No it won't adversely effect the running of a bike like our Gen1 Fazers. But in performance terms if anything it will make a smidgen less power, but I suspect that even that will be hard to measure.
Much more likely to be to do with cleaning additives, anti-knock additives etc. I still do believe I noticed an improvement on stock Fazers, less glitchiness, and I think the sheer numbers of people reporting the same bears this out.
Engines are clean on standard fuels, they were over 20 years ago too, the days of weekend de-coke sessions are well and truly gone. 92 RON has good enougth anti-knock properties (which is what RON is about) for the GEN1.
It's all about that timing. If I could buy 92RON I would, but we don't have that option. By 98 RON, the ignition - the spark, is being applied too late.
You'd have to speak to tuners about ignition advancers and whether 98RON and a suitable ignition advancer produces results with the Fazer. But seeing as the bike was designed by Yamaha for 92RON I'd take a bit of convincing to go down that route.
May I throw a couple of extra complications into the mix, as it were? The Fazer 1000 gen 1 was set up apparently to run on quite poor quality fuel as stock, and hence the fluffing at low revs they all seem to have.
No, not poor quality fuel, it needs good quality fuel of 92RON or higher.
Ivans jet kits are to set up so the carbs get round the poor set up required to get through stringent emissions tests. Those standards have been updated again, and hence Yamaha can no longer sell a bike with carbs. I would guess for example today's emissions standards will be looking for near zero emissions on a closed throttle, something a carb, unless you add little electronic stepper motors and stuff can never do (bypass holes). Carbs, as wonderful as they are, are history due to emission standards. But no - Ivans carb kits are all about getting your carbs set up to their sweetest optimum, that have absolutely nothing to do with ignition timing.
Carbs used to wear out years ago, but that doesn't seem to be much of an issue today. And wear and dirt are two different issues. Varnishing is the enemy of carbs today, which happens when you leave carbs for a long time with fuel sitting in em. It has been suggested that varnishing is less likely to happen with a higher octane fuel. So if you stick yer bike away for the winter, a tank full of 98RON might be worthwhile. But there's no day to day running benefit for your crabs.
Ignition advancer yes, different game, designed to take advantage of higher octane fuels. I'd be very wary of it though, but if a tuner like Ivan is offering such a mod, then it might be worth considering. Just remember that if you want to go back to 92 or 95 RON with a 98RON compatible advancer, well remove the ignition advancer before filling with a lower octane, it won't take that many tankfuls to burn through yer valves.
At the end of the day, for most of us, our relationship with our motorcycle is not rational, it's emotional. Ask any sales good person about selling stuff and people purchasing, it's about about interaction and emotion.
So loving your bike, you will buy it the best fuel there is, and yes it will go faster and feel smoother becuase that's what the best will do.
But take the emotion out of it, look at the facts in the cold light of day, stick it on a dyno in quiet desperation if you wish but I'm afraid..........................................................................................