Progression hole and Throttle plate in HW5200 carb

[jamyers]

In my HW5200, the progression hole is too far above the throttle plate at idle, so that as I crack the throttle open it goes WAY lean (like 20-25 AFR), then a little more throttle opening and it picks up and works fine.
It's *just* above idle, like at maybe 800 rpm. As far as driveability, it's just at that point where I'm just rolling along in first, like in a parking lot - and it starts bucking/surging.

As far as I can tell, the throttle plate is centered in the bore - you can see equal amounts of light all the way around it as it closes, and it'll close completely off without binding.

The progression hole seems to be just a bit too high, like maybe 1/8 of an inch. I think it's too high to bevel the lower edge of the throttle plate like the Weber book says.

My question is: Can I drill or file the hole downwards without screwing it up?

 

[Bort62]

Things like this remind me why I like EFI better than carburation haha

 

[jamyers]

Things like this remind me why I like EFI better than carburation haha

Smarty-boots.

Like it's as much fun chasing electrons...

 

[falcon60]

James-

Can you drill another small hole just below the current one? If so,it would be nice as then you could start out very small and enlarge it as needed to get the AFR correct. I've had motorcycle carbs built this way and they worked very well in transition. If that's not possible I do think slotting the hole downward would work fine. Any problem with "going too far" can be repaired with JB Weld.....I've used it before in carbs when I screwed up,lol.

Terry

 

[66200i6]

There are the holes in the venturi that control the transition curcuit and there are also holes drilled in the throttle plate.

You can't mess with the holes that are in the bore of the venturi.

Can you provide a picture so we know what hole you are talking about?

Ric.

 

[jamyers]

I don't have a pic of mine, but here's one hotlinked from "dimequarterly"...

Progression holes #14, just above #9. It's all below the venturi, in the carb throat just above the throttle. No holes in my throttle plates.

Think I'll bevel the underside of the throttle plate right below the existing hole, then use a knife-edge file to "walk" it downwards to just above the throttle.

 

[66200i6]

OK, got it.

I don't think the holes and final transition slot are in the wrong place. And from your discription it sounds like the plate is centered properly. There is how ever the posibility the throttle plate was installed upside down. The edge of the throttle plate is not square to the surface. The edge is actually at an angel that matches the diameter of the bore. Check that the edge of the thottle plate fits snug to the face of the bore as in view "B". Not just and edge of the plate but the intire face of the plate edge.

If you are stumbeling off idle, I would check out the accel pump and/or possible first hole of the transition curcit could also be pluged. Try using an air hose and blow out that curcuit.

Good luck, Ric.

 

[jamyers]

Looking down in there with a flashlight, it looks like the throttle plates are installed correctly, with the bevel on the right top/bottom. Plates are centered in the bores, and close nice and snugly to the bores as well.

If I get a chance this weekend I'll pull it off and get some pics as I do some tinkering.

 

[mach1 mark]

go to larger "squirter" maybe a 37#

 

[jamyers]

go to larger "squirter" maybe a 37#

That might help on acceleration, but wouldn't do anything during decell or steady slow speeds.