How to fix a Toro SR4 lawnmower that runs poorly

The guaranteed to start mower does start, but it won’t run well enough to mow. This is a makeshift repair, temporary fix, or out of warranty fix for a Toro SR4 lawnmower that runs poorly (spitting an sputtering) and has throttle or speed limiter problem. This is a jury rig type fix that I was forced into when the mechanic, at the place I bought the mower from, treated me like crap, wouldn’t listen to me, criticized me, and almost claimed the problem was me. His solutions were wrong and I pretty much knew it, but what do you say to an arrogant mechanic. For me it was “Bye” not buy.

The fix is very simple by adding a short piece of wire to replace a spring. It keeps the throttle in one position where the motor runs best. You can find the proper setting by adjusting the throttle till the engine runs smoothly which is demonstrated in the video. I don’t recommend this fix, especially if the mower is still under warranty.



29 thoughts on “How to fix a Toro SR4 lawnmower that runs poorly

  1. You should test the compression, ignition, and carburetor in that order. It sounds like it has good compression so you can probably start at ignition. You need an inline tester (can pick one up at Harbor Freight or any auto parts store), which will tell you if the ignition is firing properly. If ignition is good then it's the carb. Most likely some deposits have partially clogged up the jets and it just needs to be cleaned.

  2. low oil pressure? gas backtracking somewhere? that mechanic you took it to obviously had no idea what he was talking about, that diagnosis made no sense.

  3. OK. I had this same exact problem, and it was an easy repair via the basics: a new air filter, and a new sparkplug. I think the real fix was the air filter, but the plug was somewhat fouled due to the rough running. Fix did not immediately work – took several tugs/minutes to allow a semi-flooded engine to get going. Looks to me like there is some connection between the governor mechanism and carburetor intake airflow sensing.

  4. I have a 1984 Toro model 20672 21" rear bagger mower with a Tecumseh-made TNT100 4-cycle engine, BBC (blade brake clutch) and 3-speed rear-wheel Pow-R-Drive. What would you do as to adjusting the throttle so that the tone/pitch of the engine (blade engaged) sounds like the key of G-G# (49-52 Hz)?

  5. @rbvid
    Where you added that wire is actually the choke lever to activate the Ready Start (automatic choke). Your Ready Start system must have been keeping the choke on, and adding the wire keeps the choke fully open all the time. This is ok, but when you cold start your mower, there will be no choke, so it will be hard starting.

  6. I work at a small enine shop and see this all the time

    all you need to do is clean out the carb, and if that fails you replace the bowl nut and you should be good to go

    drain the gas tank there may be water in it

  7. Thanks for comment. I took the carb apart and cleaned a few weeks back (lawnmower and snowblower). It was easier than I thought and ran great untill recently so I may try again – perhaps replacing the bowl nt?. I made video on that process and had planned to add video comment to this one but just haven't finished it yet.

  8. yes, sometimes you just cant get that bowl nut clean again, or it is worn out so you must replace it. It will run great after that just make sure you dont get any water into your gas

  9. Thanks for your video. I used this rig to get my lawnmower to start after trying everything else. I temporary taped throttle open and now starts with no problem. Thanks again.

  10. This worked for one summer then mower acted up in 2nd summer so I ended up buying a kit (gaskets, needle valve, etc.) and taking carburetor apart to clean and replace those basic parts. It was very easy and now it runs really good. Started new video but just haven't edited.

    Ethanol is really bad in these machines. I only use non-ethanol in mower and snowblower now. Had to do same thing with kit on snowblower. Local sales guy convinced me to do this, the mechanic at shop just treated me poorly.

  11. Really helpful video and well done. Short and to the point. Question… is it difficult to find ethanol free gasoline? I know that ethanol is rough on engines, and I have a farmer friend who measures the level of ethanol in any fuel he's about to put most of his farm related tools. I live in Northwest Indiana… and I've never tried to find non ethanol fuel.

  12. Thank you Roger, you just fixed my problem. I have noticed that if I pushed the lever to the left side of the mower it would work fine but as soon as I released it the mower would die. Thanks for your videos.

  13. Kudos to you for fixing it! The spring you bypassed in the video is the auto-choke spring. The spring just to the right, and perpendicular, is the governor spring (hooked up to throttle). When you bypassed the auto-choke spring, you were essentially placing the choke in a fixed position. Fixing the choke that way probably compensated for a dirty carb. Glad you have it running better after the rebuild!

  14. Finally! Thank you!…. I realize this was shared a few years ago, but somehow I'm just now coming upon your post.  All these maintenance videos and forums do nothing but shove carburetor cleaning or crankshaft maintenance down your throat– not once has anyone mentioned this to be a potential solution. I'm so glad I finally stumbled across this video.  This is the ONLY troubleshooting video that actually solved my problem.  Kudus to you for actually posting something useful and uncommon. Much appreciated.  

  15. Thank you, you fixed my mower! I did this after weeks of trying to diagnose this problem I rebuilt cleaned the carb nothing worked. The mighty paper clip fixed it!

  16. This did not fix my problem….but removing diaphragm located just below carburetor and cleaning the three holes made my Toro run like new !!

  17. Reminds me of using bailing wire to re-attach the clutch pedal to the linkage on a '67 F100 with 3 on the column, in a Dairy Queen parking lot. The wire held up for a year until I remembered to find the proper part. I love shade tree mechanics.

  18. Its a quality control issue! I don't know how can they stay on business or sell their product those foringen made mowers; well I guess like Mr Roger Bindl we need to improvise …

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