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-   -   Holley Carb Tuning with AEM A/F gauge (https://www.fordmuscleforums.com/all-ford-techboard/653133-holley-carb-tuning-aem-f-gauge.html)

extech 04-15-2019 06:24 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
you need to use a vacuum gauge to set idle mix. not typical for both screws to be the same. without vac. gauge, turn each in to a rpm drop. (lean drop). then backout 1/2 turn. do for each side over and over. don' t worry about them being the same

65merccyclone 04-16-2019 03:59 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
Had an interesting day today. Pulled the carb off and backed the curb idle screw off thottle plate. Loosened the screws for the blades on the primary throttle shaft. The throttle shaft would not move enough to cover the transition slot. Tightened the 4 screws. I looked at the linkages and the culprit seemed to be the choke adjustment screw or a linkage problem with the choke mechanism. I also installed 65 demon mains since the wide open A/F was a little high. Another change I made was to install a bolt for the secondary throttle adjustment so I could adjust that if necessary.

I pulled the choke assembly off the carb and the throttle plates would cover the transition slot. Started to reinstall the choke mechanism but found the throttle shaft/assembly moved as I inserted the second screw meaning something was in contact with the primary throttle shaft and causing it to move. The throttle plate moved .029. The only thing I could find was the white bushing the adjustment screw goes through for the choke adjustment. I removed it and filed it down.

Reinstalled the parts and the transition slot was covered. I then adjusted it using the curb idle screw to the square position and set the idle bleed screws to the recommended 1.5 turns out.

Reinstalled carb and started it up. It wouldn't idle with the curb screw set at this position. Turned in in until I got the recommended 850 rpms. Started adjusting the idle mixture screws and ended up turning them in to where they were before 1/2 turn + 1/16. I'm afraid the transition slot will be right where it was before. The idle bleed screws were much more responsive than they were before.

Took several test runs and the A/F is a little worse than it was before. The off idle bog returned but not as bad.

Decided to adjust the secondary screw I put in. I was expecting this to increase the idle rpms by letting some air in from the secondary side. there wasn't much change at all. I ended up reversing the changes I made to this setting.

Tomorrow, I'll pull the carb to see where the transition slot is and put in some new plugs.

extech 04-16-2019 06:43 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
when you opened the secondaries to increase idle speed you didn't realize that the fuel was increased also through the tip in circuit in the secondaries. after opening the secondaries you need to turn in the idle mix screws to make a change. sometimes the tip in circuit is too rich(wrong booster assembly). nothing is as it seems with a carb

65merccyclone 04-16-2019 09:11 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by extech (Post 1629578947)
when you opened the secondaries to increase idle speed you didn't realize that the fuel was increased also through the tip in circuit in the secondaries. after opening the secondaries you need to turn in the idle mix screws to make a change. sometimes the tip in circuit is too rich(wrong booster assembly). nothing is as it seems with a carb


'nothing is as it seems with a carb' The most truthful statement all day.

Hmmm. I got it wrong again. I though opening the secondary screw gave it more air. I wasn't aware it gave it more fuel too. The idle screws are already set at 1/2 + 1/16 (pretty tight) so I don't see any benefit to opening the secondaries if that add more fuel. I don't understand why this engine needs the transitions slots open so much to idle at 850.

Thanks for the great comments.

65merccyclone 04-16-2019 09:13 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by extech (Post 1629578905)
you need to use a vacuum gauge to set idle mix. not typical for both screws to be the same. without vac. gauge, turn each in to a rpm drop. (lean drop). then backout 1/2 turn. do for each side over and over. don' t worry about them being the same


I have been using the vacuum gauge. The highest reading I get is 15 inches. I can't really turn them back out a 1/2 turn from the stumble point. The A/F ratio keeps getting richer with every small turn I make. Thanks again.

extech 04-17-2019 07:25 AM

Re: Holley Carb Tuning with AEM A/F gauge
 
are there holes in the throttle plates?

