synchi)ng carbs

I realize this is a GZ forum and that bike has only one cylinder, but since there has been some discussion of other bikes lately, including v twins, I thought I'd throw this out there to you experienced riders.

On other forums I've seen directions on how to make a simple carb synching tool (a manometer?). Supposedly an easy tool to make and an easy process to do. Has anyone out there actually synched carbs before and does it help the bike run smoother, especially the v twins?

Thanks,

Keith

[Easy Rider]

Originally Posted by kmkindred

does it help the bike run smoother, especially the v twins?

Only if it was running rough to start with. :biggrin:

It is a mechanical linkage you are adjusting. Over a short time period, there is little reason for it to get out of adjustment. If the bike is only a couple of years old and the carbs haven't been "tinkered with", then you should suspect other things first......like gunk in the carbs that a good cleaner will take care of......or the valves out of adjustment. I think you will find that there isn't a recommended interval for checking the carb sync.....for good reason; it seldom is a problem in and of itself.

Some guys just like to tinker and make things and spend more time and money than it would cost to have someone else do it. I think carb sync falls in that category. The test and adjustment is really simple and quick.....if you have the right tool. I suspect that a shop won't charge much to do it (half hour labor ??).

Why do you ask ??

Originally Posted by Easy Rider

Why do you ask ??

I recently upgraded to a V Star 650 Custom and it vibrates more than the GZ (the mirror shakes pretty good at idle, though not at speed, but I can feel the "bar buzz" for sure at higher speeds). I've read/heard that v twins are known for vibration, but I'm not sure if what I'm experiencing is normal or not. As I said before, on a Yamaha forum I now "visit" some guys have said a carb sync might help the problem.

I only felt numbness/tingling from this after one ride of 40 minutes or so (have been on several rides of this duration or longer), so it's not really bothering me to the point of discomfort, but enough to notice it. I, too, was a little skeptical of the carb sync fix, but I'm not exactly mechanically inclined generally, even less so with motorcycles, specifically. Hence, I thought I'd throw it out to the sages on this forum (in all seriousness, I respect - and appreciate - the knowledge and experience shared here).

In any event, I put some Berryman's in the tank and we'll see it that makes a difference. I've investigated bar end weights, foam and such in the handlebars (like the motocross guys do), and so forth, but I think I probably just need to accept that v twins vibrate more than I anticipated.

Thanks again,

Keith

[Water Warrior 2]

The 650 Star was designed to go the speed limit with comfort. If you want to run higher speeds it will probably pass it's sweet spot and vibrate some. Some V-twins have counter balancers or heavier flywheels to soften the vibes. By all means get bar end weights it the bike doesn't have any. A set of grip puppies over the grips will absorb a bit of the vibes also. Depending on the degree of the V design some engines will be rougher than others. My Vstrom is a 90 degree V-twin and is nearly as smooth as glass. Also the power pulses of a V-twin can be tough to live with or just right for you. Do some exploring on the net and lurk on 65o sites to gather info.

[Easy Rider]

Originally Posted by Water Warrior

By all means get bar end weights it the bike doesn't have any. A set of grip puppies over the grips will absorb a bit of the vibes also.

:plus1:
Exactly what I was going to say!

In addition, many Vtwin riders....and even some shops...... tend to set the idle speed too low. A little tweek there might help it idle more smoothly.

If the shop talked you out of doing the valve check at 600-1000 miles, I would advise having it done now. It make a BIG difference in the vibration on mine......and with only one carb, a synch wasn't an option !!

Have you considered a throttle lock? Mine cost me 75 cents.

Got kind of off the subject there for a minute; with a bike only a year old, I wouldn't normally think the carbs would be out of sync but anything is possible. Might want to keep that as a last resort. Might also want to look around for an independent bike shop with someone in the back who is older than 25. Experience is, after all, the best teacher !!

[dhgeyer]

Funny you should ask about the carb sync, and the homemade tool. I just got back from test riding my BMW R850R after doing just that. In the case of the Beemer it's a throttle body sync, not a carb sync, since it's fuel injected, but the procedure is exactly the same.

Point 1: Carbs don't get out of sync due to slippage of a mechanical linkage. What you are synchronizing (equalizing would be a better word) is the vacuum in the carb bodies. This makes sure that the cylinders are pulling in the same amount of fuel/air mixture. This draw can get out of sync if there is unequal compression, the valves aren't quite equal, or if something in a carb has changed. A good carb sync will make a bike run smoother. Or, to put it more strongly, if they are not synced, it will make for increased vibration, and if it's bad enough, it can make the bike run badly. Some bikes are more sensitive to this than others. The Beemer is super sensitive to it, and runs like shit if the throttle bodies get out of sync.

Point 2: Make sure your bike even has two carbs. Not all V-twins do. If there's only one carb feeding both cylinders, there's nothing to sync.

