Carb sync new-bie question
 

Why does this CBR600 open the first two carbs before the second two? I had assumed that a correctly sync'd carb setup would open all four carbs at the same time, but I can see the first two open before the second two when I 'bleep' the throttle. Looking at the throttle setup, it is pretty obvious why as there is a very obvious cam setting that causes this behavior. You can clearly see space between the throttle cam connected to the first two carbs and the second two. Is this intentional or did someone mess with this bike and screw this up?
https://cimg7.ibsrv.net/gimg/cbrforu...d341e8ed5a.jpg

Someone before you made a misstep.
All 4 carbs should react as 1.

Looking at that picture, there should be a spring in between those two plates, where that gap is.

Ok. And that spring would then engage the second two carbs with a little flexibility. So that probably makes sense why this bike struggles until you really open it up.

Correct. And it is impossible to sync the carbs without the spring.

So this looks better I would think. Found a spring that works in my miscellaneous parts bin from past tear-downs. Really appreciate your help this would have difficult to figure out without your insight and expertise.
https://cimg4.ibsrv.net/gimg/cbrforu...2e37bd793e.jpg

You are very welcome. Glad to help.

That is a good sign that the sync is way out. Were the carbs out? Can you do a bench sync to get them closer?

I bet it's real jumpy around town and surging.

Those springs get left out when inexperienced people rebuild their carbs. Have seen it before and very hard to diagnose without experience. Good job Hamlin!

You should be able to sync your carbs now...but I’ll bet it’s already quite a bit better with the spring in there.

Thanks Dennisgb.

It is important to note the same setup should be between carbs 1&2 as well as 3&4.

If the PO left out the one in your picture there's a fair chance they omitted those also.

Thanks everyone. Yes, the bike sounds completely different. The flutter I was sensing is now gone when just revving it up from idle and it is obvious to me now that it was not running on all four cylinders (now that I can hear the difference). When it stops raining I will go test it and see how it feels pulling up hills; where I was getting a ton of flutter and serious lack of power. I have also noticed that the bike now idles at low RPM where it would die before at idle speeds below 1200 (and yes, I know know 1200 is the spec idle speed, but a well tuned engine will not die below the ideal idle speed). The carb linkage between 1 and 2 carbs and 3 and 4 carbs are in tact. The spark plug wire on cylinder 2 was also intermittently reading OPEN due to rusty resister and spring internal in the boot. So it might have been on ONE cylinder at times :(

Will something like this work for carb sync after I do a bench sync? https://www.ebay.com/itm/Fuel-Vacuum...5.c10#viTabs_0

or this one on amazon, looks pretty much the same.

My current symptom after fixing the missing spring is some sporadic 'pings' as well as a occasional exhaust backfire. So this leads me to be believe I have a cylinder getting too little gas and a cylinder getting too much gas. No issues with bike staying running (idling) or needing the choke (in fact it needs to have the choke disengaged quickly or it will run way too quick). Also note that I turned the mixture screws to 2 1/4 and then backed them all out 1/2 turn. They were at 3 turns in before I replaced the jets and cleaned the float, except one that was a little more than 3 1/4 (second cylinder from left).

The only thing is the tubing looks a little short. Could be the picture though.
My set has tubing around 3ft long. I wouldn't want anything shorter.

Ok thanks. I was more worried about the ports as I could probably always get some longer tubing. Thanks again for your advice.

tubing is 750mm; so just under 2.5 feet.

The #1 cylinder is the only one that requires you to screw in an adapter. The other three have nipples unto which you simply slide the tubes.

The length should be fine.

I completed the bench sync, re-installed the carbs and have the sync tool plugged into the four ports on the bike. I did find there are four screws you have to remove and install the four screw in adapters; which is what is written in the manual. The vacuum needles bounce like crazy at idle so it very difficult to tell their exact position; although they appear to bounce close to the same point. Would love to hear from someone with experience with carb sync as to the best way to get this as close as possible. FYI: the bike still seems to stumble quite a bit and flutter when revving up.

Is there a knurled knob on each of the gauges?
If so just barely crack them open. That will fix your bouncing needles.

Yes there is.

There is a fine line between the knob being too closed and too open. But it's not hard to get the hang of it.

Sure. I am just concerned that the imbalance I see is because of the knob position. I will use one gauge on different cylinders to make sure I am not messing it up as a checkpoint. As you said, I am sure I will get the hang of it.

Yea, you will see that they will drop in and settle down easily.

