DRLA jetting...

[bugnut]

I've got a pair of 45 DRLAs I rebuilt for my 2017 build.  Jetting is 200 main air correctors, 180 mains, I believe and 75 idles... dont' have the emulsion tube stats off the top of my head, but everything points to what the carbs shipped with originally.

Just wondering where I'm at in the ballpark for jetting for my new engine once its ready tof ire.  The idles sound a little fat, but I'm not sure if that's typical for these bigger carbs (the biggest carbs I've had prior were Kadrons).

Specs are 78.4x90.5, 8.6:1 compression, 42x37.5 valves, 1-5/8" exhaust, 1.25 ratio rockers and Engle 125 cam.

[arnolds64]

 I guess no one replied and it has been Awhile? I would think that those numbers are fat. 55 idles, 145 mains or 150.  Airs are OK Should be F11 tubes. 45's are like almost 48 IDA's size wise. I have a 2017 and going from a 110 qithh 40 IDFS and had 50 idles, 135 mains with 220 Airs 34 vents. SO the 125 with 1.25's.

[David Ward]

There's an old rule of thumb that helps you get started with your mains.  Venturi size x 4 = target main jet size.  For idles I'd start with 55's or 60's.  Your airs might start in the 160-180 range.  It helps to know your venturi size and intake valve size.

[dangerous]

From memory the Dellorto book said 4.2x venturi and,"just stick in a 180 main".

I personally like smaller mains and airs,
so would agree with David Ward's start point for yours.

My own carbs had a 34 choke,
so perhaps should have had a slightly smaller main at 135 to begin with

Acell pump nozz was a 35, which could have come down a little too.

My own 45's had 34 chokes,
and worked well with 140 mains,
175 airs and the 70 idles it had were a bit on the rich side,
but the engine was very smooth from idle to full rpm.

You will always have to fine tune these start points
depending on you specific combo, and the altitude that you operate in.

[bugnut]

Valve sizes were posted in the initial post, 42x37.5mm Steve Tims Stage II heads.

My altitude is 4,800 feet.  Thanks!