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hs2 needle selection help...

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matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
I recently bought a set of HS2s from Joe Curto, (to replace a weber dcoe 45) but I'm struggling to find the right needle for my tune. I'm wondering if anyone has a similar setup to me and has found a needle that works well for them. I've been able to find info about richer needles for HS4s, but not much on HS2s.

So... my car is a bugeye with a 1275 from a '74 Midget. The HS2's are the vented type with ported vacuum and bias needles. I'm using K&N pancake filters with APT stub stacks. It also has a LCB manifold with larger midpipe and pacesetter muffler. Joe originally sent the carbs to me with AAC needles, but I was experiencing loss of power and sputter/farts above 3600 rpms. Joe then sent me ABE needles, but the symptoms are still there. Now he's sending me red springs and AAL needles to test out in various configurations. While I'm waiting for them to arrive, I thought I'd see if anyone had any recommendations. OR... could there be other factors causing the leaning out above 3600 rpm. (when I pull the choke, the car regains power and the symptoms go away)

note: the distributor is also newly rebuilt and curved by Jeff Schlemmer to the car's specs. I've set it to 34 degrees total advance, which it hits around 3000 rpm. Fuel pressure is set to 3 psi.

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
Have you tried turning the jets down a couple of flats? Joe has a great reputation for getting it right. Did you oil your filters properly?

matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
yes, if I turn the jets down it gets too rich at idle, but still has the problem above 3600rpm (to a lesser degree). I didn't oil the filters because they are brand new. They are pre-oiled when new, aren't they?

I also forgot to mention... I'm using blue springs, and 20w-50 motor oil in the dashpots.

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matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
Is it possible to have a vacuum leak that only shows itself above certain rpms?

66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
My K&N filters were not pre oiled, don't know about yours. I know it made a big difference on my Triumph motorcycle.

matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
the filters are oily and pink, so I think I'm ok there. I see a little soot at one spot where the header meats the mid-pipe. Wonder if that could be causing problems. What effects do exhaust leaks usually have on mixture?

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
"What effects do exhaust leaks usually have on mixture?" - almost nothing, unless it is an indication that the exhaust manifold is loose, and if that means the intake manifold is also loose, which would be a vacuum leak which would lean out your mixture.


I think Matt has nailed it: I bet you've got a vacuum leak. Maybe one that is hard to find but shows up when the intake vacuum reaches a certain point. Make sure to spray aerosol all around all joints from the head to the air filters (and there are a lot of joints, check them all, 360degrees, including all over the intake manifold). Any change in engine running sound/speed indicates a leak that needs fixing.


N

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Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
by the way, from the description of the modifications you've made on your engine, I doubt that changing needles would be called for

as Phillip said, Joe knows what he's doing so the first needle is probably the right one (or if it isn't the issue will be a subtle one, not major running issue)



N

matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
In reply to # 3535883 by Kerr by the way, from the description of the modifications you've made on your engine, I doubt that changing needles would be called for

as Phillip said, Joe knows what he's doing so the first needle is probably the right one (or if it isn't the issue will be a subtle one, not major running issue)

When Joe sent me the carbs he said that it was very possible that he K&Ns would require a richer needle than the one he installed, but we'd try it and see. It's a process, and he's been awesome about it. I'll go through everything again and search good and hard for vacuum leaks.

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
I cheated and very unscientific like put my needle in a drill and made the bottom third a little thinner. the bottom third of it. Worked for me, car runs much better. I had extra needles to play with.

matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
In reply to # 3535881 by Kerr I bet you've got a vacuum leak. Maybe one that is hard to find but shows up when the intake vacuum reaches a certain point.

I was thinking more about this... doesn't vacuum decrease under load? If so, I'm not sure that a vacuum leak would present itself at those higher rpms when vacuum pressure is reduced. thoughts?

66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
The more air supply it can get between the jet and the motor the leaner it will be. Example. My son came home with his Nissan one day and it was running really bad. I determined that #3 cylinder was not working properly. What have you done to the car? I installed a new sound system he says. He drilled from inside the car into the brake booster creating an air leak. Moral of the story is, there cannot be any way to get air after the carburetor.

matmire Avatar
matmire Matt Meyer
Studio City, California, USA   USA
I get that. I guess what I'm saying is... if it's leaning out at high rpms due to a vacuum leak, why would it only show up under load when the vacuum pressure is greatly reduced and not at idle when the vacuum is strongest?

Just theorizing, I'm still going to check everything.



Edited 1 time(s). Last edit at 2017-06-19 07:49 PM by matmire.

refisk Avatar
refisk Rick Fisk
Frankenmuth, Michigan, USA   USA
A vacuum leak is a vacuum leak. Under load is when you'd notice it the most because under load is exactly when you don't want to be lean.

S1 Elan Kurt. Appley
Akron, Ia., USA   USA
If all else fails try plugging your crankcase vent to carbs line and see if that makes a difference.

Kurt

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