[smokemangrp]

JD LA145 Mower Won’t Idle, Revs High

I have a 2010 LA145 with a Briggs & Stratton OHV v-twin 22 gross HP and 81 hours. Once the engine warms up it runs at full RPM and will not idle regardless where the throttle lever is. It will idle properly when I first start it.

Referencing the attached JD “Choke, Throttle and Speed Control Linkage” parts diagram the throttle link (#4) connects directly to the carb throttle shaft and the governor control lever (#10). With the engine off the governor spring (#5) pulls the throttle link down, which holds the throttle wide open. When the engine starts something inside the engine controls the governor gear (#17) which is connected to the bottom of the governor control lever (#10) and pushes the throttle link up, expanding the governor spring, and allows the throttle shaft to rest against the idle screw.

After the engine warms up for 1 – 2 minutes, the RPM’s begin to climb until it is running at full throttle. When this occurs the gap between the throttle shaft and idle screw is very narrow, maybe a heavy 1/16” but it is enough to cause the engine to race. If I lift up the throttle link it returns to idle but only for a few seconds before the RPM’s rise again.

For some reason, JD designed the linkage to open the throttle shaft 100% when the engine is off but the mechanism that controls the governor gear and is supposed to stretch the governor spring is not doing an adequate job when the engine warms up.

I removed the governor spring (#5) and it idles better but still increases the RPM randomly, just not as high. I replaced the spring and maybe it’s my imagination but I swear it now has an even higher RPM at full throttle.

I noticed that the shaft from the engine that the governor control lever bolts onto looks smooth, no teeth. Maybe the governor control lever slipped on the shaft?

Any ideas????

 

[ryanpf]

Re: JD LA145 Mower Won’t Idle, Revs High

You are correct. The throttle plate will be wide open at slow idle position when the engine is static. The adjust of the idle tang is supposed to correct this, but was not done on my L120 as delivered. I suspect it isn't done for a reason. JD didn't design the B&S Intec, B&S did, so wide open at idle position is their choice. The full adjustment procedures are in the 2002 L series manual here:
http://www.mytractorforum.com/showthread.php?t=23974

And, yes, you are correct on how the governor works. Look at my avatar picture. The small gear riding against and below the large valve timing gear is the governor assembly. At speed, two flyweights open and depress a rod onto the shaft's lever show below. That's the lower half of your engine with the front toward the left.

As the engine speed increases the rod presses harder on the lever and applies torque to the governor arm which passes to the outside of the engine. Under normal conditions, the governor will maintain engine speed to +/- 200 rpm from desired settings. That's when the downward pressure from the rod just balances the spring tension from the two springs (#'s 5&7 in your diagram) As engine speed increases, the governor assy. presses down harder, tending to lift the governor arm on the outside and close the throttle. If your engine was working correctly, you could press down on the throttle lever at the top of the carb air horn and RPM's would increase. You would feel the (really heavy!) pressure the governor presses back with, trying to keep the engine at slow idle. It's impressive…

Yes, the lever may have loosened on the shaft, but I haven't seen it happen before. There's always a first time. The full adjustment procedures are in the manual, but IIRC there is an error in that section. I'd have to read through it again and see where it is, but I believe one of the shaft rotations is backward.

What's confusing me is that you say it works when cool, but fails when warmed up. Perhaps the clamp IS slightly loose on the shaft and when it warms up, begins to slip on the shaft. Look to see if the clamp is loose on the shaft. Good luck.

HTH,
Paul

 

[smokemangrp]

Re: JD LA145 Mower Won’t Idle, Revs High

Hey Paul,

You just saved me a chuck of change. The nut & bolt holding the lever on the shaft was very tight but evidentially the shaft had slipped. I followed the adjustment procedures in the manual and the engine now idles properly.

Actually, I followed the instructions but the engine instantly began to rev thru the roof. I immediately shut it down then remembered your comment “IIRC there is an error in that section …. I believe one of the shaft rotations is backward”. What a memory you have!!! Page 114, para 5 states to “rotate governor shaft (C) counterclockwise” but it should read “clockwise”. I wonder how many folks have damaged their engines by following the erroneous procedure. After correcting it I realized that if rotated counterclockwise, the governor is locked full open; the linkage has zero travel.

Thanks again for taking the time to answer my post, I truly appreciate it. I owe you a couple of cold ones ……

Greg

 

[ryanpf]

Re: JD LA145 Mower Won’t Idle, Revs High

:thThumbsU

Way to go!!! It's a great feeling to fix it yourself.

And after you described the manual error, it all sounded familiar.

Enjoy your LA145,
Paul