Docmiata said:Better photo found on an old 5.25" flopppy: Balance tube and TPS set up shown more clearly
What in the world do you have that still reads a 5 1/4" drive? That died with Windows 3.1.
Docmiata said:Better photo found on an old 5.25" flopppy: Balance tube and TPS set up shown more clearly
What in the world do you have that still reads a 5 1/4" drive? That died with Windows 3.1.
twentyover said:Thanks for the feedbaack, Norman, looks like I need to buy a book as a starting place. Sorry, I'm a cheap SOB so I'm going to buy used....
Unfortunately, the manifolds build will be crappily MIG welded steel plate and exhaust tubing. Good info on the balance tube
I know that the HS6 is a better fit, but I have a rack of HIF4's hangin' from the roof of the garage. Drop in a fixed needle adapter and OIshould be set. If I decide latter I need more carb, I can make the change to HS6 and try a needle comparison because of the .100 jet used on the 6's, while the 4's use an .090 jet. The 20R is more a draft horse than a thoroughbred, so not certain I need the 6 since it won't spin 7200 (at least this one won't.)
Needle selection is my biggest worry. Figure I'll start w/ the B needle, maybe drop the jet a couple flats.
May I contact you via PM thru the GRM forum if I have any questions?
LanEvo
I understand the national attraction Mikunis or even Solex, but remember Nissan ran Hitachi licensed SU's on 1600, 2000, and 240Z cars, so I don't think I'm TOO far off base
David-
I read about the swap somewhere, & I agree i seem to recall it was not without issue, but I've never to the best of my seriously fading memory) read a Miata magazine. Anyway, I think I may have accidently retired a couple months ago, so have nothing but time to fettle something like this....
Side note- conversation between me and a best friend I've known, literally, since kindergarten-
Me- They want to get rid of me, they offered me a little money to leave. Think I should take the buyout?
Him- The offered a golden parachute?
Me- Yes, but they're throwin' me off the fookin' airplane, and we all know how well gold floats in air
If you are going to use regular pump gas, once you have needles for your SU’s you can richen up any lean spots by chucking the needles in a drill and polish up the spot on the needles that it goes lean with some ultra fine sandpaper. 400 grit or so.
The wonderful thing about SU’s is that they are insanely easy to tune for Ethanol.
E85? Just ream the jet to flow about 60% more. ( alcohol is a lot more tolerant than gasoline on getting mixture exactly correct) Even Methanol just requires 100% more. ( just don’t leave Methanol in the carbs for a long time, like overnight) oh, and Methanol you will need the brass floats!
Robbie said:What about fuel pump? Do you change the efi one out completely or just massively regulate it down to carb pressure?
SU’s will never tolerate high pressure of a EFI fuel pump. They barely can regulate American fuel pumps down to the 2&1/2 psi.
The best fuel pump is the SU ! But it has a set of points that get dirty periodically. Yes you can beat the fuel pump with a big stick, or you can spend a moment and run some fine emery paper across the points. Takes me about 1 minute from start to finish every time I change oil. ( no you don’t have to do it that often but if it’s part of your normal oil change, you’ll never have a problem ).
frenchyd said:If you are going to use regular pump gas, once you have needles for your SU’s you can richen up any lean spots by chucking the needles in a drill and polish up the spot on the needles that it goes lean with some ultra fine sandpaper. 400 grit or so.
.....
The question I've always had about whittling down a needle as you describe (outside of the difficulty in replicating it for the second carb), is how to determine where in the needle richening is needed. Without a rolling road or the ability to peer down the carburetor bore as you drive the car, how does one determine where the needle actually needs richening.
And is using any fuel pump besides an SU, ECCO, or Hardi, I would (and will) use an aeromotive return type pressure regulator
In reply to twentyover :
If you are on a chassis Dyno it’s simple*
Take a pair of dividers or compass and measure how far open the damper is. Once the engine is shut off, slide the damper to that distance and reach in with a magic marker. Now take a vernier caliper and measure from that spot to the top of the needle.
Go very lightly because the needle is brass and a little winds up being a lot. Remember you can always remove more but you can’t put it back.
The good news is alcohol is a lot more tolerant than gasoline (E85 is 85% alcohol ) so going slightly over rich isn’t a big thing.
You replicate the other needles by duplicating the mark on the other needles and using a micrometer measuring the size you settled on. I use really fine. Paper and sneak up on perfection rather than trying to get it perfect in one blast. The guy who taught me that trick could do it, wham bam thank you ma'am but I suspect he used alcohol’s tolerance a lot.
* road dyno. ;) smiley face like I used in my youth I’d strap myself to the fender and eyeball the damper as the car accelerated up the hill. Later with the Black Jack Spl I left the bonnet off and wedged myself into the engine compartment. I suppose I could have used a movie camera,now days you could tape a cell phone to the inner fender.
Rereading that I realize how easy modern laptops and EFI make things compared to my days. But using a long steep hill is free. Finding free or cheap ways to do things was often the difference between racing and not racing.
Since racing is about improving finding those ways made me a better faster racer and no doubt kept me coming back and active. Long after my budget would have sent me home.
In reply to twentyover :
One thing I neglected. If the engine is stock just look up the proper needle(s) and use them. You won’t need to change them to use E85. Just bore out the jet to flow 60% more. Note, flow 60% more not 60% bigger.
Richer or leaner is the same as stock, up or down on the jet. The only reason you need to change the needle is if you modify the engine, especially the camshaft.
LanEvo said:I love dual/triple carbs on older i4 and i6 engines.
I'm biased, but I also think they are pretty nifty
Robbie said:What about fuel pump? Do you change the efi one out completely or just massively regulate it down to carb pressure?
I don't know about SU carbs, but with Webers you want fuel pressure in the 1.5 to 2.5 PSI range. That's not easy to achieve with just a fuel pressure regulator. In my case, when switching from electromechanical fuel injection to dual Webers, it made sense to ditch the stock (90-something PSI) fuel pump and run one designed for carbs.
JoeyM said:I'm biased, but I also think they are pretty nifty
Here's mine:
In reply to LanEvo :
The problem I have with Weber’s is the cost of tuning them. I brought $2300 worth of jets air correction meters, etc etc. to my first Dyno session and by the time I had it sorted out I was out nearly $3800. That’s the trouble unless they are factory installed. Most British cars weren’t OEM users of Weber’s and when you call Redline or other distributors you’re on your own.
A lot of racers simply buy smaller jets and just team them until they are happy with the mixture. The trouble with that approach is you don’t have a baseline.
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