Holley Transfer Slot adjustment - Chevelle Tech
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  #1  
Old May 16th, 09, 10:31 PM
jjl4004 jjl4004 is offline
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Default Holley Transfer Slot adjustment

I have my Holley Street Avenger carb off and am trying to adjust the transfer slots since I have a slight bog. From what I've read using the search, the slots are supposed to look like little squares and have around .02 to .03 of an inch showing. What I can't find is a simple explanation on how to make the transfer slots smaller. Is there an adjustment screw or something? I'm taking a look at it right now, but don't want to start messing with it until I know for sure.

Thanks for any help you could provide.
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  #2  
Old May 16th, 09, 10:47 PM
rkd rkd is offline
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Default Re: Holley Transfer Slot adjustment

The transfer slots are supposed to be slots so that they are available to flow fuel over a slight range of throttle plate opening from the idle discharge openings upward. The top of the slot should be just visible above the throttle plate at curb idle.

They probably can be modified, but there would seem to be several easier ways to fix a bog. Working on the slots would be an extreme item for little gain.

I would start with accelerator pump adjustment, idle mixture adjustment using a vacuum gage, etc, and review where the timing was set.
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  #3  
Old May 16th, 09, 10:53 PM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment

ok, well I got impatient (I know I only posted a few minutes ago) and I figured out where the adjustment screw was. Problem now is that I backed it out as far as it can go and I don't have the perfect little square that I've seen in some of the searching I've done. It's really close, but not perfect. Am I ok? Its that all I can do to adjust it? It's a lot more "square" than what I had earlier.

Once the carb is back on, does anybody anticipate any problems I might have trying to fire the engine for the first time after this adjustment? Any tips/suggestions on how to get it close before I fire it up? I had the carb working in the car earlier today and won't get a chance to fire it up tonight (pesky neighbors).

One last thing. When I was tilting the carb around trying to locate the transfer slots and adjust them, a lot of the gas that was in the floats and other parts of the carb spilled out. Am I good just putting the carb back on, wiping it down and fire it up? Any issues from the fuel spilling out?
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  #4  
Old May 16th, 09, 11:01 PM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment

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Originally Posted by rkd View Post
The transfer slots are supposed to be slots so that they are available to flow fuel over a slight range of throttle plate opening from the idle discharge openings upward. The top of the slot should be just visible above the throttle plate at curb idle.

They probably can be modified, but there would seem to be several easier ways to fix a bog. Working on the slots would be an extreme item for little gain.

I would start with accelerator pump adjustment, idle mixture adjustment using a vacuum gage, etc, and review where the timing was set.
Thanks for the quick reply. Yeah, this was my second to last resort trying to fix the bog. I've adjusted the accelerator pump, set the idle mixture using a vacuum gauge and tried multiple timing settings...all to no avail. If this doesn't fix it, I figure I'll read up on accelerator pump cams and see if I should look into changing that. Before I did that though, I wanted to make sure that I've done all I could before I go and look into the accelerator pump cams.
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  #5  
Old May 16th, 09, 11:50 PM
Dave427 Dave427 is offline
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Default Re: Holley Transfer Slot adjustment

What secondary spring do you have in there?

Dave
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  #6  
Old May 17th, 09, 12:01 AM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment

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Originally Posted by Dave427 View Post
What secondary spring do you have in there?

Dave
The carb is a 770cfm vac secondary and I have the second stiffest spring in there (I think it has a brown tip). I have the spring kit and so far, that's what the car likes the best. I hope that is what you meant by spring...as you can tell, carbs are'nt "my thing"...but I'm trying!

Does it matter what secondary spring I have in there for low rpm/throttle issues? I didn't think it did.??
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  #7  
Old May 17th, 09, 1:22 AM
jbird jbird is offline
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Default Re: Holley Transfer Slot adjustment

Generally speaking, a low speed off idle bog or hesitation is caused by too small squirter, or too lean idle, or both. Make sure you don't have any vacuum leaks as well. Try adjusting the pump cam to give it a bigger/earlier squirt if possible. The next thing I would do other than that is go up a few sizes on the squirter. If it's a .028, try a .033 or .035. Good luck.
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  #8  
Old May 17th, 09, 1:39 AM
eric13617 eric13617 is offline
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Default Re: Holley Transfer Slot adjustment

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Originally Posted by jbird View Post
Generally speaking, a low speed off idle bog or hesitation is caused by too small squirter, or too lean idle, or both. Make sure you don't have any vacuum leaks as well. Try adjusting the pump cam to give it a bigger/earlier squirt if possible. The next thing I would do other than that is go up a few sizes on the squirter. If it's a .028, try a .033 or .035. Good luck.
I totally agree. At 2000 ft. above sea level, all my carb needed was a .033 squirter,on the primary.
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  #9  
Old May 17th, 09, 8:02 AM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment

ok, so now I'm confused. I thought (after doing a lot of searching on the subject) that adjusting the transfer slots so they look like little squares is a good thing for overall carb performance and that a lot of other issues can arise from the transfer slots being too far open and allowing too much fuel to get through at idle while the carb is searching for enough air to keep the car from dying. The Holley website and an article in Chevy High Performance mag both state that proper transfer slot set up is important and to check that prior to getting parts for a problem you might not have..?

