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I just had a rather disturbing experience. I've used lots of different gas and never got too fussed about it as long as it didn't ping. I picked up a GS400X a year ago and found it to be more fussy than the two valvers I used to run, but then it's a 10:1 four valve head so, despite the 'Twin Swirls', it's still supposed to have 91 octane gas.
My riding buddy [SV650] is a Shell guy and was raving about the [placebo?] effect of the new Nitro+ 91 that just came out. There's all the usual hype about Extra Cleaning Power and other mumbo jumbo about nitrogen. I decided to try it out. It ran quite well, but the next day my bike only fired one cylinder and then jammed. I put it in gear and rolled it a bit and then tried again. It started, but only on one cylinder and made a clatter for a bit and eventually calmed down.
I couldn't explain that, other than that maybe my gas tap leaked and a float chamber had overfilled and hydraulically seized one cylinder, but what about the clatter? I checked the tap and it was fine, no leak when off. I wrote it off to random fluke, but the next day it happened again. I filled it again with another brand and things seemed okay but after another tank of Nitro+ it did the same thing several times. The sense I got from it, now that I was in forensic mode, was that an intake valve was sticking open after sitting overnight. This seemed odd considering the motor has about 35,000 miles on it and should have loosened enough.
I pulled a plug and it was white and the rim and barrel looked scoured. Usually there is some sort of light tan deposit but this was just too clean. This is a plug with probably ten thousand miles on it and no beauty. Most gas has some alcohol in it and that tends to run lean and clean, but this was more so.
I ran it low and put Chevron 94 [no alcohol, so the pump says] and it's like back in the old days. The harshness that used to come in when it was over 6500 is now gone and the motor seems to run cooler. I'd never bothered to use 94 because it's overkill for octane, and I never subscribed to brand loyalty with gas - although Chevron never let me down, yet - but I'm thinking that just not having the ethanol is a big plus. As Jay Leno says….
We can't expect the oil companies to go very far out of their way to make people with carburetors happy. The government and the corn farmers come before us, and they already pay attention to density to keep our float levels right and keep the volatility within limits that fuel injection wouldn't notice. But it's inevitable that adding alcohol will lead to leanness, and that's going to make for hotter combustion. Sure, alcohol will run cooler from an evaporation standpoint but there's seemingly only enough in there to screw up your mixture. How much different should the main jet be for 5% alcohol? 10% alcohol? I can do a back of the envelope and come up with about one main jet size and maybe a nudge of the needle. IOW a 5% alky mix would lean you by about 2.5% which would mean a 1.00mm jet should be about 1.0125 [the orifice size changes as the square of the diameter] which seems negligible unless you're already on the edge of lean. At 10% you're going to need a whole jet size up to compensate. Or a water cooled, fuel injected motor with an oxygen sensor.
But the only explanation I have for the valve thing is that whatever is in this Shell gas is eating the oil off my intake valve stems and guides as fast as the oil feed from above can replace it. Intake valves don't have the luxury of getting ring/cylinder wall oil castoffs to live on. All an intake valve sees is gasoline and whatever can stay on the stem after passing the seal. Alcohol is known to wash oil films off all too well, which is why alcohol fuelled motors used to use castor bean oil, and lots of it, which adheres really well.
I'm not sure if the gas is the culprit, but I'm wondering if the Shell engineers just got too carried away with engine cleaning technology.
My riding buddy [SV650] is a Shell guy and was raving about the [placebo?] effect of the new Nitro+ 91 that just came out. There's all the usual hype about Extra Cleaning Power and other mumbo jumbo about nitrogen. I decided to try it out. It ran quite well, but the next day my bike only fired one cylinder and then jammed. I put it in gear and rolled it a bit and then tried again. It started, but only on one cylinder and made a clatter for a bit and eventually calmed down.
I couldn't explain that, other than that maybe my gas tap leaked and a float chamber had overfilled and hydraulically seized one cylinder, but what about the clatter? I checked the tap and it was fine, no leak when off. I wrote it off to random fluke, but the next day it happened again. I filled it again with another brand and things seemed okay but after another tank of Nitro+ it did the same thing several times. The sense I got from it, now that I was in forensic mode, was that an intake valve was sticking open after sitting overnight. This seemed odd considering the motor has about 35,000 miles on it and should have loosened enough.
I pulled a plug and it was white and the rim and barrel looked scoured. Usually there is some sort of light tan deposit but this was just too clean. This is a plug with probably ten thousand miles on it and no beauty. Most gas has some alcohol in it and that tends to run lean and clean, but this was more so.
I ran it low and put Chevron 94 [no alcohol, so the pump says] and it's like back in the old days. The harshness that used to come in when it was over 6500 is now gone and the motor seems to run cooler. I'd never bothered to use 94 because it's overkill for octane, and I never subscribed to brand loyalty with gas - although Chevron never let me down, yet - but I'm thinking that just not having the ethanol is a big plus. As Jay Leno says….
We can't expect the oil companies to go very far out of their way to make people with carburetors happy. The government and the corn farmers come before us, and they already pay attention to density to keep our float levels right and keep the volatility within limits that fuel injection wouldn't notice. But it's inevitable that adding alcohol will lead to leanness, and that's going to make for hotter combustion. Sure, alcohol will run cooler from an evaporation standpoint but there's seemingly only enough in there to screw up your mixture. How much different should the main jet be for 5% alcohol? 10% alcohol? I can do a back of the envelope and come up with about one main jet size and maybe a nudge of the needle. IOW a 5% alky mix would lean you by about 2.5% which would mean a 1.00mm jet should be about 1.0125 [the orifice size changes as the square of the diameter] which seems negligible unless you're already on the edge of lean. At 10% you're going to need a whole jet size up to compensate. Or a water cooled, fuel injected motor with an oxygen sensor.
But the only explanation I have for the valve thing is that whatever is in this Shell gas is eating the oil off my intake valve stems and guides as fast as the oil feed from above can replace it. Intake valves don't have the luxury of getting ring/cylinder wall oil castoffs to live on. All an intake valve sees is gasoline and whatever can stay on the stem after passing the seal. Alcohol is known to wash oil films off all too well, which is why alcohol fuelled motors used to use castor bean oil, and lots of it, which adheres really well.
I'm not sure if the gas is the culprit, but I'm wondering if the Shell engineers just got too carried away with engine cleaning technology.
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