Engine doesn't want to run. Craftsman 21HP 46" cut, Model 91728852, engine B&S Platinum 331977

[charleneje]

I have replaced three head gaskets the one I just put on is a solid copper gasket I made sure the head is flat by sanding on a sheet of glass sitting on the bed of my table saw to make sure I was sanding on a true flat surface and kept checking it with a machinists straight edge. Now the engine doesn't want to run everything was put together properly and to spec., when I started it up it didn't want to run except with the choke on so I kept it running that way wanting the engine to reach running temperature so I can retorque the head bolts tomorrow. I replaced the carburetor with a new one but it made no difference, so I took the gas tank of emptied it and made sure the fuel pickup was clear and then replaced the fuel line along with a new cut of valve and a new filter. Filled the tank and started it again and still would only run with choke on I did notice the exhaust pipe from engine to muffler went red hot the full length of the pipe, making me wonder if there could be a blockage in the muffler but it was still as loud as normal. Can someone please give me a route to take to fix this mower I bought it new March 2014 and it has done nothing but break down ever since during the first 90 days that I owned it Sears sent repair technician out four times to fix problems with the drive and other body problems with it and since then I have had to repair different problems with it several times each year. Late last year I gave up with it and just parked it and used an old MTD mower I had intended selling once I bought the new Craftsman but decided to keep it for a while because of the constant breakdowns of the new Craftsman. Thanks I just know I am going to get lots of good advice.

 

[bertsmobile1]

If the copper gasket was annealed so it was full soft then no need to retorque
The test for full soft is to roll your thumbnail on the gasket.
If it makes a crescent shaped indentation then it is full soft .
Double check your valve lash and that you have the right pushrods on the right cam followers
Turn the engine over slowly and watch the valves moving with respect to the piston position & the position of the magnet on the flywheel.
The magnet should be aproximately 1/2 way past the coil legs when the piston is at top dead centre .
Sounds to me like the exhaust valve is not closing fully .

You would not be the first person to set the valve lash on the exhaust stroke & not the firing stroke

 

[StarTech]

With you having to run on choke tells me you have carburetor problems.

As for the valve adjustment note that the exhaust valve is the one closest to the flywheel and is set .005-.007" where the intake is at .003-.005"

As for all the problem you had we don't what kind operator you are. I got one customer right now that broke his two mowers numerous times this year. Most are from his operating the mowers in an area that he should be using a tractor with bushhog type rotary mower. Just in the last three months he broken two spindles, bent 4 blades, rip out the steering both mowers, plus had both camshafts to fail which took out the governors. I got the last mower nearly ready but I had remove a belt retainer for his other mower so that now got to be replaced. Boy do I hate that NZTR steering Husqvarna keep sending parts that I got to re-bend to set the toe right.

 

[charleneje]

With you having to run on choke tells me you have carburetor problems.

As for the valve adjustment note that the exhaust valve is the one closest to the flywheel and is set .005-.007" where the intake is at .003-.005"

As for all the problem you had we don't what kind operator you are. I got one customer right now that broke his two mowers numerous times this year. Most are from his operating the mowers in an area that he should be using a tractor with bushhog type rotary mower. Just in the last three months he broken two spindles, bent 4 blades, rip out the steering both mowers, plus had both camshafts to fail which took out the governors. I got the last mower nearly ready but I had remove a belt retainer for his other mower so that now got to be replaced. Boy do I hate that NZTR steering Husqvarna keep sending parts that I got to re-bend to set the toe right.

I already thought of carburetor and after it started the first time only running on the choke was when I changed out the carburetor for a new one and it made no difference I then cleaned out the tank and replaced the fuel lines. I set the valve clearances just as you described above I am going to recheck them after I retorque the head bolts. This is exactly how it was running before I replaced the head gasket this time, which is also why I replaced it the previous time, the first time I replaced the head gasket it was blowing oil out of the breather and the head gasket was blown where they always blow cylinder to pushrod cavity. The mower had been running badly for a good year before I realized the head gasket was blown and it was from watching U-Tube videos that put me on the track to change the head gasket in the first place. I have lived on my property since I cleared it in 1983 so it is clear of any kind of brush or anything similar occasionally I might hit a small twig but thats all I am not particularly hard on my mowers except if they have been broken down for a week or more and the grass is high and then I cut it on the highest setting initially and then on my usual setting. Thanks for your advice I will be checking what has been suggested

 

[StarTech]

Then question is did you put on an OEM carburetor or Chinese clone? I recently had the displeasure having with a Chinese clone carburetor on the 331877-2371-G5 where it would only run on choke. I ended having resize the Nikki clone idle mixture jet to get it to run right.

 

[slomo]

With you having to run on choke tells me you have carburetor problems.

agree

 

[charleneje]

If the copper gasket was annealed so it was full soft then no need to retorque
The test for full soft is to roll your thumbnail on the gasket.
If it makes a crescent shaped indentation then it is full soft .
Double check your valve lash and that you have the right pushrods on the right cam followers
Turn the engine over slowly and watch the valves moving with respect to the piston position & the position of the magnet on the flywheel.
The magnet should be aproximately 1/2 way past the coil legs when the piston is at top dead centre .
Sounds to me like the exhaust valve is not closing fully .

You would not be the first person to set the valve lash on the exhaust stroke & not the firing stroke

The head is at the correct top dead center I just checked and am enclosing a picture I also rechecked the clearances on the tappets and they are correct as for the carburetor I am going to pull the one of the MTD being as its running okay and try it on the Craftsman I bought two carbs at the same time because I had a feeling the Craftsman was needing one and the MTD was definitely needing one because it poured gas out of the vent to the engine if I didn't turn the gas valve of that I install on all my mowers. What is concerning me alot is the exhaust pipe from the engine turning red as in red hot when I was running it on choke only, other weird thing is the plug when I took it out today was the normal color I was expecting it to be black from running on choke. I do appreciate all of your input and help I have just never come across this problem before but then I only work on my own mowers, weed eaters etc.

 

[bertsmobile1]

If the exhaust valve is not fully closing you get the mixture burning all the way down the exhaust pipe.
The same thing happens when the spark is too far retarded
Both of these will cause the pipe to glow red and the engine to stall out when the choke is closed off .
A leak down test is used to confirm this.
The fact that the plug is not sooty tends more to an open exhaust as retarded timing tends to also make the plug sooty
Not having the muffler on will also cause the exhaust pipe to glow a little redder than it would with a muffler because fresh air gets sucked back up the pipe and that will combine with unburned fuel coming past the exhaust valve and burn in the pipe

 

[slomo]

Top valve is the EX valve.

There are 2 TDC's on a 4 smoke engine. Make sure you are on the correct stroke.

Post up a video on youtube of it running then link it here.

 

[slomo]

What is concerning me alot is the exhaust pipe from the engine turning red as in red hot when I was running it on choke only, other weird thing is the plug when I took it out today was the normal color I was expecting it to be black from running on choke.

Tells me engine is lean. Needs choke to smooth out. Choke adds fuel to richen mixture which smooths out engine.

Normal plug color with choke on is nothing. Again reflects lean A/F ratio.

Fuel system is dirty, bad fuel line, carb solenoid stuck partially open./closed and vacuum leak/s. Did you loosen the fuel tank cap? The ol' gas cap no venting trick?