Help with carb sync

[glstine]

I have a post on here about problems I was having with my bike dying at idle. Since then I have dipped my carbs, installed new o-rings from cycleorings (boots and boot orings are only about 1 yr old), adjusted valves, checked compression (135,135,130,140 after valves adjusted). I also put in new NGK spark plugs. Spark is good and I did the coil relay mod last year and have only a 0.1V loss at the coils.

The bike will start up pretty easy and idle, but sputters badly over 2.5-3k rpms, particularly under load. Also the #2 and #4 spark plugs show running rich and the #1 and #3 plugs appear to be lean. So I think I must have some carb sync/fuel delivery issue.

I built a gauge to check the fuel level in the float bowls using a 3/16" barb that I threaded and some clear tubing.


I set up on a work bench using clear tubing for the fuel line so I could see the fuel and checked the level of the gas in the float bowls.



I found the #1 carb fuel level was low so I adjusted the float and all 4 carbs were within the 4.5 to 5.5 mm limit in the service manual.

I installed the carbs and tried to set the idle mixture screws for max rpms. Not really being able to tell a difference I reset them all and decided to go ahead and try to sync the carbs with the gauge I built. I did some research and found a few threads on forums where people had reported good results using a gauge like this:


The gauge is made of 2'-3" long pieces of 5/8" ID tubing filled partially with Marvel Mystery Oil (was going to use ATF, but had the MMO and it appears to have about the same specific gravity and I figured it was safe if it got sucked into the engine). 3/16" tubing connects these tubes to the intake boots and I used pilot jets as flow restrictors.

On starting #4 immediately started sucking all the fluid up, so I shut it down. I decided to omit #4 for the time being and plugged it off. Started the bike and then #2 started doing the same thing. Since they are sucking in the fluid so fast I can't get a chance to attempt any adjusting. These are also the two cylinders that show running rich, I'm assuming that has to do with them having significantly more vacuum than the other two cylinders.

Any advice on how to proceed from here?

[doctorgonzo]

Have you tried to "bench sync" them first?

[Nessism]

I don't think that sync gauge will work since there is no reservoir. I've seen gauges where there is a U section for checking balance between two cylinders, and in that case you don't need a reservoir, but the way your gauge is plumbed there is not enough fluid. Also if you build a reservoir you will need much longer tubes since the specific gravity of the oil is much lower than mercury, or even water for that matter, so you need long tubes to allow the fluid to go up.

Edit: found this photo showing a similar sync gauge. Note that there is a fifth tube full of fluid which will act as a reservoir.

[glstine]

I did bench sync the carbs. The layout of the gauge is similar to another one I found on line that didn't have the side reservoir and actually had shorter tube that reportedly worked fine, I may try to re-work it with longer tubes and a side reservoir though just try to get something that works. I need to get this figured out, we are starting to get nice weather again. It's getting frustrating, the bike was running fine for 3000 miles prior to this.

[almarconi]

Since you have come this far, why not just bite the bullet and purchase a carb synchronizer. Perhaps there is a member near you that will let you borrow one. The reason your tool is sucking the fluid up is because the tube are way too short. You would probably need tubes that are 8 feet high or higher with that setup. Most of the mercury setup have a reservoir in the bottom and small restricters installed in the tubes leading to the engine.

Here is a link to one that a guy built for a 4cylinder bike

http://forums.sohc4.net/index.php?topic=58677.0

Note he needed 40 feet of tubing.

[Nessism]

Since you have come this far, why not just bite the bullet and purchase a carb synchronizer. Perhaps there is a member near you that will let you borrow one. The reason your tool is sucking the fluid up is because the tube are way too short. You would probably need tubes that are 8 feet high or higher with that setup. Most of the mercury setup have a reservoir in the bottom and small restricters installed in the tubes leading to the engine.

Here is a link to one that a guy built for a 4cylinder bike

http://forums.sohc4.net/index.php?topic=58677.0

Note he needed 40 feet of tubing.

No way man, glstine has done a great job so far with his gauge he just needs to tweak the design in order to get it to work. Don't give up, figure out what's wrong and go from there.

[almarconi]

You said it yourself Ed, the tubes are too short. I'm not saying he has done a bad job, I provided him a link on how to fix his or construct a new one.

[gearhead13]

I don't think that sync gauge will work since there is no reservoir. I've seen gauges where there is a U section for checking balance between two cylinders, and in that case you don't need a reservoir, but the way your gauge is plumbed there is not enough fluid. Also if you build a reservoir you will need much longer tubes since the specific gravity of the oil is much lower than mercury, or even water for that matter, so you need long tubes to allow the fluid to go up.

Edit: found this photo showing a similar sync gauge. Note that there is a fifth tube full of fluid which will act as a reservoir.

Ummmm, he is saying he built one LIKE the picture, not a pic of what he built. Thats what I got out of it.
After fiddling around and buying the hoses and fittings, you might have been able to buy a proper gauge. With a LOT less frustration

[Nessism]

The Motion Pro sync gauge uses a fluid very similar to antifreeze, which has a higher specific gravity than oil. If the OP can build in a reservior, and extend the tubes that thing should work. Adding some restrictors into the tubes is a good idea too, that way if fluid shoots up and into the engine, only a little bit will get though.

[almarconi]

FYI the spec gravity for the ATF @60 degrees F is 0.89, water is 1.0, ethylene glycol is 1.13 and mercury is 13.57. This should clarify why the tubes need to be so long.

[glstine]

For reference this is the gauge I used as a model. Reportedly successful on an 84 venture. His tubes were 3/4" ID and 19 1/2" long.



I've spent about $25 on building this gauge for the tubing and fittings, so if I can get it to work it is quite a bit cheaper than a morgan gauge. I will extend the tubing with the fluid and see what happens.

[old_chopper]

I haven't put much tought into this yet but I think the diameter of the tubes being larger makes a difference. That should require more vacuum to pull the fluid out of the tube since the volume increased, so did the weight. Is that correct?

[rustybronco]

I haven't put much tought into this yet but I think the diameter of the tubes being larger makes a difference.

The diameter of the tube will make no difference. I lost that argument before.

[Steve]

That is the beauty of using liquid. Although there might be more weight in the larger tube, there is also more surface area for the vacuum to act on, and it balances out. You could actually mix the sizes and use unequal size tubing for each column and it would still read right. The trick with these home-built systems is getting the right length.

One other point to consider for those that are thinking of building their own manometer: do you ever anticipate the need to go mobile? How hard is is going to be to fold up 10 feet of liquid-filled tubing to take it over to a buddy's house to work on his bike?

.

[chef1366]

I'm trying to understand this

Without the reservoir wouldn't the fluid either get sucked right into the engine and after it got warm just flatten the hoses?
I would think you would need some sort of restricted air flow to keep either from happening.
Just asking