World Formula Carb settings

briggsworldformula

(Rick Brown ) #1

I’ve been racing World Formula for about 5 years now and I’ve always set the float height to spec 14mm, ran the 38 pilot, 93 or 96 main, and have played around with the clip on the needle a little bit. I’ve never had a problem and have always run up front but I’d like to start fine tuning a bit, competition is getting tight! I have the Briggs carb tuning manual and it gives baselines but could someone explain float height and what exactly raising and lowering it will do? My engine likes to bog if you hit the gas hard at +/- 3K I’ve tried going both ways with the pilot (richer seems better) then I tried 14.5 mm and 13.5mm float height (generally run 14mm) didn’t seem to change. The thing that’s confusing me most is that the bigger pilot helps but the leanest setting on the needle in the slide helps? Not sure what to try next?


(Mike Clark) #2

With the carb upside down:
Raising the float lowers the fuel level in the bowl.
Lowering the float raises the fuel level in the bowl.
This take some inverse thinking as the carb is upside down.
This richens or leans the mixture across the whole range of throttle opening. Changing only 1 jet adjust the mixture mainly in that jets range.
The guide doesn’t really tell much and doesn’t give any ideas of how much float level increments change things, Fuels specific gravity and air density would be a factor as well.

Check float drop first
Try a bigger jump on float height
Fuel pump ??


(Rick Brown ) #3

I haven’t checked the drop, I’ve actually never checked it. Fuel pump is brand new. I wish that the manual was a bit more specific. I would think my issue would be the pilot since it bogs for a second from idle and is fine after that but I’ve tried all 3 jets. It actually seems like I need something bigger than the 40 which’s the largest that comes with the kit. If I turn the idle up to 3,200 it acts fine?


(Eric Gunderson) #4

@Racer_Rick12 do you ever set your air idle adjustment and idle on the stand before running the kart? Briggs recommends setting this regularly, and depending on the day, altitude, etc. if you don’t adjust this regularly you can lose some bottom end performance as you describe.

General practice: first session prep, run the engine up slowly to 150-200 deg. on the stand (touch the rev limiter but never bounce on it, very hard on engine). Once in that heat range many racers set idle at 2000 per Briggs. I have found closer to 1750-1800 allows engine to pull harder off bottom end.

If you haven’t checked the drop, that could also be it. Too big a drop can cause massive fuel issues, and the issue you describe. There is a small tab that interfaces between the pivot area and the actual float that you can bend to adjust drop. anything more than 1.00" drop and you can run into trouble.

Another extremely common problem is dirt getting into the area where the needle moves up and down as the float moves up and down. Any dirt in this area causes the engine to run roughly.


(Rick Brown ) #5

I do adjust the Idle mixture. I’ll check the drop but it doesn’t seem to be a huge problem, I nearly won the race and was definitely the fastest Kart (lap times) it’s a brand new engine and carb. The carbs definitely clean it took a bath in the ultrasonic cleaner. Jets are also new and clean. Maybe I just haven’t found the right combo of float height, jet, needle clip, and mixture yet? I spent a couple hours yesterday and just seemed to go around in circles.


(Rob Bone) #6

I mean you could get this for practice days. Nothing like real data from the track.

https://cometkartsales.com/Mychron-4-5-Lambda-Air-Fuel-Ratio-Sensor.html

:thinking: Perhaps a sensor sharing program could be started?


(Rick Brown ) #7

That’s always an option, generally I’m most concerned with driving and setup but as you saw there are a lot of good racers in WF and competition is really close! Always looking for anything to go faster!


(Rob Bone) #8

Trip to the local wind tunnel, work on that aero?

But yeah, the WF up here in the NE is very close. Maybe I’ll join in a season or two.