Craftsman / Briggs 18HP Running on 1 cylinder

[Scooby074]

I have a older Craftsman 18Hp Lawn Tractor with the 18 HP Horizontal twin engine Model 422707.

This mower hasnt ran in at least 5 years. Originally i was having a problem with the mower blades hitting, see thread here : http://www.tractorbynet.com/forums/lawn-garden/144894-craftsman-garden-tractor-mower-blades.html

After fixing the blades, i noticed that the mower was running rich and was down on power when mowing heavy grass.

After troubleshooting, i noticed the RH cylinder had no spark and the plug was only warm, while the other cylinder had spark and the plug was hot. Unplugging the RH has essentially no effect on engine performance, but unplugging the LH plug ill result in a stalled engine.

I rotated plugs left to right and still the RH cylinder was dead, so i replaced the coil ($90)

Today i have a good spark on both plugs, but the RH cylinder still isnt firing.

Compression is good at 120PSI per side, so that rules out any cylinder or valve damage.

Ive checked the valve clearances, LH side is perfect, RH side is a little off.
RH Intake is 0.0085" , spec is 0.006" ; Exhaust is 0.010", spec is .009". Would the 0.0025" out of spec on the intake cause a no fire or intermittent fire situation??? I dont think so, so id like to know before i tear the cylinder head off and try to reduce that gap.

I cranked the engine, with the valve covers off, and all valves are opening smoothly.

Both plugs are getting very carboned up after a short (3-5 min) run. Of course the LH side is much more carboned up than the right. Neither plug smells like raw fuel.

The carb has been thoroughly cleaned.

After the last run of the day, when i shut the machine off, i noticed quite a bit of white smoke coming out of the carb. This lasted about a minute or 2.

Could a blocked exhaust pipe on the RH cylinder be the source of my issue? Putting my hand in front of the muffler, it feels like there is plenty of exhaust coming out.

 

[shot_gun]

If it is a two coil setup. I would verify your air gap on the new coil. Valves don't control spark so that is puzzling. I seemed to remember briggs having a problem with a batch of coils. You can check this by puting a magnet by the (bad) coil while it's running to see if it straightens itself out. If it does, you have a bad coil out of the box. If you have the black box though all bets are off. It could be a miriad of issues causing the box to not work.

 

[Scooby074]

No black box.. I dont think they were even invented when this thing was made (its a 1986).

There is only one coil. Coil gap is 0.010" When you say i should put a magnet against it, do you mean near the coil or the laminations??? I hope the coil is good, i dont want to have to fight with the dealer on the return... Do you have any further info on this bad batch of coils ( maybe a lot number or something) i can show to my dealer if i have to return it?

After changing the coil, i now have good spark on both plugs (at least outside the engine).

I still cant figure out why i got intermittent fire (combustion) on the RH Im assuming that the plugs are continuing to work inside the engine, and im looking at a fuel,valve or timing issue.

I posted this up on another forum, and got a reply that there's a chance that i popped a valve seat. Looks like ill be pulling the head to check.. no biggie.

Attached is a picture of the new coil. Its a different design than the original coil. Briggs part no. 394891

 

[Sonny580]

Also start with 2 new plugs and see if this will help you any!----part of your new coil could be bad too!---or weak! thanks; sonny

 

[dfkrug]

No black box.. I dont think they were even invented when this thing was made (its a 1986).

I believe that all Briggs engines used electronic ignition after 1982. I have
a 79 vintage 16hp twin B&S, and it has points.

 

[Scooby074]

Also start with 2 new plugs and see if this will help you any!----part of your new coil could be bad too!---or weak! thanks; sonny

I think your right!!!!...Yesterday i would have sworn that the new coil was working fine.

Today, im not so sure. After checking the needle and float in the carb ( it was a little sticky so i cleaned it up, now its fine) i thought id check the spark again with my trusty spark checker.

Left side has lots of blue spark.

Right side ( the side thats been giving me fits) starts firing ok, then it gets intermittent after 4-5 seconds of cranking. I get spark once every second or 2 compared to the rapid, multiple sparks per second on the left side!!!

Needless to say im ticked. THis was a brand new coil and cost me $105 after tax Plus it sent me down the path chasing other things that wernt the problem.

Now i figure its running rich, because the engine is drawing in enough fuel for 2 cylinders, but only running on 1.

Now i get the pleasure of trying to convince my dealer that the coil was DOA. This should be fun. Wish me luck .

dfkrug: Thanks. This engine has magnetron ignition, so i guess you could say it has a old skool black box

 

[shot_gun]

When you test them with a magnet you have to put the magnet on or very near the black part of the coil. Hopefully Briggs has a parts warranty. Hope you have your reciept! Good Luck.

 

[Scooby074]

When you test them with a magnet you have to put the magnet on or very near the black part of the coil. Hopefully Briggs has a parts warranty. Hope you have your reciept! Good Luck.

Thanks, I have the new coil out of the machine now, but ill remember that trick for another time.

Yes, i still have the receipt and packaging (thankfully i didnt take out the trash!!) . We've given this dealer LOTS of business over the years, so hopefully they wont give me any grief. But you never know....

 

[Scooby074]

After a little convincing (and the "we dont exchange electrical parts speech") I now have a new coil to try (thanks to my dealer for giving me a break).

Hope to install it tomorrow. will post results

 

[Willl]

Can you take a ohm reading on both spark wires to ground ?

Do you still have your old one ?, if so, compare new readings against old.