<PAGE>   1


                                                                     EXHIBIT 4.7



                             SUPPLEMENTAL INDENTURE
                       DELIVERED BY SUBSEQUENT GUARANTORS

    SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of May 15,
2001, among Generac Portable Products, Inc.*, a Delaware corporation, (the
"Guaranteeing Subsidiary"), a subsidiary of Briggs & Stratton Corporation (or
its permitted successor), a Wisconsin corporation (the "Company"), the Company,
the other Guarantors (as defined in the Indenture referred to herein) and Bank
One, N.A., as Trustee under the indenture referred to below (the "Trustee").

                               W I T N E S S E T H

         WHEREAS, the Company has heretofore executed and delivered to the
Trustee an indenture (the "Indenture"), dated as of May 14, 2001, providing for
the issuance of an aggregate principal amount of up to $140,000,000 of 5.00%
Convertible Senior Notes due May 15, 2006 (the "Notes");

         WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiary shall execute and deliver to the Trustee a supplemental
indenture pursuant to which the Guaranteeing Subsidiary shall unconditionally
guarantee all of the Company's Obligations under the Notes and the Indenture on
the terms and conditions set forth herein (the "Subsidiary Guarantee"); and

         WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiary and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders as follows:

         1.   CAPITALIZED TERMS. Capitalized terms used herein without
definition shall have the meanings assigned to them in the Indenture.

         2.   AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby agrees
as follows:

              (a)  Along with all Guarantors named in the Indenture, to jointly
         and severally Guarantee to each Holder of a Note authenticated and
         delivered by the Trustee and to the Trustee and its successors and
         assigns, irrespective of the validity and enforceability of the
         Indenture, the Notes or the obligations of the Company hereunder or
         thereunder, that:

                   (i)  the principal of, premium and Liquidated Damages, if
              any, and interest on the Notes will be promptly paid in full when
              due, whether at maturity, by acceleration, redemption, repurchase
              or otherwise, and interest on the overdue principal of, interest
              and Liquidated Damages on the Notes, if any, if lawful, and all
              other Obligations of the Company to the Holders or the Trustee
              hereunder or thereunder will be promptly paid in full or
              performed, all in accordance with the terms hereof and thereof;
              and

                   (ii) in case of any extension of time of payment or renewal
              of any Notes or any of such other Obligations, that the same will
              be promptly paid in full when due or performed in accordance with
              the terms of the extension or renewal, whether at stated maturity,
              by acceleration or otherwise, subject to the limitations set forth
              in the Indenture. Failing payment when due of any amount so
              guaranteed or any performance so


<PAGE>   2

              guaranteed for whatever reason, the Guarantors shall be jointly
              and severally obligated to pay the same immediately.

              (b) The Obligations hereunder shall be unconditional, irrespective
         of the validity, regularity or enforceability of the Notes or the
         Indenture, the absence of any action to enforce the same, any waiver or
         consent by any Holder with respect to any provisions hereof or thereof,
         the recovery of any judgment against the Company, any action to enforce
         the same or any other circumstance which might otherwise constitute a
         legal or equitable discharge or defense of a Guarantor.

              (c) The following is hereby waived: diligence, presentment, demand
         of payment, filing of claims with a court in the event of insolvency or
         bankruptcy of the Company, any right to require a proceeding first
         against the Company, protest, notice and all demands whatsoever.

              (d) This Subsidiary Guarantee shall not be discharged except by
         complete performance of the obligations contained in the Notes and the
         Indenture, and the Guaranteeing Subsidiary accepts all Obligations of a
         Guarantor under the Indenture.

              (e) If any Holder or the Trustee is required by any court or
         otherwise to return to the Company, the Guarantors, or any Custodian
         acting in relation to either the Company or the Guarantors, any amount
         paid by either to the Trustee or such Holder, this Subsidiary
         Guarantee, to the extent theretofore discharged, shall be reinstated in
         full force and effect.

              (f) The Guaranteeing Subsidiary shall not be entitled to any right
         of subrogation in relation to the Holders in respect of any Obligations
         guaranteed hereby until payment in full of all Obligations guaranteed
         hereby.

              (g) As between the Guarantors, on the one hand, and the Holders
         and the Trustee, on the other hand, (i) the maturity of the Obligations
         guaranteed hereby may be accelerated as provided in Article 6 of the
         Indenture for the purposes of this Subsidiary Guarantee,
         notwithstanding any stay, injunction or other prohibition preventing
         such acceleration in respect of the Obligations guaranteed hereby, and
         (ii) in the event of any declaration of acceleration of such
         Obligations as provided in Article 6 of the Indenture, such Obligations
         (whether or not due and payable) shall forthwith become due and payable
         by the Guarantors for the purpose of this Subsidiary Guarantee (subject
         to any subsequent rescission or cancellation of any acceleration in
         accordance with Section 6.02 of the Indenture).

              (h) The Guarantors shall have the right to seek contribution from
         any non-paying Guarantor so long as the exercise of such right does not
         impair the rights of the Holders under the Subsidiary Guarantee.

              (i) Pursuant to Section 10.02 of the Indenture, after giving
         effect to any maximum amount and any other contingent and fixed
         liabilities that are relevant under any applicable Bankruptcy Law or
         fraudulent conveyance laws, and after giving effect to any collections
         from, rights to receive contribution from or payments made by or on
         behalf of any other Guarantor in respect of the Obligations of such
         other Guarantor under Article 10 of the Indenture, this new Subsidiary
         Guarantee shall be limited to the maximum amount permissible such that
         the Obligations of such Guarantor under this Subsidiary Guarantee will
         not constitute a fraudulent transfer or conveyance.


