VStar 950 Overheating with 87 fuel - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 17 (permalink) Old 08-26-2018, 08:03 PM Thread Starter
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VStar 950 Overheating with 87 fuel

Hey Gents!

Had the VStar 950 for 3 years now and did the whole Cobra Slip On - Cobra Air Intake w/ K&N - Fi2000 FMS upgrade. Have been running her on Unleaded Octane 91 (I'm in Canada), but recently saw a pic on another yamaha forum of someone's vstar engine full of carbon residue after using Octane 91-93. So, I decided to play it safe and filled in the 87 but it definitely affected the performance:

- The bike is suddenly running REALLY HOT in the city (Light to Light) riding. Since the FMS is manually set, maybe there's an issue with running lean.
- The bike had stopped backfiring on downshifts. I guess a good thing.
- Not sure if the acceleration is any different now, and can't say that it is sluggish or not, but that overheating caught me completely off guard.

Did anyone have a similar experience or perhaps know what could be the issue?

2009 XVS950
Cobra Slip-On (with wrapped baffle)
Cobra PowerFlo Air Intake
Cobra Fi2000R O2 Digital Fuel Processor
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post #2 of 17 (permalink) Old 08-27-2018, 01:01 AM
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not sure how the fuel is different in Canada, but the 950 manual recommends 87 octane which is in line with the compression ratio for this motor. did anything else change besides just switching fuel? do you have the FMS on the same settings now as you had when running the higher octane?
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post #3 of 17 (permalink) Old 08-27-2018, 08:31 AM
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Could be a couple things.

I ran 87 ethanol free gas in my 650 a few times, the bike seemed cooler when I stopped for a light, The heat coming up off the engine. At many gas stations the hi octane gas is ethanol free, and the rest are 10% ethanol. Without a temp gauge its all subjective.

Are you having a heat wave this week. When it's 90F the bike will feel hotter.

Normally a bike will run leaner on hi octane. It has less energy for more money, which most people do not expect.
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post #4 of 17 (permalink) Old 08-27-2018, 08:35 AM
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... you will have to tune the ECM map for one octane or the other. Your bike does not need 91 or higher, so that's up to you.
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post #5 of 17 (permalink) Old 08-27-2018, 11:03 AM Thread Starter
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Quote:
not sure how the fuel is different in Canada, but the 950 manual recommends 87 octane which is in line with the compression ratio for this motor. did anything else change besides just switching fuel? do you have the FMS on the same settings now as you had when running the higher octane?
That's exactly it - I didn't! The mixture was running too lean with the FMS setting at 2.5/3/2 and, I guess, that's exactly what was causing the bike to overheat. Once I set the pots to the suggested 2.5/6/3 the bike got it's power back and seems to feel overall balanced. But, I'll keep monitoring.

Quote:
I ran 87 ethanol free gas in my 650 a few times, the bike seemed cooler when I stopped for a light, The heat coming up off the engine. At many gas stations the hi octane gas is ethanol free, and the rest are 10% ethanol. Without a temp gauge its all subjective.
Are you having a heat wave this week. When it's 90F the bike will feel hotter.
It was definitely a warm night last night, but nothing out of the ordinary in comparison to the summer rides I've had. I think it was just a bad FMS pot setting causing a lean mixture.
We don't have a lot of ethanol-free gas stations in Canada. But, if we do they are mostly at 91 octane. I'll give this option a try in the near future for sure.

I guess, my biggest dilemma was the carbon build up in the engine and how that could be avoided.

2009 XVS950
Cobra Slip-On (with wrapped baffle)
Cobra PowerFlo Air Intake
Cobra Fi2000R O2 Digital Fuel Processor
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post #6 of 17 (permalink) Old 08-28-2018, 04:13 PM
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Lower octane fuel will run more rich. The higher the octane the leaner it runs.
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post #7 of 17 (permalink) Old 08-29-2018, 06:40 AM
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A little carbon buildup is not bad - running a little rich.

Running a little lean will overheat your heads, burn your valves till they leak, and burn holes right thru your pistons.

You will never get it perfect like a stock bike from the factory, so be a bit on the rich side.
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post #8 of 17 (permalink) Old 08-29-2018, 11:18 AM
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then how would someone running a higher octane gas get carbon buildup? as the original post says?

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post #9 of 17 (permalink) Old 08-29-2018, 01:36 PM
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"...recently saw a pic on another yamaha forum of someone's vstar engine full of carbon residue after using Octane 91-93. ..."

that does not add up

maybe the poster on the other forum is not telling the whole story.

EgoRich has been describing a lean situation on his bike.
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post #10 of 17 (permalink) Old 08-29-2018, 05:17 PM
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Not enough timing. So the fuel does not burn totally. Simple :-) Trust me as a drag racer and a tuner I run into things like this ALL the time.
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