Fine tuning my carb
#52
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Thread Starter
Originally Posted by Sterling
You could, but that's not the right way to do it, and there's a reason...
Dropping fuel pressure will prematurely lean the mixture, and not always due to actual fuel consumption as associated with rpm and load. It allows bowl slosh from cornering, centrafugal push of the fuel against one side of each bowl just from going straight (G-force), and even accelerator pump usage to effect the mixture throughout a wide range of rpms and load.
All of these things will still happen, but running a nice solid pressure lessens the window of opportunity for these extranious forces to play havock with your test runs by introducing inconsistancies that effect your mixture...And afterall, the very reason fulies dominate is consistancy. It's not great atomization, or perfect mixture delivery - it's the combination of those things consistantly throughout the rpm and load.
So get your pressure right up to where it barely delivers at WOT. That is where it's supposed to be.
You see where I'm at? Make everything that you possibly can be as consistant as possible. After you do that as a matter of practice, it'll start to become apparent very soon that even then, you are already fighting a terrible battel against external forces that cause inconsistancies. (temperature, fuel differences, elevation, fuel bowls and tank slosh & push, alternator rev which causes voltage increase which causes pump output increase...You name it, it'll have an effect in some way that can cause identical runs to have VERY different outcomes.
If you can't get a handle on some of those inconsistancies, then you'll have a real hard time dialing it in.
You have to make twelve runs, throw out two, and average the rest.
And really, NOBODY'S good enough to dial without a stop watch. Any "***-o-meter" readings you're getting just says that you're still in the tuning stage where you're still making VERY large changes...Something that should not be reflected with only 1/100 mm diameter increase of a change.
This is just my opinion. But it's also been my experience.
I've spent more time chasing my tail than I have successfully dialing in carbs because it took me so long to get anywhere, and now it takes so much less time to dial in.
Dropping fuel pressure will prematurely lean the mixture, and not always due to actual fuel consumption as associated with rpm and load. It allows bowl slosh from cornering, centrafugal push of the fuel against one side of each bowl just from going straight (G-force), and even accelerator pump usage to effect the mixture throughout a wide range of rpms and load.
All of these things will still happen, but running a nice solid pressure lessens the window of opportunity for these extranious forces to play havock with your test runs by introducing inconsistancies that effect your mixture...And afterall, the very reason fulies dominate is consistancy. It's not great atomization, or perfect mixture delivery - it's the combination of those things consistantly throughout the rpm and load.
So get your pressure right up to where it barely delivers at WOT. That is where it's supposed to be.
You see where I'm at? Make everything that you possibly can be as consistant as possible. After you do that as a matter of practice, it'll start to become apparent very soon that even then, you are already fighting a terrible battel against external forces that cause inconsistancies. (temperature, fuel differences, elevation, fuel bowls and tank slosh & push, alternator rev which causes voltage increase which causes pump output increase...You name it, it'll have an effect in some way that can cause identical runs to have VERY different outcomes.
If you can't get a handle on some of those inconsistancies, then you'll have a real hard time dialing it in.
You have to make twelve runs, throw out two, and average the rest.
And really, NOBODY'S good enough to dial without a stop watch. Any "***-o-meter" readings you're getting just says that you're still in the tuning stage where you're still making VERY large changes...Something that should not be reflected with only 1/100 mm diameter increase of a change.
This is just my opinion. But it's also been my experience.
I've spent more time chasing my tail than I have successfully dialing in carbs because it took me so long to get anywhere, and now it takes so much less time to dial in.
#53
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Thread Starter
Well, to update, yesterday I put in .069 (175s) fuel jets for the secondaries, one size up from what I had (.067 - 170s), and still noticed a slight increase in bawlzyness when opening the secs. My mileage also probably dropped from 12 to 10 too
Thanks to banana boy for hooking me up at SS7 with the jets.
Thanks to banana boy for hooking me up at SS7 with the jets.
#59
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Thread Starter
So I just finished doing what I think was the last jet change. 150s for primaries and 180s for secondaries. That plus adjusting the timing which was retarded due to a malfunction in the bolt that locks the dizzy, plus replacing the presilencer with a custom made straight pipe, and the car is performing like never before. Now that I've reached this point I think I'm gonna dyno it and take it to the track to see what it can do on the 1/4 mile. w00t!
#61
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iTrader: (13)
Originally Posted by cdrad51
So I just finished doing what I think was the last jet change. 150s for primaries and 180s for secondaries. That plus adjusting the timing which was retarded due to a malfunction in the bolt that locks the dizzy, plus replacing the presilencer with a custom made straight pipe, and the car is performing like never before. Now that I've reached this point I think I'm gonna dyno it and take it to the track to see what it can do on the 1/4 mile. w00t!
start listening to your elders, oooppppssssssss you are at least 10 yrs older than me.
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