Allright, the fun has started. I spent the morning trying to get a baseline on the 511. No real success yet. Most of you guys know the engine already, but just in case heres the significant information:

511ci Aluminum block
KC Stage III heads
Victor Manifold
850 Mighty Demon, 3.5 PV
Solid roller 295/300adv, 262/268 @.050, 110lsa, 106cl, .695/.695 lift
12:1 compression
5-6 in/Hg vacuum at 950ish idle
11 in/Hg vacuum at 2500 cruise
Timing currently set at 20d initial/38d total, in by about 2400.

The biggest problem so far is getting the idle mixture set. It is running very rich, sooty black plugs, Stoich gauge showing full rich. Cleans up when I'm cruising.

I adjusted the throttle blades just far enough open to hold idle speed. Starting at 1.5 turns out on the idle screws, I adjusted them in 1/4 turn at a time until it killed the engine. No change, rich as can be. Odd. Pulled the carb, tipped it upside down, set the transfer slots to show about .020, or square. Drilled 1ea. 1/16" hole in each primary throttle blade near the transfer slot to allow additional air through the venturi without uncovering the transfers. Reinstalled carb, will test tomorrow.

I'm kinda scratching my head here trying to figure out where all this fuel is coming from to make it so rich. Any ideas?

-Scouder

 

Oh boy!

The first idea you get comes from someone that knows jack about building/tuning motors

Can your fuel pump be pumping too much fuel into the carb?

 

That is one of the possibilities that I am considering. I don't know how it could be, unless it is getting past the needle and seat. I think tomorrow I am going to dial down the fuel pressure by one pound, and lower the floats a little bit.

Considering that you claim to know Jack about tuning engines that was an astute observation.

-Scouder

 

Contact BG about installing the idle eze circuit. You should not have drilled the blades. It's a bandaid. But it will help you get a stronger signal. Keep us posted on the results.

Question, how much of the transfer slot was exposed at idle before?

Another trick is to open the secondary blades a bit more to increase idle speed, airflow and signal without exposing the transfer slot.

If you don't have success with the holes, plug the PV and retest. Just don't go cruising. You're mid range will be too lean by 5 jet sizes.

By your vacuum gauge readings, the PV is too small. You can go up to 4.5, it will drastically improve tip in response.

Fuel pressure should be 7 psi or less. If fuel is getting by the needle and seat, you'll see it dripping into the venturis at idle.

 

I was going to look in the top of the carb with the fuel pump on tomorrow. If I don't see any leakage, I'll look with the engine running.

I saw the idle eze baseplate. Don't know what they cost, but it's the same thing as drilling the blades, only adjustable, isn't it?

There was about .030, maybe .040 exposed before. Didn't measure.

Also, this problem was occurring with my 2.5 PV in it. I switched to the 3.5 tonite, but haven't run it yet. The potential exists that my PV was bad. Don't you think a 4.5 is cutting it a little close with a 5-6 idle vacuum? Of course, vacuum comes up as soon as rpm starts to climb, but all it would take is a low pressure day and I could have the PV open at idle, no?

Also, I was watching the fuel level with the engine idling, and it was dead center in the sight glass on both bowls. Like I said, I'm gonna lower it just a little tomorrow, but I think centered is what is recommended.

Thanks for the input.

-Scouder

 

The adjustability is what makes it soooooo sweet. You can set the transfer slots where they belong and adjust the circuit to get a clean idle. No trial and error like drilling holes. Plus, with atmospheric changes, you can readjust.

When you tune the idle screws, watch the vacuum gauge. If the vacuum or idle speed does not change much as you lean it out, you are probably getting fuel from somewhere else.

With the mighty demon, you've also got adjustable idle air bleeds in the top of the carb. You might want to look there. I haven't read the tuning instructions, but I'd say something is amiss. You've got em, use em. That is the main reason I am putting the Mighty on my mouse. And throw in the idle eze (now standard on speed and mighty demons), I just may be able to stop burning my eyes at idle.

4.5 might be cutting it a little close, but if you run consistely above 5 inches it will stay closed. Watch the vacuum guage while you drive. The power valve should open under moderate throttle settings and load. It is just a cover up for a flat spot in the fuel curve that exists between the activation of the mid and high speed circuits (or is that low to mid? dunno it's late). The accelerator pump circuits cover it up with a heavy foot. Sorta like the S&S but with more circuits to play with. I found that after using the vacuum gauge in cruise mode I could bump the PV up. And voila, no more flat spot.

I regret buying the MSD dizzy without vacuum advance now. There is some tuning advantage to having and adjustable vacuum pot. You could set your initial at 20, put eight in the can with a light spring to allow it to come in at idle and leave your bushing alone. As far as the mid range ping, perhaps a vacuum switch to cut it off above a certain point.

The best solution is a digital ignition that allows for different curves. You could set the initial where you want and tailor the rest of the curve to suit your needs.

You'll be able to get the plugs to clean up, but I doubt that it'll ever smell clean. Too much duration and overlap, there is going to be so much mixing of the charge that'll smell fat even when you lean it out right. Just run race gas and enjoy the smell

 

hey scouder i can try and take a wack at it but i'll first have to take it for a test drive!

 

I I had any idea what you guys are talking about, my truck would be running 13s :-)

I have got to learn about this carb!

I certainly have no advice, you guys are well beyond my limited knowledge. But, I have no doubt you will get it figured out soon.