DeepRoots 04-17-2019 01:03 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
A few thoughts:


-Wideband A/F meters are awesome. That said, don't get hung up on a "correct number" there isn't one. Some engines want to idle at 12.5, some want to idle at 14, whatever, just figure out what the engine wants and use the O2 as a reference point for that particular situation.
For instance, finding your cruise "lean limit" would be by jetting down until you encounter a slight surge at cruise. At that point you jet up until the surge is gone. Again, this leanest cruise may be at 14:1, it may be at 16.... there are more factors than I care to list, but the main ones have to do with camshaft duration, and ignition timing at that point. This will effect your overall WOT fuel flow obviously, and the appropriate thing to do is enlarge the PVCR to bring your total fuel back into the range you require.



-I was gonna say the choke screw was probably holding open the throttle, but you already figured that out. Happens all the time and is annoying.

Opening the secondary DOES add air, but if you hit the secondary transfer slot it will add a ton of fuel. The secondaries always bleed some fuel via the .024 hole below the secondary slot. 99% of the "overly rich" idle issues I encounter have to do with transfer slot settings. This is even more critical on multicarb setups.
I like to change out the Holley flat head secondary adjuster for a 10-32, 1/2inch long set screw. This makes minor changes with an allen wrench very easy.


You need to take this effort one step at a time. Order of operation is generally:
-timing curve
-idle settings
-cruise settings
-WOT settings
-Secondary WOT tuning

-fix whatever stumble via accelerator pump settings. Adjusting the idle speed even a small amount can create a stumble just by loosing preload on the pump, etc. This is why I put this last, hate to fix an issue and have to revisit it.


Good luck


Drew

65merccyclone 04-17-2019 05:38 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by DeepRoots (Post 1629578999)
A few thoughts:


-Wideband A/F meters are awesome. That said, don't get hung up on a "correct number" there isn't one. Some engines want to idle at 12.5, some want to idle at 14, whatever, just figure out what the engine wants and use the O2 as a reference point for that particular situation.
For instance, finding your cruise "lean limit" would be by jetting down until you encounter a slight surge at cruise. At that point you jet up until the surge is gone. Again, this leanest cruise may be at 14:1, it may be at 16.... there are more factors than I care to list, but the main ones have to do with camshaft duration, and ignition timing at that point. This will effect your overall WOT fuel flow obviously, and the appropriate thing to do is enlarge the PVCR to bring your total fuel back into the range you require.



-I was gonna say the choke screw was probably holding open the throttle, but you already figured that out. Happens all the time and is annoying.

Opening the secondary DOES add air, but if you hit the secondary transfer slot it will add a ton of fuel. The secondaries always bleed some fuel via the .024 hole below the secondary slot. 99% of the "overly rich" idle issues I encounter have to do with transfer slot settings. This is even more critical on multicarb setups.
I like to change out the Holley flat head secondary adjuster for a 10-32, 1/2inch long set screw. This makes minor changes with an allen wrench very easy.


You need to take this effort one step at a time. Order of operation is generally:
-timing curve
-idle settings
-cruise settings
-WOT settings
-Secondary WOT tuning

-fix whatever stumble via accelerator pump settings. Adjusting the idle speed even a small amount can create a stumble just by loosing preload on the pump, etc. This is why I put this last, hate to fix an issue and have to revisit it.


Good luck


Drew

I came close to just keeping it the way it was when it was getting 13.2 at idle and the cruise ratios were in the mid 14s. I read David Vizard's book and he mentions getting incredible fuel economy along with good power numbers so I decided to continue tinkering. I think my problem might be the carb itself. It's a 4160 and does not have the tuning options that other holley carbs offer. I might need to determine if buying a better carb is the right decision. At $4.00 + per gallon, increasing the fuel economy by 50% should make the change worth the financial cost.

The engine ran worse with the 65 main jets in it so I put those back in today. The little bit of hesitation is gone. The transition slots are not as open as they were before because I don't have the choke screw engaged as much. I thought I would try tuning it with the least amount of transition slot possible. (it's currently at square plus 1 turn of the curb idle screw so it's probably closed less than it was before) The odd thing is, it's running a little richer throughout the rpm range, more in the 'best power' range of 13-13.9 and 11-12.5 during acceleration.

I didn't know what the size or thread pitch of the secondary adjustment screw so I bought several sizes and all were wrong. I found a small bolt in my spares box that was the right thread size, pitch and length so I installed that.

