Briggs 31c707 17.5HP on Craftsman LT2000

[SpareUsTheCutter]

Hi all, nice to be here...

I recently got hold of a much abused Craftsman LT2000. Basically running like sh*t.. misfiring, backfiring, etc. Also, somebody has fitted a 42" deck to it (which is itself in a fairly sorry state) - the wrong size as this model of LT2000 takes a 36" deck.

Anyway... much work to be done, but just now am concentrating on the engine, which is a Briggs 31c707, or in generic terms a 310000

Firstly, it had the wrong sparkplug fitted, so got the correct one. Still running rough.. seems there is not enough fuel being delivered, i think it has a "generic" fuel filter on it, and am guessing that maybe the correct inline filter is needed for it to run right, however, I'm also wondering whether these engines are supposed to have a priming bulb since manually priming the fuel system seemed to help to get it starting. I can't see a priming bulb in any of the diagrams I've seen thusfar. What I do know is that some versions of this engine have a pump, but mine doesn't.

I've pondering the ignition coil although it measures the right resistance. Have reached a gap in my knowledge since I'm far more comfortable with diesel engines. Does the coil receive dc voltage after the regulator? I can't seem to find the regulator itself, which is perplexing me. Have measured about 16vac coming off the wires coming out of the flywheel, traced them and can't find a regulator anywhere!

Also, I don't think the battery is charging. I've measured about 3.5 - 4vdc coming directly off the engine to the battery with the positive lead disconnected from the battery - I would have expected 14.4vdc or more.

Clearly this machine has been messed about with a fair bit, so I'm now trying to do the detective work to figure out how it's supposed to be set up.

If anyone can point me in the direction of good resources or offer any advice from personal experience, I would be most grateful.

Cheers

I've had look at all the manuals I could find online, both from the Briggs website and the sears site - what I really need is a proper workshop manual, but I'm not sure one exists.

 

[ILENGINE]

Hi all, nice to be here...

I recently got hold of a much abused Craftsman LT2000. Basically running like sh*t.. misfiring, backfiring, etc. Also, somebody has fitted a 42" deck to it (which is itself in a fairly sorry state) - the wrong size as this model of LT2000 takes a 36" deck.

Anyway... much work to be done, but just now am concentrating on the engine, which is a Briggs 31c707, or in generic terms a 310000

Firstly, it had the wrong sparkplug fitted, so got the correct one. Still running rough.. seems there is not enough fuel being delivered, i think it has a "generic" fuel filter on it, and am guessing that maybe the correct inline filter is needed for it to run right, however, I'm also wondering whether these engines are supposed to have a priming bulb since manually priming the fuel system seemed to help to get it starting. I can't see a priming bulb in any of the diagrams I've seen thusfar. What I do know is that some versions of this engine have a pump, but mine doesn't.

I've pondering the ignition coil although it measures the right resistance. Have reached a gap in my knowledge since I'm far more comfortable with diesel engines. Does the coil receive dc voltage after the regulator? I can't seem to find the regulator itself, which is perplexing me. Have measured about 16vac coming off the wires coming out of the flywheel, traced them and can't find a regulator anywhere!

Also, I don't think the battery is charging. I've measured about 3.5 - 4vdc coming directly off the engine to the battery with the positive lead disconnected from the battery - I would have expected 14.4vdc or more.

Clearly this machine has been messed about with a fair bit, so I'm now trying to do the detective work to figure out how it's supposed to be set up.

If anyone can point me in the direction of good resources or offer any advice from personal experience, I would be most grateful.

Cheers

I've had look at all the manuals I could find online, both from the Briggs website and the sears site - what I really need is a proper workshop manual, but I'm not sure one exists.

No primer bulb used on rider engines. Sounds like you have a gravity feed carb, which sounds like it needs cleaned. Also make sure the choke is closing all the way. Doesn't take much open to mess with starting. the coil doesn't receive voltage, and voltage will kill the coil/ignition module immediately. May not have a regulator, Could be a dual circuit with a diode in one wire to basically half way rectify to DC and the other wire would be AC for the headlights. No regulator present most likely.

What voltage are you measuring at the battery with the engine running full speed and the battery connected. Should be in the range of 13-13.5 roughly. But if a 3 amp unregulated charging system may take a short period after starting to get those voltages.