Thanks for the replies so far. I appreciate hearing from others and learning more.
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  #10  
Old May 17th, 09, 8:10 AM
BillyGman BillyGman is offline
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Default Re: Holley Transfer Slot adjustment

I don't know about that type of Holley, but some Holley carbs ( like the 4500 model, and I believe the 4150 also) have an idle speed screw for the primaries, and one for the secondaries too. With the carb off of the intake manifold, you simply adjust the primary transfer slots with the primary idle speed screw. Then you install the carb again, and adjust the idle speed with the engine running, using the secondary idle screw only. That is how I was told to get the primary transfer slots "squared".

BTW, I was also told NOT to go screwign around with squirter size changes, nor with pump shot adjustments until the primary transfer slots are squared first, and the secondary idle screw is then adjusted with the engine running to obtain the proper idle RPM.

Doing the above might solve your problems. If it doesn't, then, and ONLY then, should you go on to pump shot adjustments.
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Last edited by BillyGman; May 17th, 09 at 8:25 AM.
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  #11  
Old May 17th, 09, 9:32 AM
Xtreme70SS396 Xtreme70SS396 is offline
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Default Re: Holley Transfer Slot adjustment

What BillyGman said, with the added part about timing first, carb second. Sounds like you've already got your timing set, so I'll say I hope it's in the 16-18 advanced range.

When you adjusted the slot, you've lowered or raised your idle rpm. You will likely have some issues when you first start it if you lowered it, might need a second person to keep it running while you adjust the secondary screw. (Typically a screw or allen key accessible from under the carb plate on a VS model - not the easiest to get to)

What color accelerator pump cam do you have? Different pump cams shoot different amounts either faster or slower than other colors. See chart for an example:


Heavier cars with automatics need more "shot" and sooner than a manual car and/or lighter car. I have a bunch of different color cams, if you can post what color you have now and want to try one that shoots more gas earlier (like the blue cam) let me know, I could stick one in the mail. Given your location you'd likely have it in 1 day.

After this, time to look at the size nozzle in the shooter, as already mentioned. Jump 3 sizes at a time. I also have extras of those that I don't need anymore, I might have a size that would fit your need.
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  #12  
Old May 17th, 09, 9:44 AM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: Holley Transfer Slot adjustment

There's no specific adjstment to "adjust the transfer slot".

What changes it, is the idle speed adjustment screw... the one that the throtle linkage comes to rest against at idle.

The goal is to back the idle speed adjustment screw off until the blades are in the correct relationship to the transfer slot, by opening the secondary blades, using their screw, to let in enough air.

Easiest way to do it, is to adjust the idle speed correctly on the car, the normal way; take the carb off and turn it upside dow; observe the transfer slot, and how far the primary blades are away from the desired relationship; and adjust the idle speed screw while watching for the correct relationship. Then adjust the secondary adjustment to change them an equal and opposite amount to what you changed the primary ones. For example, if you closed the primary throttles .050" to get the slot right, open the sec blades .050". Put the carb back on and see where you are. Repeat until perfect. On some carbs, you can take the sec screw out and turn it upside down, so that its head is accessible from above. Not sure about the Street Adventure carbs.

LEAVE THE SQUIRTERS ALONE!!!!! They are the VERY LAST thing to adjust anything about, until every other detail about the carb has been dialed in. From the point of view of carb design, they are merely a Band-aid for the carb's inability to deliver fuel as quickly in a throttle transition as it delivers air. The better you get the carb tuned, the less they are needed. They are almost always TOO BIG, and feed TOO MUCH GAS, and are one of the reasons Holleys have a bad reputation for poor gas mileage. People use them too much.

The correct way to tune a Holley for the street is to first get the ignition timing right. Usually this means limiting the mech advance in the dist so that when the "total" (static plus mech, no vac) advance is at the 36 or so that it needs to be for best power and efficiency without detonation, the static can be at around 16-18. Meaning, NO MORE THAN 20 of mech advance. Most stock distributors give 26-28, which results in the static (low-speed) timing being WAY too retarded. Inadequate advance at low speeds will make the motor generally run lazy, no "snap" to the throttle.

Once you get that set right, move to the carb. Get the floats right (pri with the level just barely below the sight plug, sec the fuel level should be about .050" below the sight plug), and do the transfer slot setting as described above.

