Supercharged Idf rich at cruising speed

[Boosted72]

Hi guys! First I want to thank everyone in this forum, as a new aircooled owner i have found answers to most of my questions here... and I've had a lot! This year I purchased a non running 72 convertible as a mental health project during these crazy times we live in. Lucky for me the issue was electrical and being an electrician I had it running in no time. Then it all started.... how can I make this car a little faster and have a cool factor but different after looking at several post, pictures and ideas I decided to do the complete opposite of what I've seen done.
A blow thru, single carb supercharger set up. Took me about 2 months to do it and for the most part it all works as it should. It idles good 12-13 A/F 12.1-12.9 on acceleration with 5psi of boost - a little leaner if i use my smaller pulley thats about 10 psi, but when I start to cruise it goes rich, mostly 10 or under as my wideband starts to flash. I have read countless post on tuning and jetting but most are for dual carbs and none with the same issue I have.

This is what I'm running:
Amr500 blowing thru
Single weber idf 44
32 venturi
Idle 55
Main 150
Air correction 180
Zero on the acceleration pump jet
Turbo emulsion tubes
Mod rigs
Walbro fuel pump with boost referenced regulator
009 dizzy with msd boost reference retard

Thanks in advance.

[rubenski]

Maybe mario from the dubshop can you a pointer on tuning, he has some expirience with those, altough efi....

What i've learned from the amr500 with a carb, it will always be a compromise. Hard to find the sweetspot.



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[V8Nate]

Cool setup I love the tiny exhaust tips aswell when I had the twin idf's I tried to get the cruise to a nice state but if it was lean enough on cruise it was too lean on wot. Carbs will always be a sacrifice one way or another. The best running carb i had was a Rochester 1 barrel off a straight 6 chevy that I had on top of my amr500, it was almost perfect on all aspects of driving!

[madmike]

what size motor? if 1600cc 32 vent's maybe a bit big?

[Boosted72]

Far as I now it is a 1600 DP, I was thinking the 32s might be a bit small and making my main circuit start too early I'm in the process of changing them to 36s now. I did it last week but it would fall on its face during the transition period. I didn't spend much time with them and change them back because I had plans to go to a swap meet yesterday. Priorities . V8nate made a comment that got me thinking could the exhaust be restriction the flow?

[madmike]

heck ya ,, what "goes in must come out" don't tell me ur running stock exhaust?

[Clonebug]

Far as I now it is a 1600 DP, I was thinking the 32s might be a bit small and making my main circuit start too early I'm in the process of changing them to 36s now. I did it last week but it would fall on its face during the transition period. I didn't spend much time with them and change them back because I had plans to go to a swap meet yesterday. Priorities . V8nate made a comment that got me thinking could the exhaust be restriction the flow?

The falling on it's face is probably due to the change in airspeed when you crack open the throttle with the larger venturis. You might be able to tune some of it out with a bigger accel shot but you would basically have to start over on your tune due to the completely different airflow characteristics with the bigger Venturis.

[Boosted72]

Drove it to lunch, idle is good, could use a little more fuel from the accelaror pump but still rich at cruising... RPM range increased quite a bit. Wonder if setting my float from 10 to about 12mm would make a difference I'm so out of idea's.

[VdanielW]

Admittedly I didn’t read the whole thread but I have tuned idf’s. I spent 5000 miles on my car until I had them perfect and then swapped back over to my turbo set up to start the process all over again with an edelbrock!
I found the best way to tune my idfs was to start with idles and get my afr right where I wanted it when steady cruise on the freeway. 65mph at 3000rpm with vacuum at 16-17”hg. Once that was set I started on transition so if it was going rich before my idles were off I’d put larger venturi in. If I had a lean spot I’d go smaller on the venturi. After that tune the mains to be the afr I wanted under load (lower vacuum range like 12-15”hg) and the airs for WOT afr target. If you are running draw through (carb on top of the blower) this should work just fine for you as well.
You will need to do a little driving to recognize what vacuum your car runs at for low load cruise and high load cruise. Idles are set with the idle enrichment adjusters and WOT is very close to 0”hg so that’s an easy area to recognize.


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[Boosted72]

Madmike
it is stock, since my issue is cruising and there's no boost but about 10hg of vacuum I figured it can't be much of a restriction. But now its got me thinking. I really don't what to spend money on exhaust trial and error incase I ditch the supercharger for some turbos.

[John S.]

What fuel pump and regulator. Also what size mod rings?

[Boosted72]

Inline 35-50 psi Walbro with a boost referenced regulator. 2.5psi to carb and adds +1 psi for every psi of boost. While cruising Between 50-60mph and 2k-3k RPMs with no boost its right at 2.5psi. Don't ask how i know... Mod ring are 33mm it. Tried smaller and with the stock velocity stack that are 44.

I changed to 36 venturi yesterday and ended up adjusting my float to almost 13mm. Cruise AF got way better to almost 12 but the lost of bottom end was noticeable and I rather have good power under 5k rpms.

[xzener]

I also had the rich cruise and acceleration with my NA setup (1500cc, AMR500, DCOE 40). Was in the midst of trying different jets, but have since decided to convert to EFI. Good luck tuning your engine, curious to see how you make out.

[Boosted72]

As of right now I'm pretty sure its because cause of the venturis being to small, at cruising im not really under boost but im not at its normal vacuum hg and the additional air flow and speed makes the auxiliary vents start sooner. I have some 34 mm vents coming in this weekend and will post results.

[xzener]

I tried bigger venturis as well... It did not remedy the issue. I went from 26mm to 30mm. Noticeable HP loss on the lower end, still rich during acceleration and cruise. Started chasing the mains... But have since replaced the Weber DCOE 40 with a DCOE style ITB. I believe the increase in boost brings the mains in very early... It was recommended that I remove the mains to figure out when they were being used. The car fell flat on its face just pulling out of the driveway. I hope that an ECU can properly get the mixture right... We'll see.