holley.com/showthread.php?4968-Secondary-Transfer-Slot-won-t-idle-down

 

1. Check the idle adjustment screws to see if they have bottomed out and left a round impression. This will render them useless.

2. There is a slot in the throttle body for your idle circuit. If the butterfly is open beyond this point, your idle screws won't do anything.

3. Don't drill the holes...it's not easy to un-drill them

Look up idle circuit adjustment and do it the right way

Secondary/Transfer Slot/won't idle down

1. I did remove the idle mixture screws and they look good. Nice and pointy, not flattened out.
2. Yes, exactly my condition (see picture).

Dcubedus

 

A lot of my experience with carburetors comes from 2-strokes, but carburetors work on the same principles no matter what. So I will say this - your engine is not that radically modified, it should idle fine. Do not drill the holes, double and triple check everything in your carburetor then start over - lightly bottom out all the idle and air screws and back them out the same number of turns (1.5-2).

 

That will work if your vacuum is low due to the cam lift. Been there. Done that. Stake the screws that hold the plates to the shaft when you get the hole size right. Dave R.

 

I've never had to drill the plates. The cam isn't rowdy by any means.
Edelbrock 7106, Edelbrock Performer RPM Camshaft Kits | Edelbrock - Free Shipping on All Orders @ JEGS

Surprises me you can't get that to idle... which 4150 carb? Holley makes
several sizes in that designation.

 

Definitely open the secondary throttle blades to the point where you can get your primaries set for the correct position on the T slots. It'll make all the difference in the world. You'd have to be pretty hard core to need to drill the throttle blades (unless you don't have the secondary idle stop set screw).

 

At idle, I am getting manifold vacuum around 6inHg.

^^^ Your problem is most likely that your power valve is open. That's a REALLY low vacuum for that cam. I'd check for leaks first. If none found I'd do TWO things. First is swap out the power valve for a 35 or maybe a 45. Second, I'd swap out the PCV (if you have one) for a low-vacuum version. At 6"hg it's also probably wide open.

PS: You didn't say what model 4150, but if you have a secondary PV I'd eliminate it, as well.

 

What is your initial timing?

 

Powervalves should not be flowing at idle. All fuel from the PV goes into the main wells and joins the same passage as the main jet.

It seemed like I had to run my motor pretty rich at idle with the secondary stop adjusted to get air in at idle. I think drilling is a better option since air is let in closer to the fuel. It would be time consuming to get it right w/o over doing it though.

 

Exactly right. However, the power valve will open when the manifold vacuum falls below its rating, regardless of throttle opening. In addition, a good backfire could have wiped a "pre-backfire-protected" version.

 

Thanks for all of the input. I got some more time today to look at this now that the weather is better. I have looked into some of the questions that you have been asking me. Just to clarify, I can get the engine to run and idle just fine. However, it is very rich and the idle mixture screws are all the way in.

What type of Holley 4150 is my carb?
I was told by the previous owner that the Holley carb was factory correct. It is stamped with “C70F-3510-A” and also “LIST-3793”. It does look exactly like the 4150 pictured in the Mustang Shop Manual.

What is my initial timing?
Believe it or not, the initial timing measured at ~37degrees. I have the distributor vacuum line out and plugged and the timing light cable on spark plug wire #1. According to the engine manual that the builder provided, 37degrees should have been the total timing. So, I backed it down to around 12 degrees. Of course I had to bump up the idle speed adjustment screw to keep it idling.
Where should the initial timing be for this engine?

Vacuum Leaks?
I checked all the vacuum lines for leaks. Even removed the carb and made sure the base plate gaskets were in good shape. I removed the PCV and it is very clean (the whole engine is new). I could easily blow through it in both directions. Besides that, I don’t know what to check on the PVC.
With the engine running, I pulled the vacuum line out of the brake booster and the rpm jumped up. I put my finger over the vacuum line and the engine RPM settled back down to what it was when it was plugged in. I assume that is working correctly?

Adjusting the Secondary Idle?
While I had the carb off I went ahead and adjusted the secondary idle stop screw on the bottom of the carb. I only opened it slightly as it was very close to exposing the transfer slots. I opened them to just below the slot.

After all of this I am still reading around 6inHg at idle and the fuel idle mixture screws still don’t seem to do much. In fact, it seemed to run best when they were screw in all the way. Any more troubleshooting guidance would be appreciated.

