just wondering if the marshmellow would work on the new 37?

I wouldn't do it.. It's been stated these things run pretty lean from the factory and an exhaust would make it worse. There's really no way to tune these things yet to change the fuel map so you realistically wouldn't gain any hp.

I have a non baffled Marshmellow on a 37 efi prodrive and its actually so rich it will burn your eyes. I didnt notice any difference except for noise on mine but it for sure does not run lean.

How do you know they are lean other than heresay? I know a guy who tested his exhaust on a 37 EFI with a wideband 02 it was at 13 AFR.

I plan on changing the oil and filter again on mine this weekend and running it with some fresh plugs, I'll probably take a few sets and read them and see exactly what it's doing. I don't have a removable wideband, the only one I've got is the type you permanently wire in and install. Which I may do in the future. Just not now.

You are right, I apologize. Was thinking backwards in relation to stoich ratio.

Lol so these motors come running lean? Who fed you that bullshit. They have people running exahust and heads on factory tune and it's running just fine

I posed the question on the "Fuel 101" thread- how will it be different, if at all, when running the EFI 37, regarding gas maintenance, etc. I am ignorant of the design but if there is no carb, this should mean no gumming up with varnish because of ethanol/bad gas/etc. ?? Is the EFI safe to run with 87 octane? Are all carb models 23-35 HP going to EFI exclusively? I hope to upgrade from my 27 Kohler LT to a 37 EFI LT (if available), yeah I know why not a surface drive shorty? Well, it is hard bottom/skinny/ no mud around here... the only solace from the preceding posts is that I may not feel too bad if I don't have to buy a shiny stainless steel muffler since apparently it won't do chit for the motor.

I usually run 87 towards the end of the month when money starts running low But normally run supreme..87 won't completely kill it but its not the best for it

I have ran plain 87 all the way to non ethanol 93 octane. Briggs has these set to run on whatever fuel their customers can get ahold of, which can be only 87oct in some cases. I will say I noticed zero starting, idling, or performance difference from one fuel to the next. It's a common misconception that 93 is cleaner or will make more power just by dumping it into the tank.... Not the case. A lot of times the 93 octane fuel will sit in storage tanks longer than 87 because less of it is purchased in general. Not a 100% rule but something to think about. Also, the octane alone will not create more power just by burning. The octane number only signifies its measured resistance to predetonation, or "knock".. This is tested in a controlled environment to determine these numbers. It's actually an equation that's used to come up with the number displayed on the pump. If you look real close, it's acually printed on the pump somewhere.

Now, regarding the EFI system itself. They are much less prone to fuel system issues when allowed to sit up simply based on design. In a carbureted engine has a bowl and small jetting for the fuel to sit in and create varnish in a smaller amount of time. The engine relies on vacuum created by a falling piston to pull and mix that fuel into the incoming air stream. The port located EFI system that Briggs uses does not have to worry about that. There is a pressurized fuel rail that stores fuel behind an iniector plunger, when the ECM commands that injector to open, there's 42psi of stored, positive pressure waiting to push the fuel into the intake tract. It doesn't rely on engine generated vacuum to supply its fuel.... This is one of the reasons that EFI engines in general do not have the same issue starting and running when left to sit for extended periods like a carb. Yes, the fuel still has the potential of becoming stale and losing quality, but the deposits don't inhibit the fuel flow basically. It will either push past them or the fuel will carry it along into combustion. Yes, it still may run like crap until it burns all the bad and gets to fresh gas, but chances are you wont be taking it apart to make it run.

I pulled my plugs, adjusted my valve lash and changed my oil/filter this weekend at 30hrs and aside from my rockers being tighter than spec, I did notice my plugs did appear like they had been ran on the leaner side, I would have guessed the opposite prior to pulling them. I attribute my tight valves to engine break-in and the valve seats getting seasoned and the valves recessing a bit in the process. Normal I'm sure, if gone unchecked though, an excessively tight valve adjustment will burn a seat quickly....

So after my findings this weekend... Even without an AFR readout in front of me, I would feel confident to say that anything that adds additional airflow to one of these things is asking for issues. Some may run for hundreds of hours and never have one problem, but it defies common sense to add air flow to an engine that's probably already on the lean side (Id assume for EPA BS)

Good explanation! This means that the addition of Stabil, Seafoam, Startron, or other stabilizer additive to the gas on an EFI motor still makes sense, though you will not likely be as negatively affected by "varnishing". I like that plus no messing with carb rebuild and such!

Cleaning an EFI System is simple, pull the pressure lines and spray them out or let them soak in a cleaner, clean your injectors, and roll out. Id assume that this probably wouldn't have to be done for several hundred hours. I don't run anything but gas in my gas. If it's going to sit long enough to need sta-bil or such, it gets drained into the lawnmower or pickup. Disconnect the fuel line from the tank, run it til it dies. This method has never failed me yet.

Thanks for all the input guys look like I'll just have to stay on the quiet side for now when i get my 37 gtr