little carburetor experiment

[vector1]

i have my engine up & running, it's a 9-1 383 with a rpm air gap manifold, afr205 heads, & pretty good size solid roller cam.

i had a good carb on it, looked to be a 750 size and it ran well, but i wanted to go with a bigger carb and had a bg 850 rr sitting on the shelf, so everyone knows what happens next.......

the bg carb was already ran on the previous engine, i had changed the pv, pvcr, & main jets. the previous 750 carb builder on his carb told me to cover the t-slots with the butterflies so they were just uncovered when the throttle blades moved. so everyone knows what happens next......

the 750 was made for another engine and had holes drilled in each butterfly to keep the idle with the butterflies near closed. btw, when you close the butterflies and hold the carb up to the light, there is all kinds of area around the butterflies to let air through, don't let anybody kid ya.

so i took the 850 and shut the butterflies so just as they moved the t-slots were uncovered. then i went down to the store and bought the smallest carbide bits available, 1/16". i was considering taking the butterflies out but the screws are hammered on the bottom and not coming out. a person wants to use the smallest holes here and work up, as there is no going back, other then soldering the holes shut and redrilling, which i didn't want to do.

without the holes the 850 would barely idle, with the 1/16" holes it was idling at a little less then 1000, i wanted around 1200. next size up was 5/64--this made for the correct idle rpm right around 1100-1200. keep in mind, when these holes go up, afr correction might need to take place to adjust for the holes and the fact the idle rpm is not pulling fuel out of the t slot. don't get your hole sized and then adjust the afr and end up with a runaway. best to end up a little low on the rpm or small on the hole and drive it around and make adjustments to see where things end up. so everyone knows what happens next.......

i take it out for a cruise. im using a afr gauge as my visual indicator btw as the butt meter is a little fuzzy nowadays. everything works great, cracking the throttle doesn't go lean, stays right on the money. i cruise at 14-1 range, depending on the grade. i can watch the mains come on with pv's and the afr goes to 13-12.5. there is a lean area after cruise on slow acceleration before the mains open that i'm going to have to take care of with the iab's &/or ifr's. no hesitation or anything, just lean into the 17-1 range.

so i would say the experiment is a good one so far. everyone knows what happens next.......