[baffled240]

I have a 16 hp Craftsman lawn tractor 917-255821 that has good spark, has fuel, has compression, has new battery, new spark plugs, has rebuilt carb, has new mag, but will only sputter when cranking but will not catch and run. It ran yesterday for a few minutes but will not restart.
Quick start will not start it. Any ideas... it does not make sense.

[KISS]

Your carb is here: BRIGGS&STRATTON | Model #402707 (0157-02 - 0157-02) | BRIGGS & STRATTON GAS ENGINE | AIR CLEANER AND CARBURETOR | SearsPartsDirect.com

I think is see an idle screw #48 and a mixture screw #44. Am I correct?

There doesn't appear to be a low and high speed mixture screw, correct?

[21boat]

Did this mower ever backfire bad once. There is a possibility the timing change jumped a tooth and that would throw the valves off to run.
What was the mag set at?

The sputter could be the mag is set wrong or a fuel to air mixture setting in carb is off, that's if the fuel pump working and float is set right.

Is there NEW fuel in it. Not last years. When ever having problems on season start up always get New fuel. I have tanks topped but fuel was not high in octane. Use High test when working on a mower to get started.

I didn't see a fuel filter change here was there?

What I like to do to prove the engine itself is in good running condition, I use a spray bottle of fresh gas and spray directly in carb and if the mower runs and sounds good the its carb fuel that's bad in the link. The air fuel mixture just may be off and needs adjusted. At present it needs more fuel

Never use either starting fluid...

[baffled240]

Your carb is here: BRIGGS&STRATTON | Model #402707 (0157-02 - 0157-02) | BRIGGS & STRATTON GAS ENGINE | AIR CLEANER AND CARBURETOR | SearsPartsDirect.com

I think is see an idle screw #48 and a mixture screw #44. Am I correct?

There doesn't appear to be a low and high speed mixture screw, correct?

You are correct. I changed the mixture screw #44.

[baffled240]

You are correct. I changed the mixture screw #44.

No there is no high and low speed screw.

[KISS]

OK. Try this:

Put it in whatever the start position is. Choke, fast.
Take the mix screw and turn it in all the way until it stops. Back out 1.5 turns.
Remove plug and Spray carb cleaner in the plug hole. Replace plug.
Try to start
If engine starts, play with mixture scrw until engne runs smooth.

[baffled240]

OK. try this:

put it in whatever the start position is. Choke, fast.
Take the mix screw and turn it in all the way until it stops. Back out 1.5 turns.
Remove plug and Spray carb cleaner in the plug hole. replace plug.
Try to start
If engine starts, play with mixture scrw until engne runs smooth.

Well I tried all of this and it still did not work. This is driving me crazy because I have never not been able to get a mower fixed. Any other ideas would be appreciated.

[KISS]

Does #12, the choke, close and open correctly.

Is this choke opened by the engine intake of air?

[baffled240]

Does #12, the choke, close and open correctly.

Is this choke opened by the engine intake of air?

It is a manual choke. It gets to the point where it sounds like it is running with the start going, but as soon as you let go of the key the motor stops too.

The will be combustion smoke coming out of the exhaust and everything.

I have noticed that the "drivers" side (left) spark plug is wet with gas and the right one is not, but hey both are sparking when I check.

[21boat]

but as soon as you let go of the key the motor stops too.

There may be a couple of problems here. The" key" letting go should not have this effect at all. Maybe you have a bad connection that's shutting of the engine ( kill on the coil ) I would check that out. So please be very detailed on the key thing. You may need a new ignition switch also. It can be hot wired too for testing the engine / gas plug problem/

[baffled240]

There may be a couple of problems here. The" key" letting go should not have this effect at all. Maybe you have a bad connection thats shutting of the engine ( kill on the coil ) I would check that out. So please be very detailed on the key thing. You may need a new ignition switch also. It can be hot wired too for testing the engine / gas plug problem/

I got the mower running by accident. With the right side spark plug removed to check if it was sparking the motor kicked off and ran with the spark plug out of the cyclinger. HUH? That almost seems as if it is now timing related but the keyway is in a correct. How do I check this twin cylinder engine to see if the timing is correct. To talk apples and apples please referr to the driverside (on car) cylinder as the left as seen sitting on the mower. Thanks a lot everyone for your help.

[21boat]

Is there spark on the plug you pulled? If not the problem could either be a bad plug, plug wire, magneto or a bad diode. There is one diode for each cylinder on a twin cylinder

[baffled240]

Is there spark on the plug you pulled? If not the problem could either be a bad plug, plug wire, magneto or a bad diode. There is one diode for each cylinder on a twin cylinder

The spark plug that was pulled and laying on the engine was in fact sparking good and the motor was running very smoothly which amazed me.

[21boat]

Before this gets internal lets see if the spark is "hot" strong enough. Take a good plug or the one that's there and cut the ground where it starts to bend over to center of plug.

Before testing pull other plug wire. Now put cut plug on a ground or mower lay it to see it and crank engine. If the spark doesn't make that gap then its back to magneto or a bad diode.

Plug wire on and lay plug on head

[baffled240]

Did this mower ever backfire bad once. There is a possibility the timing change jumped a tooth and that would throw the valves off to run.
What was the mag set at?

