29mm Smoothbore problem

I have a set of 29mm smoothbores that are giving me a lot of trouble. They are way too rich at idle. I haven't even started working on the higher rpm circuit.

1.5 slides, 17.5 pilots, 125 mains. (I think my mains are too big.)

Cylinder #3 keeps fouling plugs. 1,2 and 4 are running. Pipes get very hot. Pipe #3 get good and hot, but not like 1,2 and 4.

Everything seems to be in order, I thought maybe I have too much gas in the bowls. Changed float height, everything got better.

Side note: Carb #3 has had some repair done. The needle jet screws into what I think is called the jet block, in any case, the threads were stripped. Someone drilled out the stripped threads, installed a press fit plug, redrilled and tapped, and cut to shape on the inside. I can't help but think this is the culprit, as it is the only difference I see and #3 won't run.

Questions:
1. What should the float height be?
2. Do the mains influence fuel mixture at low rpm? ie, could my too big mains be getting me rich even though I'm at low rpm?
3. Has anyone seen the stripped thread problem/solution before and have any thoughts, insight?

Thanks. Julio

Brass floats in them ?

Go by fuel level not float height when you set them up. A good start is to have the fuel level about 4mm below the flange where the bowls meet the body.

IF you don't have a guage, it's possible to pull the bowls off the carbs with the fuel still in them and see where it's at. Been there..done that

Stripped jet blocks were a common problem Sudco used to carry them.

If the repaired jet block is blocking off the main air passage, that could cause the problem. Blow through that passage and see if air comes out the needle jet.

Check the main air jets. Stock was .9
Needle Jets should be O-6
5DL31 Needles [are they worn out?...are they all set the same clip position]

900 - 1015 motor, drop back to a 120 main. Might end up liking a 115...never can tell...you have to swap them and see what it likes.

Great carb when everything is in good shape but also a mother to dial in when parts are worn out... That is one reason why jetting that works great on one set is not the jetting that works on another. Other reason is the health of the cylinders on the specific motor they're on.

Larry C

juliorice wrote:

...29mm smoothbores...way too rich at idle...#3 keeps fouling plugs. 1,2 and 4 are running. Pipes get very hot. Pipe #3 get good and hot, but not like 1,2 and 4...maybe I have too much gas in the bowls. Changed float height, everything got better...Carb #3 has had some repair done...
Questions:
1. What should the float height be?
2. Do the mains influence fuel mixture at low rpm? ie, could my too big mains be getting me rich even though I'm at low rpm?
3. Has anyone seen the stripped thread problem/solution before and have any thoughts, insight?.

As Larry already noted, would check fuel level in #3 carb.
I use the clear tube test, drawing fuel from the 17mm drain bolt hole.

Main jets don't influence fuel mixture at low rpms.

WG offers a similar jet bloc thread repair, which to me seems a good solution to the common stripped thread issue. Check out wgcarbs.com.
Click > www.wgcarbs.com/index.php?option=com_con...view&id=30&Itemid=42

Would also assure the BS30/97 air jet is clear (see image below).

Good Fortune!