GreginDenver

And... Don't be like me... instead of blundering along trying to pull the socket off of the back of the bulb without really knowing/remembering how to release it from the bulb. It's better to refer to the Honda VFR800 Service Manual, page 19-6, for the step-by-step how-to on removing and replacing headlight bulbs on the bike.

you'd be surprised how much better the 5th Gen radiators can dump heat to the atmosphere WHEN THEY'RE CLEAN. many, if not most, 5th Gen owners never think to clean the 20+ years of accumulated road grime off of the radiator cooling fins. a can of spray-on foaming air conditioner coil cleaner will remove the build-up. after cleaning the radiators are able to reject a lot more heat into the airflow around them.

My bet is that all of those Revs are giving the Clutch Slave Cylinder a really good shaking transmitted by way of the clutch pushrod, and that shaking is transmitted up the line (via the incompressible hydraulic fluid) to the Clutch Master Cylinder. So it becomes a "liquid hammer" situation that is strong enough to drive the hydraulic fluid past the rubber sliding seal in the Clutch Master Cylinder. Which allows the clutch to grab as you described.

I've done the full braided stainless steel brake line conversion plus caliper refurbishment plus full system bleed on a 5th Gen VFR800 twice now, once bike with Spiegler lines and one with Galfer lines. And I've also done a full system bleed on a standard (unmodified) VFR800. And for good measure I've always done the bike's hydraulic clutch system at the same time. The best 5th Gen VFR800 linked brake system bleeding results I've had (quickest, less messy, less frustrating) has been when it was done as a 2-person team plus a vacuum bleeder (I use an el-cheapo MityVac purchased at Harbor Freight). The whole process is so much easier when you have somebody to squeeze-and-hold the various master cylinders (the front brake master cylinder lever, the rear brake master cylinder lever, the clutch master cylinder lever, and even having my helper hand-pump the Secondary Master Cylinder which is located on the backside of the bike's front left caliper). But even with the precision/efficiency that this method gives me I've always ended up having to go around all the bleeders twice to get good results. Just last month (May of 2020) I helped another member of this forum who lives here in Denver do a full braided stainless steel line conversion (Galfer lines) and complete refurbishment of the system (all new caliper seals and wiper rings, brake pads, and fluid) on his 2000 5th Gen VFR800. He brought the bike to my home's garage and we did the work over a Saturday and Sunday. I think he would tell you that except for all of the disassembly and reassembly (these two things account for the majority of the effort required) the actual mechanical difficulty just isn't that high.

not necessay. while the brake fluid (hydraulic fluid) is absolutely incompressible, air is very compressible and the volume of it under the reservoir cap is way more than needed in this case.

there are two reasons for the resistance you felt in the center piston of the rear brake caliper. one of the two reasons is that your '98 is now 22 years old and I'm betting nobody has ever refurbished the braking system (22 year-old caliper piston seals, 22 year-old caliper piston wiper rings, 22 year-old brake line hoses, 22 year-old master cylinder seals, and, most probably, some really old brake fluid). let's be honest, some parts of a motorcycle are "consumables", like brake pads. but so is the brake fluid and the seals inside the brake master cylinders, the seal inside the secondary master cylinder, and all of those VFR800 rubber brake lines too. if you want to feel the Honda-goodness that Honda had in mind for the brake performance of your 22 year-old VFR800 it's gonna need a full refurbishment at some point. the other reason that the center piston on the rear brake caliper would put up a fight is that on this particular caliper piston there's a lot of mechanical resistance between you (trying to push it in by hand) and the Rear Brake Reservoir (which is where you're trying to make the fluid go with all of your pushing). there's resistance at the PCV, resistance at the SMC, and there's resistance at the Rear Brake Master Cylinder. remember that the brake fluid is incompressible, so it's looking for a space with air (that is compressible) to occupy. the best way to push in caliper pistons is to open the corresponding bleeder fitting on the caliper then push in the piston. if you have somebody handy to help you (one person presses the piston in while the other person carefully/gradually cracks open the bleeder fitting just a tiny bit) it's easy to control the situation and avoid admitting air into the system. yeah, it's a bit messy and if you're not careful you could admit air into the caliper, but it's really the easiest way to do it. and you should probably bleed the brake system every-so-often anyway, right?

You really don't know what you're talking about. This will probably piss you off, but it's the truth.

Well, good luck with the bike. Hoping your various maintenance actions will make the odd feeling go away. Sometimes people "solve" problems without ever knowing what the problem was. Having what feels like a cylinder "dropping out" as RPMs climb is a pretty worrying feeling. Based on the VFR800 engine firing order the cylinders that I believe would cause the biggest "feel" if one of them started dropping out would be either #3 or #2 because... ... VFR800 firing order (in 90 degree increments): 1-0-3-0-0-2-0-4- so if either #3 or #2 dropped out you'd get a really long (450 degree) empty space. And the #2 cylinder might be the worst of the two because it dropping would place the 450 degree empty space just before the (signature VFR800 V4 item) cylinder #4 and #1 big-bang combo (only separated by 90 degrees).

When you get a good deal on a bike that was stored away in the back of a garage for years you have to suspect that there was a reason the bike got relegated to the dark shadows. Now it could be that there's a simple, harmless (not mechanical) reason for the bike getting stored, something like the owner having a near-death experience that scared him so badly he quit riding. But more often than not the case is something mechanical related was making the bike disagreeable, worrying or just not fun to ride any more. People put bikes like that in the back of the garage and ignore them. When you take possession of a bike with this sort of history (i.e., mostly unknown, long stored or highly suspect) you should be willing to give it a good bit of precautionary/refurbishment maintenance. You just have to accept that this "good-deal" bike might require some investment of money, time and effort.

