I'm still in search of correct idle / vacuum leak fix with a Holley Sniper installation. I have not been able to get it to idle below 1500 rpm.
Here’s my questions:
How tight should the throttle plates fit to the bores when fully closed?
How do mine look – before and after pics of the adjusted two secondaries below? I don't believe I could get them much closer than I have now, but I have not done this before.
Anyone have experience trying to get a tight fit between the plates and the bores? These are 1-11/16 diameter units. Any ‘oversized’ plates out there that can be dialed-in?

Talked with Holley yesterday (have not been very impressed with them on this problem) I got a plate diameter spec of 1.6845 / 1.6855. I’ll be surprised if these are within one thou by the looks of them, but maybe. Nominal Bore would be 1.6875, but the Tech did not have actual nominal or tolerance info on that. He’s going to send me 4 new plates, to see if I can do anything with them.

I adjusted the plates. The pics below are before and after of the secondaries. I also adjust the primaries – they were about as bad.
After this adjustment, with the curb idle screw completely out (plates fully closed), the Sniper can almost hold idle at my set point of 750 RPM. It wavers between 740 and 810.
So my conclusion is the vacuum leak is the poor fitting throttle plates. I think I need a better seal, so that I can actually use the curb idle screw to open the primaries a bit, and get into a controllable zone.

Thanks for any wisdom on the questions or otherwise.

 

Off hand it sounds like the initial timing might be set too high.

 

Hey Mark, Thanks for the response
My initial is set at 12 BTDC @ 600 RPM w/ the vac port plugged.
All-in the mechanicals go to 36 BTDC @ 3400
The vac can is 'all-in' at 10inHg @ 32 BTDC.
I have it on manifold vac, not ported. Manifold vac is 23inHg at idle.
This is exactly how it was set-up using a Carter AFB carb. 9.13:1 compression - it will ping on 87 octane under heavy load, but I can run 87 if I don't stomp on it.
What do you think?

 

I would back it off some and see how it acts.

 

I dropped it to 9 BTDC, and that did allow a bit more bandwidth to set curb idle position in a better spot for the EFI to control idle. Still not where it should be. I've got a couple throttle plate sets showing up in the mail. This weekend I'll get time to do more measuring and adjusting to see if I can get the seal better.

 

What's the IAC% at when you're at idle and what is your idle set at in the handheld?

 

Also, to your thread topic, I re-centered the throttle blades on the rear shaft of mine as well. Mine were actually catching on the bore slightly when they were almost closed all the way and prevented them from closing 100% and would cause a high idle for me.

I don't know if that's your issue, that they are not closing all the way, but you can tell when it's on the engine and running if you manually go and press on the throttle linkage and force them to close all the way when the engine is idling. You'll know if they are hanging up if you do that. If I was driving and they hung up, I'd have to blip the throttle and doing that would make the secondaries snap shut rather then gently shut and that would close them. It was super annoying at the time.

This is how they looked once they were adjusted and I made sure they were closed all the way. Don't mind all the dirt and dust, it sat outside for a while during my engine swap and unfortunately sat through a wind storm. Had to clean it good before it went on the new engine!

 

My IAC% was uncontrollable via the curb idle screw. Essentially it was 0 or 20+ and would rev the idle up above 2500. There was no resolution on the adjustment. Idle is set at 750. System was never able to get it below 1500, even with the curb idle screw all the way out. After going thru a bit of hell looking for vac leaks, I noticed how the plates were not centered in the bores - That appears to be my vac leak. I adjusted them better, but did not get them to look like yours. Currently, it can idle about 750, but is too erratic and curb idle is all the way out. I'm hoping that I can get my throttle plates fitting well, and that it will allow me to use the curb idle screw to get the IAC in a range that is controllable for the system.

 

Previously they were free to travel, but poorly adjusted and allowing tons of air to pass. Mine are hanging now - after my adjustment - so I need to get it right, and a better overall fit. I may add a turn to the secondary spring as well - depending on what I find. I'm not sure if the primaries are hanging or the secondaries, or both. I have a couple alternate plate sets as well, that I may try, or at least mic to see how the diameters and roundness compare with the plates that are in there now.
Sometimes it will hang as high as 3000 - and coming into a stop and down shift (and actually speed-up instead of slow-down) and have to clutch and brake and side-step the throttle to blip it is a bit of a handful on this straight axle rambling disaster. So looking forward to being in a better spot this weekend.
Thanks for your response and the pic. Gives me some confidence that I can get there with the stock Holley parts.

 

After I adjusted mine I had to make a couple more alterations to get things operating to my liking and feeling good to my foot. I added a turn to the spring on the secondary shaft, added an extension to the throttle lever, and then put a stiffer return spring on the throttle lever than I was previously running. Basically, the extension put a little too much leverage on the throttle lever and made the gas pedal way too easy to press and that's why I went with a stiffer return spring. Everything feels real good now at my foot and the Sniper is operating as it should.

