Accelerator pump tuning

[Gunner]

The morning drive showed more improvement in the bog than anything else - the more aggressive pump cam. I didn't get much secondary action but it's all relatively low-speed surface streets around me and I could only boot it once or twice without attracting the wrong attention.

I set the butterflies to the recommended positions before installing the carb - square slot on the primary, just-closed on the secondary. From above, it doesn't look as if they've shifted or changed any.

I'll try the richer initial setting but all indications are that it's running too rich across the board already. Plugs vary from clean-black to slightly sooty.

These are all on *very* short test drives, all I can manage at the moment. A freeway run takes over twenty minutes, time I can't spare much right now. I'm trying to tinker a bit at a time, which is not the most effective or efficient method.

The pump cam (blue, switched from stock pink) has had the most positive effect of all the changes. It's not perfect, but it reduced the bog when cold and seemed to have eliminated it on the homeward (warmed up) leg.

And, FWIW, I finally found the calculation for power valve choice. Most references are as irritatingly vague as everything else: "Go up/down a few sizes on the jets" "try a different pump cam" "go to a different power valve." According to the BG manual, I should be running about a 6 - meaning 5.5 or 6.5. It's got the stock 6.5 in it, so it's not something I'm likely to change out except in final dyno tuning.

Fine, fine, I'll go spin the idles out for my next test drive.

[jhv48]

You'll smell it immediately if you open the idles that far. Probably way too rich.

My last Speed Demon ran best about 3/4 turn out, contrary to what the guide said. And I had the t-slots square on the primaries and the secondaries were barely exposed. Idle eze was completely closed also.

It's what runs best, not what the gauges say that counts. Let your plugs, nose and seat of the pants to be your guide!

[elmariachi]

I agree, that far out will likely be too rich, but the point is to see if its a mixture issue. One thing to note....your plugs are going to look like the carb is way rich if all you are doing is running up the street and back on these short test drives. You gotta get out and spin some RPMs for a while and build soem heat before you can get a good plug reading.

[Gunner]

I'm wit' you, JHV48. I cranked the idles open to 1-3/4 and made a run to the hardware store - ironically enough, for some door seals to keep garage fumes from getting into the house. Drivability was a tad improved, last trace of bog was gone (call it 3/4 from the cam, last 1/4 from the idles)... but whoo-boy did it stink up my little town all the way there and back. Way too rich.

I think I'm going to pull the carb off this evening and do several things at once, including dropping the primary jets another 2 (to 72) and the secondaries down 2 or 3 (from 84, I think). Check the other vacuum passages, the Idle-Eze, the exact power valve, blah blah blah. Then a baseline back to max vacuum plus a quarter turn, then a good hard haul including some freeway time.

But in the meantime this Response to RFQ is not getting done.

[elmariachi]

So your bog is gone, but you think its too rich (and it probably is a tad.) Don't trust your watering eyes, go drive it for 50 miles like it sits and then look at your plugs and decide. Screw that RFQ.

Also, call Jeff at Barry Grant and tell him what you and it are doing and see what he says.

[patrickt]

I still think that cam is too mild for what he wants. This is the Elgin E-964-P as the engine builder installed it:

[elmariachi]

Originally Posted by patrickt

I still think that cam is too mild for what he wants.

That is a pretty mild cam, but I would still think he could get the car running well enough to not have a tuning bog. Gunner, did you get a dyno sheet on this motor? What kind of power did the PO say is it supposed to make?

[Gunner]

Originally Posted by patrickt

I still think that cam is too mild for what he wants.

I'm not looking for a fire-breather. If I can get another 10% over the original dyno pull (440/475), I'll take it. Joe Lapine was of the opinion that at least that much was in a good dyno-tune. I'm looking for all that power in a tractable package with no surprises. Relatively low maintenance and no sharp breakage points are plusses, meaning a hydraulic cam.

I might pull the engine next fall to make some changes, including a cam - and if the rear drip turns out to be the main seal - but for now I'll go with the hardware I have. If it's a good year, I might build a whole new ally engine instead. (Damn, those prices on Dove SOHC parts are tempting...)

[elmariachi]

Well 440HP is respectable and I would think you could get that engine humming nicely as-is. I am not sure I agree with the solid lifter insult, but I am going to let my pit bulldog Patrick take that up with you.

[patrickt]

Originally Posted by elmariachi

I am not sure I agree with the solid lifter insult, but...

If your solid lifters see 1000 miles without incident then they will still be running fine when your heirs are speculating how much they can sell "that little sports car" for....

[elmariachi]

Originally Posted by patrickt

If your solid lifters see 1000 miles without incident then they will still be running fine when your heirs are speculating how much they can sell "that little sports car" for....

Amen brother. I just crossed the 2k mile mark and she's running like a champ.

[Gunner]

Originally Posted by elmariachi

I am not sure I agree with the solid lifter insult...