The homemade tool: About 18 feet or a bit less of clear, flexible plastic tubing, 1/8" inside diameter usually. Whatever fits the vacuum fittings on your carbs. You may need a service manual to find the vacuum fittings on the carbs. They're generally in the form of small brass tube like things sticking out of the carbs somewhere, plugged either by covers that slip on, or by a rubber tube that connects the two together. Or, if you have a vacuum operated fuel valve, one fitting might be plugged and the other connected to the fuel valve. Anyway, about 18 feet of clear plastic tubing that slips firmly onto the vacuum fittings. Find the middle. Bend the middle over some kind of stick or board or something, but don't let it kink. I nailed about half an inch of the end of an old frozen orange juice tube with the metal end still on, near the end of a board and bent the tubing around that, and then ran each side up to the other end of the board and attached them. So you have a U shaped length of tubing, each side about three feet long, running the length of a 3 foot board. Some people actually use a yardstick. So now you've used 6 feet of the tubing, with equal 6 foot ends coming from the top of the board. Find someplace where you can hang this whole thing by the free ends of the tubing. Pour a small amount of 2 cycle oil into one end. Enough so that, when it all runs down into the U shaped end you have 6 inches or so coming up either side of the tubing. Pour little bits in at a time, as it takes quite a while to run down into the end. Wait till the inside of the tubing is clear each time you add some before adding any more. Go slow and take your time with this. It's a lot easier to add more than to run it out one end if you get too much in. That's it. You're done.

On most bikes, you need to remove the tank to get at the carbs, the vacuum fittings, the adjusting screw, etc. Once you've removed the tank, you'll need a long piece of tubing to use as fuel line to connect the tank to the carb. And, of course, the tank will have to be on something higher than the bike. If the fuel valve is vacuum operated, you will need to turn the fuel valve to "PRIME". If there is a "PRIME" position on the fuel valve, it is vacuum operated, so turn it to "PRIME".

To use your tool, hang it above the bike somehow with the U shaped end with the oil in it at the bottom. Keep the plastic tubing away from the hot pipes. Don't ask me how I know this. Attach each free end of the tubing to one of the vacuum fittings. There's one on each of the carbs. Do this with the bike off. Start the bike, but be ready to turn it off very quickly. If the carbs are really badly out of sync, one will suck the oil right into the carb. That's why you use two cycle oil - it's not the end of the world if that happens. If you're quick on the kill switch you'll catch it before that happens. Usually carbs are not that far out of whack, and all you'll see is the oil being pulled up one side of the tubing and, thus, down the other side. Just like if you sucked on one end yourself. Then you find the screw that adjusts the carb synchronization, and turn it one way or the other till the oil in each side of the tubing is about the same height. If possible, and it isn't always possible, you want the carbs balanced at idle, and at an engine speed that is in the useful power band somewhere. Not rocket science, but if you can get it balanced at a couple of points, that's better than just at idle. If the bike is air cooled, don't take all day doing this, as it will overheat just sitting still running. If it's liquid cooled that's not a problem.

Don't forget to cover the vacuum fittings back to whatever configuration everything was in.

This whole procedure is best done after a valve clearance check/adjustment. If the valves are way off, that could be the problem, and syncing the carbs to match would just be putting a Bandaid on it. Conversely, you should always do a carb sync after a valve clearance adjustment, since changing the valves will likely throw the carbs out of sync. They are both usually considered part of a routine tune-up.

I had already put the grip puppies on and adjusted the idle on my own, so I guess I feel pretty good that I was thinking some of the same things you more experienced riders were (the idle adjustment, in particular, seemed to make a noticeable difference). I just put some Berryman's in, so we'll see if that makes a difference, too.

I made the tool, too, DH, but I made the mistake of sucking in regular motor oil (one of the sites I saw on how to make the tool said this was the way to do it). Way too many air pockets and I think a thinner liquid is called for, so I'll have to rectify that. My bike does indeed have two carbs and the nipples aren't too hard to get at, even without taking off the tank. Bought my bike less than two months ago with 4100 miles on it (2008), so it's not time for a valve adjustment, unless I'm way off base on that. The carb sync process looks pretty simple for my bike, but it sounds like several of you guys also think bar end weights are worth the investment.

BTW, in my research on the web I came across a synthetic gel you squirt in the handlebars that solidifies and is supposed to dampen vibration called "Barbuzz Kill" (it's targeted at motocross guys, who I guess run into this all the time). Long story short, the distributor is going to send me a tube to try for free (only works with hollow bars at the moment, but they're coming out with a product that will not harm wires for folks in that situation). He said you can do 3 or 4 bikes with one tube, so if I try it and it helps, I'd be happy to send the tube along to someone else to use after me.

I may be giving some the impression that the vibration is awful and it's not. But I'm too inexperienced to know if this is normal and the guys I know personally who may know something about this have been all over the place in terms of their opinions/advice, so again, thanks for the input.

Keith

[Easy Rider]

Originally Posted by kmkindred

Bought my bike less than two months ago with 4100 miles on it (2008), so it's not time for a valve adjustment, unless I'm way off base on that.

I may be giving some the impression that the vibration is awful and it's not.

Not officially "due" for a valve check but.....do you know for SURE that the PO had it done initially at 600-1000 miles like he was supposed to do?? If not, you should consider doing it.
AND
You should heed the very good advice in the previous post, in that if you get your "tool" working properly and it appears that the flow is out of "sync", you should check the valves BEFORE you go changing the carb flow. I didn't read his whole post in detail but you should also inspect the rubber boots to be sure they are snug and not leaking too.

Sometimes I wish the people you "meet" here lived closer together so we could trade test rides for stuff like this. Wanna meet in Northern Indiana some time ?? :shocked: :crackup