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Why no throttle adjustments on engines?

Discussion in 'Mechanic and Repair' started by themow, May 20, 2008.

  1. themow

    themow LawnSite Member
    Messages: 41

    My powerwasher and my one push mower have no throttle adjustment. The powerwasher has a 6.5 horse honda and the push mower has a 4.5 hp briggs.
    I know the manufacturers probably did this so save money but it really doesnt make any sense to me.

    I have thought of converting them to an adjustable throttle but thought it may not be so good on the preuusure washer. I know that when under a load, the engine doenst run at full throttle. Would the pump not be able to handle the speed?

    I just cant figure it for the mower though. I see no reason as to why Im not able to control my throttle. I was mowing some knee high grass today and the damn thing kept bogging down on me. I had to pull my old 3.5 horse briggs murray out with an adjustable throttle. I cranked it up and that thing ate the grass with ease.

    Has anyone converted to adjustable throttles?
  2. GravelyNut

    GravelyNut LawnSite Bronze Member
    Messages: 1,594

    The reason isn't only cost to make. It is a result of a 3 letter Gov't agency. Even those with adjustments might have limiter caps on the screws.
  3. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 963

    Those 3 letters are EPA.
    Manufacturers have to meet emission requirements.
    It's easier for them to do so if they don't have a pesky idle circuit to mess with.
    Run it at one speed or OFF.
  4. themow

    themow LawnSite Member
    Messages: 41

    So whats preventing people from converting it to an adjustable throttle. I know that theres no low speed jet but im concerned about them over revving. Dont units with adjustable throttles have some sort of rev limiter?
  5. themow

    themow LawnSite Member
    Messages: 41

    Im doing the conversion i will post pics and let everyone know how i make out

    S DIAMOND LawnSite Member
    from South
    Messages: 108

    On the pressure washer, they did because you have no need to adjust it unless you replaced the pump, or have altered the governor setting.

    Is this a direct drive unit? Who makes it? Did you place a tach. on the engine and check the RPM's to determine this? Are you just bored?

    1) The pressure washer pump is constantly loading the engine. The throttle may be at approximately75% W.O.T..

    At T.N.L.S. (TOP NO LOAD SPEED) 3600 RPM, give or take, the throttle is barely open on most engines. When the engine begins loading, it opens up till it reaches its W.O.T. governed speed.

    2) Probably not. Since I don't know who makes it, most direct drive pumps are designed below the engines TNLS. Depending on the manufacturer and type (belt or direct) 3450 RPM is usually the MAX (direct drive). Over speeding the pump would just shorten the life of it.
  7. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Messages: 1,415

    Both of these engines must have a throttle, likely a butterfly type. It's connected via arm to the governor only and does not allow operator input.

    If you want to convert, a bracket with a lever must be mounted. Attach the spring to the lever thus providing adjustable pre-tension on the governor arm. Next you'll have to adjust the revs. It's a lot of work, next time buy an engine with rev control.

    Your carburetor has no idler nozzles (budget cut) and will idle very very very rough.
  8. themow

    themow LawnSite Member
    Messages: 41

    its a Karcher direct drive unit with 5 hp honda engine, pardon my mistake. I didnt not check the rpm and yes im extremely bored

  9. themow

    themow LawnSite Member
    Messages: 41

    I started foolin around withthe mower first. The first thing i tried was removing the all the throttle linkage and hooking up that blue rod from the carb butterfly piece to the old unusable throttle adjustment. That worked pretty good. I thought about the white piece that sits up by the flywheel and and uses the air from the flywheel to close the throttle. I decided to trim a little bit of that off to see if the reduction in airflow would allow the the butterfly to open up more. So i trimmed and put the old throttle linkage back on to see how things worked. It revs higher now that it did but still lacks the adjustability i am looking for. I think i may switch it back to the blue rod but for now its back to the old way

  10. VegetiveSteam

    VegetiveSteam LawnSite Senior Member
    Messages: 296

    The reason your equipment has no adjustable throttle is because that is how the equipment manufacturer asked the engine manufacturer to make the engines for them. A big part of the engine features are the equipment manufacturer's doing. They tell Kohler, Briggs or any other engine mfg what they want on the engine and if it's not something that is dangerous or just completely won't work the engine mfg will build the engine just how their customer wants it. Most of it for the equipment mfg boils down to cost. A constant speed engine probably costs them 5 or 6 dollars less than an engine with variable speed. If the OEM builds 100,000 units they just saved between 5 & 600,000 dollars. This saves a slightly more complex throttle control on the engine. It saves having to install a throttle cable and it saves on having to drill a hole in the mower handle to mount the control part of the throttle cable in. This doesn't include the time it takes to adjust all of this as well. Engine manufacturers very rarely dictate what goes on a piece of equipment. It's up to the OEM of the equipment.

    As for your pressure washer there is no reason to have an adjustable throttle. You shouldn't try to run the pressure washer lower than full rpm.

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