Briggs L head motor starts well but sputters after warming up

pugaltitude

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• Jan 10, 2018 / Briggs L head motor starts well but sputters after warming up

• #11

2 things, does it have a metal supressor cap on end of coil ht lead. They were common for breaking down electrically.
Are you using the same one when replacing coils?
Also your bio shows its a snapper. Now certain models at around 2007 08 had wrong opc cables fitted which did not allow the freewheel brake to release far enough and so the coil earth switch was slightly still connected to ground and cause rough running and bad starting.
To make lever go further tie a knot in cable to shorten inner.

 

R

Rivets

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• Jan 10, 2018 / Briggs L head motor starts well but sputters after warming up

• #12

I would remove the kill wire from the coil and see if it makes a difference. Pugs suggestion about a possible short in the kill wire, at the parking brake, or along the wire is a definite possibility. If there is no change, I would rule out an electrical problem, because of what you have told us. The next place I would look is either a sticking intake valve or valve clearance too tight, allow slight blowback when the engine get warm.

 

P

Patr

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #13

Hi pugaltitude, The coil lead has a rubber cap at the plug end not a metal one. Also the new coils each had their own plug leads that came with them. Your comment about the brake release/coil shorting switch is interesting because this mower did have that problem several years ago. I corrected it by grinding some metal off of the shorting contact to provide more clearance. What's interesting is that the way the motor behaved with that shorting switch just making light contact or maybe intermittent contact is very much like it is behaving now with a resistor plug and after warming up for several minutes. More recently I removed the shorting wire from the coil, at the coil, and this problem still occurred.

 

P

Patr

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #14

Hi Rivets, Please see my post today 1/11@3:26PM. I did remove the kill wire from the coil and it had no effect on this problem. I set the intake valve at 0.006" according to the operators manual spec of .005"-.007". What have you seen that would cause an input valve to stick? Also, I wouldn't think the input valve would heat up much in only 2 minutes of running. ( The motor typically starts easily and runs well for about 2 minutes before exhibiting sputtering and 200-500 RPM reduced speed erratic running).

 

cpurvis

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #15

You say this is an L head engine. How did you set the intake valve clearance?

 

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Rivets

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #16

You would be very surprise at how fast an engine can heat up. My thoughts were a carbon buildup on the valve stem, reducing the clearance. This could cause the valve to not fully close when it gets hot. Not very common, but I have seen it. The question of what procedure you used to adjust the valve clearance is one I to would like to know. May give us an idea of your problem. Did you clean the valve faces and seats before you set clearance? Did you lap the valves in? You must remember that the members who are trying to help you are not there with you to see what and how you did things. We may ask the same questions more than once, because we are trying to picture what is going on and don’t remember your answers to other reply’s.

 

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Patr

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #17

Hi cpurvis, I removed the head and valves and cleaned all carbon. I then lapped the valves, cleaned everything well, and re-assembled the valves. Using a feeler ga. I set the intake to 0.006" and the exhaust to 0.008".

 

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Patr

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #18

Hi Rivets, Please see my reply to cpurvis today 1/11 @6:44 right after your post @5:05

 

cpurvis

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• Jan 11, 2018 / Briggs L head motor starts well but sputters after warming up

• #19

Patr said:

Hi cpurvis, I removed the head and valves and cleaned all carbon. I then lapped the valves, cleaned everything well, and re-assembled the valves. Using a feeler ga. I set the intake to 0.006" and the exhaust to 0.008".

Click to expand...

yes, but what process did you use to "set" the valves?

 

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Patr

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• Jan 12, 2018 / Briggs L head motor starts well but sputters after warming up

• #20

Hi cpurvis. To set the valve clearance I had the piston essentially at top dead center. I then moved it slightly to find where there was maximum clearance between the end of the valve and the cam follower. This is the position where I set the clearance to be 0.006" on the intake valve. On the exhaust I was careful to avoid the effect of the compression release. As far as the actual grinding of the valve stem, I held it perpendicular to the side of my grinding wheel and rotated it while grinding. I would take off a little at a time, put it back in the motor to recheck the clearance and repeat until I obtained 0.006"