We (my 13yr old was the Junior driver) ran at OVRP yesterday, and initially used up our remaining 110 octane gas from Englishtown, which I mixed 8oz Motul 800 w/ 1 gallon of the gas. I have been running 1 1/4 turns on the high carb setting as per the Leopard manual.
The engine ran superbly, and pulled upto 16700 rpm making me change the gearing.
I then purchased 2 gallons of premixed gas from OVRP and added that, and during the heat race, the engine started bogging down on the straight, at 15000, then surge to 15400, bog, then surge to 15800, then surge to 16000, etc. He did not have the power to pass on the straight, which he previously had.
I went to the shop to ask if they had any thoughts.
It turns out that the OVRP gas is 93 octane. And they mixed it with 3oz oil per gallon (for Rotax) instead of 8oz, and someone suggested that this would cause it to bog.
I added oil to get the remaining gas to the right mix, and we tried again in the race. Same thing, bogging down.
Both sessions were long, 15-20 laps, 37 secs each. So we ran with this bogging for almost 20-25 mins total.
The spark plug was new that morning, 0.028 gap.
Again, everything ran great till we changed the gas. He had the fastest lap time in the qualifying, beating even the experienced (at that track) Rotax Jrs.
– with 93 octane vs 110 octane, do I need to run a richer carb setting? The Leopard manual does not say anything about settings for different gas, so I did not adjust this.
– would less oil in the gas cause any problems?
– Could the carb be dirty internally?
I am very nervous that the engine might have gotten damaged if this is indeed lean running. How can I inspect for this?
Should I simply wait till next week at Englishtown, put in 110 octane gas again, and see if it still does this?
Can I test this any of this on the stand? Is it OK to rev to 16000 rpm on the stand without any load on the wheels?
Yes, less oil in the fuel can cause serious problems . The extremely rich fuel/oil ratio these engines run is to protect them at high rpm’s where heat and friction can destroy an engine quickly. If you aren’t comfortable with pulling the head of your engine yourself , pull off the exhaust pipe and header , look in thru the exhaust port and inspect the cylinder visually and see if there is any scoring, galling etc. Also pull the spark plug out so there is no compression and turn the engine over while looking thru the exhaust port. Look closely at the piston as it travels by, usually the first signs of damage show up on the exhaust side of the piston and cylinder as that is the hotter side. Hopefully everything is ok. The higher octane in fuel prevents detonation in an engine , also called spark knock. It usually shows up under high load, high rpm conditions just like you have when racing wide open. Detonation can destroy an engine. If your engine seemed to run ok except at high rpm you could have been experiencing detonation, and switching back to 110 octane race fuel should stop that. Hopefully you have no engine damage.