Filling Throttle Plate Holes

In another thread, I mentioned that I got a little better idle by temporarily plugging the holes that I had drilled in my primary throttle blades, and cracking open the secondary blades instead.

Now, how do I permanently fill the holes? Do I remember a soldering method? It obviously has to be dependable. New plates?

SpeedThrills said:

In another thread, I mentioned that I got a little better idle by temporarily plugging the holes that I had drilled in my primary throttle blades, and cracking open the secondary blades instead.

Now, how do I permanently fill the holes? Do I remember a soldering method? It obviously has to be dependable. New plates?

Click to expand...

A small oval head machine screw and nut works well.
Just peen the end of the screw down so it doesn't come loose and fall down in the motor.

Ribbit!!!

Before I did anything with the holes, I'd verify where the blades are relative to the transition slots. You only want .030-.040 showing. With that cam, I've never been able to not have holes in the butterflies.

That's why most of the new carbs have a built in, adjustable air bleed system. It presents a controlled air leak so you can get your idle speed up and the throttle closed like it should be.

But there is nothing wrong with the hole. I think you still need them.

yellow rose said:

Before I did anything with the holes, I'd verify where the blades are relative to the transition slots. You only want .030-.040 showing. With that cam, I've never been able to not have holes in the butterflies.

That's why most of the new carbs have a built in, adjustable air bleed system. It presents a controlled air leak so you can get your idle speed up and the throttle closed like it should be.

But there is nothing wrong with the hole. I think you still need them.

Click to expand...

I'll try it again with the holes open (and close the secondaries). I'll see how much of the transition slots are exposed. I sure would like to avoid closing them or replacing them.

The only carb I've done it on was a 9380 I believe and I replaced the baceplate. But I have seen it where holes were welded also fuel proof epoxy filled from both sides.

I have filled them with solder before with no issues. I prefer solder as it is soft and wont impact anything should it come loose and go through the engine.

yellow rose said:

Before I did anything with the holes, I'd verify where the blades are relative to the transition slots. You only want .030-.040 showing. With that cam, I've never been able to not have holes in the butterflies.

That's why most of the new carbs have a built in, adjustable air bleed system. It presents a controlled air leak so you can get your idle speed up and the throttle closed like it should be.

But there is nothing wrong with the hole. I think you still need them.

Click to expand...

I agree.
Set the throttles by t-slot.
Count the turns of the idle speed screw to get .020, .030 and .040" showing.
Write that down.

Next with engine warmed up, do some iterative testing to find the strongest combination at a reasonably slow idle speed.
Adjust the throttle like YR just said, no more than .030-.040, but at least .020.
Use the initial timing to further adjust idle rpm.
After each adjustment of throttle position, check and adjust idle mixture screws.

If its an automatic transmission, putting it into D is a good check for power at idle. It should not significantly drop rpms or vacuum.

If you find the timing is moving around at the idle rpms, then put more tension on the distributor's primary spring.
In other words, if its idling around 950 rpm and its at 20*, and then you lower the rpms (by placing it in gear or reducing throttle) and you observe the timing has dropped to 18* at 900. Maybe not a big deal if its just an in-gear test. You'll have to be the judge on that. But it is a big deal if your trying out a little less throttle at idle. In that case you want the timing the same as it was before, otherwise its not a fair comparison.

On my 750DP, I chamferred the holes both sides a good ways, then backed the hole with something handy, then dropped a blob of solder on the hole. Then with a small butane torch, heated the plate until the two bonded. Then I dressed it pretty with a file, and that was year 2000.
Next I moved over and drilled new smaller holes.
As I discovered; a pair of 1/8s for a 292/292/108 is too big. With the DC292,My 367 liked 3/32s; one in each.
But it will depend a lilbit on your installed centerline and altitude so sneak up on it.