331 dyno session (part duex)

Cruise air/fuel is controlled mostly by the transfer slot, and only partly by the main jets. (that is if you are at highway speeds) If your at 20 - 30 MPH, it is 100% transfer slots supplied fuel.

The transfer slots are controlled by the air fuel ratio of the idle circuit. The volume ( or amount of transfer slot air / fuel) is controlled by the IFR ( Idle Feed Restrictor) in the main plate.

If the cruise is too rich, the IFR needs to be reduced, stumbling or too lean, it needs to be increased.

I am not sure if you have adjustable air-bleeds in your speed demon. If you do, you can adjust the idle air bleeds to change idle air-fuel ratio.

Originally Posted by pass1over

thankyou for all the help, but im done with it. Ive had nothign but problems with AFRs and tuning and every aspect of driving/tuning this setup. Its all coming off and EFI is going on.

Don´t have much patience? Only a week and giving up,even with all the dyno tim, and all? Listen to the guys and learn by fixing it.

Maybe you should buy a Toyota? ( Just kidding)

Keep up the spirit and fixthe problems, if there is a real problem...
I bet you would be perfectly happy with it if you didn´t have the dyno...

Sounds strange? I assume you have done all the "basic" stuff like float levels, fuel pressure, engine timing, sure pv is closed etc. Your high speed air bleed may be too small...enlarging it will lean it but also delay the start of the high speed circuit.
Exactly what carb is it? New? Where are you at with your jetting (#)?

its been more than a week of trying to tune this thing. Ive only posted about my dyno sessions over the past couple weeks. Ive been trying to tune this thing for probably over a year.
I dont know/trust anyone here in Lexington to tune my carb. The only person I know/trust to do it lives 900 miles away in Tampa, FL. So that isnt helping anything out.

I cannot get my fuel pressure to remain constant, nor the levels in the bowl. Sunday, my pump was pumping at only 5.5psi, it shoudl pump between 6.5 and 8. Yesterday before I went home from work, the pump was doin 7psi and the levels in my bowls were way way low. So without figuring why im getting erratic/low fuel pressure, none of this other stuff is going to do any go0d.

Its a Speed Demon, 650cfm. Jets are 72 P and 85 S i think.

was thinking of getting a toyota, well an infiniti, those new G37s are hot!

THe original plan was to EFI this car when the new motor was installed. We ran out of time/money and I moved to kentucky. Carb was the "easiest" way to get it moving.

Sorry to hear you've given up but I definitely understand. As Mike was saying, light throttle cruise is mostly fed by the idle well through the idle discharge hole and the transfer slot... there isn't enough airflow to get the mains going until you tip the throttle in to accelerate. The only thing you should tune with the main jets is the medium and heavy load... get the medium load dialed in with the main, then get the heavy load dialed in by drilling the power valve channel restrictors.

As far as tuning the idle circuit, it can be a real pain I know because I myself am trying to lean out a rich cruise condition. I've done the wire in the Idle Feed Restrictor trick and all that did was create a lean 'sweet spot', right at cruise... as soon as I back off the throttle a touch, or start coasting, it goes 12:1 rich again... so I think the next step is drilling the Idle Air Bleed a size or two larger.

Tuning WOT and heavy load is by far the easiest thing, just a couple jet changes and you're there. Tuning the cruise, now that's where it gets tricky, when you have a dozen different adjustments (IFR, IAB, secondary blade angle, primary blade angle, idle mixture screws, float level) that all have different effects on the mixture at low-load, low-rpm.

I would somewhat expect the fuel pressure to drop SOME at WOT... the only way it wouldn't drop would be if your whole fuel feed system was WAY overkill. 4.5psi is a tad low, but honestly I don't think that's going to cause you any problems. And as for the float level varying, that's gonna happen to some extent as well. Just imagine how much the fuel is sloshing around when you're driving, and it's easy to see how the float could let in a little extra fuel before you park it.

Also another thing that's easy to check is to see if the regulator is gummed up on your fuel pump. If I remember right, the Summit pumps are the same as the Holleys, and you can remove the botom plate to get to all the guts of the pump and clean it out.

I am planning on switching out to EFI, but unfortunately, I dont have the money now at all. Hopefully santa will be nice to be at xmas and I can get enough dough to start the EFI build.
Until then, im stuck with this damn carbernator.

Couple of things im going to try next:
1) take pump apart, clean and inspect it
2) vacuum canister on my dist. is not ho0ked up. Gonna ho0k it up and see what happens. I know its not gonna solve all my problems but it might help some.
3) clean the passageways in the carb out ... AGAIN

Gotta take it small steps at a time otherwise im liable to get PO'd and break something.

As for the level in the bowls. They were set and stayed at about the halfway mark to a little above the halfway mark on the sight windows. The next time I fired it up, they were below the bottom line on the sight plug, just barely visible on the window ... both primary AND secondary bowls. I can see and understand them moving a little, but the amount they moved .. .WAAAAY to0 much.

I agree with you guys about the idle circuit but it depends on what is termed "cruise". If he is talking "highway" cruise, it may well be starting to transition onto the primaries.
So its a Demon....aren't these carbs re-knowned for their rich running around idle??

when I was saying cruise, it was at approx. 40mph in 4th gear, T5, 3.5gears. Was about 2k rpm i think?

I would think you are probably still on the idle circuit.... though I shouldn't comment as I am not familiar with the demons.
If they have replaceable bleeds, you can't come to too much harm messing around but would reccommend you get your distributor vac hooked up and sort any fuel pressure or other concerns you have first.
It amazing what has an influence on carb tune....there is an old saying that goes - 9 out of 10 carb problems are ignition related - and its damn true.

to0k the pump apart. Ive never taken one apart before, but it seemed as if everything was in order. Didnt ntice any holes or tears in the diaphrams.

One strange thing I noticed, in the bottom of the pump, its divided into 2 sides. 1 side has the outlet to the carb, the other half is below where the fuel comes into the pump, but that chamber isnt used for anything on the outlet side. There was a square piece of this black squishy foam stuff. That a normal find in a mech. pump? I figured it was just to make sure the diaphram stayed up.