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crank ventilation effects on mixture

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Sounds fine but float levels are non critical in SU carbs. As long as the level isn't so high that it dribbles out if you park on a hill you'll be fine. There is a long article on the Burlen(SU) site on how SU's work that you should read. It was written by a Mr. Knight, I believe.

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

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Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
Thanks Adrian, the Burlen site has a lot of good info. I read some and printed the rest.

As for my carbs, they are AUD 404s. I trust this wont be an issue as the '67 calls for a different model (AUD266 maybe?). I am guessing not since the displacement is the same and I believe they use the same weight springs? I can't tell if the jet needle sizes were different, however.

matmire Avatar
matmire Matt Meyer
Studio City, CA, USA   USA
In reply to # 3659253 by Poundingsand I believe they use the same weight springs? I can't tell if the jet needle sizes were different, however.

Peer, I believe Blue springs were the standard across nearly all spridget HS2 specs. As far as needles... your 404 uses spring biased needles, and the original '67 HS2 would have used fixed needles, so matching the needles to the original spec isn't really an option without other modifications.

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matmire Avatar
matmire Matt Meyer
Studio City, CA, USA   USA
Also, what kind of air filters are you using?

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
I have the little pancake filters. I believe thw original needles were AN and I ordered the AAC. I know the mounts are different but I am wondering how the profile differ...

matmire Avatar
matmire Matt Meyer
Studio City, CA, USA   USA
There used to be a fantastic needle profile comparison tool here. Sadly, it looks like it's going to be down for a little while as he modernizes the site.

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
Thanks Matt. I will check back. In the meantime I pulled the carbs and bought a rebuild kit. A few things I noticed so far. My springs are definitely softer than the replacements. And my choke on the rear carb was ineffective since the cable stop was hitting the carb body. New jets, springs and needles plus a lot of gaskets go In tomorrow, hopefully! Also have the right cable stop now...

Going to take my time assembling and see what happens!

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Well that sounds good. Your new stronger springs will make your mixture richer over the whole rpm range. Keep us posted.

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
one item no one has mentioned yet: throttle plates

your '67 came with different carbs than what you have described, so it is clear your carbs are from a later year car

there's nothing wrong with that, I only mention it to say that it is also possible your throttle plates in those later year carbs you've got, may also have the little pop off valves in them

those little valves go bad over time, were meant to try and improve emissions but caused more trouble than they solved, especially they cause trouble with inconsistent running - replace them with proper solid throttle plates to eliminate the little valves, if you have not already done so


A quick solution is to solder the little valves shut, while waiting for a pair of new throttle plates in the mail.

By the way, when checking a pair of SU carburetors, shine a bright light through the closed throttle plates and confirm there is no light leak, or that any leak is equal between the two carbs. This is a subtle mis match that can cause balancing issues for the unwary.

N

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Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
Hi Norm. I had soldered poppet valves. Swapped in the new plates this morning. Also changed jets. But one of my plastic floats is ovaled and I can't get it right with shinning. Need to order from moss today.

In the meantime new jets needles and springs are going in...

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
So the carbs were cleaned, rebuilt and installed. I shimmed one float to work for now but ordered new.

The first thing I noticed was the car idles a lot better with minimalnpooting from the exhaust.

Also when revving the motor the piston in the carbs only lift about halfway or so, versus all the way up before.

I didnt have time to drive it but hope to tomorrow. Will report more then!

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
That sounds encouraging.
thumbs up

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
Adrian, I imagine the carbs could be tuned at idle with the weaker springs, but "fall out" of correct mixture range at higher RPMs, correct?

I am guessing that with properly prepped carbs, you should be able to set mixture at idle and have it stay in spec through the throttle range.

Sound about right?

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Sure. It's a balancing act. The factory must have spent quite a bit of time tuning the carbs for the best average settings for all conditions.

Springs are not a usual tuning adjustment. You would normally get the right ones and then just swap needles until you had it set optimally.

If you have the correct needles your fuel ratio will be as you require at all loads and speeds. (within reason)

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Poundingsand Avatar
Poundingsand Silver Member Peer Ebbighausen
Los Angeles, CA, USA   USA
UPDATE: I finally got to drive the car after dialing it in. Oddly, lifting the pins on the carbs gave no indication of mixture. Using the colortunee showed me I was almost two full turns rich.

Now the car starts cold in a crank or two, versus several seconds cranking before the rebuild. Cool and slightly warm idle is super smooth whereas the engine used to "shudder" while idling. Its still a bit jumpy at times when up to temp but much more subtle.

The car cruises well on the freeway and is much more comfortable and reponsive to throttle input. I found 75 briefly but traffic kept me at 60-65 for the most part of the two or three freeway miles I drove it.

And the clincher? I got home and looked under and not a drop of oil dripping. The blow by before was quite extreme.

Its like a whole new car. My utmost gratitude for the excellent advice and assistance. I am quite pleased!

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