                                     - 2 -

<PAGE>   3

         3.   EXECUTION AND DELIVERY. Each Guaranteeing Subsidiary agrees that
its Subsidiary Guarantee shall remain in full force and effect notwithstanding
any failure to endorse on each Note a notation of such Subsidiary Guarantee.

         4.   GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

              (a)  Except as otherwise provided in Section 5 below, the
         Guaranteeing Subsidiary may not (i) consolidate with or merge with or
         into (whether or not such Guarantor is the surviving Person) another
         Person or (ii) sell, assign, transfer, lease, convey or otherwise
         dispose of all or substantially all of its assets in one or more
         related transactions to another Person unless:

                   (i)  subject to Section 5 below, the Person formed by or
              surviving any such consolidation or merger (if other than a
              Guarantor or the Company) or the Person acquiring the assets in
              any such sale, assignment, transfer, lease, conveyance or other
              disposition unconditionally assumes all the Obligations of such
              Guarantor under the Notes, the Indenture, the Subsidiary Guarantee
              and the Registration Rights Agreement, pursuant to a supplemental
              indenture in form and substance reasonably satisfactory to the
              Trustee, on the terms set forth herein or therein; and

                   (ii) immediately after giving effect to such transaction, no
              Default or Event of Default exists.

              (b)  In case of any such consolidation, merger, sale, assignment,
         transfer, lease or conveyance and upon the assumption by the successor
         Person, by supplemental indenture, executed and delivered to the
         Trustee and satisfactory in form to the Trustee, of the Subsidiary
         Guarantee endorsed upon the Notes and the due and punctual performance
         of all of the covenants and conditions of the Indenture to be performed
         by the Guarantor, such successor Person shall succeed to and be
         substituted for the Guarantor with the same effect as if it had been
         named herein as a Guarantor. Such successor Person thereupon may cause
         to be signed any or all of the Subsidiary Guarantees to be endorsed
         upon all of the Notes issuable under the Indenture which theretofore
         shall not have been signed by the Company and delivered to the Trustee.
         All the Subsidiary Guarantees so issued shall in all respects have the
         same legal rank and benefit under the Indenture as the Subsidiary
         Guarantees theretofore and thereafter issued in accordance with the
         terms of the Indenture as though all of such Subsidiary Guarantees had
         been issued at the date of the execution hereof.

              (c)  Except as set forth in Article 5 of the Indenture, and
         notwithstanding clauses (a) and (b) above, nothing contained in the
         Indenture or in any of the Notes shall prevent any consolidation or
         merger of a Guarantor with or into the Company or another Guarantor, or
         shall prevent any sale, assignment, transfer, lease or conveyance of
         all or substantially all of the assets of a Guarantor to the Company or
         another Guarantor.

         5.   RELEASES.

              (a)  In the event of (i) a sale or other disposition of all or
         substantially all of the assets of any Guarantor, by way of merger,
         consolidation or otherwise, or (ii) a sale or other disposition of all
         the Capital Stock of any Guarantor, in each case to a Person that is
         not (either before or after giving effect to such transaction) a
         Significant Domestic Subsidiary of the Company, then such Guarantor (in
         the case of clause (ii)) or the Person acquiring the assets (in the
         case of clause (i)) will be released and relieved of any Obligations
         under its Subsidiary Guarantee. Upon delivery by the Company to the
         Trustee of an Officer's Certificate and an Opinion of Counsel to




                                     - 3 -

<PAGE>   4

         the effect that such sale or other disposition was made in accordance
         with the provisions of the Indenture, the Trustee shall execute any
         documents reasonably required in order to evidence the release of any
         Guarantor from its Obligations under its Subsidiary Guarantee.

              (b)  Any Guarantor not released from its obligations under its
         Subsidiary Guarantee shall remain liable for the full amount of
         principal of, premium and Liquidated Damages, if any, and interest on
         the Notes and for the other obligations of any Guarantor under the
         Indenture as provided in Article 10 of the Indenture.

         6.  NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, shareholder or other agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any Obligations of the Company
or any Guarantor under the Notes, any Subsidiary Guarantees, the Indenture or
this Supplemental Indenture or for any claim based on, in respect of, or by
reason of, such Obligations or their creation. Each Holder of the Notes by
accepting a Note waives and releases all such liability. The waiver and release
are part of the consideration for issuance of the Notes.

         7.  NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK
SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

         8.  COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

         9.  EFFECT OF HEADINGS. The Section headings herein are for convenience
only and shall not affect the construction hereof.

         10. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Company.



                                     - 4 -


<PAGE>   5




         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed and attested, all as of the date first above
written.



                                     GENERAC PORTABLE PRODUCTS, INC.

                                     By:     /s/ John S. Shiely
                                        ----------------------------------
                                     Name:  John S. Shiely
                                     Title: President

                                     BRIGGS & STRATTON CORPORATION

                                     By:    /s/ John S. Shiely
                                        ----------------------------------
                                     Name:  John S. Shiely
                                     Title: President

                                     GPPW, INC.

                                     By:    /s/ John S. Shiely
                                        ----------------------------------
                                     Name:  John S. Shiely
                                     Title: President

                                     GPPD, INC.

                                     By:    /s/ John S. Shiely
                                        ----------------------------------
                                     Name:  John S. Shiely
                                     Title: President

                                     GENERAC PORTABLE PRODUCTS, LLC

                                     By:    /s/ Carita Twinem
                                        ----------------------------------
                                     Name:  Carita R. Twinem
                                     Title: Treasurer

                                     BANK ONE, N.A.,
                                       as Trustee

                                     By:   /s/ Marla S. Roth
                                        ----------------------------------
                                           Authorized Signatory


--------------

*  GPPD, Inc., GPPW, Inc. and Generac Portable Products, LLC each executed and
   delivered separate Supplemental Indentures in this form as the "Guaranteeing
   Subsidiary."