Dcubedus

 

What is my initial timing?
Believe it or not, the initial timing measured at ~37degrees. I have the distributor vacuum line out and plugged and the timing light cable on spark plug wire #1. According to the engine manual that the builder provided, 37degrees should have been the total timing. So, I backed it down to around 12 degrees. Of course I had to bump up the idle speed adjustment screw to keep it idling.
Where should the initial timing be for this engine?

I don't believe it.

You sure you measured 37 initial? That would give you like 67 total mechanical timing. Car would be pinging like crazy if it would run at all. And with that much initial, I'd be shocked if the car would turn over once it's warm.

Before you do anything else, I'd make 100% sure your timing marks are accurate.

Then once you're 100% sure, get your timing right.

And AFTER the timing is right, then start working on your fueling issues.

My car seems to be fine anywhere between 10-16 initial. Any higher than 16 (and even at 16) the starter was having trouble turning it over when the engine was warm. I just changed the distributor springs out so it's all in by 2500 rpm (at everyone's recommendation). Although I'm still fine tuning the fueling to be sure if it helped or not.

This article was a TON of help for timing:
http://www.fordmuscle.com/archives/2000/03/timing/index.shtml

 

Your cam is not that radical. Do not drill your carb. Open up the secondary plates a bit and lower the primaries until the slots are not uncovered. Initial timing should be no more than 12 degrees. Check your power valve as Bartl suggested. And get one that opens at a very low vacuum.

Is this a new build ? And is the problem new as well ? Your cam many not be timed right ?

Z

 

It is a brand new build so the problem has been there all along. I guess that I will go replace the power valve next as others have suggested. I have no idea what type is in there now.

Dcubedus

 

Well, it ain't too big a carb......
application: 390ci/4speed manual transmission ( Ford Fairlane, Ford Mustang, Mercury Comet, Mercury Cougar)

600cfm, vac. secondaries, auto choke, center-hung floats

metering: 5119/ 4841

idle speed engine RPM
hot: 600
fast: 1850

initial idle mixture: 1-1 1/2

float levelprimary: lower side of float parallel to fuel bowl floor
secondary: lower side of float parallel to fuel bowl floor

 

Well, it ain't too big a carb......
application: 390ci/4speed manual transmission ( Ford Fairlane, Ford Mustang, Mercury Comet, Mercury Cougar)

600cfm, vac. secondaries, auto choke, center-hung floats

metering: 5119/ 4841

idle speed engine RPM
hot: 600
fast: 1850

initial idle mixture: 1-1 1/2

float levelprimary: lower side of float parallel to fuel bowl floor
secondary: lower side of float parallel to fuel bowl floor

its too small for performance. an 850 would be a good size.

 

Have you checked your float levels?

 

Dcubedus, I think adding initial timing will help things. It will raise vacuum allowing you to close the throttle some ay idle. 18-20 degrees of initial would be good. It will also help throttle respones.

You will not be able to adjust idle mixture until you get the t-slots almost covered. The t-slots should look square with the throttle closed. Set it there and try not to make any adjustments to the primary idle screw.

You can adjust idle with the secondary set screw as others have said. Some intakes will let you do it with a very short screw driver. You can also take the screw out from the bottom and screw it in from the top. You have to turn the engine off to adjust it, but it is easier than with it underneath. Don't worry about the secondary t-slots. Them don't even flow fuel unless it is a four corner idle carb.

I would still consider drilling the throttle blades. Opening the secondaries works, but it is effectively a vacuum leak away from the idle discharge port that will leave you poor distribution at idle. Replacement throttle plares are $10 for four if you need them for any reason.

 

I ran a Performer RPM cam on a 289 and I did not have to drill the throttle plates to get the idle adjusted. My idle vacuum was in the teens somewhere too. 13 or 15. You have something else going on.

 

I beg to differ with you BrianJ5600 about the secondary idle circuit. It does flow fuel, it's just not externally adjustable. You can make changes in the secondary idle mixture by altering the idle feed restrictions.

As for the reason for a secondary idle circuit, it's there to ensure the fuel in the secondary bowl doesn't become "stale". If you drove in such a way that the secondary barrels were never used, the "stale" fuel would have everything gummed up, even the inlet needle and seat. Imagine the result when the secondaries were eventually called for.

To the OP; before you go blaming the carb, and making modifications that are not easily undone, please check everything else first. Check to see if the timing marks on your balancer actually correspond to true TDC. The ring could have slipped over the years.

