Gravely ZTR Mower - won't stay running

[runamok151]

Disconnect the fuel lines and blow them out, then check for any grass/leaves that may have fallen into the gas tank. I've been having a similar problem w/ my used Cub Cadet since I bought it. It always seemed to bog down too easily and struggle to cut anything thick or wet. It progressed until it would sputter and almost stall out. Had my mower guy go through it and he found a blade of grass had sucked down the fuel line and was acting like a flapper when the suction increased. The thing has been running like a champ since.

 

[eric67camino]

I forgot to mention the fuel shutoff valve. Many mowers have an electric solenoid that actuates a pintle to shut down fuel flow to the carb when turned off. It's in the carb, usually in the float bowl.

If it fails or has a bad connection, etc you may not be getting enough fuel flow. Or it may be intermittently shutting it off.

It's usually pretty cheap and easy to replace.

 

[diesel4me]

If you mean the anti-backfire valve/solenoid,those can cause running issues if they fail or aren't getting full voltage,or a poor ground.

Some are not cheap either though!--some cost up to 80+ bucks,so people resort to taking them out and replacing them with a short bolt,or snip off the end of the needle so it wont restrict fuel flow...this may result in a backfire when the engine is shut down,but can usually be overcome by either running it at full throttle before you shut it off,or at idle,you'll have to experiment to see what rpm makes it less likely to back fire..

Also ethanol loves to make old rubber fuel hoses come apart inside and send bits of rubber into the filter and carb,or make a lining come loose that can restrict full flow of fuel...older machines may not have ethanol resistant hoses,those are more vulnerable to this..

I've had to use a drill bit to open up rusted or corroded fuel tank outlets and shut off valves many times too..

 

[fear_nothing]

took apart the fuel lines
Blew them out
took apart the carb
cleaned liberally w/ carb cleaner
took apart the part hi-lighted below w/ the yellow arrow. This has some debris, the only found to date.

Put it back together but no change.

The anti-backfire solenoid has some credence. I've noticed it has always backfired when I shut it off.

 

[eric67camino]

I believe the part with the yellow arrow should the fuel pump. It will be vacuum operated by crankcase pressure.

 

[ktmoutfront]

I believe the part with the yellow arrow should the fuel pump. It will be vacuum operated by crankcase pressure.

Correct.

OP, did you remove the main jet from the carburetor? Physically look through it?

I never use carb cleaner. Not potent enough. Use non chlorinated brake parks cleaner.

 

[fear_nothing]

Went back through the carb this time hitting everything with non chlorinated brake cleaner. Some pictures of the ride

Complete carb

 

[fear_nothing]

Mid Disassembly

 

[fear_nothing]

Fully apart

 

[ktmoutfront]

If those jets are clean going back in, and it does not run, it is a fuel feed issue or ingnition at this point.

 

[fear_nothing]

Focus on this part, the bottom of the fuel bowl. Is this a casting flaw, should I worry about it? Reckon its causing the issue?

 

[fear_nothing]

finally a video of it running

 

[fear_nothing]

Focus on this part, the bottom of the fuel bowl. Is this a casting flaw, should I worry about it? Reckon its causing the issue?

View attachment 347175

Bumping this up - notice the casting flaw at the bottom of the float bowl. This is specifically where the anti-fuel/backfire solenoid screws in.

 

[ktmoutfront]

In the video, is that at idle, wide open or under load?

 

[diesel4me]

It is "hunting" up & down,it could be the governor needs a static adjustment...it can do this if its not getting constant fuel delivery too though..but if was starving for gas I'd think it would tend to bog or stall,not rev right up normally when it recovers..

Wouldn't hurt to spray some carb cleaner around the base gasket and any suspected vacuum leak spots on the intake to block,etc..it could have a vacuum leak..

 

[fear_nothing]

In the video, is that at idle, wide open or under load?

Wide open... towards the end of the video you can hear it struggling

 

[wasted wages]

Try rigging a small tank of gas and hose to gravity feed the carb.... if it clears up, then it's fuel delivery or ignition. If it keeps surging, then you didn't get the jets cleaned out.

Sometimes crud will form on the jets that looks like there is no hole...you have to open it back up with a wire drill bit or paper clip.

Another thing to look at is the pick up in the fuel tank itself, I had one break off inside of my grizzly 660 that drove me nuts.. after cleaning the carb several times, it would run for a day or so and then start backfiring. Turned out the pickup inside the tank had split and had almost fallen off. And after the fourth time of finding dirt in the needle and seat... I was just going to put an online filter on the fuel line.

When I pulled the tank off, I happened to look in the tank and saw the filter screen floating around in the tank. It was built into the shut off valve inside the tank.

I was thinking it was kinda strange that Yamaha didn't have any way of filtering the fuel.... live and learn!!

BTW.....suck it ethanol !!!

 

[fear_nothing]

New carb and tweaking the pickup tube did the trick. Mowed this evening without incident. Much obliged for all of the suggestions