Quick Fuel SS-780 tuning suggestions

[Foghorn]

I have a Keith Craft 482FE in my car. The jets are as delivered, but I have changed the idle bleed, high speed bleed, and idle feed restrictors. My current settings are:

Main Jets: 69
Secondary Jets: 77
Power Valve: 6.5
Power Valve Orfices: 65 (? - I need a magnifying glass to read 'em!)
Idle Air Bleed: 67
Hi Speed Bleed: 35
Idle Feed Restrictor: 37
Idle Screws: out one turn

The timing curve is good.

My Innovate LM2 says the A/F ratio is 14.1 at idle, 13.5 cruising at 2k RPM, 14.1 cruising at 3k, 12.5 WOT.

The problem is that the plugs and sidepipes tell me that I am waaay rich (pipes are black/sooty/almost oily). Also, I when driving "spirited" the engine pulls really good, and then at 4200 RPM or so, it jumps like an old two-stroke coming up on the pipe. Almost to the point of being undrivable.

TK tells me that I have a sudden rich condition at 4200, which makes sense, except that the meter tells me I'm good and the plugs/pipes tell me I'm rich. I've thought about smaller primary jets and a higher # power valve.

Any suggestions would be appreciated.

[vector1]

air leak in the exhaust could be one culprit. if no air leak then wrong plugs or weak ignition. what's the vacuum at idle, cruise, and where the secondaries start to open?

[Loadco]

How are you attaching the O2 sensor form the LM2. If you are just using the Innovate tail pipe clamp your readings are probably not accurate. I had that problem with my LM1. You need to attach a length of tubing to the inlet on the tail pipe clamp to get it up inside the side pipes to get a good reading.

[SwiftDB4]

I would agree with both of the last 2 posts. If your Oxygen sensor is too close to the end of the pipe it will read leaner than true. Also check your ignition, distributor cap, etc. My MSD cap had a damaged center contact that caused carboned plugs. I wouldn't go leaner on the main jets though. The QF 750 on my 427SR runs 72/78 mains.

[Zoom This]

....except that the meter tells me I'm good and the plugs/pipes tell me I'm rich.

Believe in your plugs. They're the closest thing to telling you what's going on inside the combustion chamber.

...jumps like an old two-stroke coming up on the pipe. Does this mean the motor falls flat on its face or comes alive at high rpms? I assume the motor, being undriveable, falls off. As noted earlier, you'll need to stick that tube way up the sidepipe or weld a bung onto the inside of the collectors.

[Foghorn]

I have the O2 sensor in a bung welded into the collector. The sidepipes I am using are the Kirkham's SS versions. TK tells me that I will see some variance in the AFR reading due to the slip-fits leaking, however, I have not been able to verify any leaking (holding a lit cigarette next the the pipes while the engine is running at idle/various RPMs, I would expect to see the smoke of the cigarette effected in some manner).

My vacuum at idle is 8-10" at idle (it has been awhile since I drove it with the vacuum gauge hooked up, but I do remember that the PV choice was in line with the conventional wisdom of 2" less than idle vacuum), up into the teens at cruise.

The engine jumps to redline (6500) from 4200 twice as fast as it revs from 2000 to 4000, hence "coming up on the pipe" - very hard to keep a handle on it, especially in traffic.

What do you look for in a damaged center electrode? I am also using the MSD distributor (mechanical advance only).

The plugs are a dark grey on the outer half of the electrode, moving to black down in the center. Could I have too cold of a heat range plug? I have thought of changing the plugs, just to have a clean slate to base any further adjustments. When I first started the engine, it was much richer than it is now, so much of that soot could be "old data".

[cdnus]

I'm certainly no expert, but I think that is a vacuum secondary carb (correct me if I'm wrong) It sounds like you are getting the effect you describe when they are opening. Perhaps some spring adjustment is required to make the transition smoother. To me 12.5 is rich for W/O on a 2500? lb. car.

JMO

Craig

[zrayr]

Originally Posted by cdnus

I'm certainly no expert, but I think that is a vacuum secondary carb (correct me if I'm wrong) It sounds like you are getting the effect you describe when they are opening. Perhaps some spring adjustment is required to make the transition smoother. To me 12.5 is rich for W/O on a 2500? lb. car.

JMO

Craig

wide open isway too rich unless you have a supercharger, in which case it's just rich. I also think your cruising a/f ratio is too rich. 14 or even 14.5 is better. with the throttle barely cracked open and the rpm low you are not really making much HP & can run a lean(er) mixture without worry.

Now a 14.5 a/f mixture at 3500 rpm under a load like a long incline would be too lean in my experience.

I would reduce your main primary jet until the mixture is 14.0 to 14.5 at the 2000 rpm cruising scenario. After you have that where you want it, then reduce the size of the secondary jets until you have a wide open a/f ratio of 13.5

only make one change at a time.


Z.

[gsharapa]

Did you have Keith Dyno your motor? I just installed a KC 496 and it has a Quickfuel 850 double pumper. My motor made 681HP at 6700 at the crank and the air fuel was between 12.5 and 13.0. We dynoed it yesterday on a chassic dyno and the air fuel with the headers and pipes etc never went above 12.5. I wouldn't run your motor above 13 much as that's getting pretty lean. Call Keith as he is an expert at these FEs...

[zrayr]

You will never make maximum HP with a wide open afr of 12.5 Engine builders, and carb manufacturers like to err on the rich (safe) side. Street Engine builders will tell you one thing. If you want to see the winners circle, race engine builders will tell you to jet much leaner. Somewhere in the middle ground you will make much better HP than you can at 12.5 & still have reliability.

Z.

[SwiftDB4]

Originally Posted by Foghorn

What do you look for in a damaged center electrode? I am also using the MSD distributor (mechanical advance only).
.

My center electrode broke off flush with the cap so that the rotor was only contacting the aluminum collar around the electrode.

[Foghorn]

All,
Thanks for the replies. I have decided on the following, like ZRAYR advised, with a couple of mods:

changing the 69 primary to a 68, the secondary from a 77 to a 75, and the power valve from a 6.5" to a 7.5".

The jet changes will be lean out the mixture, and the power valve will be to get it's fuel in sooner, hopefully easing the transition when the secondary circuit comes in.

I will let you all know how it turns out.

[Bobcat]

Foghorn .... as said above , change only one thing at a time ! If you make several changes at once , you won`t be ab;e to tell what each did ... and it`s possible that one change could mask what another did and you won`t know what did what .
Have fun and good luck .

Bob

[gsharapa]

I agree you need to do 1 change at a time. Not sure I'd go up on the power valve as that could really give you a rich idle and off idle situation. In several of my past Cobras with big small block motors I was running 3.5 and 3.0 power valves because of the low vaccum I was loading a lot down low. Something to consider. I'd work with jet change and then air bleeds again first. After I posted earlier we ran my 496 FE the next morning with higher air bleeds and it was up at 13 across the band and went up to 13.7 over 6200 rpm and did make more HP. Going to leave it there for now until I drive it and see how the driveabilty is. I'm running a 850 Quickfuel however.