On my gauges, I can unscrew the gauge face cover and tweak the needle position so they are all statically the same. Not sure if you're concerned about that or not.

A couple things other than sync adjustment that can cause things to be wonky. 1. If you have a vacuum leak somewhere it will throw you off. 2. If your valves are out of spec nothing else you do will compensate for that.

I actually calibrated the gauges using a common vacuum source. They are very close. I figured a vacuum leak would make the bike happier with the choke on which is not the case. In general it seems to be putting gas into the pipes as evident by the backfiring it does. I am still not convinced the ignition system is 100%; but since I can't buy replacement parts for it; not really sure how to proceed on that front. The valve adjustment is a good idea. Would you expect to hear the bike fluttering with an occasional backfire based on valves needing to be shimmed? The compression numbers are good, by the way. I would think valve issues would not allow the cylinder to build full compression. All cylinders test at 150+. One was bit high hear 170. You can hear the flutter in his video:

If your compression test is good, then then valves are likely ok. A vacuum leak can cause erratic idle as well as backfiring. The isolator boots are very common sources of leaks. One way to test them is while the bike is running spray some sort of flammable around them. If your idle increases, the boots are leaking. Some people use WD-40 or the like. I prefer to use a bottle of LP or map gas (like you use for soldering copper pipes). It works pretty much the same and doesn't cause a mess.

Thanks. The mounting boots are in the mail; from China. I had this on my list of things to just replace and purchased a set since they are actually available :)

I have decided to go further with the overhaul of the existing carbs as well as ordering a second set of used carbs from a running '89 so I should be able to get enough parts out of 8 carbs to make 4. I have completely disassembled everything, soaking main components in carb cleaner bath etc. Haven't decided to use the new jets from the rebuild kit or original jets (since I feel like the bike has gotten worse). But the question is, do folks disassembly the throttle plate from the carb body and are there seals to change in there? I saw a video on an older Honda where the repair guy explained that the throttle shafts had felt seals that would result in vacuum leaks and were often not worth repairing. So do I have seals in the throttle shaft that can result in vacuum leaks that I should worry about? And is there anything I can do about it? I see no reference in the manual carb tear down manual on removing the throttle plates and shafts. Thanks.

There aren't any seals in the plates that am aware of on these carbs.

I don't remove the plates. Rather I simply open them and insert a small dowel rod so the cleaner and get to everything. The deposits usually wipe away easily afterwards.

If your original jets can be cleaned properly and are not stripped or broken in any way they are usually fine to use. I refuse them any time I can. The trick is they have to be really clean.

Thanks. I have cleaned the original jets but then had a rebuild kit that included them; so I used the new ones. No numbers on the main jet in the kit so not sure if that size is now different; but that clearly has nothing to do with my inconsistent idle and acceleration issues.

The number is usually stamped on the head of the jet. It's super tiny. You may have to get a magnifying glass or use your phones camera and zoom in. Some have it stamped on the head of the jet, some on the side.
I've not seen one without the size on it, but there's always a first.

original jets main=112 pilot=35
replacement jets main=105 pilot=35

Perhaps the bike was changed to a 112 and 105 is stock; not sure.

Do you have a shop manual? In the front somewhere it should tell you what the stock ones should be.

Yes. Stock is 105.

Another question. What is the best way to check float bowl level? They give a procedure in the manual with some special service tool that I obviously don't own.

It's not too big a deal normally. You can use basically anything that will easily give you consistent results. In the past I've used a cutout of a barcode. They have tons of little lines that allow you to use as a gauge. Not sure about your model but not every series of CRB's float height is adjustable. They either work or they don't. It's important that the spring in the needle is responsive when depressed.

Here is a decent video on the subject that uses the bar code idea you recommended.

Didn't get the link. Sorry.

I got the carbs completely overhauled and the new isolators installed. Noticed the carbs sit higher and the air intakes now line up; interesting. Bike is better at idle and seem to run a little hotter, which I think is good since I believe it was not burning fuel and pinging before. It surges at idle every 5-6 seconds. Not big deal, just a bit strange. I still hear flutter when I hold the throttle at 3000 RPM or so, but without load. Will take it for a ride tomorrow. I am still thinking there is something not quite right. FYI: I have a second set of used carbs which look really clean. I tried to run them but the fuel rail was leaking fuel, so I have to fix that first. My goal was to compare the two sets of carbs to see if any common problems still exist which point to a non-carb related issue. I will update after the ride, thanks again for all of your insight folks (well mostly Hamlin).