Craftsman B&S675 w/ auto-choke repair failed

[Quest]

Took my friend's 6yr old Craftsman 675 with auto-choke (blue handle, easy start version) model 126T02 in to service the carb.

Symptoms: hard start (you can literally yank the cord for 10+mins and it may catches and start but once you stopped it when hot, it would failed to start again (3 out of 4 times).

owner took it into an unknown small engine shop to service. Cost over 100bux and not sure what he(shop) had done, but came back the same as before.

new spark plug installed, fuel bowl still has crud in it when returned, etc.

what I've done:

complete carb rebuild with carb kit: these carbs are non-servicable: no idle mixture needle (sealed), no nothing. Just 2 plates: throttle and choke.

added a 150microns mesh fuel filter.

used a new fresh spark plug RJ19LM.

Tried swapping air filters (with a fresh one I have on-hand).

checked/re-gapped the magneto armature to 6 thou...

check vane and thermostat armature for binding.

STill no go.

When symptoms happen: it was a tad on the richer side of the mixture when the engine died out (won't start after stopping when hot). carb throat can see fuel fumes coming out...plug slightly fouled.

Suspicion:

-carb (worn out of spec)--costs 39+shipping+my labour charge

-magneto (intermittent)--costs 58bux +shipping +my labour charge

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Even with these in place, there's no absolute guarantee that the problem is completely resolved.

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the other option is to purchase a brand new replacement (either auto-choke or non-autochoke type) from online: typically runs between 100~130bux +shipping + my labour, which works out to almost 200bux.

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So far, none of these options seem all that appealing for (a ) the owner already spent over 100bux by sending it through a local small engine shop, and no-go.

(b ) this mower is over 5+yrs old, so value is fairly low.

(c )none of the repair options seems to be better than buying a new one from either big box store or Costgo which may also comes with either 1 or 2 yr warranty.

I guess I'll propose these options to the owner and see what he thinks.

(**there's a remote possiblity of him trashing it (leaving it to my disposal) so I may ended up with a spare engine(engine block still good, just bad carb**)

**moral of the story: don't expect longevity or reliability out of some of these rather "exotic" carb designs from B&S...tends to be a pain when they age....and parts can be costly also**

Q.

 

[OVERKILL]

Retrofit a carb off another small engine. I've done this numerous times in the past using small motorcycle or ATV carb's which have a heck of a lot more adjustment and can usually be picked up for next to nothing from a bike wreckers.

 

[Nick R]

IS the compression release functioning properly? Sounds like it may not be getting any compression when starting.

 

[Deltona_Dave]

The bolt that holds the bowl on the carb is the main jet. Try running a fine wire through the holes and blowing out with compressed air.

Dave

 

[Quest]

@Overkill: Yeah, I like the idea of getting one from bike wrecker...unfortunately, I don't live close to one of those..

@ NickR: compression release is working fine.

@ Del_Dave: carb is not corroded at all: all passages verified to be clean and clear. I have a 150micron mesh inline filter to filter the gas (from grass clipping, etc.)...fuel bowl verified to be clean as a whistle after running it (intermittently) for an hour or so...so I know definitely that the fuel is indeed as clean(filtered) as possible. Main jet (That brass screw from the bottom of the bowl, with a small fibre gasket) is clear and free from any debris/clogging.

I don't live close to any landfill or so, so getting a doner mower is basically out of the question.

Q.

 

[OVERKILL]

I don't know where in Canada you live, but about an hour from Toronto there is a decent bike wreckers.

 

[01rangerxl]

Are you positive the thermostat is working? This sounds an awful lot like a thermostat problem. It should move freely back and forth and spring back into place. A lot of times some Deep Creep sprayed into the spring part will free them up, at least temporarily.

 

[Quest]

@Overkill: I'm on the PNW side...

@01Rangerxl: That's a good call. I'll see if I can pull off the muffler and take a quick look at the thermostat...

(** I know that the termostat level is swinging freely, and the vane flap is definitely serving it's intended purpose of pushing the choke plate open (auto-choke BTW)...but nevertheless, worth checking...**)

*finger's crossed, for I don't have any spare exhaust gaskets for these engines on-hand*

Q.

 

[yeehaw1960]

I get several of those automatic choke Briggs and Strattons each year. Most of the time, you just have to work the choke plate back and forth a little to break loose the gum that's holding it in place or making it hard for it to move automatically. It's a shame you don't live close by. I give away several Briggs and Tecumseh coils and a few carbs each year. I have two large containers full of them.

 

[Quest]

Originally Posted By: yeehaw1960
I get several of those automatic choke Briggs and Strattons each year. Most of the time, you just have to work the choke plate back and forth a little to break loose the gum that's holding it in place or making it hard for it to move automatically. It's a shame you don't live close by. I give away several Briggs and Tecumseh coils and a few carbs each year. I have two large containers full of them.


