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Briggs 31c707 17.5HP on Craftsman LT2000

#1

S

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.


#2

ILENGINE

ILENGINE

SpareUsTheCutter said:
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.
Click to expand...
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.


#3

S

SpareUsTheCutter

ILENGINE said:
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.
Click to expand...
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!


#4

ILENGINE

ILENGINE

SpareUsTheCutter said:
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!
Click to expand...
Single wire on the coil is a ground wire that kills spark when the key is turned off by grounding the module.


#5

NorthBama

NorthBama

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


#6

S

SpareUsTheCutter

ILENGINE said:
Single wire on the coil is a ground wire that kills spark when the key is turned off by grounding the module.
Click to expand...
Thanks again - that makes sense now!


#7

S

SpareUsTheCutter

NorthBama said:
You have the best man for the job helping you. Listen to what he is telling you to do
Click to expand...
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.


#8

S

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.


#9

S

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.


#10

S

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.


#11

ILENGINE

ILENGINE

giving indications that it isn't getting enough fuel to sustain high speed operation. Which without a load would still be the idle circuit in the carb. Which is what that mixture adjustment screw should assist. You said it doesn't seem to do anything so that could be part of the issue. Also any old fuel residue in the main jet can cause similar issues.


#12

B

bertsmobile1

As you have other gear around, rig up a temporary tank, a small push mower one will be fine and with some new fuel line connect it directly to the carb
Old fuel lines go soft inside and collapse blocking off the fuel line
Debris accumulates in the fuel tank then organic bits like glass clippings adsorb the petrol which displaces the water & turns them transparent and thye will also get sucked down the fuel line like hair in the shower outlet .


#13

T

Tinkerer200

Some of this series engine had voltage regulators, not all. I can send you a Service Manual for your engine IF you like, address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com


#14

S

SpareUsTheCutter

bertsmobile1 said:
As you have other gear around,
Click to expand...
... you guessed it!!

actually, the fuel tank is near empty, although enough fuel to run, lines SEEM clear on inspection, but will certainly look further into this and try with a decent amount of fuel in the tank


#15

S

SpareUsTheCutter

Tinkerer200 said:
. I can send you a Service Manual for your engine IF you like,
Click to expand...
Yes please, that would be fantastic, I've pm'd you my email :)


#16

S

SpareUsTheCutter

ILENGINE said:
giving indications that it isn't getting enough fuel to sustain high speed operation. Which without a load would still be the idle circuit in the carb. Which is what that mixture adjustment screw should assist. You said it doesn't seem to do anything so that could be part of the issue. Also any old fuel residue in the main jet can cause similar issues.
Click to expand...
Conversely, it seems to be USING more fuel than it should... not very scientific but i recall giving it a good amount, maybe a gallon and a half when i first got it. My other half tried to mow with it for about an hour, before reporting to me that it runs like a bag of <<bleep>>. Since then, I've run it a few times to get it up to temp.. maybe 5 minutes max, twice dumped fuel out of carb and lines... doesn't seem like it should be near empty yet!

As for the mixture screw, I haven't attempted to remove it and inspect since it has the "anti-tamper" plastic surround, but a this stage I figure I have little to lose and might just have to dig in there!


#17

S

SpareUsTheCutter

just reporting back... so it turns out the float bowl seal had perished - which means: 1. a definite cause of fuel loss, leading to me thinking it was "using" more fuel than it should 2. possibly has a bearing on fuel delivery too.. although... I also had a close look at the fuel filter, which is a generic replacement - happens to be hard to see through the plastic casing, but i noticed a definite piece of crud in there, so took a hacksaw to it - doesn't look too bad apart from the afore-mentioned bit of filth, but then on closer inspection I can see it's dark at one end, i.e. tiny bits of debris have accumulated.
Genuine Briggs filter on order and hope to pick up a float bowl gasket at my local shop (crazy prices for the genuine ones online - I mean crazy for a piece of rubber anyway!). New fuel lines and a clean-up of the tank and I'll see if things improve.


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