See if it's possible to get the idle vacuum a bit higher. Low vacuum reduces the amount of air that can be drawn into the engine for a given throttle opening. Is your PCV system installed and working properly. The metered air admitted through the PCV system is taken into account when the carb is calibrated.

 

To the OP; before you go blaming the carb, and making modifications that are not easily undone, please check everything else first. Check to see if the timing marks on your balancer actually correspond to true TDC. The ring could have slipped over the years.
QUOTE]


The engine is newly rebuilt but that doesn't mean mistakes cant happen. How would I go about checking that the timing marks correspond to TDC?

Dcubedus

 

Nobody seems to be seeing the root problem here. This motor should be generating at least 15"hg of idle vacuum, not 6"hg. That's the first problem that needs to be corrected.

Now, WHERE are you measuring your vacuum? It needs to be from the port that comes out from under the front bowl, on the passenger side, at a 45* angle.

Next, the PCV valve is checked by noting the difference in idle speed when you pull the hose from the valve cover and plug the end with your finger. Idle should DROP by approximately 50-75 rpm.

Brian, if this motor TRULY has 6"hg of manifold vacuum, at idle, the throttle plates are probably open more than enough to cause the pressure differential necessary to draw fuel through the main circuit.

 

The secondary t-slots do flow, but not at the opening required at idle with the primary blades letting in air too. There is something wrong for it to have so little vacuum. The cam card says 11 inches @ 1000rpm, but that seems low. I still have a very hard time believing the mains are flowing below 1500 with no load.

 

While not overly radical, that cam is ground with a 108 degree lobe separation angle. It will probably produce at most 12 inches of vacuum. Which is still double the six he's seeing. I think there's other issues. To the OP, do you have adjustable rockers? What's the timing, was the dam degreed? I saw the timing post, mentioned some high number are you sure about that?

 

Thanks for all of the feedback on this everyone. I’ll try to answer some of your more recent questions;
The entire drivetrain on this car is newly rebuilt and was professionally done Southern Automotive in McDonough, GA. To my understanding, the carb was also rebuilt at the time. The only miles on this drivetrain are from me driving it up and down the street. I bought the car in this state and have all of the receipts and build specs. The previous owner had just had all of this work completed when he decided to sell it. I did not have any direct contact with this engine’s rebuild or those who rebuilt it. The rockers are specified as “Pro Comp Aluminum Roller Rockers”.

I did perform a quick carb check of the float levels. Admittedly, it was not on the most level spot but it was no more than a slight trickle out of the sight holes. I will take a better look at this over the weekend.

The engine timing is currently set at 12 degrees initial. When I started this post it was up around 38 degrees. I am not sure why it was set that high to begin with. There was no real significant vacuum change between those settings.

I am using the vacuum port off of the carb spacer on the backside of the carb. See picture. Is this a legitimate port to use? That seemed like the easiest place to tap into it. As you can see from the other pics, there are vacuum lines all over the place on this thing, something that I am not used to with my other 67 mustang that has a 1971 302 in it and doesn’t have all of this factory correct stuff on it

Whether needed or not (there still appears to be some debate over this), I did order 3 new power valves (3.5, 4.5 and 6.0) from Summit just in case I need to go that route. However, I agree that there seems to be something else going on here wrt to the low vacuum. Unless any of you can tell me that I am using the wrong vacuum port for this measurement, I may go buy another vacuum gauge just to make sure mine is still functioning correctly. Other than that, I am still all ears.

Dcubedus

 

Thanks for all of the feedback on this everyone. I’ll try to answer some of your more recent questions;
The entire drivetrain on this car is newly rebuilt and was professionally done Southern Automotive in McDonough, GA. To my understanding, the carb was also rebuilt at the time. The only miles on this drivetrain are from me driving it up and down the street. I bought the car in this state and have all of the receipts and build specs. The previous owner had just had all of this work completed when he decided to sell it. I did not have any direct contact with this engine’s rebuild or those who rebuilt it. The rockers are specified as “Pro Comp Aluminum Roller Rockers”.

I did perform a quick carb check of the float levels. Admittedly, it was not on the most level spot but it was no more than a slight trickle out of the sight holes. I will take a better look at this over the weekend.

The engine timing is currently set at 12 degrees initial. When I started this post it was up around 38 degrees. I am not sure why it was set that high to begin with. There was no real significant vacuum change between those settings.

