B&S 25 HP Twin ELS cuts out pointing uphill

[rwoltner]

Hi all, first post here, hope you can help.

Problem: 2001 Craftsman tractor with 25 HP Twin ELS engine runs fine most of the time. However, if I am doing a lot of work with the tractor pointing uphill (like dragging the driveway-300 ft mild uphill grade) the engine will start to miss and may cut out before I get to the top. Or, if I am mowing and I stay pointing uphill too long, it will miss. If I get pointed down hill quickly, the engine will recover. Engine starts and runs great on level ground. Engine RPMs increase when I engage the mower.

I have done/replaced the following:
New carb
New fuel pump
New fuel filter
New Air filter
New plugs
All new fuel lines
New pulse line for fuel pump
Removed and cleaned fuel tank
New valve cover gaskets
Used fresh gas
Adjusted valves to .004
Checked gas cap vent and tried running with cap loose
Changed oil and filter
Removed cooling shroud and thoroughly cleaned engine exterior
Used compressed air in fuel line from filter to tank

What is causing this uphill only condition??? I am out of ideas.

Thanks in advance

 

[Fish]

Just for testing purposes, take it out again, and head uphill, and when it starts to miss slowly pull out the choke know while still moving and see if the running improves or what.

 

[rwoltner]

Sometimes I can nurse it by modulating the choke, say 1/4 choke, but after 30 secs or so it will start to miss at that setting. Only real cure it to get it to level ground for a spell.

 

[rwoltner]

Some additional information...

This tractor has been used year round since I bought new in 2001, probably well over 200 hours a year. On some weekends, I may run it for 5 or 6 hours almost constantly (small breaks). So it most likely has over 2500 hours.

I am running straight 30 weight oil and the new oil filter is a genuine B&S filter.

 

[Fish]

Is the tank under the seat or behind the engine?

 

[rwoltner]

Under seat. Tank has been pulled, drained and cleaned. New fuel lines all way to the carb. Condition will happen even with full tank. 4 gallon tank.

 

[Fish]

Just for test purposes, run with the "kill" wires disconnected from the coils, and see if anything changes.

 

[rwoltner]

Just came in from mowing the front yard and made the following observations.....

Engine was cold to touch when I started. Ran fine for first 15 minutes in all orientations, then it started in with the uphill issues. I could nurse it with choke to a level area and idle for a minute then was good to go for a few rounds. Eventually I couldn't nurse it and it died completely. I pulled the hood and the carb was too hot to touch. Let it sit for 5 minutes and it restarted fine, no choke.

At this point I am thinking excessive heat and, duh, it is probably my fault.

Last year, one of the "wings" on the heat shield/dissipater for the muffler/exhaust broke off. I removed the shield with the intention of getting it welded. Well, as we all know, one thing leads to another and this got put of to the point of where I lost the wing, so I intended to order a replacement next time I ordered parts. As of right now, the shield is still off the tractor.

So, my question is...
Do you think that a carb could overheat enough to the point where the float would not move freely enough in some directions? I have never torn down this type of carb so I am not familiar with the swing direction of the float. As soon as things cool off enough I going to re-install what I have of the heat shield. The mounting bolts also retain the muffler so they are very hot.

After I install the shield, I still have enough work to do to give it a good test.

Fish,
I really appreciate the attention and suggestions you have provided.

 

[Fish]

Well the added info might mean a lot. Remove the hood and leave it off. Also, just for test purposes, take some aluminum foil and make a baffle to lay over the exhaust, and lock it down as best you can, then test.

 

[Fish]

the extra heat, and upward angle, with that heat collecting from the missing part, may allow a bunch of heat to collect up around the carb, and eventually make the fuel boil, or it may put extra heat on the valves and make them expand more, but this may be what you were lookin for. Leave the hood off for starters, but try and channel that heat away too.