16.5 single cylinder popping and missing greatly

[ILENGINE]

Hey Bert, this will go against everything we have ever been told about flywheel keys. The engine in question has a advance parts bulletin tied to it which increases the flywheel nut/bolt torque to 110 ft/lb and uses the 796335 STEEL flywheel key.

 

[ILENGINE]

As of this coming week I will have 18 more years before I get medicare.

 

[mr.farmall]

As of this coming week I will have 18 more years before I get medicare.

I see now!! you'll be 39, just like my wife!
But you have the wisdom of experience no matter what your age!!
As for the head gasket, I just got it today, I'll have it in tonight. Wish me well. And I'll increase the torque from 100 ft lbs to 110 ft lbs. Thanks for the update.
Rex

 

[bertsmobile1]

Hey Bert, this will go against everything we have ever been told about flywheel keys. The engine in question has a advance parts bulletin tied to it which increases the flywheel nut/bolt torque to 110 ft/lb and uses the 796335 STEEL flywheel key.

Well, that is why I am here, to learn what I do not know.
i find it supprising as tappers are supposed to be self locking and have been so since 1882 which is the earliest use of tappers I have come across.
Some of the vintage bikes I play with do use a soft steel key in hardened slots.
All the mowers I have pulled down ( about 1 % of the number you would appear to have done ) had an alloy key and that is the only one I can get from my aftermarket suppliers so i will need to look into getting some .

 

[mr.farmall]

Ten to one says you have a blown head gasket. Pull the head and take a look. Will be blown between the cylinder wall and the push rod cavity.

Well, that didn't go quite as I had expected!
I have replaced the head gasket, now with every thing back in place, the leak down tests look much better, no more noise through the body of the engine via the oil filler port.
I started the engine and it run great. I took it a short distance and turned it off to wash everything down. Now it won't start up again. let it sit for a couple of hours and tried it again, it ran ok for 10 second, then started popping badly and stopped. Put it in the garage to sit over the weekend and tried it again Monday morning, still just pops and sputters and backfires into the carburetor, but will not start.
Thinking the timing was out, I checked the flywheel key. It is not a problem, solid and not partially sheared. Then I turned to the electronics. I went through every lead on every switch including the key switch and seat switch. All were good, no opens nor grounds (except were they should be). Tried to create a problem through each contact of each switch(Isolating only one at a time) with pushing, pulling and applying pressure, but could find no troubles.
I disconnected the kill wire to the engine, (thanks for the tip Bert), and run a by pass jumper to the fuel solenoid, Still the same occasional back fire, but not even close to starting.
Pulled the new spark plug, it is black with soot again after only 20-30 seconds of running. preformed the leak down test again. Have good result with only about 20% loss on the top dead center position.
This engine must have a compression release on the intake valve during the compression stroke since the leak down doesn't show good results until the last 60 degrees of the 180 degrees of the compression stroke. then it looks great for the last 60 degrees of the stroke and the next 170 out of the 180 degree of the power stroke befor the exhaust starts to open.
I'm not sure what to do next, the valves seem to be sealing OK, the head is no longer leaking, but their is soot on the plug after just a very short run time.
any help would greatly be appreciated.
thanks Rex

 

[ILENGINE]

Remove the air filter and see if the running improves. If so then make sure the air filter isn't clogged with oil, dirt, etc. If that checks out OK then pull the dipstick ans smell the oil for gas smell.

If those two things check out then we could be dealing with a carb problem. Just don't loose the jet when it falls out of the bottom of the plastic emulsion tube.

 

[mr.farmall]

Remove the air filter and see if the running improves. If so then make sure the air filter isn't clogged with oil, dirt, etc. If that checks out OK then pull the dipstick ans smell the oil for gas smell.

If those two things check out then we could be dealing with a carb problem. Just don't loose the jet when it falls out of the bottom of the plastic emulsion tube.

Thanks once again for the info.

