Metering jet?

[Jackman]

The metering jet , run it in and where ever it stops is good or is there a certain position it belongs in such as 9 o'clock, 12 o'clock ,2 o'clock.

Perhaps a silly question but I don't get the whole metering jet thru the bowl set up, I also notice the TM Tractor only has two jets available , how does one decide that the jet is bad or clogged

[Smokeycub]

No such thing as a silly question on here. On an IH carb for a Cub the jet is seated in the body of the carb. If the jet is blocked or partially blocked the tractor will lack power, may not want to run other than choked or partially choked. Cleaning is a simple matter, soft copper wire through the orifice and inspect, reinstall. It would be fair to say the jet doesn't need replaced unless somehow it's been abused. Are you having some starting/running issues?

[staninlowerAL]

Which one are you referring to as "the metering jet"? Smokeycub's IH carb description is for the main jet which is "fixed", no adjustment. Change to the fuel delivery volume is accomplished by changing the jet to a different size. There are some posts that say IH originally used several different sizes, (I seem to remember five being talked about at DSCF a couple years ago). I don't remember the rationale but the carb ID number was linked to the size of the jet. Bob McCarty or Don McCombs will probably remember these discussions. As far as the other adjustment, the screw with the spring, this is for adjusting the air, usually about 1 1/2 turns open from the closed position will allow the engine to start, then fine tune it. The idle jet is a fixed brass tube and the orifice end screws into the top half of the carb with the lower end extending down into the bowl. I seem to remember the orifice is about .004, Bob might chime in and say for sure.

[Smokeycub]

I was going from these statements.

I don't get the whole metering jet thru the bowl set up

run it in and where ever it stops is good

I also notice the TM Tractor only has two jets available

[Bob McCarty]

I'm in Michigan with slow internet so I won't post a link. If you go to the fuel section of the GSS-1411 there is a chart that shows the part sizes of three different carbs, two Cubs and the 154. The main jet, discharge tube and bleed are calibrated to match each other. I think the main reason to change jets would be if you moved the carb to a tractor with higher fuel needs. The bleed is fixed and not removable. A lot of the aftermarket kits have jets with sizes that don't match the original which often doesn't seem to affect performance.sizes, There are several other configurations that I have seen, ie the power units and balers.

[mva1958]

Be careful re-installing the jet, it can snap in two if over-tightened. Don't ask.

[Glen]

Hi,
If you are talking about the high speed, main jet on the lower side of the carburetor, with the 6 sided head, you just screw it in until snug, it doesn't go in any certain position. It has to have a round gasket behind it.
If the engine runs normally at every speed, especially higher speeds, the main jet is not plugged, it is open and nothing is wrong.
There are different size jets for different years and carburetor part numbers used on Cubs. They have to be matched to the carb.

Below are pics from TM Tractor of the part I am talking about.

http://www.tmtractor.com/new/fl/6741fp.htm

[Jackman]

Thanks fellas! I'm talking about this jet (Pic) threads into bowl, no issues just trying to understand the carb , its a bit differant than other things that I have, also not having any significant problems the Cub runs smooth and starts easy but I am in search of more power and more RPM's , seems a bit weak in that area , however I have not yet had a timimg light or a tach on it so that is just a guess its been a loong time since it was last ran.

[inairam]

If you are going for more power some members say get an A or a 140.

If it starts and runs and you think it is underpowered: tune up, timing, valve adjustment, governor linkage adjustment maybe some seafoam in the oil and gas.

I would not recommend playing with jets to get more power and you may lose "starts and runs". More fuel does not get automatically get you more power and it will not get you more RPM/HP without a different governor.

[Jackman]

Sticking with the Cub , everything has been done , next I gotta get a tach and timing light and see where I'm at, Carb rebuilt,govonor dissassembled free and working, valves adjusted, good compression , new wires,points condensor, plugs , even a new battery, runing on a pony tank for now the original is rusted on the inside, it could be me but it seems short on RPM's ...... thanks all!

[inairam]

put on the tach and timing light. My cubs from different areas sound a bit different. Check flow in from pony tank.

[Jim Becker]

. . . My cubs from different areas sound a bit different. . . .

Regional dialect?

[Barnyard]

. . . My cubs from different areas sound a bit different. . . .

Regional dialect?

[inairam]

Jim & Barnyard, I know how it sounds strange but none of my cubs are identical between where, vertical and underslung exhaust, new vs old mufflers, state of turn. They do not sound the same to me.

But since you brought up regional dialects my 1975 is from New Jersey. That is the one that sounds the most different!