I think the accelerator pump is set right. At the current idle speed, the lever can be rocked a little bit and has a .015 gap. It moves as soon as the throttle is moved.

The advice you have given is sound advice. Thank you

DeepRoots 04-18-2019 11:44 AM

Re: Holley Carb Tuning with AEM A/F gauge
 
All I work with are older 4160/4150 Holleys. Adjustments in my case are via set screws that I drill to different sizes.


Anyway, your accelerator pump setting is incorrect.
Here is thing I wrote last time:


https://www.fordmuscleforums.com/fal...ator-pump.html

65merccyclone 04-18-2019 08:32 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by DeepRoots (Post 1629579057)
All I work with are older 4160/4150 Holleys. Adjustments in my case are via set screws that I drill to different sizes.


Anyway, your accelerator pump setting is incorrect.
Here is thing I wrote last time:


https://www.fordmuscleforums.com/fal...ator-pump.html


I have heard that installing set screws and drilling them out is a good technique. I'm not quite that advanced yet.

You are correct regarding the accelerator pump spring. I couldn't really make a good measurement with the carb on the car but it seems to be less than 5/8 in length. I put the feeler gauge on it at the idle point not wide open throttle. I'll be pulling the carb off again so I'll check it on the bench.

Good write up on that other thread. Thanks for the comments.

65merccyclone 04-24-2019 02:33 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
I thought I would post an update. Blueprint Engines sent me a replacement carb. I got it on Tuesday, transferred my stuff from the old carb to it (secondary spring kit, blue accelerator cam and demon 66 jets). I looked at the carb before installing it and found the transfer slot was adjusted properly.

I started the engine and the high idle was way too high (2600 rpms) so I turned it down and changed the setting for the choke from the 8 slot to the 3 slot. (it's warm here so I don't need that much choke) I set the idle screws to 1/2 turn where it registered A/F of 14.3 - 14.7 at idle. This was a little too low so I opened them up 1/16. A/F at idle is 13.2 - 13.7 but at cruise it's 14.7 - 15. Vacuum went from 13.5 to 15. The accelerator pump spring is at 5/8 and moves when the throttle is cracked.Throttle response is crisp, the engine is running better than it has since I've owned it.

I don't know what is wrong with the carb I got with the car when I bought it but this one is much better.

extech 04-24-2019 06:43 PM

Re: Holley Carb Tuning with AEM A/F gauge
 
bet float level was off

65merccyclone 04-25-2019 09:40 AM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by extech (Post 1629579241)
bet float level was off


It could be the floats. I had the car at a local hot rod shop last October. One of the things they did was set the float levels, along with tuning the carb.

Rusty_S85 04-28-2019 10:32 AM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by 65merccyclone (Post 1629579235)
I thought I would post an update. Blueprint Engines sent me a replacement carb. I got it on Tuesday, transferred my stuff from the old carb to it (secondary spring kit, blue accelerator cam and demon 66 jets). I looked at the carb before installing it and found the transfer slot was adjusted properly.

I started the engine and the high idle was way too high (2600 rpms) so I turned it down and changed the setting for the choke from the 8 slot to the 3 slot. (it's warm here so I don't need that much choke) I set the idle screws to 1/2 turn where it registered A/F of 14.3 - 14.7 at idle. This was a little too low so I opened them up 1/16. A/F at idle is 13.2 - 13.7 but at cruise it's 14.7 - 15. Vacuum went from 13.5 to 15. The accelerator pump spring is at 5/8 and moves when the throttle is cracked.Throttle response is crisp, the engine is running better than it has since I've owned it.

I don't know what is wrong with the carb I got with the car when I bought it but this one is much better.

Not to get off topic but you mentioned Blueprint Engines, is that the engine you are running?

65merccyclone 04-28-2019 11:58 AM

Re: Holley Carb Tuning with AEM A/F gauge
 
Quote:

Originally Posted by Rusty_S85 (Post 1629579357)
Not to get off topic but you mentioned Blueprint Engines, is that the engine you are running?


Yes. The car came with a BP 306 installed in it. Documentation says it makes 390 hp.


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