Curvy rear cylinder not running.

Hello people, back again for more help with another problem. My sv's (1999) been running pretty horribly lately, especially below 4000rpm, above that it is pretty much normal, accelerates well. So, had a day free today and started investigating. Took the airbox off and started it up and the rear cyclinder isn't running at all really below 4000 ish, the slide on the carb barely lifts, the other ones perfect. It moves freely if I push it with my finger. The carbs have just been ultrasonically cleaned and rebuilt so should be spot on so I'm inclined to think it could be something electrical. Any help would be great.

Little bit more information, I've replaced spark plugs and checked spark is good, also checked coil resistances and switched them round and it's still the same, did a compression test on rear cylinder and it was around 180psi which I think is pretty low, I'm going to do the front to compare but haven't got round to taking the radiator off yet. All vacuum pipes seem fine so I don't think there's a vacuum leak. I think the carb is okay, when I put my hand over the rear carb it gets soaked in fuel, it's just the slide is not lifting at all below 4000rpm. Any help or suggestions would be really useful.

[yorkie_chris]

Vacuum leak IMO.

[Sid Squid]

Originally Posted by yorkie_chris

Vacuum leak IMO.

This.

Check the vacuum hose from the rear inlet to the fuel tap.

Thanks, I'll give it a proper check tonight and let you know.

Right, so I found one problem, I'd put the black cap on the top of the carb on the wrong way round, very stupid I know, not quite sure how I didn't notice. There's been a slight improvement but the slide still isn't lifting properly and there is now the odd small explosion in the carb. I've checked both vacuum pipes by clamping them with mole grips at the carb and there's no improvement. The rubber boot attached to the slide is looking a bit old, quite soft and a bit saggy, the black cap seems to clamp down on it okay though, maybe this needs replacing?? Not really sure where to go from here.

It's fixed, the main problem turned out to be that the metal linking arm between the two carbs had play at one end and so the back carb wasn't opening at the same time as the front, replaced it with a spare I hd and it's running a treat, thanks for the help.

[yorkie_chris]

Balance the carbs, no way will it be near right if you just guessed at it, that problem happens slowly with wear.

Yeah, I balanced the carbs yesterday, it didn't feel too bad but they were quite a way out, so nice not to be juddering around corners.