I am using the vacuum port off of the carb spacer on the backside of the carb. See picture. Is this a legitimate port to use? That seemed like the easiest place to tap into it. As you can see from the other pics, there are vacuum lines all over the place on this thing, something that I am not used to with my other 67 mustang that has a 1971 302 in it and doesn’t have all of this factory correct stuff on it

Whether needed or not (there still appears to be some debate over this), I did order 3 new power valves (3.5, 4.5 and 6.0) from Summit just in case I need to go that route. However, I agree that there seems to be something else going on here wrt to the low vacuum. Unless any of you can tell me that I am using the wrong vacuum port for this measurement, I may go buy another vacuum gauge just to make sure mine is still functioning correctly. Other than that, I am still all ears.

Dcubedus

Photo shows it hooked to ported vacuum.

He says it is hooked to the carb spacer on the rear of the carb. Something is hooked to ported vacuum but maybe not the vacuum advance?

 

I suspect the mark at 38 degrees was to indicate total timing, not initial timing.

Are you checking the initial timing with the vaccuum advance line disconnected? I also suspect that your vacuum advance was or is hooked to full manifold vacuum which would explain the high initial timing reading. It should be hooked to a timed or ported vacuum souce which is typically the nipple on the passenger side of the primary metering block.

As is often the case this sounds more like an ignition problem rather than a carb problem.

Don't drill any holes until you are certain you have the ignition system correctly adjusted!

 

I would look for a vacuum leak ,
here's what i do , cap off all vacuum ports ! then do the spray test around carb base

 

^^ Definitely check this too.

I know you said you checked the lines, but that doesn't mean there isn't a leak somewhere that you can't see visually.

6in of vacuum is pretty low. I know your cam is larger than mine, but I'm getting 19 at idle. When I had a vacuum leak, I got 15.

Try hooking your vacuum gauge up to the intake manifold rather than the base of the carb to see if there's a difference. Just unhook something you don't need for tuning.

Also, are you using manifold or ported vacuum for your timing advance?

 

Yes. I have the vacuum guage hooked up to the carb spacer port on the backside of the cab and the vacuum advance is hooked up on the top front passenger side port of the carb.

Based on your advice, I will attempt to find TDC and ensure that it aligns with the timing marks. Then, I will move the vacuum gauge to one of those unused ports off of te PCV line. I will also buy a new vacuum guage for a sanity check. If the vacuum still reads low, I will start pulling vacuum lines (power brake booster and PCV) to find any potential leaks.

Unfortunately, the tach in my instrument cluster is not working. I had planned to send it to the Tachman fo repair. I might go buy a cheap one and install it for temporary use so that I can monitor RPM.

I will get back to you this weekend on what I find.
Thanks,
Dcubedus

 

This Weekend’s Update

Timing
I removed the #1 spark plug (fouled and a bit oily) and gently placed a wooden chop stick into the hole. I manually cranked the engine and watched the chop stick go in and out of the spark plug hole. I found that the chop stick did reach its highest point out of the hole (Top Dead Center) just as the “TDC” timing mark was at the pointer. I did have the distributor cap off as well so that I could confirm that I was on the compression stroke. I left the timing where it was, about 12 degrees.

Carb Float Levels
I double checked the carb float levels today on a completely flat surface. They may have been a little high so I lowered them just a bit.

Vacuum Leaks
I pulled the carb and put on brand new Fel-Pro gaskets between the intake & spacer and the spacer & the carb. Under the advice of some of you, I moved the vacuum gauge over to one of the unused ports off of the PCV loop (one of the two on back passenger side in the pics I posted in this thread). The vacuum is still reading ~6inHG. The RPM is unknown as I don’t have a functioning tach yet.

I pulled off the power brake booster vacuum line and the engine RPM immediately increased. I put my thumb over the end of the open hose and the RPM quickly decreased back down to where it was. Feeling what seemed like good suction, I reconnected the line to the booster.

I pulled the PCV out of the valve cover and I did NOT notice any RPM change. I put my thumb over the open end (bottom) of the PCV and the engine RPM came way down (almost stalling). I removed my thumb and RPM increased back to where it was. Feeling what seemed like good suction, I pushed the PCV back into the valve cover.

Vacuum Gauge
Instead of buying a new vacuum gauge, I fired up my 67 coupe (with mildly warmed over 1971 302 that runs just fine) and put the same vacuum gauge on one of the manifold vacuum ports. It read 16inHG. So, I don’t think that my vacuum gauge is bad.

What Next?
Should I now checkout and/or replace the carb power valve as some have suggested?
What about late valve timing? I have no idea how to check this though?
Others?

Thanks again,
Dcubedus