Bobcat 553 engine speed control linkage

shakey jake · Jan 1, 2014

I have a Bobcat 553 that I got used. It has the Kubota 3 cylinder engine. I noticed that when I have the engine speed control lever all the way forward to the fast position, the linkage is not all the way to the stop on the engine. If I push the linkage to the stop with my finger, the RPM's increase (just going by ear, it doesn't have a tach). Should the linkage be adjusted so that it hits the stop screw? Should it be set by RPM? It seems like I may be missing some power due to a misadjusted cable, but I don't want to blindly adjust it and blow up my engine. Here is a picture of the linkage on the engine. The part where the linkage attaches to the arm moves up in the picture when speed is increased. The picture was taken with the speed lever all the way to fast, but as you can see it's not touching the stop.

SSdoxie · Jan 1, 2014

In the picture, the original assembly wires that go through head of the stop bolt and the jamb nut are missing, so without taking engine RPM readings there is no way to tell if the stop bolt is in correct position or had been moved. Increasing engine RPM probably won't hurt the engine, the greater risk in over-speed off the hydrostatic pump. Pump rotation speed should not exceed 3000 RPM.
Another thing to check, and should check first, is the friction washer tension in the hand throttle. When the washer gets worn & loose, it will go to full stoke up against the stop but then spring tension in the throttle plate pushes the throttle lever back a little bit.

shakey jake · Jan 2, 2014

Thanks Dennis. I'll check that friction washer and I think I'll get one of those cheap photo tach's and set the stop at a little less than 3000 RPM, then safety wire it.

Thanks again.

shakey jake · Jan 12, 2014

Just to close the loop on this thread, I have adjusted the speed control linkage on the Bobcat. I noticed that, when I had the speed control lever all the way forward, the lever on the injector pump didn't make it all the way to it's high speed stop. Per SSdoxie above, you shouldn't run the hydrostatic pump at more than 3000 RPM, so I ordered one of those cheap laser 'photo-tach's' so I could take some measurements. They're only about $15 on Amazon, iirc. Then I removed the belt cover from the back of the engine (what a pain in the butt that was) so I could apply the reflective tape, which comes with the photo-tach, to the crankshaft pulley. Turns out it was running at about 2700 RPM with the speed control lever full forward, but if you pushed the link on the injector pump to the high stop it would easily exceed 3000 RPM. I adjusted the stop down to the point that it prevented the engine from exceeding about 2955 RPM, and then I adjusted the linkage so that it went to the high stop when the lever was full forward. I don't know yet if I will feel any noticeable benefit from the extra 250 RPM when operating the Bobcat, but at least I know that I won't over-speed the pump. After using it a bit I will re-test and if nothing changed I will safety wire the stop screws.