Whizzer Motor

Discussion in 'Whizzer Motorized Bicycles' started by tommer2, Feb 3, 2012.

  1. tommer2

    tommer2 New Member

    Hi Guys, Which Whizzer motor to rebuild, the H or the J model and why? It's going on my 1950 Hornet. Thanks!!

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  2. jbcruisin

    jbcruisin Member

    I have an H & a J and my J is lots faster. They both run great but (Quenton knows better than me) I think the J has bigger ports & maybe bigger valves. My J top speed is 5 MPH faster than my H.
    Last edited: Feb 4, 2012
  3. WZ507

    WZ507 Member

    For a simple rider it makes little difference which motor you use since both the H and J are identical with the exception of the cylinder (same bottom ends and heads). The J has slightly better ports (still quite small though) than the H and both have the same small valves in them. Either cylinder can be modified to receive big valves, port work can be done on either, and both can provide much improved performance if you desire it.
  4. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    The main advantage to the "J" is the larger & better carbuetor and a extra fin near the exhast port, and 5/16" head bolts ["H" motor afer H-120,000 also used the 5/16" bolts]. The larger bolts solved the problem of "blowing" head gaskets and allowed the head to be torqued at a higher value.

    Although the "H" & "J" are rated the same [2.5 HP], the "J" is normally a little faster.

    The "J" cylinder has larger intake and exhaust ports. Many "H" cylinders have a reduction sleeve [removable] in the intake port. The Carter carburetor is larger on the "J" than the Tillotson on the "H", and are not interchageable [different bolt pattern]. The larger Carter used on the "J" was also used on the "300" and later motors [with bigger valves, larger ports and hi-compression head].

    The "H" is normally less expensive than the "J" because of production numbers. The "H" is by far the largest series of Whizzer motors and approx. 140,000 were produced, whereas the "J" was just a little over 50,000.

    Have fun,
    Last edited: Feb 5, 2012
  5. WZ507

    WZ507 Member

    Carbs used on Model Js

    Just a clarification on the carburetors employed on the Model H and J Whizzers. The Model H made exclusive use of the Tillotson ML5B - no exceptions. However, the Model J employed both the ML5B and several different model Carter carbs. The Model J started out using the Carter N665S & N666S (fixed main jet carbs) for ~ 30,000 units, then used about 6,000 Tillotson ML5B. The ML5B used on the Model J differed from the one used on the Model H in that the carb flange mounting holes were elongated to allow fitment to both the Model H (1-5/8" spacing) and the Model J (1-13/16" spacing). Thus the ML5B provided carbs for Whizzer to mfg while Carter altered their design from a fixed main jet to an adjustable main jet model - N703S & N704S. Even after the introduction of the Carter adjustable main jet models, ML5Bs were still used on a limited range of Model J serial numbers (likely to consume the inventory of ML5B).

    So if you have a model J with an ML5B on it, it is very possibly the correct carb. See info below for correct Model J carb by engine serial number. I own 2 such Model Js fit with ML5Bs.

    Model J - SN 200,000 - 230,200, used Carter N665S & N666S
    Model J - SN 230,201 - 235,200, used Tillotson ML5B
    Model J - SN 235,201 - 235,999, used Carter N703S & N704S
    Model J - SN 236,000 - 237,000, used Tillotson ML5B
    Model J - SN 237,001 - up, used Carter N703S & N704S
  6. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Just to add a few more carburetor comments.

    A version of the Carter carburetor was also supplied to Whizzer to fit the "H" motor as a replacement carburetor and had slotted mounting holes. The Whizzer part numbers used on the Carter carburetors were slightly mis-leading, as the ealier unit with the fixed main jet had a higher part number than the later units. The Whizzer part number on the fixed main jet version was #2704, whereas the later adjustable main jet version was part #2702.

    Easiest way to determine if the Carter was the correct version for Whizzer motors is by the location of the fuel line. The Carter "N" carburetor was used on many motors other than Whizzer, however all Whizzer versions had the fuel inlet on the top, not the side.

    To add a little more confusion, Weber also supplied a special version of the Tillotson carburetor for the earlier Whizzer motors, had a larger venturi, and was model #ML3B [I have an NOS version in my collection].

    Have fun,

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    Last edited: Feb 11, 2012