Virago 700 in the shop

[cathead]

Both carburetors need to open in unison which is what I am referring to as synchronization. There was some sloppiness
in the mechanics of the carbs and if you set it so that both carbs opened at the same time and then advance the throttle a number
of times, they would revert to one opening quite a bit before the other would start to open. So that part is fixed. I'm sure the carbs
will need a little more attention and it's all part of the game. So far I have about 60 dollars total invested in the bike. I can see
the dilemma when a bike has four carbs and needing some sophisticated equipment to make it purr. I look at the Virago engine
as two single cylinder engines connected together by the crankshaft so all that will really be needed is to get them to work well
together which is what I plan to do. I could easily afford a new bike if I chose to do that but find it more interesting to have a
winter project to keep me occupied, learn a few things, and in the meantime restore an old beater to functionality.

 

[great white]

Both carburetors need to open in unison which is what I am referring to as synchronization. There was some sloppiness
in the mechanics of the carbs and if you set it so that both carbs opened at the same time and then advance the throttle a number
of times, they would revert to one opening quite a bit before the other would start to open. So that part is fixed. I'm sure the carbs
will need a little more attention and it's all part of the game. So far I have about 60 dollars total invested in the bike. I can see
the dilemma when a bike has four carbs and needing some sophisticated equipment to make it purr. I look at the Virago engine
as two single cylinder engines connected together by the crankshaft so all that will really be needed is to get them to work well
together which is what I plan to do. I could easily afford a new bike if I chose to do that but find it more interesting to have a
winter project to keep me occupied, learn a few things, and in the meantime restore an old beater to functionality.

Sorry, thats not correct. The throttle blades don’t need to be synchronized to each ither, they need to be set to the operating conditions of the cylinder they are feeding.
yes, they need to open together, but not in relation to each other.
it comes down to how each cylinder is operating . One cylinder might have better ring sealing than the other, or better valve sealing, or the valve timing might be off a little compared to the other. Can be a simple as some valves are adjusted a little tighter/looser than the ofhers.

This means each cylinder may pull a different strength vacuum signal to the other.

You synchronize the throttle blades so each cylinder pulls the same vacuum signal through the carb Venturi's. The throttle blades are essentially vacuum adjusters as restriction in a tube is what creates vacuum.

adjusting the vacuum pulled means each cylinder pulls the same fuel mixture from its respective carb, making each cylinder run smooth by producing similar power. Basically, balancing the engine power output per cylinder and resulting in a smooth running engine.

All this is determined by the throttle blade postion, which is what manipulates the vacuum signal strength in the carb venturi.

Thats why you need to balance the vacuum signal through each carb and why it can only be done with the engine running. You’re making sure each cylinder is doing the same amount of work.

 

[cathead]

Thanks! That makes sense. For now I am going to have to set the project aside until it is warm enough to
tinker with it outside. There's no point in breathing carbon monoxide indoors.

 

[great white]

Thanks! That makes sense. For now I am going to have to set the project aside until it is warm enough to
tinker with it outside. There's no point in breathing carbon monoxide indoors.

I'm glad you understood that. My brain is a little muddled today and it was a bit of a struggle to make that coherent. I wasn't exactly sure if I had actually explained it right.

I try to avoid doing or explaining anything technical when the bowl of jelly on the top of my neck isn't firing on all cylinders.....

 

[cathead]

I'm glad you understood that. My brain is a little muddled today and it was a bit of a struggle to make that coherent....

You did just fine. It's good to know there is someone out there that has your experience and willing to help.

Thanks for being there Great White!

 

[cathead]

I watched a bunch of You-Tube videos on the subject of constant velocity carburetors and learned a lot about how
it all works. After running the engine a bit, it is apparent that I have a vacuum leak or possibly something occluding
a main jet possibly. I will have to disassemble the carbs again for a very close look to figure this out. The idle
circuit seems fine for now as it idles fairly well.

 

[great white]

I watched a bunch of You-Tube videos on the subject of constant velocity carburetors and learned a lot about how
it all works. After running the engine a bit, it is apparent that I have a vacuum leak or possibly something occluding
a main jet possibly. I will have to disassemble the carbs again for a very close look to figure this out. The idle
circuit seems fine for now as it idles fairly well.

What are your indications that point you to vacuum leaks?

Vacuum leaks are uncommon on bike carbs except for the lift diaphragms cracking from age or use.

The only other place you typically see a vacuum leak problem is the rubber intake manifolds, which can also break down and crack over time.

Neither condition is repairable. You have to replace the parts…

 

[lordbeezer]

Spray lightly brake or carb cleaner around suspected vacuum leak area.

 

[Deleted member 69715]

Spray anything flammable in close proximate to a running motorcycle engine? No.
I've used a spray bottle of water and "misted" around where vacuum leaks may occur. You would notice the change in RPM.

 

[great white]

Spray anything flammable in close proximate to a running motorcycle engine? No.
I've used a spray bottle of water and "misted" around where vacuum leaks may occur. You would notice the change in RPM.

same thing can be done with a combustible spray, you listen for the rpm change as it is drawn in through the leak and burned.

But you always have to be mindful that it is combustible. As long as it's not sprayed on an open flame or spark, no problem.

I knew a guy who used to use a propane torch to find vacuum leaks. Worked fine, until one day he hit a sparking plug wire (broken down insulation). The shop got pretty exciting pretty fast that day....