1969 Cub Lo Boy 154

[Submariner768]

Got a couple of questions, but I will start with this one. Engine starts and runs smoothly. Tractor goes through all the gears and PTO engages smoothly. The issue that I'm trying to figure out is when the blades are spinning, the engine dies very quickly when I try to mow grass. Where should I start looking?

[staninlowerAL]

Does the engine stop at any other times other than when the mower is in use? Assuming your description takes place with the throttle full open? Does it happen when you begin to engage the mower or after the mower has reached its operating rpm? When was the last full tuneup to include adjustment of the valves? A compression test will give some indication of the engine condition.

[toehead]

Also wondering if the governor is free.

[Eugene]

Compression tests with complete tune up.

[outdoors4evr]

Three things come to mind. Perhaps more detail is needed about how it behaves as it is dying.
Assumption on my part: Tractor is running full throttle with PTO Engaged and blades spinning. Lower hydraulics and drive from short mowed grass into taller not yet mowed grass on a lawn. (we aren't talking 6"-12" tall grass here are we?)
1) A change in load occurs and the RPM's drop down because the governor is not detecting the change in RPM and opening the throttle to compensate. This would indicate an issue with the governor, or the linkage between the governor and the carburetor. Check the linkage first. There is a keyway that gets worn at the governor. Clean and fill with JB Weld. Look on this site for a How-To. If this is not the issue, then the governor weights are not moving so the governor is not functioning properly. Remove, clean, and lubricate or fix the governor.

2) Engine is running lean at wide open throttle (High Idle). The Carburetor Main Jet needs to be cleaned, or the screens in the fuel lines need to be cleaned. Carefully clean out the carb jet with a small soft copper wire. Clean the screen on the fuel inlet to the carburetor. Clean the screen on the water separator bowl under the gas tank.

3) A change load occurs and the engine stumbles and cuts out, then dies. Need to check to see if the same situation occurs when you have the blades turning and move the throttle from a low to high idle. This is an improper air mixture adjustment on the carb. (screw on the top of the carb)
Side Note: An improper timing advance can exasperate this. Verify that the timing advances from 0-15 degrees between low idle and high idle. If not advancing, Remove, clean, and lubricate or fix the distributor weights. They work like the governor weights.

[Submariner768]

Thank you all! This happens as I'm driving from a no load condition, like pavement, into grass that needs to be mowed. Engine loses rpm and stalls almost immediately.

[mozer71]

Every previous suggestion was from guys who really know this machine. You have to act on these, maybe one at a time. The governor is very important at the beginning and at the end. I wouldn't start messing with it except lubing and following linkages. If there is huge play in the throttle shaft clearance, that disturbs things but I stuffed an O ring around that temporarily. Every other suggestion makes an increase of power and you will see it.