VFR800 (VTEC) Starting issue

[kgm]

Evening all,

Looking for some guidance on where to go with this. Bike is a 2012 VFR800X Crossrunner.

Four days ago the bike started and ran fine, no issue. I removed the exhaust silencer to allow me to remove the rear wheel to get the tyre changed. I left it overnight with the silencer off as it was dark by the time I got the tyre back. Silencer refitted no bother with new fibre gasket and clamp. I have the bike a good coat of acf50 too.

Now it won't start. Tried a good battery straight off a full charge, no difference. Kill switch is set correctly, HISS isn't interfering, fuel pump primes and it turns over strongly.

It will start and run with a bit of throttle but runs really rough and cuts out off the throttle. Looks a little smoky inside the exhaust and it smells but the smell could just be the ACF50 as it heats. All four down pipes are warm so I reckon each cylinder is active. As for fuel, I let it sit for a few days with a fairly empty tank so its possible there was some condensation in there however I've topped it up with fresh stuff. All other electrics work fine.

Aside from the exhaust and acf50 nothing has changed so any suggestions as to where begin diagnosing would be appreciated.

[jaffa90]

""""Now it won't start. """
"""It will start and run with a bit of throttle"""
Poor info,
Has something entered the silencer or collapsed inside?
Lambda sensor?

[kgm]

Fair play. It won't start without grabbing a bit of throttle, and it's reluctant. I'm going to take the can off and stick an inspection camera in tonight after work. If something has crawled in then it'll be into the collector box. Sensor hasn't been disturbed, it's attached to the collector box.

[ADSrox0r]

Hah, sounds like you've got 'the problem'.

When you start it, crack the throttle EVER so slightly just so that it tickles up to 2000 rpm (no more, no less) and hold it there. Keep it at 2000 for around 10 seconds or so, then ever so gently let go of the throttle. If it's 'happy' it will then hold at 2000 or so, if it's not then it will bog down to 1000 or less and die. If the latter, tickle the throttle up to 2000 for a bit longer till it does hold. Once it holds, you can leave it to its thing on standard warmup.

Now, here's the thing. The VTEC has a fancy shmancy 'auto-choke' that isn't a choke at all. It's a 'wax idle' unit. Basically, when the ambient temperature is below around 10C, the wax idle valve will contract (while the bike is off) and pull on a set of starter valves. These are teeny tiny little openings right next to the main butterflies that let a farts worth of air in to get the mixture going when it's cold. It works off the coolant flow temperature so once it gets to around 40C the valve starts to let go and the rpm will drop back down to around idle.

The first reaction from anyone is always, "wax idle is faulty, replace! easy!"

Wrong. It isn't this. You can replace it but it will still do the same thing in cold weather.

There are a number of us on the VFR forums that have struggled with this puzzle for quite a few years and the truth is, we can't solve it! It has something to do with the MAP sensor though, we know this because if you electrically disconnect the MAP sensor and fire it up then it will start perfectly normally without issue. Replace the MAP sensor you say? Tried that, no different.

I thought I had solved it last year by tightening slack clamps on the boots but it's doing it again this year.

In all honesty, it doesn't seem to affect anything and you get used to having to tickle the throttle for a while on startup. Just be aware if you don't follow this 'procedure' and let it bog and die then you will flood it.

Sorry this doesn't help you cure it, but it's not uncommon and won't hurt it.
____________________
Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[kgm]

[ADSrox0r]

If you mean rough when it's warmed up and you're riding then no, it doesn't do that.

I'd suggest you might have a vacuum leak. I've omitted to reconnect a vacuum before and it ran like shit on the throttle.

Not too difficult to trace out the vacuum lines, they're all under the airbox but the engine-side connections are buried deep under the throttle bodies.

Run her up using the tickle trick till coolant temp is above 50 or so, then see how it runs.
____________________
Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[kgm]

So I tried your starting procedure ADSrox0r. It settled down and idled on its own afterwards so I think you have hit the nail on the head. Despite having read hundreds of VFR related posts over the years I have somehow missed this issue so thanks for your advice. I have shared your post with a friend who also owns a crossrunner just in case.

It did run a bit fuelly smelling and smoky to begin with (probably mostly water vapour) but settled down quickly. I think you are right about it flooding as I didn't hold it long enough on the throttle last night and it became progressively harder to start. Seemed smoother from the beginning tonight.

[ADSrox0r]

Welcome to the exclusive club then

You'll find it pretty much always does it when ambient temperature is below 10C. I'd say that you removing and refitting the exhaust had nothing to do with it, it just coincided with a particularly cold morning. You might also find your fuel consumption is rather...hungry.

For reference, here's one account I still have bookmarked of it in discussion from over the years...

https://vfrworld.com/threads/issue-cold-start-and-idle-rough.50635/

Honda have been of no use either btw, pretty much drawn a blank.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Cartam]

I also recently had this issue and think I may have found a fix. Good news is the fix is very easy and simple.

In Australia you can buy a product called Fuel Doctor. It's a fuel system cleaner and fuel stabiliser. I won't go into the details on here, but you can soon do a Google search and also find it on Youtube. I'm not sure if they send overseas, but there are numbers you can call to enquire. I've been using it in my diesel 4wd for the last 12 months to keep the fuel system clean. As it's also fine with petrol, I thought it's worth a try.

Failing that there might be a similar fuel system cleaner where you live.

I added about 50ml and filled the tank with fresh premium unleaded. After about 50kms of riding I parked the bike up. The next day (about 8 deg Celsius) I started the engine and straight away it went to fast idle (2000rpm) and no longer has stalling and low idle issues. This was about 4 weeks ago and no issues since. Seems the issue may be a dirty fuel system or gummed up injectors.

If anyone wants to discuss this please let me know. Happy to help where I can.

Cheers, Matt.

[xX-Alex-Xx]