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HD8s easily rebuilt at home

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steveg

steveg

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My car had been backfiring at low speeds and it turns out the butterfly shaft plastic bushings were worn and the jets were off-center.

This book describes exactly how to hand-roll the new bushings and how to install them and the shafts. That plus new jets, centered with new needles and voila, the carbs are rebuilt.

Car runs much better now. Idles normally and the lift pin works!

The book is also useful in that it describes how the SU carbs work.

SUbookCenterTool.jpg
 
Thanks for that tip steve I have just located a used copy of it, look forward to reading it before servicing my frogeye carbs this winter could save a bit of head scratching :encouragement:
 
After being plagued for years with an idle which would start at 1500 then descend to <500 and die, after replacing the plastic bushings, my carbs now idle steadily at 750 rpm with the slow-running screw only. At shutoff, there is less running-on but it's still there. Will follow up on that if I manage to solve it.

What I've learned from the Des Hammill book:
--piston springs need to be the same length and strength - how to measure with kitchen scale.
--if carbs not balanced one set of 3 cylinders is fighting other set.
--float chambers need to contain same amount of fuel - he says dismount carb and empty into measure. I plan on sucking fuel out with measured syringe.
--main jet depression to be set with dial caliper to be the same for both carbs -- he says they're precision instruments and if you can't do that there's a problem elsewhere, such as an air leak.

Moving forward with making wood indicator rods to show position of needles at different speeds as you drive.

Not quite ready to address modifying needles (per Dave Red57) :smile:

PS - carbs running much better since re-bushing. Wonder if HD6s couldn't be bored out to accept the HD8 plastic bushings.
 
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