Adding vacuum barbs

[ninskrillz]

Hey guys I'm looking for ideas for adding vacuum barbs to use a manometer to synch my carbs. I have vm34 carbs with Tc bros aluminum manifolds with rubber hose to connect the two. Any ideas to get some barbs in there?

 

[Signal]

Here are some photos I took when drilling and taping my VM 36's should give you an idea.
There was a small rectangular casting on the carb body, that I spot faced then drilled and taped to take the barb.
650 central sell glue in barbs.

 

[ninskrillz]

Here are some photos I took when drilling and taping my VM 36's should give you an idea.
There was a small rectangular casting on the carb body, that I spot faced then drilled and taped to take the barb.
650 central sell glue in barbs.

Nicely done. Was hoping to not have to drill the carbs. Open to other suggestions!

 

[5twins]

There is another option but you probably won't like it either. The early models had vacuum ports into the bottom of the intake tracts right through the heads. These were connected to one another for balancing between cylinders I guess. They weren't there for balancing carbs. They had 90° barbs facing in towards each other so removing the hose and installing gauge hoses wasn't very feasible. The castings for these ports were never removed so you could drill, tap, and install barbs there. The down side is the head would have to come off to do so.

 

[Signal]

If you have one of those big fin barrels the top fin obstructs the ports 5 Twins is talking about, which makes it impossible to fit the barbs without machining the barrel. Using a standard size fin barrel there is no problem. I found out the hard way.
Here is Goran Persson's photo of the mod.

 

[ninskrillz]

ooo yikes yeah that'll be even more intesive.. Any synching tips in the meantime before I get around to installing some barbs?

 

[grizld1]

Thread-in barbs are also available from 650 Central, and I'd advise you to use those. Refer to the pics on the 650 Central site for placement. Remember that you have two synch adjustments to perform with cable lifted slides. Read the VM section of the Carb Guide; I wrote it once, and I'm not about to write it again one piece at a time.

 

[ninskrillz]

Thread-in barbs are also available from 650 Central, and I'd advise you to use those. Refer to the pics on the 650 Central site for placement. Remember that you have two synch adjustments to perform with cable lifted slides. Read the VM section of the Carb Guide; I wrote it once, and I'm not about to write it again one piece at a time.

ive read it 20 times. cable and slides synched, idle mixture is the only one im having trouble with. i dont know of a way to do the dead cylinder method without vacuum barbs.

 

[grizld1]

Pilot mix adjustment and synch are two different adjustments. But here's what you need.

Start the motor, warm the motor, bump the idle speed up to ~1400 rpm. If you have breaker point ignition, just pull a plug cap. If you have TCI or other aftermarket ignition, shut down, pull a cap and attach it to a well grounded plug, and fire on one cylinder, or fabricate a grounding clip. Alternative: if you're running two petcocks, turn one of them off. This ain't rocket science, don't make things harder than they need to be.

After you get initial settings on the mix screws, you may get lean signals like exhaust popping under engine braking and too big a difference between first steady idle and full warm idle (shouldn't be more than ~250 rpm). If that happens, richen the mix screw settings a bit in 1/8 turn increments.

 

[ninskrillz]

Pilot mix adjustment and synch are two different adjustments. But here's what you need.

Start the motor, warm the motor, bump the idle speed up to ~1400 rpm. If you have breaker point ignition, just pull a plug cap. If you have TCI or other aftermarket ignition, shut down, pull a cap and attach it to a well grounded plug, and fire on one cylinder, or fabricate a grounding clip. Alternative: if you're running two petcocks, turn one of them off. This ain't rocket science, don't make things harder than they need to be.

After you get initial settings on the mix screws, you may get lean signals like exhaust popping under engine braking and too big a difference between first steady idle and full warm idle (shouldn't be more than ~250 rpm). If that happens, richen the mix screw settings a bit in 1/8 turn increments.

Thanks a lot man.