Carb syncing with a manometer.

[toglhot]

I thought I’d make one more video before tearing the bike apart. This one deals with carb syncing with a manometer.

This manometer has a relatively large body of water, and the vacuum lines are fitted with a .6mm jet. This has the effect of slowing down the movement of water stabilising the readings and making the device extremely accurate. Just a miniscule turn of either idle screw or throttle adjustment screw greatly effects the fluid levels.

I have great trouble with my fingers, so you'll notice me changing hands frequently trying to turn the adjustment screws. I also turned the adjustment screws the wrong way a few times, putting the levels out.

 

[Mikey]

Thats quit unique
Back in the day (which day is anybody's guess) I would adjust my 75 using the dead cylinder method but a manomter is the way to go now

 

[Tinker Taylor]

That was sweet!
'TT'

 

[toglhot]

Same here, along with popsicle sticks, tube in the ear and so on.

 

[5twins]

How about telling and showing us more about your manometer and how it's made. That looks like a nice one.

 

[toglhot]

How about telling and showing us more about your manometer and how it's made. That looks like a nice one.

Two short lengths of 30mm, clear acrylic tube, linked at the bottom by a short piece of 6mm plastic tube. The tubes are clamped by two, two piece ply platforms with a neoprene gasket between, by three lengths of allthread. Each inner piece of ply has two 30mm holes drilled to locate the acrylic tubes. Two long lengths of 6mm plastic tube exit the top for connection to the manifolds. These tubes are fitted with a .6mm jet, I made from Delrin, these, along with the relatively large body of water, slow and stabilise the fluid levels. The 30mm acrylic tubes have holes drilled, top and bottom, .5mm smaller that the 6mm plastic tube, the holes are smoothed and the plastic tube forced through the holes to prevent leaks. Each tube is filled less than halfway, to ensure that water can't enter the inlet tract.
You can just use two coke bottles if you choose, does the same thing, just not as neat!

 

[5twins]

A picture is worth 1000 words, or so they say .....

 

[BluzPlayer]

A picture is worth 1000 words, or so they say ....

Hey 5.
Not sure how to put it here but he posted a pic of it in his Last Start thread post 6

 

[bosco659]

 

[5twins]

Sorry, missed it

 

[Kevin Werner]

So... (newbie here) now the manometer is hooked up to presumably vacuum ports. Now what? Run the motor at 1500, 2000, 3000 rpm? Make the mechanical adjustment between the butterflies until both sides are equal? If pilot jets get changed, or mains, do we do this again?

 

[5twins]

You adjust the sync at idle, and if it's a carb set with a linkage, the sync should be good through the rest of the RPM range. You could rev it up and check it but it should be the same. Changing jets shouldn't change the sync but adjusting the mix screws might if that changes the idle speed on one of the cylinders.

 

[bosco659]

On the water Buffalo, it’s difficult to sync the carbs with a manometer or gauges because the 2 stroke engines pull such low vacuum at idle. All the reading I’ve been doing suggests a bench sync is all you need to do on the bike. I’ve just rebuilt my carbs and have done a bench sync but will still hook up my manometer after testing the bike on the road. I like the large reservoirs on Toglhot’s set up.

 

[Kevin Werner]

You adjust the sync at idle, and if it's a carb set with a linkage, the sync should be good through the rest of the RPM range. You could rev it up and check it but it should be the same. Changing jets shouldn't change the sync but adjusting the mix screws might if that changes the idle speed on one of the cylinders.

Thank you. I have played a little within screws but I let them confuse me. I went to chart 1 1/2 out (77) and either in or out increased idle speed. I will get around to putting a piece of cardboard between my tracker style exhaust outlets after a full warm up ride to see if I can discern a left to right variance. Then @mm1ut1 (?) 3 blocks away has a new, never used manometer.

 

[5twins]

That 1 1/2 turns mix screw setting is just a suggested starting point that should be close. From there you'll want to fine tune the setting for best running (smoothest and fastest speed). I work the screw out (richer) about 1/4 turn at a time until the idle speed starts to fall off and the cylinder starts stumbling, then I turn it back in just enough to get it running good again. I find setting the screw at the rich end of this good running area helps with eliminating popping on decel.

You want the mix screws to dial in pretty close to that suggested setting. If you need to go more than a turn or so from that to get it running right, that would indicate a different size pilot jet is needed.

 

[Kevin Werner]

That 1 1/2 turns mix screw setting is just a suggested starting point that should be close. From there you'll want to fine tune the setting for best running (smoothest and fastest speed). I work the screw out (richer) about 1/4 turn at a time until the idle speed starts to fall off and the cylinder starts stumbling, then I turn it back in just enough to get it running good again. I find setting the screw at the rich end of this good running area helps with eliminating popping on decel.

You want the mix screws to dial in pretty close to that suggested setting. If you need to go more than a turn or so from that to get it running right, that would indicate a different size pilot jet is needed.

Wish I could bookmark this response. Thanks

 

[Jim]

Wish I could bookmark this response. Thanks

Click the Bookmark button.

 

[Jim]

 

[Jim]

 

[Kevin Werner]

That 1 1/2 turns mix screw setting is just a suggested starting point that should be close. From there you'll want to fine tune the setting for best running (smoothest and fastest speed). I work the screw out (richer) about 1/4 turn at a time until the idle speed starts to fall off and the cylinder starts stumbling, then I turn it back in just enough to get it running good again. I find setting the screw at the rich end of this good running area helps with eliminating popping on decel.

You want the mix screws to dial in pretty close to that suggested setting. If you need to go more than a turn or so from that to get it running right, that would indicate a different size pilot jet is needed.

1 full turn IN gave best idle after separating the tracker exhaust outlets with cardboard so I could hear the individual cylinders better. However, lots of decel popping .