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Closed VTEC intake valve...fuel puddle?


TurdFerguson

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Rookie to all this VTEC nonsense but after looking down the intake tract something seems horribly wrong.

 

If the injector is spraying fuel to the center of the intake port and the motor is only operating on 1 intake valve...the 2nd intake valve is acting like a bathtub plunger and pooling a crap ton of fuel on its backside. That port is very deep too, I bet it holds a half ounce of liquid or more before it spills over to the other intake valve.

 

No wonder the VTEC hit is so damn hard and the mileage is so poor.

 

Am I off my rocker ?

 

Let me know what you know Daddy-O.

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Not a VFR expert (yet) but I am a mechanic and something is for sure wrong there. 

That much liquid fuel being dumped into a cylinder in one go is just asking for a hydraulic lock up and serious engine damage, I would hold off any further riding until someone can fill in the blanks here....

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Rob......it's how the motor was designed....read up a bit on VTEC, or take a look down the throat of one, you'll see two intake valves separated by a fairly high port bridge......then visualize what is happening when only one intake valve is opening, but the injector is firing above both ports.

It'll have you as puzzled as me....

 

Could it be that the intake valve is so hot that it simply boils off the fuel pooling on its backside and that it's consequent fuel vapor gets drawn into the cylinder by the one open intake valve?

 

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To the best of my knowledge there has never been an issue with what you are describing. Given the VTEC valves will not operate till Engine Coolant Temp is 65 degC/149degF surely any fuel pooling would have long vapourized or simply been sucked through the normal intake valve by then.

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On 2 February 2019 at 5:44 PM, TurdFerguson said:

No wonder the VTEC hit is so damn hard and the mileage is so poor.

 

 

What do you mean? Mileage poor only in the VTEC zone or mileage poor generally? Either way I disagree, assuming you don't have any EFI issues etc.

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A closed valve means there is no gas flow down that pipe, in other words there is no (or very little) fuel getting there at normal running. If you see a lot of fuel accumulated on your VTEC-valve you most certainly have other problems not related to the actual VTEC functionality. My guess would be leaky injectors or perhaps a broken fuel pressure regulator. Those errors would also explain your poor milage. The milage of a fully working VTEC VFR is not poor, it might not be excellent but not poor.

 

Question: Do you have a fuel puddle on ALL your VTEC intake valves? If yes, what have you fed your injectors?

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6 hours ago, TurdFerguson said:

Rob......it's how the motor was designed....read up a bit on VTEC, or take a look down the throat of one, you'll see two intake valves separated by a fairly high port bridge......then visualize what is happening when only one intake valve is opening, but the injector is firing above both ports.

It'll have you as puzzled as me....

 

Could it be that the intake valve is so hot that it simply boils off the fuel pooling on its backside and that it's consequent fuel vapor gets drawn into the cylinder by the one open intake valve?

 

I understand the VTEC operation on the VFR, what I am saying is that you clearly have an issue with the fuel pooling on top of the VTEC intake valve - as you describe, and dumping all that liquid fuel into the cylinder in one go when you hit VTEC RPM could cause a hydraulic lock up - however if the injector is located evenly above both VTEC and non-VTEC intake valves then It must have been designed that way?? I will have to visually check one out. Prehaps there is some system that is designed to prevent fuel flow to the VTEC port prehaps someone that has pulled a few of these apart or has a bit more experience with them could explain ??

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I think you will find the OP is making a theoretical discussion & on starting a cold bike I would agree the situation is as per his hypothesis. But the intake valve will heat up very quickly & rarely is a VFR ridden below the Vtec transition point for any length of time. The fuel would only pool on a cold engine & that is effectively what a choke does, adds much extra fuel to a cold combustion chamber to create a flame regardless of the chamber conditions. The unused valve will get hot very quickly because it does NOT receive any cooling from the incoming air/fuel charge because it is still on the valve seat, the walls of the unused inlet port will also heat up quickly again due to lack of air flow through the port, any fuel will stay in or quickl return to vapour state & due to the pulses of the working valve you are unlikely to see fuel deposits in the unused intake port after a few seconds.

 

So never worry, all good, nothing to see here, move along 🙂

 

YMMV 

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Mohawk read and comprehended exactly my thoughts and confirmed my eventual theory. Thanks for the input. Weird design though eh?

 

Im getting 36-ish MPG on the VFR, 30mpg on the 6 smoothbore equipped CBX1000, 48 on the FZ6 and would get approx 52 on my 1200 BUELL? A V4, a Inline 6, a inline 4 and a V-twin. Each within the 100hp range and each (aside from the 6cyl beast) get better fuel mileage than a "state of the art" V4. Just posting my personal experience, not pointing fingers.

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The VFR’s have never been very fuel efficient I think is down to the RC45 derived motor that was build for racing. When you think that the 1993 released RC45 had an included valve angle & valve sizes that were still the same on 2007 Blades which although a few degrees tighter on included angle use the same valve sizes. Honda designed that head to flow 170+hip & the VFR only produces about 2/3rds of that. So there is a lot of wasted potential there. 

 

My old CBR600FiY (2000 model) managed 55UK/mpg & 60 when ridden very sensibly,where as my VFR manages 40 as an average & only 45 when ridden very conservatively ! Which is generally less than many more modern 1000cc bikes manage 😞 But I still love it 🙂

 

As always YMMV 

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