Not meant as an insult. I've lived with a variety of solid-lifter engines and if I've done my last break-in and adjusted my last valve lash, it will be a relief. I'm willing to do a lot of ongoing maintenance for a high-performance vehicle, but any tasks I can eliminate with little if any loss in performance can go. Given the state of the art of both flat and roller hydraulic lifters and cams, I'm not convinced that solid flats are the advantage they used to be. They're like audiophile vinyl: if you think all the expense, fussing, hassle and potential fragility are worth it, power to ya. I'll take 99% as good, 500% less temperamental CDs all day long.

[elmariachi]

Originally Posted by Gunner

Not meant as an insult. They're like audiophile vinyl: if you think all the expense, fussing, hassle and potential fragility are worth it, power to ya. I'll take 99% as good, 500% less temperamental CDs all day long.

I was just kidding. But based on your audiophile analogy........................................you might ought to sell the Cobra now and get a Prius.

[jhv48]

It took 73 posts for this thread to turn personal.

A new CC record!

[elmariachi]

Originally Posted by jhv48

It took 73 posts for this thread to turn personal.
A new CC record!

No, we are simply side-barring while Gunner is switching carb jets.

[Gunner]

Originally Posted by elmariachi

you might ought to sell the Cobra now and get a Prius.

I said 99% as good, not 0.9%.

It's occurred to me that someone, somewhere, is probably putting a hybrid powerline in what they'll call a Cobra.

[Gunner]

By Jove, old chaps, I think I've nailed it. I went for a short drive (to fuel up - necessary as I went through a tank doing this tuning etc. and managed a stellar 6 mpg!)

Idles very well, moves out on command, very sharp throttle response at street speeds, pulls like a tractor and doesn't diesel on shutdown. I don't know when I will have time for a freeway run but I'm looking forward to it. Idle is that happy, stable Let's-go-Boss, Let's-go-Boss.

Will also chirp the tires in second with no effort at all - I was just a touch aggressive off the line at one light, heard a funny birdie sound, realized what it was... then saw the ominous black motorcycle in the rearview. It wasn't a cop, thank Shelby. So I did it again coming home, this time checking six first.

This all comes from a complete baselining and re-tune this morning. Final settings: 1.0 turns on the idle mix and long, careful experimentation with the primary butterfly setting and the Idle-Eze setting.

I don't think Idle-Eze does squat-a-roonie on my engine; the cam is milder than the problems it's supposed to correct. I ran it all the way open and shut at many butterfly settings and a variety of mixture settings, and at most it affected idle speed by an amount somewhere in the noise and flutter region. It was closed for all prior testing; I ended up leaving it open one turn and then redoing all other tuning around that.

Best idle (smoothest, fastest) was at about 3/4 turns, so I carefully reset all four screws to exactly 1 turn.

Idle speed was only adjustable with the butterfly setting, so I tweaked and tweaked for the smallest opening and finally got it nice and settled at a nominal 750.

Results already stated. This is with the long-oval air cleaner and a K&N filter - I can't fit anything taller than stock, so it's only got about an inch of filter area. I did some calcs and measurements and figure it's got about twice the area of the K&N in the little AC.

Final settings and changes overall, from the box-stock carb:

• Blue accelerator pump cam, much more aggressive profile than the stock pink.
• 1 turn open on Idle-Eze, probably has little effect.
• Careful mixture setting to best plus one quarter turn.
• Distributor changed from 15+21 to 18+18.
• Idle set higher than I was using - 750 instead of about 680+.
• Primary jets dropped to 74 instead of stock 76.
• Vacuum secondary spring brought down one step.

I will probably leave this untouched for a while, until I can get a look at some plugs that have actually been worked out. I will almost certainly work on the jetting, fore and aft, once everything else is settled. I might try the orange pump cam, which is about halfway between pink and blue with the gentler pink curve. (If I can save that fuel without any loss in off-idle response, I'd like to.) I might need to go back up one spring on the secondary, as I did get some hoppity-bog on the freeway yesterday... will have to see if it persists with the current tune. I may well have to change the power valve as well if I lean out the jets much.

I think I was right in the first place - not 100%, but the accelerator cam did the most to solve the bogging problem. Opening up the screws from "ideal" helped a lot, too. The distributor... can't tell how much it affected things, but given FEs' love of advance, it can't hurt. The higher idle was the last bit... that, and me learning not to be quite so soft on takeoffs. Being gentle on the pedal compounded the inherent problems.

Thanks very much for all the input on this, gents. I didn't realize how much I'd forgotten about carbureted engines. Buy yourself all a round next time.

[*13*]

Good to hear! Now, get out & drive that beast!

[elmariachi]

Originally Posted by Gunner

Idles very well, moves out on command, very sharp throttle response at street speeds, pulls like a tractor and doesn't diesel on shutdown. Thanks very much for all the input on this, gents. I didn't realize how much I'd forgotten about carbureted engines. Buy yourself all a round next time.

Good news Gunner, glad you are happy with the progress. No need to buy ourselves a round...we have all been drinking this whole time while you were pissing around with cams and springs.

Thanks for at least coming back and reporting on your progress, many don't.

[Gunner]

Originally Posted by elmariachi

No need to buy ourselves a round...we have all been drinking this whole time while you were pissing around with cams and springs.

Yeah, and you left the cooler empty, thanks SO much...

Gee, guess I'll have to make a beer run... bye!