GreginDenver

This thread keeps reminding me of another thread from a couple years back. There was another owner (of a 5th Gen, I think) who had a "misfire when warm/hot" situation, and after a lot of searching and trouble shooting he discovered that one of the coils had a crack in it's plastic covering which was affecting the coil's ability to fire the spark plug (apparently the crack in the coil cover was allowing a partial grounding of the coil field to occur). I can't remember which VFR forum this thread was on, I searched around a bit but couldn't find it. Have you done a thorough/close visual inspection of the bike's ignition system, to include the coils?

As I am naturally unafraid of re-wiring the electrical wiring in cars and motorcycles, the question I would be asking myself is... If the '86 trigger wheel is discontinued and only the '87 (and onward) trigger wheel is available, how hard would it be to fix the issue by working from the other end of the system by substituting/retrofitting an '87 ignition control box on an '86 VFR? The question would be: How much of the bike's wiring harness was changed from the '86 model to the '87 model? If the only change was the obvious switch from analog trigger wheel to digital trigger wheel for ignition control then swapping in both an '87 trigger wheel and the matching '87 ignition control box would be possible. I can tell you from experience that these old-school ignition control boxes (on 1980s carbureted bikes) often only have 6 or so (maybe up to 10) inputs (wires). It wouldn't be too hard to track down all of the inputs to see if you could make the swap (you might have to "re-pin" the connector to bring in all the correct inputs to the correct placement on the ignition control box).

No, both of my FI project bikes are "batch" injected. I am using an Arduino to sample a MAP sensor attached to each throttle body, the Arduino then sends the lowest value to the MicroSquirt via a DAC. This effectively simulates the vacuum stability of having a large central intake manifold. This setup isn't my creation, a guy named Dennis who lives in Germany thought it up and he was nice enough to help me copy it. If I remember correctly Dennis tried sequential on his 750 race bike but it didn't deliver any improvement in performance (for a lot of extra effort) which I think is a common conclusion people reach when they're dealing with a motorcycle engine. The RPMs are so high it makes a mockery of the attempt to impose the higher order that is sequential.

But here's a question: Have you done the "Flapper Mod" on your 5th Gen VFR800? If the answer to that question is "yes" then we should not discuss anything vehicle-related (it just won't be productive).

I have worked with MegaSquirt/MicroSquirt fuel injection conversions since 2005. Yeah, I know there are many ways to combine parameters to achieve good FI. Yes, I think Honda PGM-FI is a bit old-school compared to modern day FI ECUs but it got the job done for a whole bunch of Honda products for a lot of years.

Actually... Chapter 21 of the VFR800 Service Manual says... And then Chapter 21 goes on to say...

While you're learning stuff... the explanation for why your bike was still able to run pretty well with a MAP sensor problem is contained in Chapter 21 of the Service Manual. In this magical chapter all is revealed, including the fact that the ECM (Honda PGM-FI) only uses the MAP sensor during low throttle openings (i.e. small throttle position sensor opening angles). As you wind on more throttle the ECM switches modes to a pre-programed fueling method (usually referred to as Alpha-N). This mode does not reference the reported MAP sensor value because at higher RPMs small engines (like motorcycle engines) deliver wildly chaotic MAP sensor values.

not to thread-jack, but... I think it's worth addressing the unavoidable, engineered-in weakness that naturally comes as part of a "side-radiator" design. This is something I've been thinking about for a long time (whenever I find myself thinking about how hot the VFR800 runs). The built-in problem with side-radiators is you have to move coolant from one side of the bike to the other. You have no choice but to run a large diameter tube full of coolant right past the headers for cylinders #2 and #4 (less than about 1.5 inches). I don't know what the math of this situation is like, but you know there has to be substantial radiant heat-energy transfer in this area. I've been thinking of putting heat protection on this coolant tube since I first rode my 5th Gen in summer heat.

I'd like to imagine plasma-transferred wire arc (PTWA) technology (like Ford is using in their Mustangs) someday, somehow "trickling down" to the aftermarket world because PTWA gives very good performance and wear to a cylinder liner.

Those of us who ride the VFR800 know how heavy the bike is, and how just a single moment of brain-fade can allow that weight to catch you out and put the bike on the ground. I had my moment two years ago when I pulled into a do-it-yourself car wash in Huntsville at the end of a 3-day ride from Denver to Alabama. I'd ridden through quite a lot of bugs and such, wanted to clean the bike up. Ended up with the beast on its right-hand side. I was tired, didn't realize my situational awareness was at a pretty low point. Wow, if the guy in this video can ride like that all the time, jumping on and off, balancing that heavy bike, then my hat is off to him. (but if I were in his shoes I'd definitely pick my routes carefully, if you tossed in something like a steep hill or potholed/poor condition pavement in addition to a stop light things easily could get out of hand).

Here's my vote for you to restore/keep the airbox flapper mechanism in its original configuration... Why? Because there are two types of people in this world: There are those who understand that air acts like a fluid, and there are those who do not understand. Can you guess which group does "the flapper mod" on their 5th Gen VFR800s? On the 5th Gen engine (being a non-VTEC engine) the dual-track intake system has a definite function, and even better than being functional it (the dual-track intake system) makes great sounding noise. You (the rider) can hear the bike's airbox/intake horns/throttle body hit a hard resonance as the RPMs go over 7,000. Then the airbox flapper opens up and the resonance noise happens again at about 10,000 RPM.

So what about your bike's 23-year-old Fuel Pressure Regulator? When I purchased my two 5th Gen VFRs (one is a '99 and the other is a '01) I replaced the fuel pressure regulators, because they were about 20 years old. Because I replaced the Fuel Pressure Regulators on my VFR800s immediately after taking possession of the bikes (as part of my "new owner" maintenance efforts) I haven't had to deal with the problems/symptoms that a failing Fuel Pressure Regulator might cause, but the odd conditions you've described could be FPR related. So this is just a thought: I wonder which one of the engine's 4 cylinders would be most affected if the Fuel Pressure Regulator was allowing gas to pass into its vacuum line? Cylinder #3 maybe? But even if your bike's FPR hasn't begun to fail it's still 23 years old, you should go ahead and replace it. I'm pretty certain the Honda engineers viewed the bike's FPR as a "consumable item". Good luck with the problem.

This is great, it's like a 1970's disaster movie where a pilot on the ground is talking on the radio to a flight attendant who has to land a damaged Boeing 747 at night on a short runway because the pilots are both dead.

One big problem with owning a 21 year old bike is that the maintenance honeymoon is well and truly over. 5th Gen VFRs are great bikes IF they're kept in good shape as they age. The fuel pressure regulator is 21 years old, how long is it supposed to last? I didn't wait around to find out when I purchased my '99 5th Gen. Likewise, the fuel filter is 21 years old... And all the rubber seals that hold the fuel injectors are old and hard (they might still look good but after 21 years they're not what they used to be) And what's the mileage? Is the engine overdue for a valve clearance check and adjustment (as necessary). Have the starter valves been synchronized recently? Your hard-cold-start problem could be due to one particular thing, or it could be due to the interrelated effects of several minor issues.

You can also see from the drawing that in both cases (both the 180 degree crankshaft engine and the 360 degree crankshaft engine) the primary headers are on cylinders that provide the widest possible spacing of exhaust pulses into both the primary "Y"s and into the final merge (the "collector"). This is how you arrange things for good gas flow through an exhaust system.