The oil smells like oil and the air filter is clean. it doesn't start so I can't tell if it improves it or not with the air filter on or off.

I disconnected and removed the carburetor. (Nikki version for the 31000 model). Upon dismantling it, I could see the jet imbedded in the bottom of the plastic dip tube, but I'm thinking it is the shut off valve for the electronic solenoid or maybe it functions as both the shut off and the jet, but it was secure. Looking at the info on the service manual, it appears that the spring that goes between the bottom end of the dip tub and the bottom of the bowel is missing.(The manual say to keep an eye out for the spring because it just fall off and can easily be lost). The dip tube connects to the shut off solenoid with the spring in between the two. You have probably seen this before, but if you would like a picture, I'll post one.
This carburetor is a lot different than most lawn mower carbs I have seen, it has a plastic insert with various passages and a very complex o-ring type seal between the plastic and the metal of the carburetor. It covers the entire top of the bowel which is also the bottom of the carburetor body. The gas intake float connect on the bottom of this insert and hangs into the bowel around the plastic dip tub of this insert.
The carburetor looks really clean at first glance, but I'll clean it anyway. I'll see what I can get for parts on the carburetor. Any other suggestions are welcomed.
One question more, torquing down the flywheel bolt is not easy. trying to hold the fly wheel and putting 110 foot lbs on the bolt just doesn't seem to be working. Is there a method that will hold the flywheel in place so that the bolt can be torqued correctly?
Thanks Rex
edit note;
the B&S parts manual 31e877-1502-g1 doesn't show this spring while the service manual does. Now I'm confused!

 

[ILENGINE]

Some of the carbs had the spring you are talking about and other didn't I just went through the same thing a few months ago thinking I had dropped the spring. the jet I am talking about sits up inside the plastic piece you were talking about. It goes in ffrom the top, and will fall out if you turn the plastic piece upside down.

As far as torquing the flywheel the briggs tool for holding the flywheel is a strap wrench. And even then it is fun holding the strap wrench in one hand and trying to pull the torque wrench with the other.

 

[mr.farmall]

Remove the air filter and see if the running improves. If so then make sure the air filter isn't clogged with oil, dirt, etc. If that checks out OK then pull the dipstick ans smell the oil for gas smell.

If those two things check out then we could be dealing with a carb problem. Just don't loose the jet when it falls out of the bottom of the plastic emulsion tube.

Thursday
I've taken the carburetor off to clean it on Tuesday. It looked very clean, almost as if it were new. Very carefully taking it apart with the aid of the service manual from Briggs. I placed it in an ultrasonic cleaner then dried it out with air in a cloth just in case something came loose or was blown out. nothing did.
While it was apart, I removed the heads to check the valves once more, they had some build up but were good. I cleaned them and then lapped them to make sure I could see a good seal around the entire valve. Both valves looked good.
As for the Carburetor, it's pristine clean. I placed the float in a cup of water and it floats OK. The little shut off needle looked good and had a pointed rubber end on it, so I think is was good also.
Now the engine's back together and the carburetor is back in place.
The engine did start this time, but with great effort and many back fires. Once started, it stopped backfiring but had an occasional miss until the governor called for more throttle, then it would backfire and take off again until a few moments later (5-10 seconds) when the governor opened the throttle again. This lasted for about 4 minutes then three or four back fires in a row and the engine stopped.
It will start again, but with lots of backfiring.
This was tested with the kill lead to the engine disconnected and a 12v supply directly to the fuel solenoid to operate it. This was how the engine acted when I started working on it.
new head gasket
leak down test looks good
valves are good
timing key OK
wiring checks out
carburetor clean.
New spark plug
clean air filter
I'm really at a loss of what to check next!
thanks for any help
Rex

 

[bertsmobile1]

Check for air leaks,
Spray some ing like WD 40 FROM A TRIGGER PACK ) all around the carb to engine area.
If it makes a difference then you have an air leak.