FR691V 24 HP surges and dies under load and or when hot

168 hours on it. Husqvarna tractor.

It started out not too bad but has progressed to be unusable. At first I thought it was out of fuel. It would surge like it does and usually that is my cue to cut the blades off and book it towards the garage. That time it wasn't out of fuel. So I replaced the fuel filter and air filter. Still continued to get worse. I then replaced the fuel pump next, but very little change immediately, then eventually went back to progressing to be worse (shorter time after startup before the trouble started and shorter time I could mow at full power before I have to stop and let it cool I assume). I then took the carb off and inspected and cleaned it. No change again. Next up was plugs, no change with new plugs and the NKG's I installed a couple years ago looked good when I pulled them out. Next up was both coils. This made a small improvement for 20 minutes or so, then back on track of getting worse. I have since pulled one of the new coils off to check things out and it pulled the connector off the plug wire, so I am back to one new coil and one old. No difference, but getting worse.

I still in my mind cannot determine if it is actually starving for fuel as it seems or if it is getting hot and other potentially electrical issues are showing up. I can sit (usually turn the blades off and throttle down a bit) for a couple of minutes and get a bit of mowing time in. When it is acting up the governor arm is fluctuating quite a bit. I don't understand exactly how that works or why exactly it is needed either.

Any more ideas? I have made sure the gas cap is on and tightened until it clicks a few times. I haven't replaced fuel lines as it will run strong for a bit. I don't think I have any blockage, it is a heat related issue it seems.

Something most folks never consider is the fuel hose has braided nylon string in the middle of the hose. The hose can feel strong, not soft spots anywhere on it's entire length. However, a fuel hose can have a small spot anywhere on the inside that turned loose from the nylon braid and become a valve. Have found that in several units over the years and more usual in an automobile than a mower, tractor or other small engine type units. However, it does happen from time to time.

Really only way to check for that is to install a new lime temporarily to test and if this resolves the issue, guess what. Thread the hose into the unit properly, support it properly, secure it properly and go back to mowing.

You may also have some trash in the bottom of the fuel tank or a fuel filler cap that isn't venting properly. Loosen the fuel filler cap and operate the unit. If the problem goes away, replace the cap or repair the vent or gasket for the filler cap.

Good luck,

Max