Strange (?) behaviour when testing for air leaks

[MolleMeck]

Hi,
recently bought a 2005 VTR which is in pretty good nick but runs a bit rough below 3000 RPM. It's clearly not getting the right mixture and has what feels like the odd misfire now and then. It also doesn't respond well to pulling the throttle wide open below 3000. Not much happens. It's not a behaviour I remember from my previous 1998 VTR which I had from new many years ago.
Firstly I should say that I haven't had time to look at the thing properly. Haven't dug any deeper into that side of the bike than changing the air filter. The problem was there before the filter change.
Anyways, before starting to tear the thing apart to possibly clean the carbs I figured I'd check for air leaks and dug out an old can of starting spray (apologies if it's got another name in English) which has been in a corner of the garage for at least 15 years without me having any use for it.

(For gods sake man, get to the point!)

Here's the funny thing. I warmed the bike up just idling till the guage starting showing a value. I think it was 40 ish degrees so not fully warm. But the bike was idling at 11-1200 RPM without choke.
I sprayed some gas in through the side of the frame toward the carbs expecting the revs to rise if there was a leak. Instead the revs sank and the engine died. Restarted and tried again and the same thing happened a few times. Not stalling every time but there was marked drop in revs.

I think it's safe to say I have an air leak which would be consistent with running rough at low revs but ok at a higher RPM and I should find and fix the air leaks before tearing apart the carbs.
But why would the revs drop when I spray starter gas? Any ideas?

Cheers,
Anders / Molle Meck

[tony.mon]

If your carbs aren't properly seated, or if there's a split in the intake rubbers, and it's running rich, adding more fuel will cause this.

Pull the carbs off to check.

[sirch345]

I agree with Tony on both

Chris.

[MolleMeck]

Thanks for your comments.

I think it's well established that there is an air leak and I will have a look at it over winter.

I'm certainly not a proper mechanic or a tuning expert. I just pretend to know what I'm talking about sometimes, much like at work really. But I would have expected it to run lean if the carbs weren't seated properly cos of extra air getting sucked in. How could it run rich?
Or did you mean it runs rich cos of the starting gas getting sucked in? That would make sense to me.

[tony.mon]

It's possible that the previous owner changed jets or airscrew settings to try to compensate for the air leak, but it's best to pull it apart to diagnose it properly.

There are other possibilities, a very dirty air filter, a piece of air filter foam (there are two triangular filters inside the airbox) blocking a carb, etc. Or a failing vacuum tap allowing too much fuel in.

All should be obvious when you take the carbs off.

If all seems ok, suspect the plugs, coils or HT leads.

[MolleMeck]

Thanks for expanding on it a bit. The bike is coming off the road for winter soon so I will take a good look at it then as well as doing the stopper mod to the cam chain tensioners.

Cheers