Potentially controversial fuel question

[JimmyR]

I have been tuning my Mikuni RS35 flatslide carbs to suit my GS1100G for a while now. I have gotten them pretty good - the bike runs really well at all levels of throttle but although it runs well it is slightly rich. Rich enough to leave the plugs black and smell rich at idle. It won't run smoothly if I change the pilot jets or jet needle setting at all leaner. It pops and splutters under acceleration at just off idle to about 1/3 if I go any leaner at all.

I mentioned this to my local Suzuki dealer. He is no ordinary dealer - his parts service is outstanding and he and his staff incredibly helpful. He used to race bikes and sidecars and is very knowledgeable. His advice? Try running on premium (98) rather than regular (92) and go down one size in pilots.

I think he might be onto something. Today, before I visited Suzuki, I happened to top up with 95 fuel. I can't remember what they called it but it's halfway between regular and premium. I still had some regular in there but it's mainly 95 right now. I have noticed that compared to yesterday when it was all regular I am getting slight bogging at just off idle that wasn't there before, ie symptoms of richness. So now I want to empty the tank, fill it up with premium and change my pilot jets right away!

Am I imagining things? Has anyone else experienced this? I noticed the way the bike was running before I asked about my bike, but it makes sense to me.

 

[Killer2600]

I don't get what would be controversial in this but your not imagining things.

Fuel quality is noticeable and low octane burns/ignites easier than higher octane. Many here and elsewhere will tell you the bike was made to run the cheap stuff and buying the expensive stuff is a waste of money but, from the way my bike now runs after being fed the cheap stuff all season long this year, I'm going back to the good stuff. A cousin and friend, one a motorcycle mechanic and other a marine engineer, told me to use premium gas and I did until this year when gas prices tempted me to follow advice on here. The lesson learned, some internet wisdom isn't wise at all and you get what you paid for.

 

[Buffalo Bill]

If the blind lead the blind?

If the blind lead the blind?

In the first place, I have no idea why your 1100G has flatside carbs, because the CV carbs were standard.
If it runs so rich your plugs are fouled, you gotta lean it out until they burn clean.
Buying 95 octane because it cost more, well that's clueless.

You need an education, and for that you gotta pay tuition.
If you pay tuition, the better you're gonna pay attention in class, and learn something.

 

[Badooka]

Agreed. Tune your bike to 87 octane and you'll have zero worries.
If the bike is fouling plugs and running bad, no fuel change is going to correct it.
Your bike will actually run even richer because of unburnt fuel and added octane.

 

[JimmyR]

We don't have 87 here. The lowest is regular which is 92. See - I said it potentially controversial.

I would be perfectly happy to tune my bike to 92. As I explained in the OP I can get it to run well on 92 but it has to be rich to do so. As soon as I lean it out at all it doesn't run properly. If I move the jet needle one notch leaner it runs rough. If I reduce the pilots by one size it runs rough. As the rough area is a symptom of running too lean just off idle and is solved by going slightly rich can you see my problem?

Buffalo Bill my bike has flatslide carbs because I put them on there. I actually knew that CV carbs were standard because that's what was on the bike before I changed them to flatslides. So now you know!

So the idea was to "Try running on premium (98) rather than regular (92) and go down one size in pilots."

 

[Steve]

We don't have 87 here. The lowest is regular which is 92.

Where is "here"? :-k There is no location in your profile (hint, hint).

If you are not in the USA, your 92 might be exactly the same as our 87.

It all depends on how it is measured and displayed on the pump.

.

 

[Guest]

Where is "here"? :-k There is no location in your profile (hint, hint).

If you are not in the USA, your 92 might be exactly the same as our 87.

It all depends on how it is measured and displayed on the pump.

.

What he said! Tell us where you are from. Here you can't find get higher than 91 octane so I'm kind of surprised. Its 87 reg, 89 (10% ethanol), 91 Premium

 

[Guest]

When your GS is properly tuned, with the stock setup, if will run well on 87 octane with no problems.

 

[Steve]

When your GS is properly tuned, with the stock setup, if will run well on 87 octane with no problems.

True, but our octane numbers on the pump are an AVERAGE of two numbering methods.

Some parts of the world (maybe everyone but us? :-k) only use the higher number, so as I mentioned earlier, our 87 might be the same as their 92.

.

 

[gearhead13]

True, but our octane numbers on the pump are an AVERAGE of two numbering methods.

