Aviation Fuel in a yamaha 2 stroke

[jukes23]

Hi,

I ran my Yamaha 115 2 stroke a week or so back and it had some hesitation in the holeshot. I was talking to a friend who is a small engine mechanic who suggested that the carbs have some varnish built up due to a long sitting period (not used in over a year) and suggested I use a high octane fuel...like racing fuel or aviation fuel. I called around looking for racing fuel and one of the places that sells it (I spoke with the lead mechanic) also suggested aviation fuel first.
I can easily get this, but from what I can tell, this is leaded fuel running around 100 octane. My plan was to run 3-5 gallons through it to try and clean out any gunk. If that doesnt work, I will have to take the carbs apart and clean it.
I still feel kind of leary running this type of fuel through my engine. Is it ok? I read something about it causing issues with oxygen sensors and such, but I dont think those are on my outboard.
Any help is appreciated.

 

[steelespike]

Re: Aviation Fuel in a yamaha 2 stroke

Just get a product something like sea foam mix per directions.You will probably
need to rebuild the carbs anyway.

 

[jukes23]

Re: Aviation Fuel in a yamaha 2 stroke

I tried that already..was going try this as the nuclear option.

 

[rodbolt]

Re: Aviation Fuel in a yamaha 2 stroke

why not try methanol and nitro methane or maybe some liquid rocket fuel or even jet fuel like JP-5?
actually your motor is designed to run on unleaded 87 octane.
snake oils and such usually just blow the motor
if the motor is running lean due to a clogged or varnished jet piston temps increase and detonation occurs.
would it just be to simple to fix the dang thang ?
cleaning the carbs on that enginer is simple, most times just replace the fuel pump dissasemble and clean the carbs use a new fuel bowl gasket and your done in an hour and a half.
more than that and your milking it .
dont worry about sensors and such your engine has none.
you will find a loss of power with av gas.
try speaking with a real mechanic that has actual training in yamaha two strokes.
DO NOT run snake oils and AV gas.
why would you think a higher octane fuel would clean anything? do you even know what octane rating is and how its derived?

 

[pine island fred]

Re: Aviation Fuel in a yamaha 2 stroke

What RODBOLT said. Higher octain will not clean the fuel system nor will it hurt the engine. Where you gettin 100LL anyway? FBOs are only supposed to pump that stuff in piston planes only.
History of octain ratings is pretty interesting. Rating went to 100 with the use of tetreteral-ethal-lead ( spelling??) All base on detonation. Later the refiners came up with aromatics and a product called iso-octain which pushed the octain rating over 100. Tops was what they called 115/145, 115 was the rating for if the carb was leaned out, could be adjusted in flight, and 145 was the rich mixture rating. Remember gas being color dyed to identify the octain. Big old radials today have a limit on manifold pressure as the highest octain available today is 100 low lead.
Dont know the real octain rating on the SUNOCO 260 that came out of the custom blending pump. Had to be an advertising number as gas never went above 145 RICH.
RODBOLT, your son in school? regards FRED

 

[jukes23]

Re: Aviation Fuel in a yamaha 2 stroke

ok, so is there a good step by step instruction or diagram on how to clean the carbs?
Pine, there is an aviation center next to our airport that sells fuel. Its AVGAS100, not AVGAS 100LL.

 

[rodbolt]

Re: Aviation Fuel in a yamaha 2 stroke

Fred
yep son is at western carolina university and daughter is trying to get into the advanced automotive program at martin community college.
glad to see your still kicking about,when ya gonna see us at the crab again?

Jukes23
using the service manual but the basics on that V4.
remove the choke solinoid,remove the airbox,carefully remove the oring holding the choke plunger to the carb,unclip the oil link,remove the choke links,remove the throttle links,remove the top carb and fuel line,remove the lower carb and fuel line,remove the fuel pump,clean the engine filter.
remove the fuel bowls from the carbs,carefully remove the main and pilot fuel jets and floats. mark or lay out the floats so they can be reinstlled in the sme location with the same needles.
clean the bowls,jets and nozzles.
nozzles are NOT removable.
reassemble bowls using new gaskets.
reassemble carbs and install new fuel pump.
perform link and sync as per service manual.
go fish.
unless they sink its rare to have to dissasemble anything from the carb body as only the bowl holds the fuel that turns to jelly/varnish.
pay careful attention to the pilot fuel jet,main jet and the tiny passage from the main well to the pilot fuel well.

 

[pine island fred]

Re: Aviation Fuel in a yamaha 2 stroke

Never saw AVGAS100, however most of my experience was with turbins. Commercial engines use JET-A which is basically kerousine. Military use to use and maby still do, JP-4 which was about 60% gasoline. We had a procedure to adjust the fuel controls if only JP-4 was available but I never saw it happen. Have seen JET-A pumped into military craft, maby thats what they use now. regards FRED

 

[rodbolt]

Re: Aviation Fuel in a yamaha 2 stroke

the turbines on the USS Arliegh Burke used JP-5 as did all our P-250 dewatering pumps. we carried no gasoline onboard.

years ago we tried running a highly modified 427 chevy on the 110 octane blue gas from Cleburne airport.
other than the hassle it really did nothing.
we later found the additive package to prevent excessive vaporization at altitude and keep fuel icing down worked to our disadvantage.
in other words av gas simply isnt blended for use on land/water craft.

for the 2 stroke yamaha 115 87 unleaded pump gas is what its designed to run on if it wont its broke and needs repairs not snake oils.

 

[jukes23]

Re: Aviation Fuel in a yamaha 2 stroke

Hey Rodbolt,

Thanks for the quick overview. I am going to order the parts I need and do this next weekend. I checked the parts schematic and by bowl gaskets, do you mean Float chamber gasket? I want to make sure I order the right parts. So parts needed are two float bowl gaskets and one fuel pump.

Anything else (ordering the manual too )

 

[rodbolt]

Re: Aviation Fuel in a yamaha 2 stroke

that is where I would start. depending on your carb design you may need orings for the main jets. if your main jets are a 12mm brass hex with a screw driver slot you may need them, if the fuel bowls have a shiny 12mm plug no slots you wont.
make sure you carefully follow the link and syn procedure and understand throttles closed vs throttles sitting on the idle stop screw.
inspect the throttle roller for flat spots.
check idle timing,pickup timing and WOT timing.

 

[jukes23]

Re: Aviation Fuel in a yamaha 2 stroke

Great,
I went to my local marine supplier (help the local peeps when I can) and picked up the filter strainer (figured I would replace that) and the bowl gaskets, I had to order the fuel pump and fuel pump gasket and should be in around wednesday. Will keep you posted on progress.

Thanks for your help.

 

[jukes23]

Re: Aviation Fuel in a yamaha 2 stroke

Just a quick update on the issue above. I took the carbs off, cleaned the bowls, floats and jets out. there was some build up on a couple of the jets which we flushed out with carb cleaner. I also replaced the fuel pump. Afterwards, we had to adjust the carbs, but needed to do this with a dunk test. We wanted to put it in the water and do it, but we had about a 20-30 mph head wind. kept it on the trailer, dunked it in at the ramp and did the final tune.
Took it out today and it ran like a scalded cat!! Was pulling 5500 rpms and no issues with the hole shot. Just wanted to thank those that provided insight and help on this issue.