312-8 backfires , chokes

[Rubberman 6]

I have a 92 toro wheel horse 312-8. This year I replaced the mechanical pump but it never really worked right so I went with the electrical pump that I seen on YouTube. Problem now is that mower, under load, starts backfiring, choking out. I have to throttle it down and choke it some. Do,I need a fuel pressure regulator to correct this?

Edited July 22 by Rubberman

[ebinmaine 67,483]

3 hours ago, Rubberman said:

I have to throttle it down and choke it some

 

This would indicate that you're getting too much air which is also ... not enough fuel. 

 

Do you use non Ethanol gas? 

 

Have you replaced ALL of the fuel lines?

 

Have you removed cleaned and reassembled the carb?

 

Does the carb have a loose throttle shaft? 

 

[Handy Don 12,217]

3 hours ago, Rubberman said:

Do,I need a fuel pressure regulator to correct this

If the fuel pump that you added is delivering at no more than 3 PSI, then the float valve in the carb is enough to manage it. If it is more, you need a different fuel pump, not a regulator.

Backfiring means that unburned fuel is getting to the hot exhaust pipe/muffler. This will gradually kill the muffler.

The usual causes are a leaking exhaust valve that lets fuel/air out during the compression cycle or not getting a good spark.

What level of mechanical skills, interest, energy, & time do you have to dig into this?

 

[Rubberman 6]

2 hours ago, ebinmaine said:

 

This would indicate that you're getting too much air which is also ... not enough fuel. 

 

Do you use non Ethanol gas?  87octane pump gas

 

Have you replaced ALL of the fuel lines?  Yes

 

Have you removed cleaned and reassembled the carb? No

 

Does the carb have a loose throttle shaft? No

 

this backfiring didn’t happen before the electric fuel pump

 

 

[Rubberman 6]

1 hour ago, Handy Don said:

If the fuel pump that you added is delivering at no more than 3 PSI, then the float valve in the carb is enough to manage it. If it is more, you need a different fuel pump, not a regulator.

Backfiring means that unburned fuel is getting to the hot exhaust pipe/muffler. This will gradually kill the muffler.

The usual causes are a leaking exhaust valve that lets fuel/air out during the compression cycle or not getting a good spark.

What level of mechanical skills, interest, energy, & time do you have to dig into this?

 

 Fuel pump is rated between 2-4psi. Backfiring didn’t happen before the electric pump 

 

2 hours ago, ebinmaine said:

 

 

Edited July 21 by Rubberman

[Handy Don 12,217]

1 hour ago, Rubberman said:

 Fuel pump is rated between 2-4psi. Backfiring didn’t happen before the electric pump 

 

I’d wonder if the float valve was being overpowered by the pump, but that would make the engine run rich or even flood. You are having to choke and back off on throttle. But backfire came after the pump add. These are contradictory outcomes.

The only thing that explains it to me is that the float valve is sticking due the higher pressure. As the fuel in the bowl drops the engine starts to run lean and needs choke. Then the float unsticks and the engine is running rich on a gush of fuel and boom, a backfire.

My impression is too much fuel pressure and/or a worn needle valve/seat combo. I don’t think you’ll easily find a fuel pressure regulator for pressures that low and if you do it’ll cost much more than a lower-pressure pump.

 

 

[gwest_ca-(File Mod) 11,041]

Have you checked the valve clearances? May be too tight and under high heat a valve may be not closing.

 

Lean condition could be a vacuum leak where the carb mounts on the block. I use a propane torch and replace the tip with a rubber hose so raw propane can be applied around the base of the carb with the engine running. If there is a leak the propane will affect the engine performance. Use a very low flow of propane. Get it turned on before starting the engine so you can hear the propane supply. You do not need much.

 

Have you ever cleaned the fuel tank? You would be amazed how much junk they collect in 35 years. The tank screen is not very big.

[953 nut 55,220]

10 hours ago, Rubberman said:

Do you use non Ethanol gas?  87octane pump gas

Regular pump gas with ethanol will destroy internal components of a fuel system over time. We have seen many threads on here with photos of containments left in carburetors from ethanol. If you add a significant amount ( four to five times the recommended amount)  of Berryman B-12 or Seafoam fuel treatment to a tank full of non-ethanol gas it may clear up the problem though a thorough cleaning and rebuild would be best.

Switch to non-ethanol gas to avoid future problems, this site will guide you to stations that sell it.         https://www.pure-gas.org/

[953 nut 55,220]

8 hours ago, gwest_ca said:

use a propane torch and replace the tip with a rubber hose so raw propane can be applied around the base of the carb with the engine running.

Gary didn't mention this part,          Don't attempt to light the torch!                    

[lynnmor 7,305]

12 hours ago, Rubberman said:

Have you removed cleaned and reassembled the carb? No

 

I think the answer is right here.

[Rubberman 6]

9 hours ago, lynnmor said:

 

I think the answer is right here.

