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.

 

[jaxs]

"Any advice would be gratefully appreciated."

#1 Unless you are female,in which case I understand,try to be less wordy and stick with relivent info.
#2 Always look at these things with logic before acting. Logic tell's us it's probably related to removing final drive and the only switch that kill's engine is the reversing safty switch. Check your diagram for reversing switch circuit. You might even try activating the over-ride to see if that make's a difference.

 

[TractorGuy]

Since you had the deck off make sure you reconnected the linkage or cable that releases the spindle brakes when you engage the mower. You can check that with the engine off.

 

[Hefner]

Here's an up date - I've tested all the switches ( 6 in total) and they all seem to be working fine. I kept trying to engage the blades after each test but no joy. Then the engine would not start! I then notice what seems to be a mixture of oil and petrol dripping out of the muffler. I then took the valve the cover and that was full of oil. I then took the spark plug out and lots of petrol came out through the spark plug hole.

Does anyone know the engine is now full of gas and the valve cover also full of oil. When I took the valve cover off a few weeks for the first in 9 years there was no oil in there.

Once I get the engine running I will remove the kill wire and see what happens.


Thanks.

 

[TractorGuy]

Fuel shutoff solenoid has failed and filled sump with gas.

You can probably find a whole new carb with a solenoid for the same price or cheaper.

 

[RandyT]

Fuel shutoff solenoid has failed and filled sump with gas.

You can probably find a whole new carb with a solenoid for the same price or cheaper.

Fuel solenoid didn't fail. the float valve isn't closing off the fuel flow and overfilled the carb and either ran down the intake into the cylinder and past the rings or into the breather tube into the crankcase. Contrary to what a lot of people think the fuel solenoid on the carb doesn't control fuel flow into the carb. It just helps prevent the after fire bang at shutoff by preventing fuel from entering the high speed jet of the carb. It will not prevent fuel from overflowing into the carb through the vents.

 

[Hefner]

Thanks Tractorguy. Luckily I had a spare carb so just changed it over. Drained all the oil and and refilled and engine started again.

I have now disconnected the kill wire and engine started and when I engaged the blades the engine did not shut down. I presume that this means it is a definitely an electrical problem. As all the switches seem to be working I'm at a complete loss to understand what could be causing the problem. I have checked all the other electrical connections and they seem fine and I cannot see any bare cables that my causing the engine to ground.

 

[ROUSTABOUT]

Fuel shutoff solenoid has failed and filled sump with gas.

You can probably find a whole new carb with a solenoid for the same price or cheaper.

If he hasn't bent a rod.

 

[Hefner]

i appear to have sorted the issue. I have no disconnected the bagger switch and everything works fine.