Help required - engine cuts out as soon as I try to engage cutting blades

[Hefner]

I’ve been reading this forum during the pandemic and it has given me the confidence to do some work on my lawn tractor that I would not otherwise have done.

I have a McCulloch lawn tractor M155 107HRB (model 96051005100) made in 2012. It essentially a Husqvarna. It has a Briggs Intek 15.5hp engine. I change the engine oil, spark plug etc. every year and it has always run well. The tractor hadn’t been used for a couple of years but having charged the battery it started first time a couple of weeks ago.

I then decided to change the oil on the Torq Tuff K46 transmission having read how to do it in this forum. It was a nightmare getting the transaxle off the mower and when I was putting the transaxle back on the mower fell on the jack and hit the garage floor with a bit of thud.

Anyway everything seemed fine and I started the engine and took it for a small drive with the cutting deck off. No problem going forward or backwards and no loss of power as a result of the oil change.

I then put the cutting deck on to start cutting the grass and as soon I try and engage the lever for the lever for the cutting blades the engine immediately dies. I only have to move the lever a couple of inches before the engine dies. I have tried seeing if it will work using low, medium and high revs but the engine still dies immediately.

I have greased the spindle bearings and the blades are running freely. I also checked the carb, which was surprisingly very clean.

I think the problem must be an electrical issue. I live in the middle of nowhere so I cannot take it to a shop to be looked at. It driving me mad trying to sort the problem and I need to cut the grass!!

Can anyone offer any advice on whether it’s electrical problem and whether it likely to be an issue with a safety switch. It seems to have lots of safety switches some of which appear very hard to access! Here is a link to the McCulloch website where the electrical schematic can be seen. User Manuals | Official McCulloch Website

Any advice would be gratefully appreciated.

 

[K5lwq]

I would look closely at the seat safety switch. If it is not completing the circuit I believe you would have the symptoms you described.

 

[Slowpoke Slim]

I would look closely at the seat safety switch. If it is not completing the circuit I believe you would have the symptoms you described.

I'm thinking the same thing. From what you describe Hefner, I would be looking at a safety or interlock switch. Either a seat switch, or an interlock switch that prevents the mower from mowing in reverse?

 

[rjpotts]

Any advice would be gratefully appreciated.

If a stuck pulley or faulty safety switch aren't the cause it may be lack of engine power. If it uses an electric clutch demand on the engine is almost instantaneous, it's enough to stall an engine if there isn't enough power to overcome it.

 

[5030]

Carb gunked up with crud gas from sitting 2 years maybe?

 

[Roadworthy]

Check the reverse safety switch. Normally, if you're mowing and decide to reverse, the tractor will die unless you intentionally go through some override sequence. Your tractor may "think" your gear selector is in reverse.

 

[Hefner]

Thanks for the replies. I have taken the seat safety switch off and tested it with a multimeter. Without the seat button being pressed down there is continuity when I touch the prongs at both ends of the switch and also when touching the the two middle prongs. See photo attached. When the seat button is pressed down there is no continuity at all. Does this mean that the seat switch is faulty?

I have checked the carb. When I last used the mower two years ago I drained all the petrol and turned the engine until there was no fuel left in the carb. When I took the carb off a couple of days ago it was a clean as a whistle.

 

[Brotherdan]

Try it with the gas cap removed. If it goes away your cap vent is clogged and your tank draws vacuum when the pto engages.

 

[grsthegreat]

Thanks for the replies. I have taken the seat safety switch off and tested it with a multimeter. Without the seat button being pressed down there is continuity when I touch the prongs at both ends of the switch and also when touching the the two middle prongs. See photo attached. When the seat button is pressed down there is no continuity at all. Does this mean that the seat switch is faulty?

I have checked the carb. When I last used the mower two years ago I drained all the petrol and turned the engine until there was no fuel left in the carb. When I took the carb off a couple of days ago it was a clean as a whistle.

i am not sure if that particular machine uses a normally open or normally closed switch, but my guess its working correctly. most of those switches close contacts when nothing is on it thus grounding out ignition system. when pressed with weight, the system opens and allows ignition system operation..

 

[Popgadget]

Remove the kill wire from the engine, and see if it keeps running. That will confirm that it’s an electrical interface issue. You should connect a wire to the ignition terminal on the engine that you can manually ground to stop the engine at the end of the test. Just be aware that this will bybass all safety interlocks and make absolutely sure that you and and anyone else is clear of any moving parts.