I removed the carb, there was junk in the bowl. Reassembled. I didn’t check needles. I had a couple mechanical fuel pumps so I made 1 good pump. Removed the electrical pump. It starts and runs but still back fires using the mechanical pump when engine is at high rpm’s or under load. So I guess my next move is to make sure needles aren’t clogged and check valve clearance. 

Edited July 21 by Rubberman

[lynnmor 7,305]

4 minutes ago, Rubberman said:

I removed the carb, there was junk in the bowl. Reassembled. I didn’t check needles. I had a couple mechanical fuel pumps so I made 1 good pump. Removed the electrical pump. It starts and runs but still back fires using the mechanical pump when engine is at high rpm’s or under load. So I guess my next move is to make sure needles aren’t clogged and check valve clearance. 

It is easy to miss dirt, use a can of carb cleaner with a straw to flush all holes.  You should have new spark plugs to rule that out.

[Handy Don 12,217]

26 minutes ago, Rubberman said:

I removed the carb, there was junk in the bowl. Reassembled. I didn’t check needles. I had a couple mechanical fuel pumps so I made 1 good pump. Removed the electrical pump. It starts and runs but still back fires using the mechanical pump when engine is at high rpm’s or under load. So I guess my next move is to make sure needles aren’t clogged and check valve clearance. 

Full carb cleaning and valve clearance and operation check. Valve issue could be as simple as accumulated carbon in the combustion chamber preventing full closure.

Edited July 21 by Handy Don

[953 nut 55,220]

1 hour ago, Rubberman said:

It starts and runs but still back fires when engine is at high rpm’s or under load.

If an engine idles well, but runs erratically when revved up, like it hits and misses, pops and backfires, then chances are, it needs a new condenser/capacitor. And always install a condenser/capacitor with the wire facing downward so rain water and/or when washing off engine, water will not enter inside condenser/capacitor, ruining it. With water inside the condenser, this will also allow it to idle well, but cause it to run erratically when revved up.

The Kohler 230722 Condenser fits all battery ignition single cylinder and twin cylinder from the K-90 to the K-582.  The 235786 condensers are for the magneto equipped Kohler engines only K-161 to K-301.

[Rubberman 6]

Adjusted the valves to spec, disassembled carb again. Removed needles, cleaned needles, blew out passages. Still back fires at higher rpm when I engage blades. Low rpm’s it idles fine and engaging blades is fine. 
 

next step I guess replace plug and condenser. I cleaned the plug earlier today. Ran it several times and it’s black again.

[Rubberman 6]

20 minutes ago, 953 nut said:

 

The Kohler 230722 Condenser fits all battery ignition single cylinder and twin cylinder from the K-90 to the K-582.  The 235786 condensers are for the magneto equipped Kohler engines only K-161 to K-301.

The engine is model M125

[ebinmaine 67,483]

2 minutes ago, Rubberman said:

cleaned the plug earlier today

 

I stopped cleaning plugs several decades ago. 

The smaller engines can be very sensitive to having excellent ignition components.  

 

I've CLEANED plugs with slightly better running and immediately CHANGED the plug to have it run perfect.  

 

 

[Rubberman 6]

I don’t this wheelhorse  has a condenser 

[ebinmaine 67,483]

2 minutes ago, Rubberman said:

I don’t this wheelhorse  has a condenser 

Late 80s should have a Magnum engine which won't have a condenser 

[tunahead72 2,412]

5 hours ago, Handy Don said:

Full carb cleaning and valve clearance and operation check. Valve issue could be as simple as accumulated carbon in the combustion chamber preventing full closure.

 

I like this train of thought...  Next time you take your plug out, take a look through the hole with a good flashlight, look for any carbon buildup in the combustion chamber.  If you see a lot of carbon, it might be time to remove the head for a closer look and thorough cleaning, I'd recommend replacing the head gasket, and flatten the head while you're at it.

 

[ebinmaine 67,483]

5 hours ago, tunahead72 said:

flatten the head

 

Good advice. 

We use a carefully chosen,  known flat,  piece of steel. 

Tape the paper to it. 

[Rubberman 6]

Update:

 

replaced the spark plug and everything runs just fine. At full throttle and blades engaged it runs fine. No

more backfires or popping. 

[ebinmaine 67,483]

2 minutes ago, Rubberman said:

Update:

 

REPLACED the spark plug and everything runs just fine. At full throttle and blades engaged it runs fine. No

more backfires or popping. 

 

 

Excellent!  Glad to hear that. 

 

 

[tunahead72 2,412]

43 minutes ago, Rubberman said:

Update:

 

replaced the spark plug and everything runs just fine. At full throttle and blades engaged it runs fine. No

more backfires or popping. 

 

All good for now, but you mentioned earlier that your old plug turned black soon after you cleaned it.  I would keep a close eye on the new one and make it be the first thing to check if your engine starts running poorly again.