62 F.I high idle

[Tim S.]

I have been finishing up the injection install on my 62. I am dealing with a unknown unit. The car fired up just fine and kicked to high idle. After warming, I cannot get the car to idle down. I do not believe I have any vacuum leaks. So, I have 2 questions. See the picture below. Is the clearance on the bottom of the throttle blade enough to cause my high idle? Plus, what does a person have to do in order to break loose the 2 screws? I cannot budge them. Thanks!. Tim

[Jim L.]

Re: 62 F.I high idle

Tim,

That gap does look large to my (un)calibrated eyeball. But you don't want to adjust it by removing the two screws which secure the throttle plate. Those are staked specifically to keep them from loosening and possibly getting pulled into the engine. You need to have a very good reason for removing those screws and this isn't it. OK, with that out of the way........

An uncontrollably fast idle can be caused by several things:

1. Cold enrichment which hasn't turned off after the engine warms. Verify that the fast idle screw isn't in contact with the fast idle cam.

2. Throttle blade idle stop screw which has been improperly adjusted. In spite of what the shop manuals say, you want to see about .0015" clearance between the edge of the throttle blade and the wall of the air meter. Use a feeler gauge to check this. If you need to adjust this clearance, you do so via a stop screw on the bottom of the air meter.

3. Vacuum leak between the adapter plate and the feet of the "doghouse". With the engine running, use a length of tubing as a stethoscope to listen for vacuum leaks. The sound of rushing air when you locate such a leak is hard to miss. If you do have a vacuum leak between FI and adapter plate, a "Bubba" fix is to add a second layer of gaskets. A correct fix is to machine the bottom of the doghouse flat (they are capable of warping as time goes on).

4. Gummed up threads of the Idle Air adjusting screw. It's possible but unlikely that reversion has deposited soot and other junk in the threads of the Idle Air screw (Large spring loaded screw, rear of air meter) preventing you from screwing it in far enough to limit the amount of idle air the FI unit is passing to the engine. A visual inspection of the large passage right at the top edge of your picture and some carb cleaner will take care of this if it's the cause.

Good luck,
Jim

[Bill W.]

Re: 62 F.I high idle

Tim, Do you have a copy of the GM service manual? Clearance between the butterfly and the housing should be approx. .0045 thou. Looks to me like you have way to much. Before doing anything check to make sure your choke linkage is not the culprit. Butterfly to housing clearance and it's adjustment is described in the manual. There is a lead sealing ball that must be removed to gain access to adjust. Let's see what others have to say about this. Back to the garage! bill

[Tom P.]

Re: 62 F.I high idle

I'm in total agreement with Jim and Bill------------------------that throttle opening is way too big. Like Bill mentioned, the throttle blade gap should be about .004in. Personally, I like to set the gap at a TIGHT .004, and then adjust idle speed with the idle air screw (the big screw with the spring).

[Tim S.]

Re: 62 F.I high idle

Thanks for the response guys. Yes, I do have the manual and yes, I did see that. As you can see, the butterfly is tight on the topside, yet loose on the bottom. To the best of my knowledge, there is nothing binding. I have the throttle stop backed off. It seems to me, the butterfly needs to be centered (hence why I asked about the screws) Is this a job left for a professional? I am not afraid of these F.I. units, but do not want to destroy anything in the process.

[Duke W.]

Re: 62 F.I high idle

A similar situation happened to a friend with a Cosworth Vega that has two 1.75" throttle bores, which is a huge amount of throttle bore area for a two-liter engine. He couldn't get the idle down to a reasonable speed.

The screws are probably staked, but you can probably turn them enough to allow the throttle shaft to slip. You can also "undo" some the the staking to get them to move.

Once just slightly loose, open the throttle with a stiff return spring, then let them snap back. This should center the valve in the bore and allow idle adjustment.

Retighten and restake the screws if necessary.

Duke

[Jim L.]

Re: 62 F.I high idle

Tim, it's OK to try loosening those two screws. If you can, then rotate the throttle shaft all the way closed, repositioning the throttle plate as needed until it is seated all around its circumference. I'd suggest applying some blue LocTite on the screw threads before you tighten them.

Be sure to set the throttle plate clearance with the stop screw. Use .004" if you want and see if it works for you. I've never found a gap that large on any unmolested air meter.

I set the clearance to .0015 on the units I repair because on every unmolested air meter I've examined, the factory setting has been less than about .002". I've always gotten good results with the tight clearance.

Jim

[John D.]