 

I tried get another turn on the secondary shaft to ensure closure, however the the spring seemed wound way too tight and kicked it out at an angle that didn't seem like it would last in that position for long. Is there a trick I missed?
I'd like to add a throttle extension, because my pedal is way to touchy off the line - I'm chirping the tires when I don't want to. Problem is that the full travel of the foot pedal is just enough to fully open the throttles, so I need all that mechanical advantage. I have the floor mounted pedal with the z-bar going through the firewall. My big problem is off-idle: The pedal is pretty vertical and when it 'rolls' over the rounded end of the bar to initiate throttle movement, it's apt to 'break-loose' and jump a bit, rather than smoothly moving the z-bar. I've tried lubricating the pad between the pedal and bar, and have added UHMW tape (low friction) on the plate, but still it's touchy. I'm thinking to add an actual roller bearing to the bar somehow, to remove the stiction.

BTW, I got the throttle plates adjusted again - they look much better. Used a new set of replacement plates. I found that the plates were all within a .001" diameter of each other, however some were bowed or potato chipped a few thou - and I guess that made the difference with fit capability. I was able to get good control of the curb idle screw and the IAC - probably something like the intended action, so I think I solved the problem. However the idle hung at very high rpm again on a test drive - though I'm not sure if that was a mechanical or if it was 'learning', as I reset everything to factory settings.

I'm not convinced this will 'learn' how to enable good downshifting to slow the truck. It likes to hold idle a bit high for a moment (which doesn't slow the truck fast enough), and then has stalled when the engine has been driving it, but at the stop and the clutch is engaged, idle falters and then dies. Hopefully it will learn some, but I think I'm going to need to tweak it to get what I need to help my braking

 

It was pretty difficult for me to get another turn on mine, but I managed. It's been a couple years since I did that, so I don't remember exactly how it felt once I did it and if it looked like it was too much for the spring.

Winding the spring, along with re-centering the throttle blades fixed my issue with the secondaries staying open slightly and creating a high idle. However, it created a throttle tip-in issue for me, which sounds like what you're experiencing. I'd have to push harder to get the throttle to open, but once it opened, it opened a lot because of how much I was pressing on the pedal to overcome that initial resistance. I didn't have it bad enough to chirp the tires, but I was getting a pretty good lung off the line.

The throttle linkage extension I put on eliminated the tip-in issue by giving added leverage, so I didn't have to press so hard on the pedal, but then the pedal was essentially too easy to press through the whole range of motion, so it was difficult for me to hold a steady throttle position. That's when I tried a few different throttle return springs and got one that gave me a good pedal feel where I could rest my foot on the pedal without it wanting to go to the floor easily.

Like I mentioned in a previous post, for me, I would fix one issue, but the fix to the issue would create another and that happened a few times. At least it's all sorted now!

And for the people who say that you shouldn't have these issues out of the box, I agree, but I was able to pretty easily fix my problems and have the product function well, so I didn't get too bent out of shape over it and send things back. I figured Holley would have worked this all out by now, though. I bought mine like 3 years ago.

 

Oh, and as far as drivability goes, I didn't have any issues with that out of the box. It started right up, idled well, took off and stopped well. The only time my idle would hang, where the throttle blades weren't shutting all the way on the rear shaft, was when I would close the throttle slowly as it was the snapping shut from letting off all the way suddenly that would cause them to fully seat.

I did do what the instructions with the Sniper said to do to help it learn though. I varied how I drove. Long slow clutch releases occasionally (I would even go as far as not using the throttle to take off in second with my NP435), letting it engine brake to a stop, combos of things like that along with long steady revs in each gear and varying the engine load. Just giving it every possible scenario I could rather than firing it up for the first time and just hammering it full throttle down backroads or something. I don't know if doing all of that will help you, but I'm sure it wouldn't hurt you.

There's various settings in the handheld that can affect how it comes back to idle as well ("ramp decay"). I've seen people adjust that to have it get back to idle faster when they experience what you are. I never touched any settings like that with mine, so I can't say what it will or won't do. I suppose I got lucky with the ecu on mine?

I did update the firmware a couple times since I've owned my Sniper, though I'm sure it's not the most up to date version. I only updated it once they came out with the setting for using progressive linkage as I was going to try using that vs the throttle linkage extension, but never did. After that, I never downloaded another version of firmware. Don't fix it if it ain't broke kinda deal there.

 

Thanks for the additional details. I’ll continue to work through it. I did have a look under the hood, and my high idle was a hanging throttle – so I need to review it again. It’s odd now that a quick snap won’t close it, so something else may have got out of whack while I was in there last.

Currently, my grievance with Holley is that they shipped a unit with the throttle plates way out of adjustment, and then when I was working with them on my idle problem, all they could do is say I had a vacuum leak, and never offered that the plates could be the problem. It turned out to be a cluster since I spent a lot of time and money looking for a vac leak: pulled the manifold and ran into problems while doing so, etc. So I’m actually pissed off. But I like the way the EFI accelerates, and still hope once I get it dialed, it will stay that way and put carb tuning behind me on this one.