Accelerator pump tuning

[elmariachi]

Good point, I don't see where Gunner ever mentions how far out he is on the screws.

[Gunner]

I haven't opened the distributor but from glancing at the MSD charts, I'd say it's running either two light silver springs or (more likely) one light silver and one blue. That matches the approximate (very quick) curve I've encountered. It appears to have the 21* stop installed (although I'm getting closer to +23* total). I can see where going to the 18* stop and 20* initial might improve things; I will experiment. Since I can't get the curve much faster than it is I'm betting against it being a factor.

I baselined the idle mixture by bringing all four screws out to one turn and working from there with a vacuum gauge. Let me go check... grumble can't find a rassafrassin' flat driver... yeah, I'm 3/4 turn out on them. The vacuum peak is pretty sharp at that point; an eighth turn in won't sustain idle and a quarter turn out loses 20% of vacuum. I fiddled around quite a while with idle speed and the corner screws. Since I never had any trouble with the idle other than at the very lean end the Idle-Eze adjustment never had much effect; I left it at the original setting. I've only got 10-11 inches of vacuum; I could try bringing the screws out a bit and see but all things considered, it doesn't sound like a fix.

Zoom This, right off the bat I'd say an 850 is too much carb for a 418, even if it's got a 7k redline. A 750 would seem optimal; why did you go down so far in size?

[elmariachi]

I would scrap the vacuum gauge for now. Your mixture screws are not out enough and once you get them out about 1.5 turns you see what I mean. No way I'd be running this engine without knowing what's in the dizzy. Takes 2 minutes to open it up, remove the rotor and see for yourself. I'd start at 18 base +18 bushing and both blue springs. Take it for a spin, I'll bet you'll be surprised.

[jhv48]

Mine eliminated the stumble by opening up the idle screws another 1/8 to 1/4 turn AFTER achieving peak vacuum. Just try it and see what happens. You probably have an off idle lean condition and this is one way to eliminate it.

Start with the simple stuff first!

[Gunner]

I in no way disagree with you... but I ain't got no MSD kit. It got lost somewhere between Danbury, the original owner and me. I was putting that off until I had the parts in hand. (I wish I had the 3000 rev limiter chip, too...)

Let me see if the local shop has a spring kit.

As for the idlers, a turn and a half out was clearly off - I tried taking them out a ways to see if there was a vacuum peak further up the scale and the result was pretty bad (don't recall the specifics). I can try it again, though.

[jhv48]

Ok, one more time. Adjust the idle screws to max vacuum ( mine only took 3/4 of a turn out from bottom to get max vacuum). Then, disconnect the vac gauge and put it away. Now turn the screws out another 1/4 turn. Go drive it. Stumble gone? turn the screws IN 1/8 turn and go drive it. Stumble returns, back out the screws to the 1/4 mark and leave it alone. If stumble still gone, leave it there. Sometimes the best vacuum peak is NOT the best driving setup.

[Gunner]

Guys, guys - I'm not arguing any of the things suggested but I am (at least nominally) at work - a quick jaunt out to the garage to check things is about as much time as I can spare at the moment. I've noted all the suggestions and will try them in good turn.

I did just pull the disto cap. It's running one blue and one light silver spring, as I guessed. I can't tell the color of the stop but as it goes from 15* initial to ~38* total I'd guess it's a 21* stop.

The interior of the distributor shows a lot of corrosion - the prior owner lived right on salt water and it shows throughout the car in minor bare-metal corrosion I'd planned to take care of over the winter. He told me he'd just replaced everything from the rotor to the plugs because of corrosion, but he should have started with the distributor itself. I think it's completely functional, but it's not good and certainly not helping anything to have that crud in there. (Honest, it looks like something off a poorly maintained boat!)

So that MSD kit will likely come with a complete distributor. Oh, joy.

[elmariachi]

Come on Gunner, we can't let work get in the way of play!

Good progress, let us know how it works out but I think cranking open the mixture screws is a good next step. Put the spurs to her!

[Gunner]

Originally Posted by elmariachi

Come on Gunner, we can't let work get in the way of play!

Well, you don't understand. I've trained my dogs to keep me at the grindstone, so if I get up and fiddle around, they let me know.

After several quick trips to the garage, I have *two* Great Danes growling in my face. This means I REALLY need to get back to work. Now. Good thing they think all this typing is work.

Good progress, let us know how it works out but I think cranking open the mixture screws is a good next step. Put the spurs to her!

While the puppies were distracted, I ran the screws out a quarter. I may take it for a lunch drive.

[elmariachi]

And the verdict is....?????

[Gunner]

It's still a work week!

Actually, I am so pee'd at myself - I had an hour, dashed to the speed shop, they had everything (new disto, air filter, small bits and pieces)... but I forgot my frackin' wallet. So instead of having a few minutes today to fiddle, I had to spend the time running back to get the junk.

The only thing I've had time to do is open the screws a quarter and drive it for about half an hour. Idle was improved, especially cold idle; drivability was better. Still a hint of the bog, but opening the screws was a move in the right direction. I will need to spend a good hour driving and ...uh... screwing to see if I can find a better optimum, especially once I have the new distributor in and the accel pump and secondary parts in hand.

