Problems from running premium gas in an engine rated for regular?

"E. Julius" (soonerfrommi)
05/06/2015 at 08:45 • Filed to: Questions

Edit: question has been thoroughly answered. Thank you all for your time.

I’m currently shopping for motorcycles, and there’s one that looks like a decent buy, except some joker who didn’t read the manual is proudly proclaiming that it has a full tank of premium gas. I know there won’t be serious issues like you would find if the situation was reversed (knock, damaged pistons/valves, etc.), but my intuition tells me that this wouldn’t be good on a carbureted engine. I’m not sure, but I’m thinking you might find things like excessive carbon build up, which could of course lead to hotspots and knock with correct octane gas, or other long term reliability issues later down the line. Is my intuition correct, or would it be a decent buy as long as I flushed the tank and filled it with correct gas after I bought it?

DISCUSSION (36)

CalzoneGolem > E. Julius
05/06/2015 at 08:51

I believe premium just has less ethanol in it so it should just leave less crap behind.

505Turbeaux > E. Julius
05/06/2015 at 08:54

It won’t hurt it, though I dont know why he would be super proud he spent an extra 40 cents when filling it up

E. Julius > CalzoneGolem
05/06/2015 at 08:55

I believe both regular and premium gas are available with and without ethanol. The difference is that premium gas is harder to ignite, so engines can be designed with higher compression ratio to avoid pre detonation in the cylinder. My line of thinking is that since the premium gas is more difficult to ignite, and since the carbureted motor can’t compensate for it on the fly like an EFI system can, you would get less complete combustion, therefore more carbon buildup. I don’t know if this is correct, but I don’t think the ethanol content has much to do with it.

E. Julius > 505Turbeaux
05/06/2015 at 08:56

We’re talking about a 2004 Kawasaki Ninja 250 here man, this guy is a high roller .

StndIbnz, Drives a MSRT8 > E. Julius
05/06/2015 at 08:56

There is no problem with running a higher octane fuel in an engine designed for lower. And no problem running Premium in a carberated engine. My 2001 R6 is carb’d and needs premium. Only difference is knock resistance. Now, if he was putting E85 in an engine that wasn’t designed for it you would have problems, or putting 87 instead of 93. All he was doing was spending more money on gas then he needed too.

Nibbles > E. Julius
05/06/2015 at 08:57

Better mistake made on a carb'd motor than a catted one. May see some backfires, lowered economy, but you should be able to run through the tank without major issue

E. Julius > StndIbnz, Drives a MSRT8
05/06/2015 at 08:59

My thinking wasn’t that premium can’t run in carbureted engines, but that unlike a modern EFI system the carburetor can’t adjust to the fuel on the fly and so it might have some other, less significant issues. It sounds like it’s generally not a big deal though, so I guess it’s nothing to be worried about.

505Turbeaux > E. Julius
05/06/2015 at 09:01

that thing would run on diesel likely enough

Alfalfa Romeo > E. Julius
05/06/2015 at 09:04

To my knowledge, the only damage he’s doing is to his wallet. In fact, all he’s doing at all is hurting his wallet.

RamblinRover Luxury-Yacht > E. Julius
05/06/2015 at 09:05

No flushes necessary. A slower burn is not by any means necessarily a less-complete burn. The only situation in which there might be an incomplete burn would be in an engine with horribly low compression and poor combustion chamber design - and in that case, why would you be running a Model T-engined bike? Actually, why wouldn’t you? That sounds amazing.

E. Julius > RamblinRover Luxury-Yacht
05/06/2015 at 09:07

Ok, that makes sense. I was wondering if it could be something like that, but I wasn’t sure. Thanks for your answer.

Also, would hand crank my motorcycle engine (kick starters are for fools!)

Jake - Has Bad Luck So You Don't Have To > E. Julius
05/06/2015 at 09:09

The only difference is that a premium is less likely to pre-detonate. I actually *have* to run premium fuel in my LeSabre to avoid knock because of how old the engine is. There is a small chance is might dirty up a carbeurated engine due to it not having nifty things like on-the-fly timing adjustments and stuff, but you could probably fix all that by running some Seafoam through the fuel system

StndIbnz, Drives a MSRT8 > E. Julius
05/06/2015 at 09:09

Well just because its premium doesn’t mean the A/F mixture would change, so still no issue with the carb. Run the premium out of it and fill w/ recommended octane, or keep using premium. Whichever you decide it should be fine.

What bike you looking at BTW?

Confused Miata > E. Julius
05/06/2015 at 09:10

Sometimes on older vehicles carbon buildup can cause it to run better on higher octanes. I would stick with whatever the manual says next time you fill it up.

RamblinRover Luxury-Yacht > E. Julius
05/06/2015 at 09:11

It’s still the same *amount* of fuel, basically. That means that when combined with a given amount of air, it burns for about the same thermal release, etc. etc. without needing extra air - or it’s supposed to. It just burns slower by a few milliseconds.

E. Julius > Jake - Has Bad Luck So You Don't Have To
05/06/2015 at 09:13

Yeah, I knew that premium was necessary for high compression ratio engines and stuff like that, and my thoughts were exactly along the same lines regarding the lack of adjustments to the carburetor. Seems like it’s not going to be an issue though after what everybody has said.

DisplacementForDayz, ironically lusts after a Honda Grom > E. Julius
05/06/2015 at 09:13

Paying more for gas.

