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Discussion Starter · #1 · (Edited)
Just synced my carbs for the first time (excluding bench syncing) and wanted to share the stuff I used to do it for pretty cheap.

First you need an auxiliary tank, there are thousands of ways to do this. Some are cheaper than others, some are safer than others. Use your imagination plus the knowledge that the carb will take a 1/4" ID hose to make something work. I used cheap air tubing and an old coolant tank, fuel tubing would be much smarter (less leaks). My system could be better but it only cost about 11$ (canadian too). 12$ once I add in a hose clamp
IMG_0765.JPG IMG_0765.JPG

Now, no matter what goes on the other end you need some adapters to screw into the head ports. If you're reading this for actual advice you probably want to buy the motion pro set of 5.0 x 0.8mm ones (yes there are four, lend two to the guy who always wants to borrow your stuff or convince yourself you'll have a 4 cylinder bike some day). The hardware air tubing size I got to connect them is 3/16 ID, 1.4 OD (0.17" ID printed on them for some reason). It's a tight slide on fit.

Now you're ready for gauges. I tried the two jars method, didn't work too well for me. Here's how you can make gauges for less than a motion pro set.

Buy two liquid filled vacuum gauges with threaded ends (1/4" NPT) on ebay for cheap, then order matching barbed female connectors: 1/4" NPT (or whatever your vacuum gauge ends up having) to 3/16" barb. I had a fair amount of difficulty with this. The easy way is to wait for them to arrive, bring them to a plumbing store near you, bring the 3/16 tubing and the vacuum gauge and tell them you need to connect these two things.

Then hook it all up, add some fuel, do your sync and hopefully do better than this. Don't forget to swap the hoses at the end and confirm your result is the same.
IMG_0764.JPG
 

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Thx for sharing!

I'm curious to know how you bench synch them and how accurate they were when you did them with the gauges?

Thx again
 

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The two bottle method is simple and accurate and should work great. If the liquid moves too fast you could use oil instead of water or thin hoses from the engine or reduce the air flow in another way. Seems to work fine for the guy in the video on his CM400.
You don't need the liquid level to be even but they shouldn't move when the carbs are synchronized and you don't need to get those black plugs if you have bottles with screw locks. Just drill and glue the hoses so its air tight.

 

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I made my first "Manometer" from a 2x4 with clear tube stapled to it with a big "U".. filled it with used motoroil and was amazed how much better my Triumph ran.
Food for thought.. make sure the hoses u use stay away from the exhaust or head...
I'm sure u already know the answer ...

I'm also curious how well the gauges worked? I was fortunate enough, a memeber here sent me a old mercury manometer .. has enough left to do a 2 cylinder..
 

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I also used a homebuilt manometer similar to this:
A pair of small forceps locked on each tube was enough restriction to dampen the engine pulses.

14132d1338758391-manometer-doo-doo-do-do-do-hpim0089-small-.jpg
 

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I also used a homebuilt manometer similar to this:
A pair of small forceps locked on each tube was enough restriction to dampen the engine pulses.
OK, Alan - what exactly do you use those "forceps" for when not using them for this??
And why are they burnt on the ends??
 

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Honestly no not me Bill, but plenty of my neighbors do partake. I can't understand how they afford it though.
 

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Discussion Starter · #9 · (Edited)
I might just be incompetent but I could not get the air tubes to seal into the jar lids with silicone or epoxy, I gave up and decided I wanted gauges. These can easily be scaled up to 4 cylinders as well for about 50% of the cost of a professional gauge set (assuming it costs 100 CAD). If you only are doing twins it's 25%.

Bench sync is the LDR method of flattened solder or even just adjusting them in a way that allows you to see the idle jet holes (?) and verify that the throttle plates are open an equal amount. It's probably more accurate on some bikes than others due to differences in wear. It has always let the bike run fine but syncing with manometer/gauges should do better. I'll see if it makes a great amount of difference today, I didn't get a chance to test ride last night.

I think the only problem I see with those U manometers is that there's a possibility to suck stuff into the engine. I wanted something stupid proof :D

The gauges work great, the liquid dampens the pulses, basically what you see in the picture is the typical variation (one gauge is at one extreme, the other gauge is at the other). My sync was off since I hadn't tightened the lock nut (my way of forcing me to sync them sooner rather than later), so using the gauges to adjust, the idle jumped up and got smoother. I also forgot to mention, I swapped the gauges at the end to make sure the result didn't change and it did not at all.

Also, the service manual calls for 200-240 mmHg, you can see the gauges read just about 200 (=20cm Hg), which seems about right for this engine with 35,000 km on it.
 

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If ur motor is closely set proper.. the manometer just helps "dial it in better"...
yes, you can do damage to an engine by sucking in fluids into the cylinders.. there are ways to prevent it from happening with this design.. YouTube can be a good reference..
 

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Great to see home built tools. The two bottle method is safe, the liquid can't get sucked in unless the bottles falls but you can always use motor oil instead of water.
 
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