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HS-4 Carbs

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tony barnhill

tony barnhill

Great Pumpkin - R.I.P
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How much trouble is it to mix & match parts from different HS-4 carbs? I have a set of AUD326's in which the pistons are stuck & won't come out of chamber...have a set of AUD135 pistons,chambers,springs/jets....why can't I just fit them to the AUD 326's?
 
Tony, I did exactly that in order to go to the fixed needles for a set of HS4's that I was running on a race prepped 1275. I had a good set of dashpots and pistons on some 135 bodies that had worn throttle shafts, and a good set of 326 bodies. Worked great.
Jeff
 
Jeff...did you just drop the pistons on the 326's or did you change out anything else?
 
Tony, other than installing new jets (They needed replacement), I just installed the entire dashpot assemblies. I think I did swap springs, but that was just a performance thing. The suction chambers, pistons, etc, were a direct swap. As far as I know, the bodies are the same, the main difference is that the 326's were spring loaded needles, and the 135's are fixed. I did't have any trouble centering the jets and the needles, and they ran just fine. The manifold I used was a B manifold, that I cut and rewelded to fit the 1275 head. As a matter of fact, I have one of the carbs on my F Production 1500 Spitfire right now. It's nice that so much of this stuff interchanges!
Yeah, I know I'm wandering a bit, but I'm old, Dammit!
Jeff

[ 12-26-2003: Message edited by: Bugeye58 ]</p>
 
Hello Tony,
if those part numbers you quote are from the tag on the dashpot, that is the specification for a particular set up. The variables are basically the needles and springs, dashpot 'hand' and angle, if any from the horizontal. The basic components are interchangeable and flexible. I believe that you cannot readily swap a piston or dashpot cover seperately as they are matched pairs, and affect the running to some degree.
I suggest that you may be able to rescue the stuck assemblies by soaking them in thinners or the like to dissolve the laquer that is probably why they are stuck.

Alec
cheers.gif
 
Tony,
You can swap parts amongst HS4s, but first soak your stuck pistons/dashpots around the outer circumference of the dashpot and where the damper goes into the dashpot top with penetrant of your choice. If it frees up, get it cleaned up and see if it passes the piston drop test. Also see if the the pair you're thinking about swapping in pass the drop test (in the carb section of the emissions supplement of the factory manual). A piston being able to move up and down the chamber means little - it may be worn out and moving TOO easily, resulting in lost performance. Sometimes you can even swap pistons amongst dashpot chambers. Use the piston drop test to see if you have a match that works within spec.
Safety Fast, Wade
 
I just pulled a good set of AUD135's off the shelf & put together everything I need for a complete set - I'll rebuild them & use them on the '78 I'm building for resale....easier for the next owner.
 
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