And Briggs doesn't have step by step repair manual their manuals assume you have been to the School and will make the assumption that you have knowledge to perform repairs without complete guiding ie, to remove the stator the manual will say remove the blower housing, replace the ignition coil, remove the fan, remove the flywheel. How to do those task will not be explained.

 

[SpareUsTheCutter]

No primer bulb used on rider engines. Sounds like you have a gravity feed carb, which sounds like it needs cleaned. Also make sure the choke is closing all the way. Doesn't take much open to mess with starting. the coil doesn't receive voltage, and voltage will kill the coil/ignition module immediately. May not have a regulator, Could be a dual circuit with a diode in one wire to basically half way rectify to DC and the other wire would be AC for the headlights. No regulator present most likely.

What voltage are you measuring at the battery with the engine running full speed and the battery connected. Should be in the range of 13-13.5 roughly. But if a 3 amp unregulated charging system may take a short period after starting to get those voltages.

Thanks - that would make sense if it has no regulator - a bit confusing as the parts manual mentions one.. but then that could be only for specific models. I will investigate to see if I can spot a diode somewhere. What threw me about the ignition coil is that it has a wire on it, so assumed it was "fed" with voltage. If only I had a wiring schematic, all would be clear, but the manuals on briggs site don't have anything and unfortunately the sears site doesn't have a manual for my specific model of mower (MODEL-917.257160) - I found a nice pdf for a different model complete with wiring schematic on the sears site (917272220) but of course that's only partially useful... and it does include a regulator in the circuit!

 

[ILENGINE]

Thanks - that would make sense if it has no regulator - a bit confusing as the parts manual mentions one.. but then that could be only for specific models. I will investigate to see if I can spot a diode somewhere. What threw me about the ignition coil is that it has a wire on it, so assumed it was "fed" with voltage. If only I had a wiring schematic, all would be clear, but the manuals on briggs site don't have anything and unfortunately the sears site doesn't have a manual for my specific model of mower (MODEL-917.257160) - I found a nice pdf for a different model complete with wiring schematic on the sears site (917272220) but of course that's only partially useful... and it does include a regulator in the circuit!

Single wire on the coil is a ground wire that kills spark when the key is turned off by grounding the module.

 

[NorthBama]

You have the best man for the job helping you. Listen to what he is telling you to do

 

[SpareUsTheCutter]

Single wire on the coil is a ground wire that kills spark when the key is turned off by grounding the module.

Thanks again - that makes sense now!

 

[SpareUsTheCutter]

You have the best man for the job helping you. Listen to what he is telling you to do

indeed! I am in good hands clearly. Think I'll be having a good look at the carb tomorrow, already tried the usual few squirts with carb cleaner, but sounds like it needs deeper investigation, fairly sure there's a fuel starvation issue. Specs say idle speed should be 1750rpm (holding governor back with thumb) and I found it hard to maintain that without the engine dying completely.

 

[SpareUsTheCutter]

Ok... so i gave the carb a clean, boil-washed it with detergent, sprayed out all the orifices with carb cleaner and compressed air.

Back on the engine, still no better. idles ok at slow speed but very rough (sometimes backfiring) at high speed.

https://flic.kr/p/2nBa84p

Still wondering if the carb is kaput or whether it might be something else.

 

[SpareUsTheCutter]

another bit of info... the manual (for the mower) states carb can be "adjusted" by setting idle speed at 1750rpm and then turning mixture screw.

setting idle speed is done by holding the governor back with thumb while bringing the idle screw to the correct position to achieve 1750rpm.

bit of a tricky procedure as I'd really need three hands, but I tried it with a tachometer pointed at the flywheel and making adjustments to the screw a little at a time. As mentioned in my OP, it's difficult to hold the engine at 1750 rpm without it running down rapidly and stalling entirely. Again, this points to fuel supply issues as far as I can reason it... air filter is brand new BTW.

 

[SpareUsTheCutter]

oh.. forgot to mention the mixture screw doesn't seem to do a whole lot. Apparently the thing to do is turn it fully clockwise, then back it off until the engine runs rough - then set it at halfway between those two points. Honestly, I couldn't detect any difference no matter where i have the mixture screw.