E. Julius > StndIbnz, Drives a MSRT8
05/06/2015 at 09:14

I’m looking at a few different things right now. This particular bike was an older Ninja 250. I’ve never ridden before so I’m just looking for a basic starter bike.

Party-vi > E. Julius
05/06/2015 at 09:14

Wat?

I’ve only ever run high octane gas in my carb’d vehicles because you can 1) reduce the chance for knocking and 2) advance timing for moar powah.

There is no issue running premium fuel in a vehicle that doesn’t require it other than the extra cost at the pump.

E. Julius > RamblinRover Luxury-Yacht
05/06/2015 at 09:14

Makes sense.

E. Julius > Party-vi
05/06/2015 at 09:16

Sorry, I’ve learned everything I know about engines from teaching myself stuff out of books and have no practical experience, so sometimes my intuition leads me astray. Exactly why I ask these kinds of questions!

StndIbnz, Drives a MSRT8 > E. Julius
05/06/2015 at 09:18

Well thats a good choice. Buell Blast would be a good one too, slow but nice to learn on. Take the MSF course as well, $25 bucks well spent.

E. Julius > Party-vi
05/06/2015 at 09:18

Thanks for the answer by the way, my last reply wasn’t meant to be snarky or rude at all.

bob and john > E. Julius
05/06/2015 at 09:19

no problems. I regularly swtich back and forth between 91 and 87 on my SV. Dont really matter.

and on a ninja 250? really nothing to be worrie about. if anything, i would say it better, as it does leave any shitty eathonal residue.

If only EssExTee could be so grossly incandescent > E. Julius
05/06/2015 at 09:21

Many older bikes have a CVCC-style pre-mix system. If this one does it would probably mitigate the things you’re concerned about due to the more complete combustion.

Party-vi > E. Julius
05/06/2015 at 09:22

No need for sorry - not many younger people have experience with carb’d vehicles. Most engines with EFI can detect knock and have the ability to advance or retard ignition timing to decrease the likelihood of detonation occurring. Carb’d engines usually don’t have this feature, so most of the time you just go with higher-octane fuel to prevent knocking in the first place.

Party-vi > E. Julius
05/06/2015 at 09:24

No snark or rudeness was interpreted. Also you don’t need to be in eggshells around mods if that was a concern. When I’m commenting on posts in Oppositelock I’m an Opponaut. I don’t pull out the Mod Card to get people to agree with me.

E. Julius > Party-vi
05/06/2015 at 09:26

Ok, I was basically thinking DON’T use higher octane fuel because of the lack of on the fly adjustments, but that makes sense too.

E. Julius > Party-vi
05/06/2015 at 09:28

Nah I would have done that for anyone. After posting I thought my response could possibly be construed as overly defensive, but I figured it was too late to ninja edit so I over corrected.

E. Julius > StndIbnz, Drives a MSRT8
05/06/2015 at 09:30

Yep, considering the Blast as well, and surprisingly easier to find in my area. Already enrolled or MSF as well : )

E. Julius > If only EssExTee could be so grossly incandescent
05/06/2015 at 09:32

I don't know what that is. Got any helpful links?

If only EssExTee could be so grossly incandescent > E. Julius
05/06/2015 at 09:39

Cant give you links because kinja hates mobile, but basically the fuel and air were mixed in a pre-chamber rather than in the cylinder itself, and then pulled into the cylinder using vacuum pressure. The mixture was much more even so the fuel would burn cleaner and more completely. This is how the original Civic was able to meet late 70’s smog restrictions without needing a catalytic converter. I know for sure that Yamaha used a similar system on their bikes, and I thing a few other makes did it too.

JEM > E. Julius
05/06/2015 at 09:57

I feel like this is a lot more common with bikes than cars. I think a lot of the reason people put premium into bikes (that don’t need it) is they tend to sit for longer periods of time, and the higher octane supposedly doesn’t degrade as quick or something.

StndIbnz, Drives a MSRT8 > E. Julius
05/06/2015 at 10:11

Good! Have fun and welcome to the wonderful world of 2 wheels!

E. Julius > StndIbnz, Drives a MSRT8
05/06/2015 at 10:12

Thanks! Looking forward to it!

You can tell a Finn but you can't tell him much > E. Julius
05/06/2015 at 14:57

You can always run premium in an engine, even one that only requires regular. The stoichiometric air/fuel ratio is identical regardless of octane. Premium is more resistant to igniting due to pressure which is why it allows for higher compression ratios, but it is no more difficult for the spark plugs to ignite it. If the carb is set properly for regular gasoline it will run just fine on premium with no ill effects AT ALL. There is no performance benefit or cost to running premium in an engine that doesn’t require it.

In my small engines (lawn mower, chainsaw, etc.) I always run premium because it is easier to find ethanol free premium. This reduces the likelihood of running into problems with water in your fuel, especially on things that sit for long periods of time between running.

I also run premium in my boat engine even though it only requires regular. I do this because the boat generally sits for long periods between getting run and I don’t want to put ethanol in the fuel system. The ethanol can eat seals and tubing that is not rated for ethanol, even if it is only E10.

If you are going to be riding the bike regularly to the tune of a tank per week I would go with the recommended grade. If you are only going to be riding it occasionally and it is going to sit for long periods of time I would recommend running premium. If it is an older bike premium might be a decent idea to avoid damaging fuel system components with ethanol.