old bike+high octane=horrible performance?

[GSJoe]

I made a big mistake yesterday by putting 94 Ultra in my KZ. It started fine cold blooded as usual but fine. Soon as I got on the road, however, it bogged real bad and soon as I got it into the lot of a nearby lawyer's office it stalled. It took me 10 minutes to restart and at one point it even belched black smoke and backfired. After I finally I got it running, the was a lot of smoke coming from the engine block. I took it for a little ride and it seemed to be running but not as smooth as when it had 87 in it. After I got home, I let it sit all day and that night it would not start. I think that it was detonating real bad which caused the backfire and black smoke and also the engine smoke. When I get payed tommorrow I am going to get a spark plug wrench and pull the plugs to see if they are fouled. I'll probably wind up replacing the plugs and draining the tank. I just hope that I didn't cause any more damage.

[earlfor]

I dont think you can hurt anything by putting hi test in the bike, but its a waste of money. It will run as well as it can on the specified 87 grade. Guess you already figured that out though. :-)

Earl

[SqDancerLynn1]

I would bet you got a tank of water ?? Your bike should run fine on 94 Drain the tank & the float bowls

[Jethro]

Yep, I run the 93 in im bike when I wanna look cool in front of my friends. It runs fine, but no better than 87. When I'm alone, gimme the cheap stuff.

[GSJoe]

I would bet you got a tank of water ?? Your bike should run fine on 94 Drain the tank & the float bowls

Well we had just gotten a delivery not long before I filled my tank so that could be possible.

[brveagle]

i routinely run anywhere from 87-91 octane in my bike.. no problems...granted it's not 95, but still. Octane doesn't affect performance. (unless you go too low)

I think you just got a bad batch of gas...

[Hotblack]

That definitely seems out of order. Higher octane gas is more difficult to ignite than lower octane stuff, but not THAT much. No way should good 94 octane gas cause that in any street engine. AV gas (over 100 octane) could cause problems, but not THAT serious. Sounds like water.

I agree on the lower octane angle - as long as you're not pinging your octane is fine, no need to go higher. GS engines are relatively low compression, and designed for low octane gas. small combustion chambers also require less octane than larger ones. Something that could increase octane needs are carbon deposits, which can bump compression and also provide surface irregularities which help cause detonation.

[GSJoe]

Yeah I just talked to the guy at Advanced and he said the higher octane probably knocked something loose. I'm gonna change the plugs and put gas treatment in and see what happens.

[rckrzy1]

you guys with cool air cooled engines can use the cheap stuff but when your air cooled engine is being cooled with 110F air the high octane helps keep the knocking down.

[dpep]

Yeah I just talked to the guy at Advanced and he said the higher octane probably knocked something loose. I'm gonna change the plugs and put gas treatment in and see what happens.

I wouldn't take very much parts advice from this particular Advanced guy. As has been mentioned higher octane gas is actually LESS volatile than lower octane gas. It is that way so it can be compressed more compactly without combusting before it is supposed to (with the piston on the way up). There is no danger of the mixture combusting after it is supposed to (that is what the spark plug is for). The risk of engine damage comes with too low octane, not too high. You just got some bad gas, or you have some other problem.

[GSJoe]

I think he meant that the additives knocked the carbon and dirt and whatever else loose.

[dpep]

you guys with cool air cooled engines can use the cheap stuff but when your air cooled engine is being cooled with 110F air the high octane helps keep the knocking down.

True, here in Florida I usually run high octane, especially in the summer. Traffic is a lot worse now than it was when our bikes were built. Even when you are travelling on the Interstates now a trip of any length will usually include some dead stop and inching along time for construction, accidents or just too many vehicles.

[RotaryRodder]

every other bike I have had ive had to put 91 or 93 in it.

I have an 82 GS1100GKZ, what octane should I use?

[fgh]

GS750ES wants High Octane

Well I checked the manual and sure enough it says that 87 octane should do fine. My experience tells me otherwise. Mid grade and it doesn't make as much noise, but to really get it to purr the high octane is the way I have to go.

[mkaczmarek]

94 Octane caused violent backfires...

I recently got a '79 GS1000E, after repairing the inside of my rusty tank with POR-15 I decided to get some Ultra94 Octane gas and filled the tank. The bike seemed to start fine at first when on choke, but after a minute or so it started to backfire randomly at various rpm's, and these backfires were violent at times and very loud.

I mentioned this in one of my posts and a fellow member told me to not use the 94 Octane gas as these low compression engines don't really take advantage of it, I guess if you play with timing, maybe change from points to Dyna ignition ? but my bike is stock for now. I have since filled up with regular 87 Octane and the bike has not backfired even a single time since the fuel change. I must say the conclusion I drew from this is that on a stock low compression bike from those days higher octane is not always a good choice, at least it wasn't in my case.

I am thinking of switching to Dyna ignition in the future, just haven't looked into this yet as to what pro's and con's come with the change versus staying with the stock points.

================================================== ================================================== ===================
1979 GS1000E

"The less you know, the more you believe."
"We thought that we had the answers, it was the questions we had wrong."