Jerky at constant speed low gear

Yeah, I've read in a few posts in this forum that this can happen on VFRs. Basically, the bike is smooth when accelerating, but it becomes kind of jerky when it's accelerated and is maintaining a constant speed, especially in lower gears (1-2). The higher the gear, the less jerky it is.

One of the suggestions in posts was to adjust the chain, i.e. mention it. Did that. The problem jerkiness disappeared and it became velvet smooth! Even accelerations became much smoother (and I thought they can't get any better). But then I noticed the noises coming from the chain - it was too tight. And the sticker on the swingarm says the chain should retain a slack of 2.5-3cm, which was the case before my adjustments (i.e. when it was jerky), and after adjustments it was ~1cm

So.. Any ideas? I mean, adjusting the chain clearly helped, but that's the tension way above the recommended spec and I'm worried it might wear it off along with the sprockets faster. And that constant clicking noise from the chain (front sprocket) under high tension is soo unpleasant.

What should I do?

P.S. I've laxed the chain for now. It doesn't feel right riding with it tensed so hard.

 

Ride it fast and hard.

Depending on how many kilometers are on the bike, perhaps the cush rubbers in the hub need replacing. Maybe your chain and sprockets need replacing. Verify your throttle cables don't have excessive slack (you need some).

If that is all good, might look into a Power Commander to load a revised ignition map. That can help, it did quite a bit on my friend's 02.

Or get used to it.

 

Is this a fuel injected bike? If so, especially on the first FI generations, for me it helped to synchronise the starter valves and do the pair valve removal. I think 5th gen will always remain a bit jerky in te low gears because of being first generation fuel injection.

 

If you read chapter 21 of the service manual you'll learn that in the low throttle opening range (low volumetric demand) the Honda PGM-FI ECM uses the Manifold Absolute Pressure Sensor to determine how much fuel to inject. Because of this it's important for everything involved in the bike's intake system to be squared away all Factory Original so the Manifold Absolute Pressure Sensor gets good information.

The reason your VFR800 is smooth while at larger throttle opening conditions (high volumetric demand) is because the Honda PGM-FI ECM uses the Throttle Position Sensor to determine fueling. This is a simpler sort of FI algorithm and there's less that can go wrong (as opposed to the Manifold Absolute Pressure Sensor).

 

Also, another thing that can increase motorcycle drive train lash is the rubber pieces inside the rear hub "cush drive" getting old and hard with age and as a result shrinking up a bit after 20+ years. Honestly, the rubber parts of your VFR800 are considered "consumable items" by Honda and when the bike is 20+ years old there's a good chance it would make things better if you replaced them.

If you dig into your VFR800's rear hub and find there's room (slop, lash) between the cush drive rubbers and the aluminum casting, but you're not totally convinced you should replace them, you can simply cut up a piece of thin hard plastic to make shims which can be inserted to take up the space (which greatly reduces the cush drive contribution to drive train lash).

 

Aaaaaand also, if at 20+ years down the road from new the bike's fuel injectors have never been removed and sent out for professional cleaning that might be a good idea. Clogged/dirty fuel injectors just can't deliver the ECM metered fuel in the smooth, progressive way that the ECM is commanding.

 

Thank you. I think I've seen those aspects mentioned in this forum before.

Naturally, I can't do it all at once, so I started from the simplest points in the list, i.e. tensioning the chain. And when tensioned, the jerkiness disappeared completely. I understand there's lots of "could be"s and "should check"s, but the chain is one thing that worked. However, it was over-tensioned, so it's not a long-term fix. And because of the fact that it worked, I'm focusing on the chain (not FI, not valves, but the chain). If it were engine-related, I would not expect the chain to have any effect.

Why did it have this effect (i.e. jerkiness disappeared)? Could it be that tensioning the chain had an effect on those pillows in the rear hub? (btw that's a good point, the rear hub pillows, thank you)

 

To me, it points at worn out chain and sprockets.

 

yes, if the chain has a series of loose -then -tight spots, it's done woe out. get the rear wheel up, press on the chain, and turn the wheel to check.

always set chain tension to be correct at the tightest spot.

 

What they said.

And, you don't want a tight chain. Your suspension won't work properly and you lose vehicle control.