briggs&stratton starting problem

[donald girod]

I have a Briggs lawn mower, solid state ignition. It runs normally (good power, etc) once it starts, and it starts eventually, BUI...

I have to pull many, many times, and after a while the engine starts to fire weakly. It will fire weakly 10 or 15 times and die, each time doing a little better. Finally, it fires weakly, doesn't die quite, and slowly picks up speed. Then it takes off and runs. It will restart readily when warm, but if left even 10 minutes, it reverts to the painful starting. The spark is strong (obviously), and I can see gas splash up in the carb throat when I take the air cleaner off and pull the rope. When it does start, it does NOT throw black smoke, as it would if the carb was seriously loaded up with gas, in fact, it throws no smoke at all, and I would bet that in fact it has been starving for gas. Maybe.

I have seen other Briggs engines do this, and I have never figured out what the problem has been. I have done things like take apart the carb and put in a carb kit (mainly, new diaphragm gasket or whatever that thing is called), and sometimes I have "cured" the problem. But if somebody recognizes this syndrome and can tell me what the most likely problem is, I would surely appreciate it.

[Dan Espen]

This may be too simple, but it sounds like you are not pushing the primer button the required number of times.

[donald girod]

Yep, too simple. It has no primer button. This is not a new mower.

[David Martel]

Don,

Dan may be right that your engine is not getting enough gas. Check for possible vacuum leaks around the carb by spraying carb cleaner at obvious connections while the engine is running. If there's a vacuum leak the engine will suck in the cleaner and stutter or die. Also, check the needle valve adjustments. My guess is that you've adjusted the carb too lean or air is entering by a vacuum leak. These are both easy to fix.

Dave M.

[Oren]

I would clean and re-gap the spark plug and clean the air filter, if it has been awhile. Will is start easier with the air filter off?

Oren

[donald girod]

I've never touched the carb, but a vacuum leak is plausible--something could have shaken loose. It would also be easy, as you say, to open the needle. I'll try this. The problem has developed gradually.

[donald girod]

No, the air filter is clean, and taking it off makes no difference. I swapped plugs, no difference. But thanks for the suggestions.

[ds549]

check your flywheel key too, and snug up the head bolts.

[Bob]

Is the choke closing all the way when you push the throttle to the start position?

Bob

[Jeff Wisnia]

This may seem like an obviousity, but if it's an old engine and there's no primer bulb, then I'd think there'd be a choke valve on the carb. Usually those are pushed closed when the engine speed control lever is moved all the way to it's high speed end.

And, with the choke closed, as soon as the engine startes the speed control lever should be moved back a bit, so the choke opens.

If I'm correct and the carb has a choke, maybe the speed control cable has gotten sloppy or out of adjustment, or the choke operating linkage has fallen off so the choke won't close.

Have a look see, it should be pretty easy to see if there's a choke butterfly valve near the air inlet on the carb.

I've also seen small engine chokes which are closed by a spring when the engine isn't running and opened by engine vacuum bled through a small orifice to a rubber diaphragm which pulls the choke open against the spring force. The orifice delays the choke's opening for a second or two after the engine starts.

HTH,

Jeff

[Oren]

Speaking of orifices and not taking away from the OP. One Briggs I have has a manual choke; choke - run. When rebuilding the carb once I learned and cleaned these "tiny holes" with a wire from a wire brush (stainless). It would not run or start until I cleaned these little "vents" as I called them. Do not break off the wire..

Are these the orifices you mention? Along the carb tube, right at the choke butterfly and very small like a wire I mention? I could never get the proper term.

Oren

[John Lawrence]

[Tom G]

If the carb and ignition, plugs, etc are ok, it sounds to me like a possible lack of compression to pull the gas into the cylinder when cold. I've found that on the old B & S engines, it's necessary to pull the head now and then and clean off the carbon. If the rings are ok I think a carbon build up will also affect compression.

Tom G.

[Nick Hull]

When I have that type of problem, I try putting an unlit propane torch into the intake. Propane burns from about 5% to 95% so the engine usually starts right up, confirming the problem is fuel.

[donald girod]

And he gets the cigar! I took the shroud off and cleaned out the mouse nest (not the problem), took off the carburetor, blew it out with air, and cleaned the mouse fur off the main fuel pickup (not the problem), put it together, poured some gas in the throat, and tugged about 25 times. It fired a bit, and I noticed gas blowing out between the head and the cylinder. Hmm....

All five bolts were loose, some looser than others. I tightened the bolts, and bingo--a running engine. So I guess "vacuum leak" is about right, also compression leak (but not real bad, the compression felt pretty normal. I'm guessing a previous owner had the head off and didn't use loctite.

[Stormin Mormon]

Does it start with a squirt of ether into the air intake? If so, I'd suggest a bad gasket betwen the carb and the engine. Or, a missing gasket.

[Stormin Mormon]

Plese let us know if the mower starts easier with a squirt of ether.

My second thought is dirty valves. Which requires some level of skill to repair. And a replacement cylinder head gasket.

[Stormin Mormon]

Carbon on the valves.....

[David Martel]

Don,

Uhh, you claimed to have rebuilt the carb. Or that was my interpretation of your "carb kit". If you replaced a few gaskets but did not remove, disassemble, clean, reinstall, and adjust the carb then that may be your problem. Get a carb kit, and follow the directions.

Dave M.

[mm]

I think this problem is why they went to using a primer button. So get a can of starter spray and spray a burst into the air cleaner before you pull.

I found the ones with the primer buttons work a lot better, but I even have one of those that needs a spray each time, unless it's within 15 to maybe a longer time I haven't measured.

They make spray with upper cylinder lubricant, it says on the can. Same price.

Although in the 50's and 60's I had a lawnmower with B&S that started just fine when cold by merely setting the throttle to choke. Maybe another one in the 70's too, but I can't remember.