OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Quantum XM50 stuck at full throttle at all times.

Another annoying little issue that needs fixing with my mower. I remember last year sometime I must have hit the side of the throttle linkage and it bent slightly.

Now ever since this happened the mower will only run at full throttle, if I adjust the throttle control on the mower nothing happenes (I can see the throttle move at the mower end), though when I close it completly the mower shuts off as it should.

It also seems to be reving higher then it should.

It is probably hard to diagnose without a picture, so I will take a photo tomorrow.

Thanks

It sounds as if you have bent part of the governor, which is a tin plate with a spring and link on it, mounted on top of the carburetor. Most times when this happens it is just the tin mounting plate that is bent, but usually that makes it run slowly, so you may have bent something else. A picture should clarify it. From your description the linkage is simply jammed between where the speed control cable (bowden cable) attaches to the moving link, and the throttle butterfly lever where it comes out of the top of the carburetor. I suggest you give us a picture rather than bending things though - six faults are harder to fix than one.

Here is a picture, sorry for the delay.

Can we see it with the speed control at both ends of its movement, please (fast and slow), and can you show a bit higher up, so we can see the anchor point of the top link that runs out of the picture? The spring is completely slack, but the throttle is slightly open.

When you move the speed control, it has to move the bottom of the spring upward and downward, by quite a lot. However in your picture it looks as if the bottom of the spring is directly above the pivot of the bell-crank, which is impossible since that would mean the spring was not stretched when you change the speed setting.

yeah I will take a few more photos tomorrow, but you are right the spring does nothing at all when I change speed settings. It is always in the relaxed position.

If I look through the air cleaner housing not even the throttle butterfly will move when I change settings. However it will move if I manually move the goverenor part.

I hope the next pics will show us whether the lower attachment point of the spring is actually right above the pivot of the bell-crank it is on, so the spring's lower point does not move when you change the speed setting. If that is the case, the bell-crank seems to have become very badly bent - perhaps it used to be bent the other way, to the left instead of to the right, so the spring attachment is way to the left of the pivot. Anyway, let's see the pics and maybe we can work it out from first principles. Otherwise, someone else with a Quantum might post a picture of his governor, and we can go straight to the answer instead of working out the design of the governor linkage from scratch.

Throttle Open:



Throttle Closed:



Spring Attachment Point:



Now this last pic, I think this could be the problem, I reckon it should be straight instead of it being bent 90 degrees like it is currently, but I may be wrong?

Something is wrong there, as in both photos with the throttle open and closed the carb linkage has no pressure on it from the govenor spring, I will look again at the photos tomorrow when I have a fresh set of eyes lol

I don't know what piece you are referring to as being bent 90 degrees in the last picture. Like Joe, I believe the governor can't work the way it is currently set up. If you look at the bell crank the governor spring attaches to, the spring's attachment point is directly above the crank's pivot, so when you move the speed control, the end of the spring does not move. This can't work - the whole purpose of that bell crank is to stretch the spring when you move the speed control toward higher speed. The rest of the governor mechanism, which you can't see, pulls the throttle the other way, toward closed, when the engine goes faster. Most likely the part of the bell crank that the spring attaches to, is badly bent. There seems to be a 45 degree kink in it halfway between the spring attachment point, and where it bends back into the flat plane of the body of the bell crank, where the pivot is.




I suspect that 45 degree kink should be much less, possibly zero degrees.

There may be something else wrong as well, though. If you partly straighten that kink, the spring will stretch as intended when you advance the speed control, but I do not see why it is overspeeding at present, with the spring permanently relaxed. If the rest of the governor mechanism is pushing the throttle closed as intended, the way it is right now should result in it just idling all the time, so I'm missing something - maybe a stuck link somewhere.

Ok, I tried straightening out that kink and still no change, didn't make any noticible changes.

Then I noticed something. When the mower is in start position with the governor wide open and then when I go to start it as soon as the engine is running the governor goes back to the closed position and when I go to change the throttle control nothing happens.

I have to manually move the governor just like the way an accelerator of a car works. It's like there is some vacuum assist or something holding it back.

Then I noticed there are two extra holes around the linkage setup, maybe it needs an additional spring?

Really need a photo of someone elses quantum50 to confirm.

Hopefully i'm one step closer.

Thanks

I'm not clear on what is happening now victa. Does the spring now stretch when you set the speed control higher than idle, and contract when you set it to idle? If so, progress seems to have been made, and the next issue is a broken governor. I seem to recall that the Quantum has the governor mechanism inside the crankcase, instead of having an air vane inside the cowl like previous B&S engines. Joe Carroll is the Quantum man, and can fill us in on that.

If you can post new pics with the speed control in min and max, and tell us something about what the governor link is doing, we can move on to that second fault. In most cases the governor link (the heavy wire connecting to the throttle butterfly) should move freely back and forth when the engine is not running, and when it is running, it should push the throttle toward closed, and push harder when the engine runs faster.

Sorry for the late reply, have had a busy week and didn't have another chance to have a play with it until now.

Anyway it seems to be a bit tempremental, the other day I cut the lawn with it and it was running at full speed but as usual couldn't adjust the speed.

Now today I went to start it and it's doing the exact opposite, it's running at idle.

The spring did seem to be working fine the other day but now it's not doing anything. But if I manually hold the governor it does stretch a little.

The governor link has no movement in the mix & max positions.

With the engine running, I can manually move the governor linkage and it does alter the revs between idle and full throttle.

It has me stumped at the moment.

victa, I think we need new pictures of the governor plate and linkage now that you have adjusted the link. These should show both maximum speed and minimum speed. We also need to know the answers to the questions in my previous post.

Whats meant to happen is that the throttle when closed should have nearly no tension on the spring.

When the throttle is open the spring should have tension, how much tension is directly related to RPM. The end where the spring is anchored to the bellcrank is the fixed end. The end that goes into the govenor rod end is the fighting end, the throw of the govenor and the tension on the spring move the throttle butterfly to maintain constant RPM. How tight the spring is relates to how high the RPM.


So whats needed is some creative bending of that tab on the bellcrank. It can be a pain on those motors, like was mentioned the arc of movement you get bending it sets it over the bellcranks pivot point. A bit of a Z bend can help. Ive had trouble with some of those Quantum motors. They dont idle very low, especially if fitted with a brake handle. The arc of the spring attachement point does not vary much in distance from the loop in the govenor rod.

Looking at the picture i would say that the spring anchor point needs to be bent around to at least 90 degrees. Then it will be pulling on the spring. When the throttle is shut off, it will be moving the right way.

Bob.