Riding mower chokes out at high rpm

I'm about to break down and take it to a mechanic.....ugh

Here are the specs.
Briggs and Stratton 16.5 hp ohv
Model # 313777
Carb model # 696353

My mower was working just fine and the next minute it starts throwing black smoke out of the exhaust.
It starts fine and runs smooth at low to mid throttle.
Put it under a load or run it at high rpm and it wants to flood out.
I took the carb off and soaked it three times now, it's spik and span. No change.
Installed a new needle valve in the float. No change.
I installed a new plug and coil thinking it was maybe weak. No change.

I don't think it's a plug in a jet because that would starve the motor of fuel, this is getting to much fuel.

Any ideas? I hate going to mechanics...

What's the filter Look like?

When re installing the needle, did you clip it back into the right groove?

The float bowl can flood if not adjusted, like a toilet tank.

I'd pull spec on proper float setup online.


I would pull the spark plug, turn it over a few times, then hold your finger over the spark plug hole and see if its getting decent compression.

But keep the plug wire away from hole or fingers.

A major smoke out of oil during operation may be a ring, or valve failure. Allowing oil blow by.

This is also assuming it's not over filled with oil, or was at a weird angle before smoking.

a reply to: Mandroid7

New filter
And as far as I can tell everything is back in the right place.

Needle may not be seated correctly. You may need to just buy a rebuild kit with new parts. Sounds like the float is getting stuck.

Also soaking the carb may have not cleaned it well enough. Take the carb cleaner, then find a bread tie, burn off the plastic on the bread tie, then use it with the carb cleaner to clean out ALL of the holes/jets.

I've done a lot of carb rebuilding and cleaning in my time, and sometimes you don't quite get all the crap out.

a reply to: Bluntone22


If the choke position on the dash is above the highest throttle setting on the dash, than possibly the choke may not be returning to the open position once you move the control down for high speed.

Maybe time to do some WD-40 squirting to the side of the motor where the throttle and choke reset parts are spring loaded to turn the choke off. I'm thinking that the actual choke butterfly is not returning to its proper position of being "off" even when the speed control is removed off of the choke position. It other words, the choke is sticking partially or fully on causing a over-rich running at high rpms.

a reply to: Aliensun

I have the air filter off while it's running and the choke is operating normal. I had that same thought early in the process.

a reply to: eXia7

I run a small copper wire through the jets to clean them out.
This is the first carb to ever give me this much trouble.

link

I wanted to add, also check placement and condition of choke butterfly return spring, as well as all the little o rings, especially the one on the main jet. Your fuel will bypass main jet and needle and od if its not perfect.

Alien sun had a good point about the linkages also, but I would start with a compression test before you diagnose carb issues, so you don't waste your time, since you had a smokeout during normal use.

Good luck, keep us posted

a reply to: Mandroid7

I would pull the spark plug, turn it over a few times, then hold your finger over the spark plug hole and see if its getting decent compression.

That and... check the oil? Pick up could be clogged, burned valves, rings.

a reply to: Mandroid7

Poor compression/ring problem will blow blue smoke from burnt oil. Gas flooding, as you suspect is black smoke and poor running.

When you soaked the carb did you take the jets out and clean them? Sometimes you have to run a small wire through them.

Edit - nvm I just saw your last comment. I recommend getting a carb rebuild kit.

a reply to: Mandroid7


I will check the compression as a next step, good idea..

Now I get to go tool shopping..lol

If you have gas mixed with 10% ethanol.......we do here in N.C. it gums up newer machines like crazy. Cause's a varnish like film to build up and it does just what your describing.

a reply to: Bluntone22

Where's your fuel filter?

a reply to: Bluntone22

I had the same problem with my car recently (black smoke at higher rpms). It turned out to be a crack in a plastic connection tube that was sucking (or blowing) air.

soulwaxer

a reply to: openyourmind1262

Three soaks in carb cleaner should have removed the varnish

originally posted by: randyvs
a reply to: Bluntone22

Where's your fuel filter?

In the fuel line about 4 inches before the carb.
The fuel pours right through it.

a reply to: Bluntone22
Head gasket or breather valve?

a reply to: Bluntone22

The fuel pours right through it.

Wait what? You mean the way it's supposed to flow thru it?
If it free flows replace it.

Something is killing your spark it sounds like to me. And if it's only going on at high rpm?
uh! Get a toro.

All I know is you better have that lawn mowed before mom gets home!

I have an older Craftsman riding mower that had the exact same problem. My fix was a bit unorthodox, (I used the same method to fix weapons system problems on the old F-4 fighter aircraft)... a properly aimed whack with a "Louisville Slugger" should fix it.

If not, you at least feel a bit better after hitting the crap out of it.....