81 xs400 got 87 octane!

[bornloser]

So I went cheap the other day and just put the lowest of the low octane in my xs400's tank at the gas station and I immediately regret the decision. I started losing power in spurts on my 40 mile ride home from work about ten miles out from the gas station in the form of slow or no response from the throttle then the engine puttered out like it was running too lean a fuel mixture. Managed to get the bike home and have started playing with it to see whats what.

The bike will start up with the choke half open and then idles up pretty high but dies if I adjust the choke. What strikes me as oddest is that if I crank the throttle from a flat idle the bike just sputters out. Any ideas?

 

[honda53rider]

Thats crazy man i havent gotten my 77 running like a top but this may be part of my issues on getting it going. Well i hope that it started running when you got some fresh gas in the tank.

 

[mydlyfkryzis]

More likely a bad load of gas from the station. Most Japanese street bikes are designed around 86 PON. You should not have any issues with 87 PON.

More likely you got water in the fuel, or something else.

Check the petcock for water in the bowl. Drain the bottom of the carbs. Drain into a small container and see if any water or debris comes out.

FWIW, my bike was running fine. I filled up, pulled away, and it started missing and running on one cylinder. The left spark plug cap decided to fail at that moment. I thought I had bad gas at first too...

So something else might of gone wrong, coincidental with your fill up. Heck, your tank vent might of clogged, and gas stopped feeding to the carbs....

 

[fresh_c]

Lower octanes are more likely to have a negative effect in the form of pinging/detonation if you are running very high compression. Basically, the higher the octane, the more stable the gas is at higher compression. I have to run 93 in my truck because I'm running 9 PSI of boost, but a bike making 10:1 compression should be good with the cheap stuff. I have found (in my truck) detonation typically occurs when running in a high gear/low rpm and grabbing a handful.

Your bike should run fine on 87 and like others have said, the poor running is probably from bad gas, not from lower octane.

 

[orlowskij]

Yep, sounds like an issue unrelated to octane. Drain the carbs and check the plugs.