Kohler 7 series sputtering, backfires, loses power

[ShanO]

Hey all,
Running a Kubota with the 7series 750cc 25hp Kohler. Chasing a power loss issue, 400 hrs..
Runs perfect each day for the first hour or so then it'll start, decreased rpms, backfiring, both under load and not. It's typically intermittent once it begins. Could be a few seconds to minutes then run fine for a bit and it'll start again....
Here's what's been done thus far, between myself and 2 dealerships..
New plugs, air filter, carb clean, inline fuel filter.
Just got it back from Kubota and of course they couldn't get it to replicate the issue. All they ended up doing was cleaning out the fuel tank.
So perhaps a coil once it gets hot?? Any help would be great as I'm not sure what to do with it next.
Thanks

 

[ILENGINE]

Lets start with the actual model and spec number off of the engine tag. series 7 750 cc doesn't mean anything other than to confuse people. Could be a coil breaking down due to heat, but some of those engines had other issues that may be caused by other things.

 

[slomo]

Here's what's been done thus far, between myself and 2 dealerships..
New plugs, air filter, carb clean, inline fuel filter.

Some real CSI deductions going on. LOL

Any of those parts actually test bad?

Last dumb comment, I would avoid those so called dealerships. Look for a small shop with one guy. Usually get better service.

then it'll start, decreased rpms, backfiring, both under load and not.

Where is it backfiring from exactly?

If it was mine, I would do the below tune-up items.

1.Clean block and cooling fins yearly. Neglect this and you get engine damage.
2.Dump and flush fuel tank again. Blow out with compressed air both ways.
3.Install new fuel lines, filter and shut off valve from tank.
4.Adjust valves to factory specs.
5.Check spark, coil/s hot and cold.
6.Oil at the full mark, Not over or under.
7.Boil clean carb.
8.Sharpen and balance some blades.
9.Check tire pressure.

 

[sgkent]

I had this sports car. Every day about the same time, same mileage from home it would start mis-firing for a while on the freeway. I chased all the usual culprits. Then I realized it was really happening in the same turn on the freeway. A distributor wire was rubbing on the fender and grounding the distributor out a little. Had nothing to do with time at all except I was in the same spot at the same time each day.

Keep a log book for a while when you start, when it runs rough and what you were doing. If it is still time and or temperature related, the shop can better recreate the conditions. To be frank, lots of mechanics have no interest in chasing intermittent problems other than throwing parts at it. That said - the tune up was a good place to start. I hope they adjusted the valves too.