But kudos to jhv48, the idle mix was too lean, vacuum gauge be damned. (Hey, it's always worked for me before!)

I'm trying to decide whether it's worth having a couple of O2 sensor bungs welded in...

[elmariachi]

Originally Posted by Gunner

Still a hint of the bog, but opening the screws was a move in the right direction. I will need to spend a good hour driving and ...uh... screwing to see if I can find a better optimum, especially once I have the new distributor in and the accel pump and secondary parts in hand.

I'm trying to decide whether it's worth having a couple of O2 sensor bungs welded in...

That's good news. I have done all the tuning I can do on mine and am trying to get a Saturday where I can get on the chassis dyno to finish it up. I have ceramic coated pipes or I would have already welded in a bung because I believe I could get really close to final tuning/jetting myself if I could measure the A/F. If you can do it or have it done, I'd say go for it.

[jhv48]

By the way, I had my first Cobra dyno tuned and it ran great.

But, I took it to a guy who specializes in tuning these cars for max driveability. He was manually tuning a 12 cylinder carbed 60's Lambo when I first approached him. He changed my distributor advance curve and springs, experimented with timing, fooled with the carb and did it all by ear and seat of the pants feel and by checking the plugs.

Felt like he had added 50 horses after he was through. Jumped like a scalded cat when you nailed the throttle and would cruise all day at 2000 rpm. So, my point is, instruments give you a starting point, but every engine is different and it just needs an experienced tuner to get the most out of it. Sometimes you need to get rid of the instruments and do what your engine likes. They all have their idiosyncracys (sp?) and it's our job to put them in their happy place.

And yes, it is voodoo!

[Gunner]

Originally Posted by jhv48

took it to a guy who specializes in tuning these cars for max driveability. He was manually tuning a 12 cylinder carbed 60's Lambo when I first approached him.

I came this -><- close to buying a 400GT around 1980. One of the main selling points was that he'd just brought it home from the best Italian tuning shop in the Bay Area.

I passed - not wisely, because I love the early Lambos, but wisely because the engine tune likely would have lasted about long enough to get home. Harpsichords. That's what they are.

(Joke around this household of musicians: "What's the difference between a piano and a harpsichord? You spend longer playing a piano than tuning it.")

[jhv48]

The guy who balances my tires uses a 60's machine that spins the tires while they on the car and then he places weights on the rim until he doesn't feel any vibration when he holds his hand on the fender. No computer, no strobe light it is all guess work on his part. But I had had the fronts balanced three times by a Hunter Road Force machine at TWO different locations and every time, my steering wheel still vibrated at 65 MPH. Took it to him and in 30 minutes, smooth as glass.

Once again, Voodoo!

[Gunner]

Sort of a non-report: I put the new distributor in (straight replacement of the MSD 8495) and fitted it with the 18* stop and two blue springs beforehand. Showed my son how difficult it can be to get a disto to drop in over the oil pump shaft , started right up, timed it to 18* initial and 36* total.

(Left the garage door open a crack to vent it overnight, got up to little damp cat footprints all over the car... arrgh. Neighbor's cat, very nice but nosey.)

I also finished fitting the new AC - long oval with a K&N. Drove the combination for a while. Decent, still some hesitation early in the takeoff curve, smells a little rich even after warmup. Thought I heard some detonation on a couple of hard pulls.

I don't have the freakin' carb parts because a FedEx delivery stamped DELIVERED was not - they're tracking it down. And now rain is moving in for the weekend, so my road testing is done for the short term. If I get the parts and the weather clears, I can adjust the secondary spring and try the bigger squirters. I suspect I need to redo the baseline idle mix tune with the new air cleaner setup as well.

So: other than the richer mix after vacuum tuning, nothing has made much difference on the off-idle bog. Will need to get all the tuning parts, wait for clear weather, and start pretty much from scratch.

Meantime there's the front and rear suspension to look over...

[Jerry Clayton]

Sooooo---you really don't want to try what I wrote????

[Gunner]

Originally Posted by Jerry Clayton

Sooooo---you really don't want to try what I wrote????

I said I was going to try most or all of the suggestions as part of a systematic tuning process, and I haven't ignored yours. I've already gone down two steps on the jets and don't think I will mess with them further until I get the other settings in range. 74's are close - at least, there's no sign of them being over-rich.

Ditto for the power valve, which has more effect on upper-end power than the off-idle and low end power I'm working with right now. It probably could benefit from a change, but has to wait until I can see how the secondaries and upper power are working. Without the secondary spring set, I can't even get into the secondaries - the stock spring is much too strong for this engine.

Opening up the idle mix helped, but only to a degree, and I think the baseline is messed up by the air cleaner change, so I have to start over there. The distributor recurve doesn't feel quite right but I'll leave it for now and go back to less initial only if I'm still seeing detonation after the carb adjustments.

Since I've tweaked the idle mix and timing and still have some bog coming off idle, I am back to suspecting the accelerator pump tuning and possibly the stalled secondaries. When and if my parts ever come, I'll be able to test my theory. If the rain stops.

[Dwight]

Are you using the ethanol gasoline? A few of our gang had same problem and changed to 100% gas. Problems solved.

Dwight

[Gunner]

Ethanol mix is not common here. I use brand-name all-dino juice.