Some good info here, Yeehaw! the choke plate/shaft is not binding at all, just somewhat "out". Carb has been thoroughly washed and dried with compressed air; all passageways, orifices, etc. cleared.

Anyways, like I said before: it could be an intermittent coil (that I don't have spare) and neither do I have any extra doner mowers around to do a retro.

Say, if you come across these types of mowers (675 or similar with sidedraft carbs), can you help by saving the air filter box (with primer bulb type) and the carb? I have no problem compensating you with that (for I have a primer bulb version of 675 that I restored and using with satisfaction)your inconveniences (to ship it to WA).

Keep in touch.

Q.

 

[jyoung8607]

Is this mainly just a hot-restart problem?

If so, take a close look at your valve clearance. If there's too little clearance, compression can drop a bit when hot as parts expand and valves can't quite close all the way. I ran into this same problem when fixing my neighbor's Briggs-powered mower and this was the fix. Started pretty much fine when cold, ran decent except for a very slight no-load misfire when warmed up, was a giant pain to get started again until it cooled down.

 

[Quest]

Good point! Many thanks. I'll wait til I get the gasket kit before I come along and tackle it from there...

Q.

 

[yeehaw1960]

How do you adjust valve clearance on a small engine like this?

 

[Hokiefyd]

I'm working on one of these myself. It's a 6.75 tq Briggs on a Craftsman mower. No start/no run when I got it. I fixed the no start by cleaning out the carburetor jet. Now for the no run. It'll start and run, but the choke doesn't pull off. I can manually open the choke and it purrs like a kitten. The thermostat moves freely, but I think the air vane mechanism is dragging. I need to take it back apart today and see where to lubricate it. It doesn't quite move off the choke position easy enough. Give me a manual choke any day.

On valve clearance, from what I recall, and this was YEARS ago, it's not really adjustable, because it's an L-head design. The camshaft lobes directly operate (or closely operate, through solid lifters) the tops of the valve heads. You may be able to replace lifters or buckets to effect a valve clearance adjustment (like a Toyota engine), but I don't think you can adjust the valves like in a Honda engine (or any small OHV engine). But that's been many years ago, I could be dead wrong on that too.

 

[Quest]

I haven't have the time to check valve clearances in that problematic B&S 675 engine yet (it's a 126T02, BTW, built in 08). I've been staying away from tearing it down completely, knowing full well that I won't get compensated for the gaskets I need to properly rebuild the engine.

The one I restored to proper condition was a 127K02, which is, IMHO, one of the best engine by far (primer bulb type carb, non-adjustable ( I believe it either falls under "flowjet" LMT series (low-emissions) or "flowjet" LMS series (low-emissions).

B&S service manual is not very detailed about the garden varieties of walbro carbs they used in the engines...mssing a lot of info here and there...But then again: these are chinese made walbro, very crude in terms of quality..so i don't expect miracles to them.

I'm a tad disappointed with these B&S675 "easy start" series engines with auto-choke. If only they can add a bit more quality into their original designs with better carb and adjustable on the valves part, i bet we won't see these kinds of issues a few years down the road....

Q.

 

[Quest]

Oh and BTW: in case I didn't answer your question fully: for these cheep air-cooled OHV flatheads, valve (intake/exhaust) clearances cannot be adjusted easily.

To reduce the clearance: grind the valve seat; to expand on the clearances is to grind the end of valve square.

Either way: it's not something that I would like to do due to lack of tools. For me it's just a matter of having extra doner engines on hand I can swap parts until the desired valve clearances can be obtained. A new exhaust or intake runs around 12 bux + shipping.

Q.

 

[JTK]

Originally Posted By: Quest
...these cheep air-cooled OHV flatheads, valve (intake/exhaust) clearances cannot be adjusted easily.


I assume you mean flat head and not OHV??

 

[Quest]

Originally Posted By: JTK
Originally Posted By: Quest
...these cheep air-cooled OHV flatheads, valve (intake/exhaust) clearances cannot be adjusted easily.


I assume you mean flat head and not OHV??


UR right...not paying attention these days...

Q.

 

[JosephHarmon]

Check the flywheel key for shear.

 

[yeehaw1960]

So, it starts well when it's cold, but not when it's hot? Compression or coil. Tie off the dummy bar on the handle. Remove plug, then put wire back on it. Ground side of plug to engine. Pull cord and look at spark (in very little light preferably). Nice and blue/white?. Get engine hot and repeat test. Spark yellow and or dull and/or small. Bad coil (OR PLUG).

Before you check for spark when cold, put your finger over the plug hole and see what kind of compression it has when pulling the rope. It should blow your finger away from hole.

I hate it when I clean a carb, sharpen a blade, change oil and tighten/troublshoot everything else, then find a motor doesn't have enough compression to bother with it. It happens a couple times a year. I occassionally forget that when a customer says it ran last week, they may actually mean it's been three years and it ran badly then.