Re: 62 F.I high idle

Gail Parsons and I used to talk about the throttle butterfly clearance on various models. Several factors contribute to just what the clearance should be.
Are the bushing wore very bad in the air meter housing? Does the throttle shaft have much clearance with these bushings?
Would you believe that '62 is one of the hardest ones to adjust. There really isn't just one setting for ALL '62's. Notice in the Corvette Servicing Guide that "Clyde" is holding a .003 feeler gauge. hmmm. Then notice that the writer tells us to set the butterfly clearance at .005. Then remember that this book is supposed to be for 58 to 62 FI units. But is it really? The answer is no it isn't but it's still the best manual ever written.
Here's is what Gail and I concluded on setting '62 Butterflies. Anywhere from .002 to .007!!!! Yikes you say. Well I never went up to .007 because I was scared to do so. I have set the '62's anywhere from .002 to a tight .004. I couldn't set one like my pal Lockwood at .0015 as the smallest feeler gauge I have is .002.
So I guess you could use a tight .002. Meanwhile what is soooo neat about most of the '62's is the set screw on the bottom of the throttle shaft can be adjusted quite easily. Unlike the '57 to '61's. The '62 have a pan head screw with a thin lock nut.
Now we are told that the proper way to adjust the idle is thru the venturi circuit. But if you want to cheat a tad you can play with the set screw on the bottom of the shaft.
YOu see the wide clearance in the photo Jim posted. YOu don't need a feeler gauge to see it's really messed up.

I forgot something very important. In all '57 to 65 FI's the throttle butterfly must be centered in the bore. If it is off to one side very strange things happen.
One of them is this. The throttle will stick and the owner will have 10 fits. So center the butterfly in the bore and make sure you don't install it backwards or have it turned 180 degrees.
62 butterflies: Some were cad plated steel. But the majority were/are brass. I have no idea why. John

[John D.]

Re: 62 F.I high idle

Tim, Years ago my ex bought me a reallylneat tool from Sears. A ratchet screwdriver. That's what I use to break loose and tighted those two oval head `10/32 screws. By the way. I always put new ones on.
I use a drop of the green Loctite 290 on those screws. It's permanent.
'62 choke shafts are very long. Doesn't take much for that shaft to bind in the 4 holes of the air meter cone. That cone is very flexible. How you tighten up the 4 screws holding the cone to the air meter body can also flex the cone so that throttle shaft will bind. Thanks be to God Rochester Products only made that wild choke set up for one year.
I use a machinists drill rod aka straight rod and run it thru the bore. If it binds then I know I have to attend to that. John

[Richard M.]

Re: 62 F.I high idle

On the '61 7320 unit that Chuck McSheehy and I are rebuilding, we had a similar dilemma. We had to remove the throttle plate to prep to get the housing refinished and the shaft arm plated, and to clean the plate and pieces properly. It took some careful work but we got the screws out. I don't recall exactly, as Chuck was the screwdriver guy and took them out, but I don't remember if they were staked or not. I don't think they were.

PC130019.jpg PC130020.jpg PC130022.jpg P1300003.jpg

However, after having much success removing stubborn hardware on other items lately, including rusted/seized/broken UNF 5/16" diameter bolts from a '56's rear spring fwd mount brackets, and other various seized fasteners on my projects, I have had 100% success using the CRC Freeze Off product. I highly recommend you use it for those throttle plate screws. If I knew about it when we took the unit apart I'm sure it would have been much easier.

Rich

[Tim S.]

Re: 62 F.I high idle

I measured the clearance on the open side, and that is at .008. Naturally, the opposite side is tight. The shaft and bushings are tight and smooth. I will say, I was able to get some additional torque on the plenum. Too boot, I replacement gasket for the throttle body is thicker that what was on the car. Man those screws are TIGHT! I am afraid of rounding the heads. I took another crack at loosening them so I could attempt to center the butterfly (no luck yet). So..................I continue on

[Jim L.]

Re: 62 F.I high idle

I measured the clearance on the open side, and that is at .008. Naturally, the opposite side is tight. The shaft and bushings are tight and smooth.

The throttle shaft tends to wear egg shaped because the force on it due to manifold vacuum is greatest when the throttle is closed. Best to assess bushing and shaft wear after you adjust the throttle plate such that it can completely close.

.

Man those screws are TIGHT! I am afraid of rounding the heads. I took another crack at loosening them so I could attempt to center the butterfly (no luck yet). So..................I continue on

They are almost certainly tight because they were staked at the factory. You are going to want to use a Dremel motor with a grinding bit to remove the portion of the screw threads which were distorted by the staking operation. After you do that, the screws will come out fairly easily.

Jim

[Richard M.]

Re: 62 F.I high idle

Yes after talking to Chuck, when he disassembled this Air Meter he said the screws weren't staked too much and they came out easily. He said others he's done needed the Dremel cutting wheel to cut the staked portion off to remove the screws.

A few pics of this one's screws. Clearly staked as Jim and Chuck said so I'd do what Jim suggests and Dremel off the staked part. A little penetrant will likely help too.

Edit.....Actually, if you're just going to adjust the plate, you don't have to remove the screws completely, just loosen them a bit. The holes in the plate are enlarged for adjustment. The screws are #10-32 (apx 0.185"), and the holes in the plate are 1/4" diameter (0.250").

P3220012.jpg P3220013.jpg P3220014.jpg

Rich

[Tim S.]

Re: 62 F.I high idle

It's fixed! I was able to loosen the screw just a touch and reposition the butterfly. That changed the clearance to around .003 to .0035 ish. A fresh throttle body gasket and bam.................................was able to tune it down to a 900 rpm idle. Thanks to all of you who took the time to help me along (which I need plenty of!)

Tim