Primary metering rod selection for recipe 2

[Nko]

Hi, this is my first time messing with a carb. I think that my engine will be somewhere between recipe #2 and #3 so I am starting with Recipe #2. My question is for the primary metering rod- for APT carbs use a tapered rod at least .029" less than the main jet at the widest point. If I am using a 74 jet then I need a rod that is at least .045" But the double asterisk says for single main air bleed carbs use 50, 52, or 54M rods. If I use a 50 it would only be .024" smaller. What rod should I go with? The rod that was in the carb has a .026 power tip. and measures .049 at the largest part of the taper. I appreciate any help.

carb # 17081206
Idle Tube .039
Idle DCR .052
Idle air bleed upper .070
lower .080
Idle bypass air .080
Mixture screw hole .097
Fuel inlet .130
Sec Tube res. .032
Sec POE Well .038
Sec POE Res .051
Secondary hanger P
Single Main air bleed(horn) .085

[Cliff Ruggles]

That carburetor uses "M" series primary metering rods.  M rods have .010" taper on the upper section and .036" tips.  So a 50M tapers from .050" to .040" on the upper section, then "steps" to .036"

We make a full tapered rod for them that tapers from .050" down to .036" if you want more control with the APT system.

I would also get one of my rebuild kits for it.  It will come with the correct SOLID fuel inlet seat, and complete accl pump assembly with a USA made pump cup (lifetime warranty) instead of the "soft" imported pump cups others are using......Cliff

[Nko]

Thanks for the response. So I need the M rods, check.

My question was more about the size rod I would use. Maybe I am not understanding the measurements. But in your book it says, if your carb has APT to choose a tapered rod that measures at least. 029" less than the jet. It also says to use a 74, 76, or 78 jet. My question is: if I use a 74 jet should I use at least a 45 rod to get the minimum. 029" difference? According to my calculations a 50 rod would only give me .024" difference and a 52 or 54 would be even less clearance. Or am I not understanding this right.

As far as the rebuild kit goes, I have a rebuild kit that I bought before I found your site. I don't know if it has a good fuel inlet or accelerator pump cup. But after reading your book it looks like I could use a bigger opening on the inlet and I might as well get the accelerator pump cup while I am at it. Once I know what rods I am getting I can put together an order.

[Cliff Ruggles]

Your kit will NOT have a good accl pump and probably has the windowed seat and it will not be the high flow variety.  Good results start with good parts and ALL of these "blue" seals being supplied at this point come from offshore and will not hold up in this new fuel.  Every single carb I get in here having issues has a failed or failing accl pump cup in it.  They swell up and get tight/stick in the bore and eventually fail completely, but they also do NOT allow the well to fill effectively under the pump so we get all sorts of complaints about difficult cold starts after sitting and performance issue going quacking to heavy and full throttle.

As far as metering rods you will be fine with pretty much any "M" series rod in that carburetor.  If you want a wider range of control with the APT get a set of my 50C rods.  They actually measure closer to .052" at the top of the tapered section so you will have more control with them than any "M" series rod.  I'd also add that most used metering rods are worn/flat sided anyhow and should be very carefully measured before being put back in service.

Same thing with jets, rare to find a pair that aren't worn or egged out and these days I don't even check them anymore.  Folks also had a BAD habit of drilling them out over the years, so all my builds get new jets and metering rods.......Cliff