carb sync mystery

[goatman]

I was trying to sync my carbs, and get no movement on the Carbtune, like there is not enough vacuum to operate the Carbtune. I then noticed that my #4 cylinder is not firing, spark is there, but header pipe is cool. Could the fact the #4 is not firing cause enough vacuum loss to not get readings on the Carbtune? I put my tongue on the gauge hoses, and can feel some vacuum, just not enough to move the rods in the Carbtune. I tested the Carbtune on another bike, and it works fine. Thanks for any replies.

 

[tugla]

should get the other three moving atleast?

 

[[email protected]]

should get the other three moving atleast?

Thats what I would think.
You sure you're doing it correctly? Connected to the correct vaccum ports? If the engine is running and you whack the throttle you should definitely be getting a reading on the other three.

 

[goatman]

I am sure I am doing it correctly, done it many times. If I rev it up to 5-6k I get some movement, even more movement on decel, but certainly not normal. Also, this bike only has 18,500 miles on it so I wouldn't think it would be valve related. The bike is new to me and has obviously sat for some time. It's actually not my Vmax, but a 93 Venture, so same carb setup.

 

[tugla]

sounds like a leak in the vacume lines hooking it up? but you said it worked fine on another bike, mmmm gotta think about this one then

 

[dannymax]

Could the carbtune need cleaning? They get clogged up pretty easily.

 

[sdt354]

I was trying to sync my carbs, and get no movement on the Carbtune, like there is not enough vacuum to operate the Carbtune. I then noticed that my #4 cylinder is not firing, spark is there, but header pipe is cool. Could the fact the #4 is not firing cause enough vacuum loss to not get readings on the Carbtune? I put my tongue on the gauge hoses, and can feel some vacuum, just not enough to move the rods in the Carbtune. I tested the Carbtune on another bike, and it works fine. Thanks for any replies.

The columbs are seperate. So, take #4 hose off for a try, put the plug back on #4. Oserve the other 3 connected hoses. I misplaced a hose and did it with 3 hoses no prob. Let us know what happens? A very small blip of the throttle should send the rods up.
A vac leak should be checked for, on the bike I mean.
Steve-o-o

 

[sdt354]

I'm assuming the v boost is closed?

 

[wildweasel_pt]

I'm assuming the v boost is closed?

That should not be a factor... He would get close/same readings on 1/2 and 3/4. Is fuel getting on that cylinder? Did you check the carbs working well? If you have spark but no fire its because either one of them is not arriving properly: fuel, air, both. If you get no reading on carbtune it means the cylinder is not sucking properly so to speak or that sync port may be obstructed

 

[naughtyG]

There's no Vboost on a Venture..

I say vacuum leak somewhere too, it kinda has to be. Are the carbs seated well and tight? Are any of the rubber rings above/below the carbs perished?

 

[goatman]

Update. I got the #4 cylinder running, and low and behold, the Carbtune showed some action on #3 cylinder. I adjusted sync screws from that point and got them balanced. They were way out of sync. I still have a ways to go with this bike, but I feel much better about it now. Thanks for the help.

 

[SpecOps13]

Wow, Congrats Bro....

 

[RaWarrior]

I wouldn't think the cylinder not firing would affect the vacuum....as long as the dead piston is still churning away, it's moving air(just as the expense of the other three) and should generate manifold vacuum. Weird problem....

Good you got it sorted though.