18hp Briggs and Stratton twin tuning help

[rjames]

Need some expert advice here. Craftsman LT4000 with 18hp b&s twin.
I've had it for a few years, its a '93 but in very good shape. When I first got it, it ran ok but surged really bad at most any throttle position. I richened up the carb a bit and it runs great, has ever since. It has all tune up stuff done, but nothing cured the problem, which is terribly offensive exhaust.

The older lady I bought I from had the engine replaced due to original blowing up, I'm guessing from lack of pm.

I almost hate using it because I have to wash my clothes or leave them hanging outside to air out after I mow or blow snow. Can't figure out why it's like that, the plugs look perfect, and it runs really good, no backfire, starts right up, yada yada.

Any ideas why it stinks so bad? Or how to go about fixing? Smells rich to me but no symptoms and like I said, it runs fantastic other than the stink.
Any help greatly appreciated.

 

[Moparmyway]

Check air filter, make sure it can breathe easily ?
Choke pulling off 100% ?

If them 2 are good, then lean it out a smidge .......

 

[rjames]

Check air filter, make sure it can breathe easily ?
Choke pulling off 100% ?

If them 2 are good, then lean it out a smidge .......

Filter and pre filter are new(er) oem and clean. Only carb adjustment(that I'm aware of) is idle air screw and if I lean that one out it goes back to surging, and still stinks. I'm stumped hence the cry for help lol

Edit: I will double check the choke pull off. That's a good tip kev

 

[Moparmyway]

If the choke aint it,

I have had to just drop the carb bowl and clean out everything, then have had to remove carbs and clean them out real good.

Sometimes you just throw a new carb on them and they run like new

 

[AVB]

Considering the age and that it is a twin. It is most likely an opposed engine; therefore, there no way to drop the fuel bowl as itis integrated into the carburetor and is bolted to the intake.

The carburetor would need to be removed and serviced. Depending on the carburetor it may have a fix high speed mixture jet which when not seated will cause over rich condition. Note: most of these engine runs off the low speed circuits until loaded then they start drawing fuel through the high speed (load) circuits. These carburetors also have a fuel pump integrated into them and if the float valve is leaky it can cause an over-rich condition.

Surging can be caused by improper static governor adjustment. Even when the carburetor is prefect they will still surge; unless, you have an over enrich the carburetor.

I would recommend servicing the carburetor and do the static governor then go from there. Service procedures are in the Briggs 271172 Twin L-Head service manual.

 

[Fish]

As far as any decent advice on working on it, we really need a pic or the model/type/code numbers off of the engine.
As far as the smell, I would guess that there is a mouse nest/dead mouse up under the covers somewhere.
You need to get it out of there, so you won't overheat the engine.

 

[rjames]

Thanks guys. @Fish It's not a dead animal smell, its a took a nap under an exhaust pipe of an old running hoopdee smell.
I've put a ton of time running it this way, doesn't overheat. I mostly use it for snow blowing and dragging my homemade grader down my road. Vey little mowing.
Ill get pics and engine model later on, I know it has the three screw early style fuel pump cover and that older style carb, if that helps.

 

[Fish]

Well mice make nests out of interesting things, chew wiring, etc. Pull the top cover and peek.

 

[Fish]

Especially in units that sit around barns for a long stretch of time.

 

[rjames]

Well mice make nests out of interesting things, chew wiring, etc. Pull the top cover and peek.

Will do sir. I'll snap a pic when I do so you'll see what I'm working with.

 

[Fish]

Your description of the carb gave me a good idea.

 

[Fish]

Something like this?

 

[rjames]

@Fish
Identical to the engine on the right.
Same color and stickers.

 

[Al Smith]

I think Briggs calls it a pulsa jet carb .That thing probably has a self advancing ignition coil which can be problematic at times .I had one stick on full advance,about burned the starter out and never would start until I replaced the coil .I've got three of them ,two vertical shaft and one horizontal I might use on a bandsaw mill plus two or three in pieces blown up by others mowing the wrong direction on side slopes .
Edit: Forgot to mention if the governor spring is not installed correctly they will surge .Found that out the hard way .

 

[Al Smith]

If you need technical information just do a Google for Briggs and Stratton .They have oddles of info on line .

 

[rjames]

Thanks Al.
Here's the engine, model number and such. @Fish

 

[AVB]

I think Briggs calls it a pulsa jet carb

Nope...It is a Flo-Jet down draft carburetor.

Here's the engine, model number and such.

If read post #5 you will the pn for the SM you will need to service this engine.

 

[FergusonTO35]

I used to have a 1996 model exactly like yours. It didn't stink but after a few years it developed the surging and dying problem. Rebuilt the carb and it still surged a bit but ran well enough when mowing to make my in-laws happy so I gave it to them. That thing was a gas hog even when new, it burned more fuel than my 62 year old avatar does. I'm a Briggs & Stratton fan but the horizontally opposed side valve engines were not very good. The V-twin versions are way better, especially the OHV models. I have a 2000 Troy-Bilt V809 garden tractor with a 22 hp Vanguard OHV and it runs and cuts great, love the varidrive transaxle with high and low range.

 

[Fish]

Vanguards were good, Inteks not so much.

 

[AVB]

I have a 2000 Troy-Bilt V809 garden tractor with a 22 hp Vanguard OHV and it runs and cuts great, love the varidrive transaxle with high and low range.

It more likely to have a 2 speed manual transaxle that is not a variable speed as this tractor/mower uses the sliding sleeve pulley system. BTW the two motion drive belts can be a pain to change out with variable to trans belt wearing most often. They are also can be very picky about what belts you can use. A lot of the will fit aftermarket belts won't work correctly.