4412 throttle blades

[SP70Nova]

So far, we have not had an opportunity to get to the track yet - NE Ohio weather…
Before I pulled the carb, I checked a couple of things:
Before I started the engine, I pulled a couple of plugs. It sounds like these plugs only had 3 heat races on them from the end of last year besides a little idle time from loading/unloading. There was a good coating of dry carbon completely around the base that easily wiped off with my finger and the porcelain was stone white as far down as I could see. The heat/color change on the ground strap is barely visible in the pic - was unable to see with my decent eyesight. All of the plugs basically looked the same.

One thing that stood out to me last weekend was that the engine was stone cold, the outside temp was @ 50°, and the engine started with a minor throttle stab and idled by itself after about a minute (carb has choke horn, but no choke plate). I checked the Manifold vac – steady @ 14” HG with it idling @ 1300 rpm - the Idle speed screw was completely backed off (1/8” gap) and the throttle blades were fully closed. The Idle mixture screws were @ 1-1/2 turn out. There was no temp registering on the water gauge.

I pulled the carb apart and re-measured/verified the metering block and IFR & Air bleed sizes (must have had the #’d drill bits mixed up – I confirmed the drill bit shanks w/ a dial caliper this time):
IFR - .035”
Kill/Anti-Syphon Bleed - .028”
Both Emulsion Bleeds - .028”
PCVR - @ .063” (b/t #52 – slightly loose, #51)
MAB - .028”
IAB - @ .069” (b/t #51 – fairly loose, #50)

Here’s what was changed:
Plugged throttle blade holes (.090”) with 2-56 brass screws & nuts – the nuts were notched/staked to the screws (removable/temporary-permanent plugs)
Increased MJs to 71s (based on how the plugs looked)
Added .007” dia wire to IFR to reduce to @ .028” (based on my math)
Added vent baffle to metering block – extends 7/8” into bowl (bowl is 1-5/8 deep) to middle of float

Installed the carb and now the engine needed some help idling throttle wise until there was temp registering on the water gauge. Idle mixture screws ended up at 1-1/4 turn out. Manifold vac was steady @ 15” HG with the Idle at 1000 rpm with the idle speed screw 1/2 turn past contact at temp. Nice thing was that the outside temp was @ 50° just like last weekend. The float height and the accel pump linkage were readjusted to get everything in synch. At temp, the engine idles smooth and will take any throttle opening (part throttle to WOT – fast/slow) with no issues. There was & still is no PVC on the engine.

Verified the Vac adv was operating – could see vacuum pot stem moving on the distributor, but didn’t have time to get the timing light out.

Now we’re waiting on the weather to get to the track to see if/how much it improved.

Thanks again for all the help.

Scott

[rgalajda]

"Installed the carb and now the engine needed some help idling throttle wise until there was temp registering on the water gauge."

Very rich idle (IFR ) = using a choke. This is why so many people say they don't need a choke for warm up. The idle is way to rich.

#64 MJ to #71 MJ is a big increase . But what might save you is the reduced IFR, because that leans it slightly all across the board.

[SP70Nova]

rgalajda - I was trying to get closer to the factory jet size based on the plugs. Holley's List sheet for the 4412-5: Stock 73 jets, 5.0 PV, 28 squirter. With the Idle mixture screws 1-1/4 turn out, I figured I was pretty close on the idle circuit with the reduced IFRs to run it.

Waiting on track time to see.

Scott

[rgalajda]

Throttle blades #172

https://allcarbs.com/product/holley-throttle-plate/

[SP70Nova]

Update from the track on Saturday:

The lap times dropped/improved 0.4 secs compared to the end of last year. Outside of the carb adjustments, the rest of the engine and suspension was the same as last year so it was as good of an A to B test that we could get.

The carb is in a much better tune than last year. It pulls well down the entire straight and doesn't have any issues entering the turns. Last year, it fell on it's face all together - could only run 2nd gear (manual trans) because the engine couldn't pull 3rd gear... Saturday, after several laps in 2nd gear, the driver tried 3rd gear. He was able to run 3rd gear pretty well except for a small hesitation coming off the turn that showed up only in 3rd gear.

I have not pulled the plugs to compare them to the previous set (pictures).

I think it's close - so far it looks like the float/vent baffle is good, but still need to verify/tweak the main jets and work on the Acc pump. The timing setup needs figured out.

Scott

[SP70Nova]

Update:

The carb's been working well with some minor AB & jet fine tuning and I was able verify/tweak the timing & dist advance. The engine was running well until it dropped a valve on the #3 cyl (piston has a new gas port). Looks like we're done for the season.

Thanks again for all the help.

Scott