Baby Viff - 1986 Honda VFR 400
 

I've finally run a tank through my little V4, and was a lot disappointed. Anyway, here it is. This is the only picture I have of it. :p Right now it has the seat on it(of course), but the rear side panels are still off for now since they aren't doing a great job of staying on. It also has the front fender on it, which has little fork deflectors for the first few inches. :thumbup:

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This was the first bike that the new trailer I convinced my dad to buy(instead of renting the u-haul barn door, thread in success stories) hauled home. We bought it for $2000 CAN not running, but looking great. Turns out the kill switch had failed. It had sat for long enough that the gas in the carbs turned green. Tons of bolts were loose, clamps were missing, coolant looked rusty. Whoever was working on this bike had no idea what they were doing. Thankfully me and my dad rescued it.

I rode it for less than 100 km with the stock gearing, 15T/45T, which put it at 5000 RPM at around 48 mph. I decided that was ridiculous so I dropped down FIVE teeth in the rear sprocket and have a 40T on there now. It should be noted that the "bolt pattern" so to speak is different between the NC21(my VFR) and the NC30(newer, dad's vfr), so you can't just buy sprockets from an NC30 or NC35 and slap them on there. Thankfully, JT sprockets has a well filled out catalogue that even had sprockets for my rare bike. The new sprocket puts it at around 4400(?) RPM at the same speed. I still feel like I can go taller, first gear isn't even as tall as the NC30's yet. I can go as tall as a 36T rear sprocket, so when the chain and sprockets wear out, that's probably what i'm going to get. On the highway, I am just under 6000 RPM at 110 kmh(new gearing), while my dad's NC30 should be at almost 6800 RPM for the same speed.

Here is the new sprocket overlaying the old sprocket.
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While I was in there, I swapped over the sprocket's rubber dampers to the CORRECT ones. Seriously, who put this thing together??? The drivetrain lash(more like CANYON) was just stupid with those little dampers. The larger dampers are the correct size.

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So about a third of this tank was with the stock gearing, the rest with the new taller gearing. All of this tank was done without the rear side panels, which may have hurt the mileage a little. I ended up going 101.2 miles with 2.084 gallons, getting 48.5 MPG. To compare, my dad's NC30 went on the same trip with me(excepting the first 1/3) and got 54.6 MPG. I told him when we filled up that he better not have gotten higher MPG than me, that's not allowed. He thought that was funny, cause I was trying so hard(for 2/3 of this tank, anyway), I was tucking at higher speeds, shutting off the engine at stops, short shifting, coasting for stops, P&G'ing, and I had taller gearing. And he STILL got better mileage than me. :eek:

So, what I think caused the bad mileage is the fact that I was pushing my little brother on his bicycle(while straight piped....), and I did a good amount of hard acceleration this tank. My bike is also running brand new bias ply tires, so that can't be helping the mileage either. Hoping for AT LEAST 55 MPG next tank.

Currently, the bike has a deadzone between 5500-6500 RPM, and the choke barely works, so I have some things to figure out.

In 60-65 degree weather with my riding style, the temperature gauge was only sitting around 1/3 the way up, so I MAY have a stuck open thermostat. When I got home, I measured some temperatures. The oil filter(in close proximity to the headers) was 145F, the oil cooler was 125F, engine cases were around 150F. I should block the oil cooler with temperatures like that.

Here is what it sounds like when straight piped. :thumbup:
https://www.youtube.com/watch?v=Ao8MilWWdLs



Some shenanigans.
https://www.youtube.com/watch?v=ZVROmz17_WI

Finally got a picture with all the pieces attached.
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Went for another ride today, and am pretty sure I know why the gas mileage is sucking so bad. The temperature gauge gets to around 1/4 of the way up and doesn't get any higher! So my little viffer probably has a stuck open thermostat, will pull it and check. Even with all my hypermiling, a stuck thermostat overrides all of my opportunities to beat the NC30's gas mileage. I got 49.6, the NC30 got 53.7.

When we got back home I took some temperature measurements at the radiators after sitting for a bit. NC30 was 158F, NC21 was 122F! :eek:

Before the ride, I made a oil cooler block off panel. I wasn't able to conclusively measure oil temps, I got readings of 143F and 167F. On the NC30 I was able to measure the oil temp and it was 185F.
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Found some time today to work on the little viffer.
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Sure dun diddly doesn't look stuck open to me... :confused:
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Maybe its opening up under heat but not closing for some reason??? It takes a good bit of force to open it and it seems to spring back just fine. What is going wrong?

Perhaps its leaking by? Wouldn't take too much flow to cool that whole engine I'd imagine.

Nice looking bike btw. :thumbup:

I suppose its possible, the o-ring in the housing looks pretty flat. I'll check that when I have time.

Thanks. :D

If the spring is weak it will open too early and stay open too long.

Best bet is just to replace it if it's not crazy expensive.

You hit the nail right on the head! That is exactly what it was doing. The O-ring I pointed out is just to keep coolant from leaking out, so it is unrelated to this problem. You can shake the thermostat housing and hear the thermostat rattling around in there. I did a flow test by pouring water in one side and seeing how fast it would flow out the other side. Well, it flowed a whole lot more water than what the little bypass hole in the thermostat should be able to flow.

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I took it apart and put a spring in there to put pressure on the thermostat so it wouldn't move. Put it back together and voila! No more rattle, and it passed the flow test too. So that's what the problem was. I really do not want to rely on the spring though, it could come loose at any time and destroy the water pump.

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While I had it apart, I put it in some hot water to test opening temps. It appeared to open at 172F, and was fully open at 185F.

New thermostat is on its way, REALLY HOPING that it won't rattle like this one does. Considering the slapped together nature of this bike in other areas, it is certainly possible the PO just threw a thermostat that "fit" in there.

Just found transmission information, a forum post said that the Haynes manual for the NC30/35 lists NC21 and NC24 specs in the back of the book. Well, my dad just so happens to have that Haynes manual, so I finally know my gear ratios! :D

Stock, with 140/70/18 rear tire(Haynes seems to think a 130/70/18 is stock. It may be, but my bike has the larger size tire.

45 mph: 4453 RPM
70 mph: 6927 RPM


Same as above but with a 40T rear sprocket instead of the 45T stock.

45 mph: 3958 RPM
70 mph: 6157 RPM


With a 36T rear sprocket...

45 mph: 3562 RPM
70 mph: 5541 RPM


To compare, the NC30 with stock gearing is at:

45 mph: 4487 RPM
70 mph: 6980 RPM


Off to gearingcommander to add another bike!

I sold thousands of thermostats for cars, all had the spring firmly attached.