Technical: Carbs: Model HD
Jerry Raino, Mostly Ironheads, and Many Others

The 1966 – 1969 Sportster boasted yet a new carburator- the Tillotson Model HD. This carb is way different - it doesn't even have a float. The Tillotson was especially beloved by Sportster owners for its propensity for hard-starting. Tillotsons came in various models, on the Sportster and Shovelhead.

The OSKRG's Identification Guide and What Fits What - Version 1.1 (PDF)

OSKRG presents Original Tillotson Documentation (PDF)

Initial Adjustments

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Quick Reference for Initial Adjustments

When you get your carburator completely out of whack, here's what to do...


Turn both the low speed needle (1) and the intermediate speed needle (2) all the way in (to right). Do not close off either needle too tightly or damage to needle and seat may result.

Back up (to left) both needles about 7/8 turn. With needles in this position, engine will start, but low speed mixture will probably be too rich.

Start the engine and after it has reached operating temperature and the choke has been moved to the open position, adjust throttle control so engine runs at approximately 2000 RPM.

Without changing throttle setting, turn intermediate needle slowly in direction which produces highest englne speed (RPM). Engine should not miss or surge at this adjustment position.

Back off intermediate needle 1/8 turn to slightly richen mixture. This is the correct intermedlate needle adjustment.

Readjust idle needle and idle speed stop screw to produce a smooth idle at desired idle speed (900 to 1100 RPM).
NOTE: Use of an electric tachometer is recommended.

Changing either mixture setting also affects the other setting to some degree. Therefore, it will be necessary to recheck the low speed mixture after the intermediate mixture final setting is obtained.

NOTE: Inlet fitting (7) and vent fitting (8) have strainer screens located in threaded holes in carburetor body. If faulty carburetion indicates fuel flow is restricted, remove elbow fittings (7 and 8) from body, extract both screens with a bent wire, and blow out passages with an air hose. Replace screens and elbows, belng sure that screens are not bent or damaged so as to allow dirt to pass through.

No float, so nothing to adjust.