Next thing to do to the carb is to set the main jets right. Holley main jets are usually a couple of sizes too large. Get yourself a few sets of jets, maybe 2 sizes larger than the stock ones, and 2, 4, and 6 sizes smaller. (a change of 1 size is imperceptible; 2 sizes is a fine tweek; 3 sizes is a standard step; 4 sizes is a large step; 5 sizes is HUGE) Decrease the jet size and drive the car on a normal road in a normal way. Keep dropping the size until it just begins to surge going up a slight hill inthe higest gear at the lowest speed you would customarily drive at; then go back up 2 sizes from there. Ignore all other behavior, good or bad, while making this test.

Then get yourself some power valves. Holley almost always puts too low of a number in their street carbs, meaning, no power enrichment occurs until you have given the car ALOT of throttle, which is why they make the jets too big. Raise the PV in steps until the bog goes away.

THen last, tune the secondaries. Find the loosest spring that prevents a bog when flooring it from a stop, and then out the next stiffer one in. You'll probably end up with the brown one; almost cetainly not the yellow one. Then set the sec jets for max mph in the .

If you tune up a Holley by this method, you'll be able to get better driveability and gas mileage than you ever thought possible. As well as spark plug life.
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  #13  
Old May 17th, 09, 12:45 PM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment

Quote:
Originally Posted by Xtreme70SS396 View Post
What BillyGman said, with the added part about timing first, carb second. Sounds like you've already got your timing set, so I'll say I hope it's in the 16-18 advanced range.

When you adjusted the slot, you've lowered or raised your idle rpm. You will likely have some issues when you first start it if you lowered it, might need a second person to keep it running while you adjust the secondary screw. (Typically a screw or allen key accessible from under the carb plate on a VS model - not the easiest to get to)

What color accelerator pump cam do you have? Different pump cams shoot different amounts either faster or slower than other colors. See chart for an example:


Heavier cars with automatics need more "shot" and sooner than a manual car and/or lighter car. I have a bunch of different color cams, if you can post what color you have now and want to try one that shoots more gas earlier (like the blue cam) let me know, I could stick one in the mail. Given your location you'd likely have it in 1 day.

After this, time to look at the size nozzle in the shooter, as already mentioned. Jump 3 sizes at a time. I also have extras of those that I don't need anymore, I might have a size that would fit your need.
Mark- thanks for the reply. I have the initial timing set at 18*, have tried 16-18 and it seems to like 18* the best. The total timing only gets to 32*, which will soon be solved (hopefully) after I get a DUI/performance distributors unit, which I plan on ordering this week...but that's another story.

As far as the idle adjustment screw, I first backed that all the way out and I still didn't get the "square" I was looking for on the transfer slots. The only way I got it (which I now think was incorrect) was to adjust a bolt that was attached to the primary throttle shaft, on the opposite side from the trottle lever, which I now think might have been the choke cam (don't know I'll take and post a pic once I get the chance today). Is the secondary srew you are talking about #185 in this diagram?

http://www.holley.com/data/TechServi...ded%20View.pdf

Regarding the accelerator pump cam...I have what came with the carb, which is the black one. The car is a 68 with a 396 big block and TH400 transmission. You think a different one might help? It would be great if you would send me one that you think might work. I'll pm my address to you, just let me know what you think.
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  #14  
Old May 17th, 09, 1:21 PM
BillyGman BillyGman is offline
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Default Re: Holley Transfer Slot adjustment

Quote:
Originally Posted by jjl4004 View Post
Is the secondary srew you are talking about #185 in this diagram?

http://www.holley.com/data/TechServi...ded%20View.pdf

.
Yes. And if you loook on the third page, you'll see it listed as the "Secondary throttle plate screw" in the parts list. They usually have a spring over them in order to keep tension on the screw so that it won't back off. As you turn it in (clockwise) you'll see the throttle plates open up a little bit.
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  #15  
Old May 17th, 09, 2:15 PM
jjl4004 jjl4004 is offline
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Default Re: Holley Transfer Slot adjustment





Here are two pictures I took of the bottom of the carb and the only other screw that I could find that offered any adjustment to the primary throttle blades, other than the curb idle speed screw (which I have all the way backed off and alone, didn't get me the "square" transfer slots). Does anybody know what this screw is(my finger is pointing to it in the first pic)? After looking the diagram, it appears to be the choke cam adjustment screw, but I've never heard of anybody adjusting that (other than me right now) to get the transfer slot problem solved. Do you think this will work? You think the choke will be all jacked up now? I'm guessing yes, but that's secondary to getting the carb to run correctly.

As far as adjusting the secondaries...my carb doesn't have the #185 screw in the secondary blade, as it appears on the diagram. However, I did find another screw that offers adjustment on the secondary throttle blades (seen on the first pic, below my finger on the small tab on the baseplate - flat-head screw), but I thought that you were not supposed to have any of the secondary throttle slots showing. If I open them up any more than they are now, I'll expose the secondary transfer slots. Any thoughts?
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