Racing Fuel Systems

Re: 4412 throttle blades

2023-07-17T17:22:25+01:00

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

Statistics: Posted by SP70Nova — Mon Jul 17, 2023 5:22 pm

Re: 4412 throttle blades

2023-05-10T18:09:09+01:00

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

Statistics: Posted by SP70Nova — Wed May 10, 2023 6:09 pm

Re: 4412 throttle blades

2023-05-04T09:30:00+01:00

Throttle blades #172

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

Statistics: Posted by rgalajda — Thu May 04, 2023 9:30 am

Re: 4412 throttle blades

2023-05-03T18:03:31+01:00

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

Statistics: Posted by SP70Nova — Wed May 03, 2023 6:03 pm

Re: 4412 throttle blades

2023-05-03T10:07:33+01:00

"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.

Statistics: Posted by rgalajda — Wed May 03, 2023 10:07 am

Re: 4412 throttle blades

2023-05-02T20:34:11+01:00

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

Statistics: Posted by SP70Nova — Tue May 02, 2023 8:34 pm

Re: 4412 throttle blades

2023-04-19T17:37:37+01:00

Well, the weather didn't hold out for us this past weekend - we're looking at next weekend...

I really haven't put hands on the engine yet besides getting the carb to idle, so I don't have much info on the manifold vacuum, timing, the distributor and or its setup/operation yet...

GTO Geoff - No PCV currently. If I need help in getting the idle position back to a more normal squared transition slot exposure after I seal the blade holes, I may need to add a PCV valve.... We'll see.

rgalajda - those are the blades #'s. With the hole finish and their positions being visually identical blade vs blade - I was wondering if that was the case. I'll take note of the manifold vac before & after sealing the holes. The flush plugs are above the Idle wells - I shouldn't have called them cups.... Yes, both the Main Well cups and Idle Well plugs look like brass.

I still have my to do list and will go from there.

Thanks again for the help.

Scott

Statistics: Posted by SP70Nova — Wed Apr 19, 2023 5:37 pm

Re: 4412 throttle blades

2023-04-19T06:29:25+01:00

Since the carb is 'used', check for worn throttle shaft [ air leak, fast idle ].

Statistics: Posted by GTO Geoff — Wed Apr 19, 2023 6:29 am

Re: 4412 throttle blades

2023-04-18T11:48:05+01:00

Those throttle blades are # 215 I believe. Those were factory drilled for V8 cars. These are the same blades as a 750/780 holley # 172 , not drilled, about .440 " thick.
#173 blade are the same size , slightly thicker at about .640 " thick.

Do you know how much vacuum you have at idle now, and after you close up the holes in the throttle blades ?

Also , those well plugs are flush at the top, not solid brass?

Statistics: Posted by rgalajda — Tue Apr 18, 2023 11:48 am

Re: 4412 throttle blades

2023-04-18T05:37:11+01:00

Yup, seal the holes in the t/blades. If PCV is used, make sure it is working properly & not adding excessive air at idle.

Statistics: Posted by GTO Geoff — Tue Apr 18, 2023 5:37 am

Re: 4412 throttle blades

2023-04-17T17:51:49+01:00

Like mentioned, there is a similar thread on the other site.

Here's some more info:

This is a local 1/4 asphalt track. It's an 4412-5 with a factory choke horn and the older 2 hole emulsion block with the screw style (fuel level) fuel bowl.

I found out this carb came off of a v-8 and sat on a shelf for several years - outside of that we don't have any history on this carb. This makes sense as why the throttle blades are drilled... It basically was given to my buddy to try - low buck operation.

Based on Holley's List sheet - Stock 73 jets, 5.0 PV, 28 squirter.

Here's the metering block - (I only have #'d drill bits - using the shanks so the diameters are approx.)
2 hole emulsion block - @ .028" ea
drilled kill/anti-siphon bleeds in angle channel @ .026"
Recessed Main Well Cups & Flush Idle Well Cups (top of metering block)
Lower IFRs - @ .031"
Main Jets - #64s
PV - 6.5
IABs - @ .076"
MABs - @ .028"

Factory Brass float with .110 N&S
Fuel line has Inline reg set @ 3.5psi

Found no gasket on PV
The squirter had no gaskets & the weight underneath was stuck
The acc pump arm that rides the pump cam was partially froze up - not returning down on the cam

Cleaned out all passages
verified PV with vac pump
replaced missing gaskets
cleaned, reset accel pump arm
set the float to bottom edge of bowl screw threads.
Set mixture screws to 1-1/2 turn out to start with

I didn't change the existing jets - I wanted to see how the carb ran to get a base line.

With the Idle speed screw backed off throttle plates 1/8" (gap) - idle rpm @1200. The throttle blades are fully closed and t-slot is not even close to being exposed. Engine has a noticeable tip-in studder on a major/quick throttle opening (rev, cough, rev) from idle with no load - out of gear.

Still need to verify distributor timing - vacuum advance is connected to full manifold vacuum port currently.

Here's what my to do list is - let me know what you think:
Seal the holes in the throttle blades and get the idle position back to a more normal squared transition slot exposure with an idle rpm closer to 7-800 range.
Increase the squirter if needed.
Verify Dist timing (intial & mech) and see what the vac pot is adding to the timing.
Jet according to engine/plugs

We should have some time this weekend to see what the timing is after plugging the throttle blade holes and resetting the idle position. We might even get to the track weather permitting.

Thanks again for all the help.
Scott

Statistics: Posted by SP70Nova — Mon Apr 17, 2023 5:51 pm

Re: 4412 throttle blades

2023-04-13T15:35:22+01:00

Statistics: Posted by FC-Pilot — Thu Apr 13, 2023 3:35 pm

Re: 4412 throttle blades

2023-04-13T15:14:08+01:00

Statistics: Posted by 57 210 — Thu Apr 13, 2023 3:14 pm

Re: 4412 throttle blades

2023-04-11T17:48:03+01:00

Statistics: Posted by rgalajda — Tue Apr 11, 2023 5:48 pm

Re: 4412 throttle blades

2023-04-10T13:18:43+01:00

Statistics: Posted by ojh — Mon Apr 10, 2023 1:18 pm