Vacuum leak?

[Magnatic]

I'm still trying to get my 96 magna sorted out, and I'm stuck again. I installed Dave Dodge's jet/shim kit along with Vance&Hines pipes and K&N filter. Before
this, the bike ran OK except for the usual stumble around 4k that most stock bikes seem to have. Now, under throttle, the bike goes great, but at light throttle it runs rough and pops both decel and accel. I called Dave Dodge and he said it's a vacuum leak somewhere. I removed and reinstalled carbs making sure everything was tight, and still have the same issue.
 
Could a small air leak in the airbox cause this much rough running?  Also, there
is one hose near the hose that connects to the back of the airbox that is not
connected to anything. It comes off one of the tubes that runs between the carbs. I can't find anywhere that it could go. Maybe just some kind of breather hose?

Any ideas of probable vacuum leak areas would be appreciated. Thanks.

[lragan]

Don't think there should be hoses not connected.  I have attached pages from the shop manual showing carbs and hoses, along with instructions for disassembling carbs.

Hope this helps.

[attachment deleted by admin]

[Greg Cothern]

I agree does sound like an airleak.  Places to look would be the airbox, as well as the rubber intake boots.
Also make double sure a diaphragm did not get out of its ring when putting the black plastic cover back on...

[Magnatic]

Thanks for the replies, I went ahead and ordered new carb insulators since mine are 12 years old and a bit stiff. I am still wondering about the hose near the rear of the airbox that is not
connected to anything. Does anyone have their tank off and can look? It is about a 1/2" OD
hose that runs up from the carbs and ends in a half loop next to the hose that is attached to the back of the airbox. Thanks for the picture from the repair manual, but I can't tell from that.

[Greg Cothern]

Its a vent line.  It goes up and makes a 180° turn down??  With a "bendy" bail holding it in place at the top from the back middle airbox bolt? 
If so then it vents to atmosphere.

[Magnatic]

That's it, thanks Greg. I think I'll try wrapping the airbox seam with duct tape while waiting
for the new carb insulators.

[Greg Cothern]

On the "D" shaped pilot jets, where did you adjust them too??  I have found that on V&H I have to put them at least 3 1/8 turns out on a setup such as yours.  Matter of fact we ended up putting on a second set of shims to help on one..

[Magnatic]

3 1/8 is where I have it now as a matter of fact. I tried everywhere between 2 1/2 and 3 1/2. Right now, when you open the throttle, from 5k to redline you better hold on, but it is just not right at part throttle, very rough running.

[Greg Cothern]

Does it do this at any particular RPM range?  Or is it when you simply hold steady at a set speed??

[Magnatic]

It's not a particular rpm. If you're not accelerating it does it. It is worse when going
say 30-40 mph versus 60-65 because I'm giving it more throttle to maintain the higher speeds.

[Greg Cothern]

Alright that helps a lot...  I believe its too lean on the low to mid range transition, you would benefit from another shim added to the stock and DRP shim you already added.
It helps, wont completely aleviate it, not that I have found YET.  I have some ideas about it but still working towards proving them.

[L J VFR]

I too had to add the extra (3rd shim) on my magna as Greg suggested, and it helped my midrange, stumble-shutter  quite a bit. I can still find a little bit of "flutter" if i look for it but just going up and down the rpm range, the extra shim helped my 01 out a lot.  Good luck... Lance

[Magnatic]

OK, thanks Greg and Lance, I will stop by Radio Shack and try the
extra shim set-up. Probably can't get to it until the weekend, but I
will report the results.//Matt

[L J VFR]

Something I should note Matt,  Some MOOTsters thought that my k&n air filter caused me to run lean, that is why they recommended the 3rd shim, otherwise it would have probably ran fine with stock air filter and 2 shims...  Good luck to ya.    Lance

[Magnatic]

Well, I added the 3rd shim and started with the pilot jet out 2 3/4 turns.  It runs
worse by far now.  The rough running, bucking and popping is much worse. To me,
it seems rich, like it's trying to clear out the extra gas and then eventually it takes
off, although now even under heavy throttle, it runs rough. Before with one extra shim, it ran fine under throttle. I didn't have time to experiment with the pilot screw, but I
can't imagine it will cure this.  On the bright side, I'm getting pretty fast at carb
removal and replacement.

I checked the plugs before starting it up, and they were damp with gas, and one of
them was very loose and very wet. So I think it was rich before adding the next
shim. If the one plug was loose enough, could that have caused the rough running at
part throttle?

At any rate, it doesn't seem that the extra shim is the answer in my case. It also
doesn't seem to me that I am leaking vacuum from the boots, carbs, or airbox.

Any ideas, thoughts?