Switched to premium gas, now idle is very rough

[paulcbrowne]

After a couple of discussion threads I looked at what my RT owner's manual said and switched to premium gas. I noticed an immediate boost in power. After two tanks of 93 AKI, I think the gas mileage is better, but too early to tell.

 

However, my idle seems to have gone to the dogs. The bike sometimes stalls when first warming up and the idle is really rough. Has anyone else noticed this side effect of switching to premium fuel?

 

Previously I had been running 89 AKI and an occasional tank of 87. The bike has 4,000 miles on it. The idle was pretty good for and RT before the switch.

[Firefight911]

My guess is that it is not the gas you currently are using.

 

You may have had a bad tank flow through at some point.

 

Try running some Techron fuel system cleaner in a tank.

 

Check the bell cranks on the throttle bodies to ensure that the throttle cables are laying flat in them without any pebbles or debris that could cause one of the butterflies to go out of synch.

 

Double check your throttle body synch (TBS).

 

You are coming up on a 6k service shortly and you may be experiencing a situation where your valves are seating and they may be in need of adjustment. This will take your bike out of synch. and potentially cause a rough idle.

 

Double check to make sure you have no air leaks. Are all the ports either covered or connected appropriately.

 

That should get you going.

 

Hope this helps! Let us know how it goes.

[Ken H.]

I didn't "go there" in the other thread that is going right now about regular fuel in a hexhead, but I would just about swear my 12GS runs rougher in general on premium fuel.

[pbbeck]

So what do you use in your GS – midgrade (89) or regular (87)?

[Ken H.]

So what do you use in your GS – midgrade (89) or regular (87)?

regular (87)

[Paul Mihalka]

I may be mistaken (happens often) but I think adding ethanol raises the octane number but leans out the mixture. Is it possible that 93AKI has the full allowed 10% ethanol and the 87 has less? With premium it might be running a bit lean at idle and low throttle/rpm causing rough running. My devaluated $.02.

[RFW]

I may be mistaken (happens often) but I think adding ethanol raises the octane number but leans out the mixture.

That is exactly right. Ethanol requires less air to burn, since as C2H5OH, it carries some of its own oxygen. It also has a higher octane number. Too bad that, when all things are considered (including the greenhouse gas -CO2- produced, and energy used, in the production of ethanol, and also the poorer mileage you get with ethanol), there is no environmental benefit whatsoever to using it. The main benefit is that it lets politicians strut around pretending to be environmentally conscious.

[Boffin]

I may be mistaken (happens often) but I think adding ethanol raises the octane number but leans out the mixture.

That is exactly right. Ethanol requires less air to burn, since as C2H5OH, it carries some of its own oxygen. It also has a higher octane number. Too bad that, when all things are considered (including the greenhouse gas -CO2- produced, and energy used, in the production of ethanol, and also the poorer mileage you get with ethanol), there is no environmental benefit whatsoever to using it. The main benefit is that it lets politicians strut around pretending to be environmentally conscious.

 

It is worth bearing in mind that in Europe, high octane fuel is obtained by adding synthetic esthers that improve the burn of the fuel and increase its calorific value. It can even give better gas mileage in engines designed to run on lower octane fuels. IOW, we get the benefit of F1 fuel technology in street fuel pumps. It is for this reason that BMW tuned the hexhead RT to run on 98RON (about 93 US octane)

 

 

Andy

[Heywood]

That is exactly right. Ethanol requires less air to burn, since as C2H5OH, it carries some of its own oxygen. It also has a higher octane number. Too bad that, when all things are considered (including the greenhouse gas -CO2- produced, and energy used, in the production of ethanol, and also the poorer mileage you get with ethanol), there is no environmental benefit whatsoever to using it. The main benefit is that it lets politicians strut around pretending to be environmentally conscious.

 

Sorry Bob, me thinks you are wrong about the net energy gain. Using the average US corn yield, an acre of corn will produce around 450 gallons of ethanol. You'll also have 2750 lbs of high quality animal feed from the process. The vast majority of that land is already producing corn or soybeans. The difference now is that demand is pushing the price of corn and beans to profitable levels for many farmers, without the need for price supports.

 

Even if the net energy gain was zero and there were no environmental benefits, I'd sure as hell rather produce as much domestic ethanol as possible in order to reduce the need for imported oil from all those places that seem to hold us in such contempt.