Bad Boy Magnum issues

twgoats · Oct 2, 2018

I have a Bad Boy Magnum zero turn mower with a Kohler KT740-3029 25 hp engine. It starts and runs initially but, after about 10 minutes will begin to loose power and surge. It will then stall out, and restart a few times but, will continue to surge and stall. Then after few minutes will stall and not restart, Last year it did the same and we put it in for service. The mechanic cleaned the carb and did a basic tune up. It ran okay, but still acted up every once and while. Now it is doing it constantly. I have replaced the fuel filter, the fuel pump, and the carburetor, checked the fuel lines for blockages as well as the vacuum line to the pump. Any ideas what might be happening?

Tia,

Doug

hawkeye08 · Oct 2, 2018

is the fuel cap vented? perhaps blocked?

twgoats · Oct 2, 2018

Tried running it with the fuel cap cracked open, still had the issue. I am currently ordering a new gas cap to try.

tomplum · Oct 3, 2018

View attachment Kohler SB348 KT stall.pdf

bobmisi · Oct 3, 2018

tomplum said:
View attachment 573409

On my zero turn it was a bad coil. It had two coil packs, so I replaced them both. Dealer had thought it was fuel related and rebuilt the carb, changed fuel filter etc. Most dealers today just throw parts at a problem hoping something will work. Anytime you have an engine that acts up after it heats up, check the coil first.

dalola · Oct 4, 2018

bobmisi said:
On my zero turn it was a bad coil. It had two coil packs, so I replaced them both. Dealer had thought it was fuel related and rebuilt the carb, changed fuel filter etc. Most dealers today just throw parts at a problem hoping something will work. Anytime you have an engine that acts up after it heats up, check the coil first.

Agree with this 100%. Had a Kawasaki that had the same issue.....you'd swear it was a fuel problem, but no, it was coil packs also.

twgoats · Oct 5, 2018

Thanks for the suggestions. Mine does not fall into the serial range for the mod. It only has one coil, they call it a Magneto Module, it seemed to test well but, I am going to replace it just to see. I'll update when I get the parts.

Thanks,
doug

tomplum · Oct 5, 2018

This engine should have a coil for each cylinder. If you feel you may have a coil pack issue, then replace both. 32 584 09-S It is very unlikely that one coil faltering will cause a stall. It will continue to run on one cylinder, sound anemic and have very poor power. If your unit has the vapor recovery hose from the tank rather than a vented cap, try running w/o the hose attached at the carb as a test to see if the stall continues. Best of luck on whatever you decide.

badnewsbears31 · Jul 3, 2019

tomplum said:
This engine should have a coil for each cylinder. If you feel you may have a coil pack issue, then replace both. 32 584 09-S It is very unlikely that one coil faltering will cause a stall. It will continue to run on one cylinder, sound anemic and have very poor power. If your unit has the vapor recovery hose from the tank rather than a vented cap, try running w/o the hose attached at the carb as a test to see if the stall continues. Best of luck on whatever you decide.

Where are the coils located at on a BadBoy MZ Mgnumn 54"?

I am having a lot of the same issues talked about above. I lose power about 10-15 minutes into operation. I have to operate much differently for the next couple hours.

If i disengage the mower deck, about half the time I regain full power, but lose it once I reengage the deck. Sometimes, I have to choke the machine, and engage the park brake to get it to maintain full power.

It has fresh/new fuel. Tank is full. It flows when disconnected from the filter. It flows to the pump with the filter installed. It flows to the carb when disconnected and the key turns the mower over.

I am at a loss as to what I can diagnose next.

Thanks for any advice.

CL

twgoats · Jul 3, 2019

The coils and there are two are under the top plastic cowling/cover. I ended up replacing just about every part in both the fuel and ignition systems. It kind of worked. Things went well until the weather started to get warm again this year. And the problems returned. We finally figured out if we back down on the throttle to about 2/3, it doesn't stall (often). It slows us down a little bit but, it is still faster to mow with this zero turn than the lawn tractors we have had in the past and is cheaper than replacing the mower.
so, we are just living with it for now. Good luck with yours.
Doug J.