The sputter could be the mag is set wrong or a fuel to air mixture setting in carb is off, thats if the fuel pump working and float is set right.

Is there NEW fuel in it. Not last years. When ever having problems on season start up always get New fuel. I have tanks topped but fuel was not high in octane. Use High test when working on a mower to get started.

I didn't see a fuel filter change here was there?

What I like to do to prove the engine itself is in good running condition, I use a spray bottle of fresh gas and spray directly in carb and if the mower runs and sounds good the its carb fuel thats bad in the link. The air fuel mixture just may be off and needs adjusted. At present it needs more fuel

Never use either starting fluid....

I still do not have this mower running yet and it is driving me crazy. I looked back at this answer and things are beginning to make more sense. I recently got the mower to run with only the "driver" side plug in and the other side out. That seems almost as if it is timing. What did you mean if it backfired it may have jumped a tooth? This could be the answer or at least a start. Thank you for your help.

[KISS]

I think what 21boat says makes sense. I'm not up on 2 cyl lawn mowers, but if there are two diodes then one must fire on a positive edge and the other on a negative edge, so I'll bet that the cyl with the plug removed has a bad diode. It's firing at the wrong time or twice (positive and negative edge).

Although, this link might suggest otherwise: http://books.google.com/books?id=p3Z...um=9#PPA162,M1

Look at this and the next page using "page dn"

There is a diode on the breaker points. That may be the problem.

Hence, it would mimic a timing problem.

I reiterate. Never use starting fluid. Use carb cleaner. It's a bit more volatile than gasoline and it contains a lubercant.

[baffled240]

I think what 21boat says makes sense. I'm not up on 2 cyl lawn mowers, but if their are two diodes then one must fire on a positive edge and the other on a negative edge, so I'll bet that the cyl with the plug removed has a bad diode. It's firing at the wrong time or twice (positive and negative edge).

Although, this link might suggest otherwise: Outdoor Power Equipment - Google Book Search

Look at this and the next page using "page dn"

There is a diode on the breaker points. That may be the problem.

Hence, it would mimic a timing problem.

I reiterate. Never use starting fluid. Use carb cleaner. It's a bit more volatile than gasoline and it contains a lubercant.

This answer makes sense. Where is the diode located? I found what may be it on the 2 wires coming out from under the flywheel from the electronic ignition coil.

Is this the diode? It would make sense why the key is all correct, I have fuel, spark, compression but the timing seems off.

Can you add to this as to how to check the diode. Where it would be located? What it would look like etc?

[KISS]

Guessing here: A cylindrical object with two leads probably covered with heat shrink tubing and soldered in series with the wire. Could be somewhere between 1/8 dia to 1/4 diameter and no more than 3/4" long.

Some have a Bullet shape and olthers have a band on them to identify polarity. One band probably goes one way and on the other diode it may be pointing in the other direction. They may be pointing in the same direction too.
When they point in the same direction, they can act as an or gate without interference from the other cylinder.

They usually start with 1N. 1N400? And 1N500? The ? Digit is related to the PRV or Peak Reverse Voltage.

Diodes are usually checked in the diode mode with a multi-meter. One way measures about 0.6V and the other is infinate. If you don't have a diode mode, then check on the lowest scale. If near zero in both directions, it is shorted.

Radio-Shack and some hardware stores sell heat shrink tubing and Radio Shack sells diodes. I can guess what can work. I'm guessing a 3 A 400 or 600 PRV, but a 1 A diode might also work. So 1A 400 PRV is the minimum and a 3 A, 600 PRV would be the most reliable.

Can also guess current by knowing body diameter.

[baffled240]

Guessing here: A cylindrical object with two leads probably covered with heat shrink tubing and soldered in series with the wire. Could be somewhere between 1/8 dia to 1/4 diameter and no more than 3/4" long.

Some have a Bullet shape and olthers have a band on them to identify polarity. One band probably goes one way and on the other diode it may be pointing in the other direction. They may be pointing in the same direction too.
When they point in the same direction, they can act as an or gate without interference from the other cylinder.

They usually start with 1N. 1N400? and 1N500?. The ? digit is related to the PRV or Peak Reverse Voltage.

Diodes are usually checked in the diode mode with a multi-meter. One way measures about 0.6V and the other is infinate. If you don't have a diode mode, then check on the lowest scale. If near zero in both directions, it is shorted.

Radio-Shack and some hardware stores sell heat shrink tubing and Radio Shack sells diodes. I can guess what can work. I'm guessing a 3 A 400 or 600 PRV, but a 1 A diode might also work. So 1A 400 PRV is the minimum and a 3 A, 600 PRV would be the most reliable.

Can also guess current by knowing body diameter.

Well I found the diode. It is on the red wire coming from under the flywheel (electronic coil) The diode is black about 1/2" long and 3/8" wide with the letters IN540. It appears to have been fooled with because it is not in the plug well. In fact it swivels easily so how do I know it is in the right way as the current would see it? Your help is greatly appreciated.

[KISS]

http://www.datasheetcatalog.org/data...uji/1N5407.pdf

There is a digit missing. It's probably, or should be, a 1N5404.

Note hat there is a white band on one side. This side goes away from the coil.

It probably should not swivel. It may have been crimped, but that isn't a good way to make a connection to a solid piece of wire.

Are you able to test with a multimeter?