white smoke and hesitation when going full throttle

[bostonbear]

Hello. I'm new to the small engine repair scene.

I have a John Deere L118, B&S Intek V Twin 407777-0131-E1.

I just finished replacing a broken connecting rod and damaged piston. The engine has about 280 hours on it. I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Anyway... it runs again. Seems fairly solid. I adjusted the valves and even took the carb apart and cleaned it. Idle RPM is about 1750... full throttle no load about 3100 RPM.

Here's the issue. When I go from idle/low and just slam the throttle lever to high... the engine races and or hesitates a few seconds... burps out some white smoke... and then runs fine.

Any clues? It runs fine beyond this fairly minor issue. I assumed the carb was dirty but I cleaned it out fully... no luck,

 

[bertsmobile1]

Could be a loose inlet valve guide or faulty valve stem oil seal or the head gasket is leaking.
Or some thing as simple as the rings are yet to fully bed in.
Installed wet the rings can take 50 or so hours to bed in, installed dry on a freshly honed barrelthey should bed in in 10 minutesunless you left it on low idle for extended periods.
Run the mower for 10 minutes then pull the dip stick
If whisps of white smoke come out it is a head gasket.
OTOH they are mower engines, not GP race engines so no reason to "slam" it wide open

 

[bostonbear]

I think I figured out the root cause of my original problem. Over time the gas line gets "fatigued" where it takes a right angle turn/bend near the battery on these mowers (L118). This causes it to collapse like a wet straw at times and not start. I was getting around this by blowing into the gas line whenever it happened (fairly rare). I thought it was only an issue during start. In this case I think it was not collapsing but restricting the gas flow as I pushed the throttle. I replaced the gas line and problem solved. For the record, I don't expect the mower to perform like a GP race engine... but previously it never had this behavior... so when it started having this behavior I knew something was wrong.

Having solved this issue there is still an issue after my original repair. Seems to have an issue once it gets warm. It hunts a little and makes a strange sound when not under load. I *think* the sound is a bit of a "bark" coming from the carb intake area. I see a little black puff at times when the air filter is off. I'm guessing this comes from the breather tube that is connected to the crankcase.

Any advice appreciated. I have fully cleaned the carb and replaced the needle and main gasket. No change.

 

[slomo]

Check head gaskets as was suggested by Bert.

slomo

 

[bostonbear]

Check head gaskets as was suggested by Bert.

slomo

Yeah. White smoke out the oil tube.

Does that mean I just didn't torque the head gasket enough when I fixed my connecting rod? I have a bad feeling when I put the rings on the new cylinder I lined the gaps up instead of stagger them. I'm really hoping that's not the issue. Having to bust the crank case open again would be a PITA... but I'm learning anyway.

 

[hlw49]

What do you mean didn't torque them enough. Did you not use a torque wrench and torque them to factory specs?

 

[bostonbear]

What do you mean didn't torque them enough. Did you not use a torque wrench and torque them to factory specs?

Yes I did. I guess my question is... if the torque isn't right... an the gaskets are new... what else could be the issue? Warped head? Should I do a leak down test?

 

[hlw49]

Leak down test is the best test you can do to diagnose the engine you can hear where the leak is, You will always get a leaking sound in the crankcase as you cannot seal the cylinder with rings. You can hear leaking valves and head gasket. I love leak down testers a service techs best friend.

Hello. I'm new to the small engine repair scene.

I have a John Deere L118, B&S Intek V Twin 407777-0131-E1.

I just finished replacing a broken connecting rod and damaged piston. The engine has about 280 hours on it. I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Anyway... it runs again. Seems fairly solid. I adjusted the valves and even took the carb apart and cleaned it. Idle RPM is about 1750... full throttle no load about 3100 RPM.

Here's the issue. When I go from idle/low and just slam the throttle lever to high... the engine races and or hesitates a few seconds... burps out some white smoke... and then runs fine.

Any clues? It runs fine beyond this fairly minor issue. I assumed the carb was dirty but I cleaned it out fully... no luck,

When you slam the throttle wide open you should get a slight hesitation since the carb. does not have an accelerator pump it depends on transition ports in the idle low speed circuit to do this and the transition ports can't supply the fuel the engine needs quick enough to keep up with demand.

 

[slomo]

I suspect the damage was from a mouse house on the cylinder head fins. That and probably low oil.

Cleaning the cooling fins is a YEARLY maintenance item per your engine maual. These are air cooled engines. Neglect this and you are looking at engine damage as you found out. Clean the top of the engine block too. Should see silver aluminum all over the engine.

 

[slomo]

Yes I did. I guess my question is... if the torque isn't right... an the gaskets are new... what else could be the issue? Warped head? Should I do a leak down test?

Every removed head should be checked for warpage. Get a 1/2" thick piece of plate glass from a glass shop. Not a lot of money. Take wet/dry sandpaper and level the head and block.

Torque the head in 3 steps in a criss-cross pattern. Start at 5ft lbs, 10 and 15 or what ever your max torque value is per your engine manual.