Carburetor Fine Tuning, Trying to get my dual EMPI HPMX 44's as close to perfect as possible - Now running Spanish Weber 48 IDF's... Options

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I've been working on my carbs for the past few weeks to try and get them to run as close to perfect as possible. Here are the details at this point:

2315 Raby built engine

EMPI HPMX Dual 44's
52 idle jets
150 main jets
200 air correction jets
55 accelerator pump jets

New CB Performance Rotary Fuel Pump - 3.5 psi - stock location
No fuel pressure regulator - just a TEE fitting
Stack electrical fuel pressure gauge 0-15 psi - reads 3.1 psi when cold, 2.4 psi once everything warms up and is running
Wide band AFR gauge

Fuel lines flushed and fuel filters cleaned
Gas tank pulled and re-installed lines at base to be sure there are no kinks

I rebuilt the carbs with the EMPI rebuild kits which includes all new gaskets, accelerator pump diaphragm, new mini fuel filter, new float needle valve assembly, new washers for the accelerator pump jets, new o-rings for the idle jets and idle mixture screws. Floats are set to factory specifications as well.

I pulled the throttle plates and was extremely careful to be sure I put them back exactly the same way and that they do not hang up - their action is perfect and they cover the progression holes.

This project started a few weeks ago after running into lean issues under load - turned out to be the fuel pump relay was going bad. There was a significant voltage drop across the relay and it finally ended up failing completely during testing.

Once the engine is fully warmed up, my AFR is reading 12 to 13 at idle; adjusting the idle mixture screws can make a big difference in AFR readings without changing the idle significantly.

I started out with the accelerator pump jets set to factory setting of 7mm of thread exposed. During my test drives today, I turned them in (richer) to about 10mm. Response is better but still not perfect.

I'm getting AFR readings in the 12-14 range during "regular driving" on the highway. Going up hill under load at 60-70 mph in 4th gear (say around 3500-3800 rpm) and very slowly pushing on the throttle creates a lean condition. Once I step on it, the AFR drops down to 11-12 and then settles again in the 12-14 range.

I would really appreciate some input on adjusting the accelerator pump and any other suggestions on how to get the most of these carbs. Are the accelerator pump jets (55) big enough? They can certainly be reamed out. I did measure the output and got around 0.3 ml fairly consistently for each jet. All 4 jets spray straight right into the center of the carb in an even stream.

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On a hunch that the transition circuits were likely plugged up I decided to replace the EMPI's with a pair of Spanish Weber IDF's. After discussion with CB and a very strong recommendation by them to go with 48's instead of 44's, I went ahead and ordered a pair of 48's.

First impression, WOW! What have I been missing!! My Raby 2316 loves the 48's. Top end is much stronger and it really feels like the low end is better as well. Transition is good, drivability is not an issue.

I started out with the factory jetting - 55 idles, 150 mains, 180 air corrections. It was rich in the main circuit, like 10-12 on my wide band AFR. I switched the AC's to 200's and then switched the idles to 57's. Very, very nice, but a touch lean on decel and in transition. I kept it this way for a week and waited for 60 idles to arrive.

Put in the 60 idles yesterday - way too rich. Amazing that such a small change could make such a difference. The transition was close to perfect but it was just way too rich throughout the entire RPM range. We are talking AFR's of 11-12 under load.

Back to the 57 idles today. With the 57's, the AFR reads 13-14 under load.

I also added a second light spring on the linkage (running the McMark linkage) and I can get the engine to idle smoothly as low as 500 rpm's. With a really low idle, the engine didn't coast very well on downhills - a bit of back firing. At a 700-720 idle, and an extra quarter turn open from fastest idle on the idle mixture screws, the engine coasts without any back firing.

I might try the 180 AC's again next. Not sure they will have any effect at all on the transition or coasting...

I think it's time to buy a jet gauge and measure everything. I'm shocked that going from a 57 to a 60 idle would make such a difference. Gotta measure and verify.