I installed a set of Galfer lines on a 2000 5th Gen just three weeks ago. It wasn't my bike. A friend brought the bike and all the parts to my garage (he doesn't have much experience wrenching on bikes). A couple of years ago I installed a set of Spiegler lines on my 1999 5th Gen. We removed all three calipers. Disassembled them for a thorough cleaning. And then we replaced all of the caliper's piston seals and wiper rings (yeah, 20 year old rubber should be replaced). We also removed, cleaned and rebuilt the front brake master cylinder, the clutch master cylinder the rear brake master cylinder and the clutch slave cylinder. We chose not to remove the Secondary Master Cylinder from the Front Left Caliper. And we were very careful not to disturb its original adjustment. Messing with the Secondary Master Cylinder is a bit of a perilous thing, if you get it messed up at all it can cause all sorts of trouble with the bike's rear brake (the Secondary Master Cylinder controls the center piston of the rear brake). We decided that we were doing enough other things with all the removal-disassembly-cleaning-refurbishing plus installation of the new braided stainless steel lines. So, to repeat, we decided to defer cleaning and rebuilding his bike's Secondary Master Cylinder until a later maintenance day when it will be the only thing we're doing. Installing the new set of Galfer lines was easy. Galfer provides a very precise set of step-by-step instructions. If you're any good at following directions the install is easy and logical. This was the easiest, most enjoyable part of the whole day. When the install work is complete, bleeding the brakes is a two-person job. The Honda Service Manual has a (kinda confusing) description of the order in which you are meant to bleed the brakes. The first time you read through these directions you'll end up confused. The second time it will begin to make sense. The third read-through will make enough sense that you'll be able to make a personal set of notes on the proper order. The fourth very careful read-through will be necessary to confirm the order you've written on your personal set of notes. I have a MityVac that I purchased at Harbor Freight. As we moved from one bleeder valve to the next I would put the MityVac suction on it, then I would tell the bike's owner to pull the brake lever in and hold it (or push down on the rear brake pedal and hold it, or pull in the clutch lever and hold it). Then I would open the bleeder for a second to pull brake fluid through the lines. The thing that makes these Honda Linked Brakes so hard to bleed is (duh) because they're linked. You have to keep track of which bleeder is for which caliper pistons. Without doubt the trickiest part is properly bleeding the Secondary Master Cylinder to the Proportional Control Valve (just behind the fuel tank) to the center Rear Caliper piston. You have to hook the MityVac to the correct bleeder on the Rear Caliper and have your helper compress/pump the Secondary Master Cylinder. In my experience it takes at least two full rounds of bleeding all of the bleeders in the correct order to achieve success. And the full job that we did: disassembly, cleaning, replacing rubber parts, re-installing the calipers, installing the new lines and bleeding the brakes took two full days in the garage.

I just watched this short video explaining the Triumph 900 "T-Plane" 3-cylinder engine. Near the end of the video there's an on-board-camera clip that gives you a good opportunity to hear the engine rev under hard acceleration. You're not going to believe how much this engine sounds like a VFR800 engine. If you don't want to watch the whole video just skip to 3:10 and listen to how Triumph stole the sound of our VFR800s. https://www.youtube.com/watch?v=Woh023WrZlQ The cylinder firing order of the "T-Plane" engine is almost exactly the same as our VFR800, just without cylinder #4 VFR800 = 1-0-1-0-0-1-0-1- Triumph = 1-0-1-0-0-1-0-0-

Every time I see one of these I'm reminded of the line from the Tom Cruise movie Risky Business, "Who's the U-Boat commander?"

Honda just wants you to use a high-quality RTV (room-temperature-vulcanizing liquid gasket) in the semi-circles. Locktite makes good stuff. I use a tiny line of RTV along the entire mating between the valve covers and the gaskets when I reinstall the valve covers (after valve clearance check/adjustment) because I once had a leak after doing the work. I was test riding the bike after a valve adjustment and it started leaking oil from the forward cylinder head. I discovered that the engine-generated vacuum pull (on throttle off overrun) had actually pulled part of the valve cover gasket inward and once it (the gasket) was displaced from its normal place it stayed there and oil was freely leaking from the gap. So from then on I've used a thin line of RTV to securely locate the gasket into the valve cover before re-installing on the cylinder head. And I want to be perfectly clear: I don't put anything on the surface between the gasket and the actual cylinder head top.

I'm with Grum on this one. It sounds like your bike's charging system is failing. The Regulator/Rectifier on the 5th Gen is a known fail point (it's an old-school Shunt-type Regulator/Rectifier, this type of R/R doesn't last forever, heat issues caused by the shunt-to-ground method of its rectification function eventually kill it). Sometimes the R/R failure is precipitated by corrosion in the multi-plug that connects it to the lines from the alternator stator (this can lead to high temperatures in the plug which will result in a burned/melted appearance). Occasionally it's the stator itself that fails. Either way the R/R ends up compromised and now it won't be able to maintain your battery, which is why it fails during rides. The MAP sensor problem could easily be nothing more than a by-product of worsening situation with your battery and R/R. So, yes, Grum is pointing you in the right direction: Trace the bike's charging wiring looking for connectors that are corroded or have a "burned/partly melted" appearance. If you don't find anything like that you should test the R/R (there are plenty of YouTube videos that can run you through how to do this). Bear in mind that by now your bike's battery may be in poor condition (possibly in need of replacement) you can take it to a shop and have it tested to see if it can still deliver AMPs. It might be that your battery needs to be replaced. It might be that both your battery and your R/R need to be replaced. That's a start...