New 425 question

   / New 425 question #1  

Frank Sorbello

Gold Member
Jul 12, 2011
Power Trac PT-422
Curious, PT is offering a 28hp Robin/Subaru Fuel Injected motor for $500 more. Would you do it or stick with the 25hp carb R/S engine?
What are the pros and cons to going FI?
   / New 425 question #2  
I put the 28 hp engine in my tractor and am glad I did. I find it easier to start in the winter and it has the extra power I needed on my hilly land. It also uses measurably less fuel.

Having said this, I would recommend the FI engine only if PT also switched to the stock Robin exhaust header/muffler and put in a side fan. If all they did was disconnect the temp sensor wire on the crankcase, you will fry that engine. I trust Subaru to determine if their engine is overheated, not PT. The temp sensor protects the engine from overheating by immediately shutting off the fuel pump.

Here is all I had to do to make the 28 hp FI engine work in a PT-425:

What did PT do?

If they did everything I did, then it is definitely worth the extra $500.
   / New 425 question #3  
Personally, I'd take FI over carburetor any day of the week for $500. You'll save on fuel, you get more HP, and you aren't going to have fuel spilling into your oil. Oh, and you won't be accidentally coking your engine when you forget to open the choke back up again. But, YMMV...

Kent's photos should give you lots of ideas on how to improve the cooling, and there are some great threads on how to insulate the 'standard' design muffler.

Good luck,

   / New 425 question #4  
Well that is good news. Looks like they finally took some of the innovation from this forum and put it to good use. I know there have been several people over the past 4 years who asked PT for this option, after they read about Kent's 28FI conversion here.

OMHO, best $500 option you could buy. All you have to do is search this forum for "cold weather starting" to find out why. And then take Kent's advice and ditch the crummy PT muffler/exhaust header.

Pros: starts easier in cold weather, gets significantly improved gas mileage.
Cons: could have issues with overheating unless the muffler is improved.
   / New 425 question #5  
I did not see this on their Web site. It is a great idea.
   / New 425 question
  • Thread Starter
yes, Christy in sales did.
   / New 425 question #9  
Have any taken temps on the header, or the muffler after the mods. I took some today on my stock machine, after working for about 2 or 3 hours, and the header was 425 and the muffler on the outside was 525. Just wondering what temps people are seeing after a mod.
   / New 425 question #10  
Have any taken temps on the header, or the muffler after the mods.

From Kent's post (note this is with the Robin 28FI, which reportedly runs hotter):

With the Robin exhaust and the side fan running, the temperature sensor screw dropped to 172 degrees! There just isn't as much heat to move out from under the heat shield. While the PowerTrac muffler is I suspect OK with regard to minimizing backpressure, it does poorly with respect to velocity. The Robin header and muffler more speedily remove gas and heat. The temperature at the top of the muffler is only 220 degrees, the bottom a mere 128 degrees. The middle of the flexpipe is only 130 degrees. Compare that with the 672 degree PowerTrac muffler in the same location! The tub under the muffler (which is also further away from the tire but high enough so the tip is above the bottom of the tub) is 160 degrees, down from the original 235.