VFR800FI doesn't go as well as my VFR750

[Zen Dog]

So, I've had my 750 for about 15 years now, used it for everything, and it's honestly a bit of a wreck now. So a couple of months ago I bought an 800FI to replace it. It's fine, it all works, but it did feel like it needed to be revved a bit more to get it to really go compared to the 750, which I wasn't expecting (I'm sure I read somewhere that the 800FI was meant to have better midrange than the 750).

So the other day, I rode them back to back. And the 800 feels better in pretty much every way, except the midrange. The 750 definitely has more get up and go between 4-8k rpm. The 800 also feels more vibey, and there is a slight "tappy" sound.

A couple of factors that may or may not be related. First, the 25k valve clearances have not been done on the 800 (it's on 33k). I'd have had them done already but most garages don't really want to do them because it's such a PITA and tell me it's a "winter job". Secondly, there is a dent in one of the rear downpipes, though I'd expect that to strangle the top end, if anything, and it feels fine at the top (happy to be corrected on that assumption though).

So, I suppose the question is, is the 800 just like this compared to the 750? Is getting the valve clearances done likely to make a significant difference? (People on the VFR forums seem to think they don't even need doing half the time.) Is the dented downpipe responsible? Is there anything else I should be considering?
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Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011

[Robby]

My experience with Honda V4s is that vibration and a tapping sound (usually from the clutch) points at carb balance being off. I don't know if synchronising the throttle bodies is a thing on the 800, but valve clearances being off can have the same overall effect.

That said, I doubt it will make any noticeable difference, same goes for the exhaust unless it's really seriously dented.

A remap would probably help. I don't about that specific bike, but many fuel injected bikes feel better with a bit more fuel in the mid range.

[Zen Dog]

Thanks for that. I have noticed that the 800 feels a bit..... linear? anodyne? in the way it revs compared to 750, but I've been putting that down to the FI/carb difference.

When I had the clearances done on the 750 at 50k, it did feel slightly smoother, but as you say, it wasn't a massive difference.

I think I'll get the clearances done (they need doing anyway), and if that doesn't have much of an effect, I'll look at a remap. Cheers.
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Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011

[Easy-X]

Could it be when the bike switches from closed-loop to open-loop? I read into this when swapping my exhaust system as in "what's this thing do?" (the oxygen sensor.)

Apparently some bikes do this seamlessly and some are rubbish at it. I'm thinking the midrange is probably where this switchover occurs the most Don't know how hard "O₂ sensor elimination" is on your particular bike.
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Zen Dog]

[Easy-X]

I did wonder... just a remap then. Have you checked for mice in the air box?
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[MarJay]

Get the throttle bodies balanced. They are extremely sensitive to them going out of phase.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[kgm]

How of a faff are the throttle bodies to sync on the VTEC bikes? I've got the gear but only even done twins. Mine would probably benefit.

[to v or not to v]

[Zen Dog]

[Zen Dog]

So just a follow up on this, should it be of use to anyone. I've synced the starter valves on the carbs, as explained in this guide, which is honestly much better than the haynes manual - https://www.vfrdiscussion.com/index.php?/forums/topic/32-starter-valve-syncronization-5th-gen/

But I stumbled on this thread - https://www.vfrdiscussion.com/index.php?/forums/topic/94504-5th-gen-starter-valves-sync-incorrect-for-last-22-years/

Which basically says that ambiguity in the service manual has lead to people setting the sync incorrectly. For example, the haynes manual (the service manual is similar) says "Adjust number 3 valve until its reading is 20 mmHg below the base setting then adjust number 4 valve until its reading is 10 below the base setting". But what is "below"? Is it more vacuum or less? On a rotary type vacuum gauge, below would indicate more vacuum, but on a linear one (like a carbtune), a lower reading indicates a lower vacuum. The poster assumes that most people will take "below" to mean less vacuum (and the guide posted above adjusts it that way), but that actually it should be more vacuum. So I thought I'd try it, and I've set valves 3 and 4 to have more vacuum than 1 and 2. It definitely seems better than it was, though whether it's better than less vacuum, i'll have to try it and find out.

Does the above make any sense to the folk who, unlike me, actually know what the hell they're talking about? Should it be more vacuum, or less?
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Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011

[Zen Dog]

Having ridden round North Wales on the weekend, I can say that it's a lot happier at low revs than it used to be. Previously it was all a bit lumpy below 4k, and now the lower limit is about 2.5k (which is about the same as my 750).

I'm still going to try setting the other way on my next fettling day, just for science.
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Current - '94 VFR750FR, '00 VFR800FI Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011