Some parts of the world (maybe everyone but us? :-k) only use the higher number, so as I mentioned earlier, our 87 might be the same as their 92.

.

Must be unless all their vehicles have real high cr. I am at 11-1 cr and have 190 psi compression cold/dry. My bike runs fine on our premium (94) I even run 91 when I cant get the 94

 

[JimmyR]

Well there you go - that's one reason I ask questions like this here. I live in Western Australia, and as I mentioned we have (according to the pump) 92, 95 and 98 octane fuel depending where you go.

I would have thought that I could tune these carbs to run perfectly on regular too, but I can't seem to achieve that. I wish I could. As I said, it runs well right now but seems to be rich. The area it is rich is idle and just off idle. That area is governed by the pilot and jet needle, and if I go one setting leaner in either the engine coughs and splutters. I'm not sure how else to say this, so telling me to tune it properly for regular fuel is not really very helpful. If you know how to do it tell me. Please!

And saying things like "blind leading the blind" is not helpful at all, just insulting and completely unnecessary. I like the helpful comments I get here but if you want to be a grumpy old man then be grumpy somewhere else.

 

[Janx101]

As far as I have ever seen on any forum .... Mentioning fuel type and usage is automatically highly rated controversy wise!!!

So I'm not gonna mention right now that I have recently given up 95 and 98 Ron Ethanol free fuel .. In favor of 94 Ron e10 ..... Cos i can ...

If I mentioned that then it'd just bring a whole other order of controversy eh .... Just as well I didn ....... Oh damn!

 

[JimmyR]

Yeah that's why I said potentially controversial. I have noticed before that things get heated around fuel discussions. FWIW I think that running the 95 that I put in today has helped. I just reduced the pilots from 125 to 122.5 and so far it's looking good. Tomorrow I will do my favourite test route and see.

It could also just be that the new rings I installed 500kms ago have worn in a bit. I just changed the oil to celebrate 500ks of new rings and valves seals. So tomorrow's ride will be fun.

 

[Steve]

Well there you go - that's one reason I ask questions like this here. I live in Western Australia, and as I mentioned we have (according to the pump) 92, 95 and 98 octane fuel depending where you go.

To help minimize some confusion in the future, would you mind going into your profile and at least putting your location in as "Western Australia"?

If you need help with that, let me know.

I just reduced the pilots from 125 to 122.5 and so far it's looking good. Tomorrow I will do my favourite test route and see.

Ah-haa. I think I am seeing a problem now.

On the US-spec 1100G, the MAIN jets are 115, the pilot FUEL jet is 40. I think you are changing the wrong jets.

And I have a question for you, too. Since you seem to be running rich only at idle and low-throttle, what is the setting for your idle mixture screw?
That is what will fine-tune your idle and low-throttle richness.

I realize that the jetting of your 36 flat-sides might be a bit different, but not that different.


.

 

[Buffalo Bill]

Not much info in your question?

Not much info in your question?

You ask an engineering question without including full info.

In each of your later posts, you reluctantly include just a bit more relevant info.

Now we know your bike is modified, and that you live in another country with it's own gasoline standards.

Did you really want our help, or do you just want to play a silly game?

 

[JimmyR]

Sorry Steve - I meant the pilots went from 25 to 22.5. The mains are 130. I always get those confused because they are close except the mains have a "1" in front.

 

[Steve]

OK, that makes more sense. Actual numbers can't be compared to stock jetting on stock carbs, but it appears you are getting closer.

I don't know anything about your carbs, but I am going to assume there is a screw or two that will adjust pilot mixture? :-k

On our older VM carbs, there is a pilot fuel screw on the bottom and a pilot air screw on the side that will be used to fine-tune the pilot mixture.

On the newer BS carbs (also called CV carbs), the mixture is preset by two jets, but the amount of the mixture that is admitted is adjusted with a screw.

If you have such a device on your carbs, you might be able to lean out your idle mixture a bit.

.

 

[bccap]

I use Chevron 94 whenever a station is available. It is ethanol free in Canada. When a Chevron station is not around I use 87 or regular. Haven't noticed any difference in running or idle.

 

[Steve]

I use Chevron 94 whenever a station is available. It is ethanol free in Canada. When a Chevron station is not around I use 87 or regular. Haven't noticed any difference in running or idle.

How much more expensive is the Chevron 94?

Why are you willing to pay that extra if you don't notice any difference?

.

 

[Badooka]

They say a fool and his money are soon parted!:-\\\