Starting a new thread for the next chapter of: in the search of correct idle / vacuum leak with the Holley Sniper
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?
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?

I’ve read threads of people looking for tight fits on secondary carbs on a multi-carb setup for the same reason – that these secondary carbs are vacuum leaks that result in high idle if there is any gap.
Talked with Holley today (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.

More of the back story:
After replacing the manifold gaskets and checking everything thoroughly for vac leaks, replaced the Sniper and all items and then had the exact same response / problem: Will not idle below 1500. The engine pulls 23inHg steady vacuum at idle. It is not pulling the plates open at idle.
Went through all the same set-up and checks that I did before – nothing new, all the same. Then I covered one of the secondary bores with my palm, and the engine died. Then I covered the other one, and the engine died. I pulled the Sniper again and checked the throttle plates and they were not well aligned.
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.

 

I am far from a carb/fi expert but, to me, that doesn’t look right. Every intake I can recall inspecting, the plates nearly bind in the bore as they close. I’ve seen some that sit at a slight angle, yet the bores are closed. Perhaps someone can make a pair with a cnc....simple circle...to test your theory.

 

I've had the same issue, but on much older Holleys. You can likely back off the attachment screws just enough to loosen them and allow them to find their happy home. If your gonna replace the plates then you have to remove those screws anyway and should do the same with the new ones during installation. Understand you'll have to grind off the mashed end of the screws to actually remove them, go easy. Better consider how you can "re-mash" them after installation and adjustment.
What you show can certainly impact idle speed.
I need add, that not only left, right, fore, after adjustments, but rotationally too, because the screw are not on bore center. +/-.0005" I find laughable.

 

That's my experience as well, and looking at the Carter AFB I removed, the plates fit in their bores much tighter than I got these on the Sniper.

 

Thanks. That is basically how I did adjust them - cracking the screws and moving and rotating to try and get the best fit. I was able to get them better than as-delivered.
I guess I'm wondering if I need to do a better job of it, or if the plates and bores just aren't set-up to be that tight, and I should try a different plate. For instance, maybe they opened up the nominal gap to make it cheaper to assemble, and this works for most installations, or...?

 

Very timely post for me. I just installed a Fitech EFI on my 66. I had the exact same problem and could not get it to idle below 1500 RPM no matter what the tech line guys told me to try. They finally had me send the throttle body back to them and they said they would install and run it on their test engine to see if they could duplicate my problem, and then hopefully fix it.
I can’t wait to hear what they tell me was wrong.
I’ll let you know what they find. I’m hoping to hear something next week.
Rich

 

I look forward to hearing. Thanks.
I would have sent mine back, but schedule was unknown numerous weeks or more, and I didn't want to do the fuel delivery mods and tuning to put my carb back on (yet).
I went through all the tricks and tips that go with this problem and the Sniper. None of it worked and everything pointed to a vacuum leak. I went through it all thoroughly and R & R'ed the intake manifold. Restarted with the exact same problem. Then I found the possible throttle plate explanation. That's where I sit today...

 

If the idle jet/orifice is below the throttle butterflys could you block/seal the throttle body and see if that changes the problem?
Not sure how you do that, rubber sheets of some such to reduce the air leaking past the butterfly.

 

Thanks. After I noticed what I thought were large gaps in the throttle plate fit, I did that with some large rubber stoppers which seemed to solve the problem, which is how I concluded it could be the problem. What I don't know is if throttle plates usually fit tight? If I should work harder to get mine to fit tight? and how do I get there from here? Should I be able to get my existing plates tight with more fiddling? Have others had this problem and found an aftermarket plate that fit better? Is it common to dress-in the edges of the plate to create a tight fit?
Or, is what I have normal, and I should be looking for another solution?

 

I've never used a throttle body injector. But the throttle plates are the same as a carburetor. They should close completely when adjusted to fully closed. They look like this picture with slots where the screws go so, they can be adjusted for a tight fit something Holley should have done before they shipped it. If you mess with them, you absolutely need new screws the screws are not reusable. Once the plates are where they need to be you crimp the screws with big pair of needle nose vice grips being very careful not to bend the shaft.

 

Mine fit snug. The two on the right of the pic sit slightly open, but I can push them down, and they both fit snug. I hope this helps???

 

That helps. Do you know if they are stamped 354V on the backside?

 

This helps. Looks like I'll be going for a tighter fit. Hopefully the installed plates can get there with more fiddling.
When I adjusted the plates the other day, I just cracked the screws and did not back them out far enough to engage the factory crimp into the tapped hole in the shaft. This allowed enough room to adjust the plates and re-tighten. I assume the crimp is still OK and at least will not allow the screw to fall into the intake. My plan now is to give it another go, with just cracking the screws again, and to dab in a bit of Loctite 242 (blue) when tightening, and not be concerned about the crimp. However if I do find a really good position for the plates, I might give it a crimp with the vise grips for added security against moving in the future.

 

The one in my pic on the left is a 354V, 1 11/16 throttle plate. Quick Fuel 9-172QFT Steel 1 11/16" Throttle Plates (4 Pack) 9-172 (holley.com)
The screws are available separately. I would not recommend trying to reuse those screws. They are soft brass and if you break the head off or it cracks and falls off later, not good.

 

I ordered the -172 kit from Summit. Arrived today apparently. This weekend I'll have the -172 with screws, the replacement 354Vs from Holley, my currently installed 354Vs, and the 1-11/16 plates in my Carter AFB to measure and find a solution. Currently my plates are hanging a bit and I find myself downshifting to slow down but idle is at 2500, so I need to sidestep the throttle to give them a kick to go down -all while the brakes are pulling right and fading - so it's a bit of a show, and I've learned to be a more thorough in setting and testing the plate fit to the bore