Help Weird knocking sound from below front end of tank @ low speed - Suzuki VLC Intruder

If it was bottom end it should be there the whole time and increase with revs, so might not be it. If it's happening all the time post up a video as it will be easier to help . Maybe try to put a screw driver handle on your ear lobe with the other end on the engine - if it's coming from there you'll hear it on top of standard engine noise. It might also be a loose chain slapping on the inside of the cover or something, so you can try that as well - on occasion lower RPM when there's slack you might get something like that.

 

The hose issue needs to be sorted before you fixate on the knock issue...the engine runs faster when you block the hose, so that means something isn't right it shouldn't do that. whats happening is its leaning out due to an air leak which has been compensated for by rising the idle till the needle comes up and riches the mixture ....Follow the hose back if it go's to the carby then it come off something (no Idea what though), if as I suspect it go's to the barb on one of the inlet manifolds, block it off with a bolt as someone has put it on to make access to the barb easier....

 

Ok so with the hose think about what it's doing. If you block it the idle speed increases. That means you're making the fuel/air mix richer. If it was leaner, the opposite would happen until the engine stops. Given that's what is happening I'd guess it's probably a breather hose coming from your carburetor. I had something similar on my CBF250 (for the life of me I can't find the photo I took of it) but here is the CBF parts diagram to show you (I don't have a VL one). It's probably just unclipped from somewhere close by...



I don't know what that knock is, it's too hard to tell for me. But you need to narrow it down to the top, middle or bottom of the engine by doing the ear lobe trick I already mentioned. If it's coming from the engine you should be able to hear it as a distinct noise separate from the rest of the engine.

Hope that helps.

 

yeah thats what Im saying ...air leak from open hose.... engine stalls someone raises the idle speed adjuster till engine idles...plug leaking hose engine increases in speed due to high idle setting, shouldn't be any richer unless the carb has also had the mixture screw altered....honestly its not hard block hose drop idle, take for a run see what happens....This is a single carb feeding 2 cylinders setup (from what i can see on the net)

 

To be honest I didn't read your previous post, I was just commenting on what the OP was saying haha.

I know where you are going with it now, just remember you can richen the mixture two ways - reducing the volume of air without touching the fuel (less air same fuel) or putting more fuel in (more fuel same air). A choke works on the first principle in many cases, a mixture screw works on the second

I'd take the tank off @Federal Agent at Large I don't think we're going to get any closer in helping you resolve the issue until you do. Not a big thing, just turn the fuel tap off, pull the fuel hoses then lift and pull the tank back at 45 degree angle to pull the grooves off the rubber stoppers. Maybe do it without a full tank though

 

np.....One other thing, on the scant info I could find there is 2 barbs 1 on each of the inlet manifolds. cant see them being used for balancing the carb as there is only one wondering if it they use a balance hose between the manifolds or something else emission related.....

 

Now where have I heard that before...

Oh that's right

Nah seriously glad you got it sorted. With no arrogance intended, as I have learned this lesson many times myself - if you think logically about what is happening sometimes you can ascertain where it is happening. Also, next time pulling the bloody tank helps lol

As for the knock... well that's anyone's guess now. If it's gone then even better!