C121 engine bogging down with mower

[HorsinNC 2]

So I've got a C101 with a 121 engine swap and I have this problem that's been getting worse and I can't figure it out. It doesn't really matter if the grass is tall or short, but after a while (sometime between 15 minutes and an hour) the engine will bog down to the point of barely running with the PTO engaged. If I take the PTO it will remain bogged down for about 10 seconds and resume normal running speed. 

 

I've gone through most what I could think of and I'm not sure what's going on. The blades are sharp, I've tried loosening and tightening the belt tension, pulleys are freshly greased, I've played with the tension on the PTO lever. It's got a new air filter, fuel pump, and spark plug. Oil and transaxle fluid are in good shape. The friction disk is getting a little low, but I still have about .025" until I'm at the rivets.

 

When I first got it about 6 months ago it was running like a champ, now I get maybe 15-30 minutes of run time until the engine bogs down and I can't mow anymore. Sometimes if I let the tractor sit about an hour I can get another 5-10 minutes until the problem comes back. 

 

What do you folks think it could be?

[c-series don 12,374]

Sounds like the same thing that happened to @Dan 312-8. He had crap in the fuel tank that after driving around for a while would stick to the screen on the fuel tank valve. I believe that he ran the tank dry and then blew air back through the fuel line to clear the screen. Then when the tank was totally dry he vacuumed it out. He may chime in on this, but I’d give that a try. Either way it can’t hurt to clean the tank and screen. I’d also install a new fuel line, it could slowly be collapsing and squeezing the fuel volume. 

[Ed Kennell 47,061]

Fuel tank vent clogged ...loosen cap.

Screen in tank clogged...

 

OOPs,  that Donnie types really fast.  

Edited 4 hours ago by Ed Kennell

[ri702bill 12,879]

35 minutes ago, c-series don said:

Then when the tank was totally dry he vacuumed it out.

Hmmm... Gasoline fumes can be dangerous when collected near a sparky-sparky e-lectric motor....

[HorsinNC 2]

37 minutes ago, c-series don said:

Sounds like the same thing that happened to @Dan 312-8. He had crap in the fuel tank that after driving around for a while would stick to the screen on the fuel tank valve. I believe that he ran the tank dry and then blew air back through the fuel line to clear the screen. Then when the tank was totally dry he vacuumed it out. He may chime in on this, but I’d give that a try. Either way it can’t hurt to clean the tank and screen. I’d also install a new fuel line, it could slowly be collapsing and squeezing the fuel volume. 

 

It's got new fuel lines when I installed a new fuel pump and filter. Why would that only affect the engine while the PTO is running and resume normal operation when it's pulled off? I'll take another look, but I don't think the tank has a screen. It just goes straight to the petcock and down into the new fuel filter and pump

Edited 4 hours ago by HorsinNC

[adsm08 5,049]

2 minutes ago, HorsinNC said:

 

It's got new fuel lines when I installed a new fuel pump and filter. Why would that only affect the engine while the PTO is running and resume normal operation when it's pulled off? I'll take another look, but I don't think the tank has a screen. It just goes straight to the petcock and down into the new fuel filter and pump

 

Engine load. More load needs more fuel. A fuel restriction may only show up under max load.

[HorsinNC 2]

38 minutes ago, Ed Kennell said:

Fuel tank vent clogged ...loosen cap.

Screen in tank clogged...

 

OOPs,  that Donnie types really fast.  

It's got a new cap from wherlhorsepartsandmore, I can try to loosen it next time I'm running it

[HorsinNC 2]

2 minutes ago, adsm08 said:

 

Engine load. More load needs more fuel. A fuel restriction may only show up under max load.

I've got a 2.5-4.5 psi fuel pump on it, it looks like it's getting plenty of fuel

[peter lena 10,024]

 @ Horsin NC  ,  ever check out the hand moved pto  to mule belt movement  ease ?  regularly see  and hear  , screaming  clutch  disc engagement  , on  mowers ?  would bet  there are a number of  failed bearings involved , there are  12 involved , frayed  related belts tell the story , cracked , spilt , from  bad  bearings . pete  

[Dan 312-8 610]

22 minutes ago, ri702bill said:

Hmmm... Gasoline fumes can be dangerous when collected near a sparky-sparky e-lectric motor....

Well @c-series donwas close. I did remove the tank, drained it, blew it out with compressed air and then I set my air compressor regulator to about 5#, and let the air tank deplete while running air into the gas tank, the I baked it in the summer sun for hours, blew it out again and then replaced the grommet and shutoff valve, replaced the fuel line to the filter and the filter. Has been running like a top ever since.

[kpinnc 18,916]

Glad you found the problem. Be sure to put up pictures of your machine. 

Edited 3 hours ago by kpinnc

[HorsinNC 2]

10 minutes ago, Dan 312-8 said:

Well @c-series donwas close. I did remove the tank, drained it, blew it out with compressed air and then I set my air compressor regulator to about 5#, and let the air tank deplete while running air into the gas tank, the I baked it in the summer sun for hours, blew it out again and then replaced the grommet and shutoff valve, replaced the fuel line to the filter and the filter. Has been running like a top ever since.

I haven't replaced the petcock yet, maybe I could try that, but the grommet fuel line, glass bowl fuel filter, and fuel pump are all new on mine

[HorsinNC 2]

25 minutes ago, peter lena said:

 @ Horsin NC  ,  ever check out the hand moved pto  to mule belt movement  ease ?  regularly see  and hear  , screaming  clutch  disc engagement  , on  mowers ?  would bet  there are a number of  failed bearings involved , there are  12 involved , frayed  related belts tell the story , cracked , spilt , from  bad  bearings . pete  

The belt is on my list of things to replace. It's got a little fray from when a stick caught it. I haven't replaced the bearings yet, but I did regrease the ones in the PTO bell a week ago trying to solve the issue

Edited 3 hours ago by HorsinNC

[Ed Kennell 47,061]

Just remove the fuel line at the petcock.   You should see a full 1/4" diameter stream of fuel.   I've bought some non running tractors for cheap that had petcocks completely blocked.

They had new carbs, fuel pumps, fuel lines, and filters, but the fuel was never leaving the tank.