Everytime I open my mouth and post on this topic, I end up in trouble... Because it is complex and not everything applies to everyone.
Caveat one: In a <b> properly working </b> pump, there is little need to adjust anything relating to the diaphragm, including the no-air setting, the spring tension, OR the rate (turning the diaphragm). If you want more power, turning up the fuel a little, or changing injectors makes those settings high enough to be very responsive - and pretty much negates any need to fiddle with them to obtain full power and a 12 or 14 exhaust housing makes boost quickly enough to make the engine very responsive.
The problem here, is that a lot of shops AND the factory AND Cummins ReCon often set these at the bottom of, or below the specifications. I don't know why. But doing so often results in "low power" complaints or even poor fuel economy. "Why" you ask, "does low fuel settings result in poor economy?" I've never understood if it's driver style or some strange engineering principles, but it is often the case.
Caveat two: My background is working in a fuel injection shop. Our cardinal rules were: 1. It should never smoke - smoke means you did something wrong. 2. Do stuff the best way (not the cheap, easy, or convenient way), because it's far better to explain to the customer why his bill is a little high, than to make up excuses why you did something half-baked. After the first time you try to save him a few bucks and he has trouble, you realize he'll eventually forget the size of the bill if you did it right, but he'll NEVER forget you did a crappy job.
And again, you, the driver, have no means of carefully tuning the pump, probably are unable to ascertain the effect of several inter-related adjustments. For instance, the reason to turn the diaphragm is to change the RATE at which the fuel inecreases vs the boost seen at the manifold - how quickly it comes in. But, because of the way the thing works, turning it changes your no-air, starting and endpoint for the boost compensation. Your "seat of the pants" test stand isn't that sensitive enough, and your "smoke meter" review mirror isn't all-revealing anyway...
So what do you do, when your truck seems to have no power below 2000 rpm? You make adjustments, and probably because it wasn't right in the first place. And, doing so will probably improve your efficiency and power. And that CAN'T be bad, can it?
And so I gulp, change threads, log off, go somewhere else, or, as I did in my once in a 1000 times, I respond to someone who appears to think that the first thing you should do is break open the boost compensator and twist, turn, and screw in the innards.
It's simply a matter of diminishing returns. Unless your injection pump is very poorly calibrated (and there's far too many of those... if you have one, well, this really doesn't apply to you... but, you have no way of knowing. If your truck doesn't "go", and you don't know how it "goes" when "right", then... ??? You see my dilemma?) changing those things generally doesn't result in even 1 more horsepower. The most you can do is get more power when you don't have turbo boost. But it has no effect (when the pump is set right, again... ) on anything once you get past some 12 psi boost, if memory serves. That is controlled by the fuel screw on the side.
The major effect of this is rarely correcting a serious deficiency (but, sometimes it does, pumps that will never reach full fuel because the settings are SO bad HAVE been seen), but just creating a short blast of smoke until the turbo winds up.
And, as I said at the beginning of all this mess, if you're going to drag race... you DO need full power at every possible moment. But if you're not, why make the smoke and waste fuel and create more heat than you need?
I understand you want your truck to run "good". I detest poor-running vehicles. And I am rarely satisified with merely as "good as factory" performance. That being said, the little "belch" that comes out when you start, the short stream of smoke if you happen to "lug" it in traffic, or the smoke you get from high altitude are unavoidable. I know that, you know that, and so do a few others. But they ad fuel to the fury of the environmental movement, and to the mis-guided souls who think that your engines are "dirty" and a danger to clean air. They are wrong, but how do you convince them of that when they see vehicles with a long stream of black stinky stuff coming out? Trying to explain to them that stuff isn't hazardous to their life is like trying to explain nuclear fission to someone who doesn't speak your language.
And so, my one in every 500 posts on keeping the air clean and not fiddling with adjustments you can't possibly fine - tune comes to a close... Probably without affecting anyone's eventual actions...
If you're thinking that the last elusive 5 horsepower is to be found by twisting and turning things there, but your truck runs really good as it is now... I implore you NOT to change things. For all good and virtuous reasons, too. If it won't run right... then do what you have to do... In small steps, stopping before you create an excuse to regulate you, by imposing things like smog checks (I think they are mostly useless, but... it makes regulators happy to have more to do, and it gives those who lobby for them self-annointed virtue, but that's another story altogether) that'll make it really hard to have your truck run "good" and be legal.
Now, was I clear, or did I just bury myself and pull the hole in with me?
Attention: TDR Forum Junkies 
Secondly, smoke is cool in tractor pulls or if you're making goobs of horsepower, but I am not doing either, and I am with Power Wagon on that issue; less smoke and more power is obtainable. Third, look at my sig for Dad's specs, not much I know. Finally, I turned the full power screw on the side nearest the block 1/2 a turn CW until it hit the collar just to see what would happen. Then I turned the smoke screw 1/2 a turn CW. Small changes are safe in my mind. The truck went from 10lbs of boost to 16+lbs of boost, and very little if any change in smoke 
I must say that I am impressed even with the small tweak power is real nice and smoke won't concern local fire departments 
" Anyway, do you think that running a turbo like the PDR HX-35 or modifying the compressor housing on our H-1's would allow us to make the power with out all the smoke? Or, are our heads just a major limiting factor towards the increased heat of more boost, fuel and power? Thank you for being on the TDR, I saw your post about leaving, and it just won't be the same... . Thank You! 
