Carb Tuning, Order of Things..

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jryftc

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Working on a CB550 tonight...the bike runs and rides. Carbs just need to be tuned up because I noticed between 4000-5000 RPM there is a popping when accelerating like 1/2 throttle..regardless just wanna get her to 100%.

The third carb is running lean...the cylinder fires but not as well as it should be. Slight putting out the back of her as well, I think that's a sign of that..
I also have a vaccum gauge, which I just got got, so I wanted to use that to double check the synchronization of everything.

I guess my question is, is there an order in which I should do this? I just planned on adjusting the float height on 3, then doing the syncing and hopefully that resolving the problem. Carbs are clean, other 3 don't really need attention as far as I know. But I guess before I pulled the carbs I was curious if I could just sync them first to see if that fixed it and save the hassle of pulling them. Unsure how much of an effect the one lean running carb would have on a correct sync. If anyone has an idea let me know. Thanks.
 
Syncing them first won't hurt and it might tell you something.

It could also be the mixture screw on #3 is wrong. What do the plugs look like?
 
Okay thanks. When you sync them, you can kind of like ignore what the diagnosis on the gauge says right? Just go for equal pressure? Unsure of condition of plugs off the top of my head..I guess it could be the air screw on 3 would that affect it that much though?
 
Hard to know "how much" until you see the plugs. A fresh set of plugs will help alot if the old ones are grubby. You'll get a better reading off them.
 
Plug set is fairly fresh. Just changed them while troubleshooting a bad coil but I will get back to you when I get a chance to look later. Thanks for the advice man.
 
Nothing to do with jetting I don't think at least...bike is 100% original and always has been so that should't have to be replaced I don't think and are in good shape. I double checked the floats for stock height (12.5mm) today and the air screw for stock (1.5 turns out) today. Put the carbs back on the bike and compared them to one of the ones of the cylinders that runs a little bit better by seeing where the one that runs well lets / shuts gas off in, adjusted the one poor running carb to to that spec. Stopped popping noise on third cylinder, but still there a little bit with acceleration, only when I really gun it though. When i ran the carb sync gauge 3 had lower pressure, but I'm going to have to get into it another day. Ran out of daylight.
 
I forget which one of y'all was looking at condition of spark plug, but this is it on one of the cylinders running well. This is on cylinder 4. 1, 2, and 4, all appear to be running well and in sync. 3 is just off. See attached pic for plug. I guess it's a little black...
 

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Also is this screw with hex nut lock the one you would use to adjust the pressure if you were doing carb synchronization? I had to take the top off the carb to get to it, unsure and don't really wanna touch it until I'm certain. Watched a synching video for a 77 cb550 four k and the screws were on the outside of the carb. They weren't there on my bike (Mine's a 78 cb550 four k)
 

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yes that is how BUT first
do a compression test on all cylinders
get 2-3 new sets of plugs
get new spark plug caps ,then start over, unless something got bent or badly worn on one carb(highly unlikely)the carb synch will not be very far out at all in the slide lift situation.. and it will not effect anything but idle smoothness .. so you need to get those other things i outlined above coverd first
 
I'll grab a new set of plugs. However, I don't need boots, just replaced them. The timing, points, all that stuff, was just done and double checked by a professional mechanic. Between his experience and mine we think the popping issue with acceleration is strictly dealing with carburetion. He was saying replace intake boots on the carbs to the engine and to the air box? What's your two cents on that? I think they're in pretty good shape, and can try and get some pics. How would I go about doing a compression test? The synching in general isn't that far of either, just a little bit on 3 and its something I'd wanna go though.
 
do a compression test the standard way
warmed up engine
pull all spark plugs
keep kill switch off
keep gas valve turned off
test each cylinder by cranking with elec starter.WHILE HOLDING THROTTLE GRIP WIDE OPEN untill gauge stops rising it shouldn't take more that 4-5 revolutions of the crankshaft as long as you have a battery and starter in good shape
write down the specs you observe
the low reading on the vaccum gauge is likely a poor conditition cylinder(not a mis synched carb) and you MUST know for sure before you go further

you can test for air leeks at the carb to engine joints by carefully spritzing a shot of ether starting fluid right at the boot whilst running/idling... if leeking it should change idle speed
unless the boots to the airbox are not keeping dirt out as they should there is no reason to get new ones
 
I'll get into that. Could I do the test just by unplugging all the cylinders but one and using the vacuums gage hooked up where it was when i synched it? Plugs need to be out or just boots?
 
no you are stuck until you do a proper compression test as i outlined ,you can get a good gauge for less than 50$ or some auto stores even loan them
 
Fingers crossed the compression is good. I'll get my hands on a gauge and get back to everyone hopefully by the end of the weekend. Standby. Thanks for the help.
 
http://www.autozone.com/test-scan-and-specialty-tools/compression-tester/actron-compression-tester/87580_0_0/

This would work okay? 18mm threads I'm guessing is what I need. Just making sure I don't need anything else especially for the 2-3 holes they're deep in there
 
okay so sorry for the delay. waited to get my hands on a good compression gauge. the cylinders read 120 PSI across the board. I just did coils and timing, so I'm assuming its not electrical or any of that crap. I'm going to go ahead and say carburetors. I was riding this weekend, and she was doing like 70-75 with a bit of popping every now and again, then things got worse. So i'm thinking about a full scale carburetor rebuild. So with that I have a few questions...

1. Should I jet if my bike is completely stock? I plan on getting a stock rebuild kit but I wasn't sure if with wear and tear of the bike bigger jets may be necessary.
2. Does anyone know if there is a stock needle height and how to adjust the needles on a 78 cb550. My plan is just to return the carbs to stock, not sure what the previous owner did.
3. what speed do you set the idle to while doing carb synchronization
4. rubber boots going to the air box. If they're a little cracked, how badly would that affect performance?

I'll be on top of this post, and making moves within a week. ordering kits now, so any advice is appreciated so I can get this fucker back on the road ASAP. Thanks for the help as usual, cheers.
 
Ordered kits...I guess the 550 air box adaptors (boots from carb to air box) are hard to come by...anyone have a source if theyre necessary to replace?
 
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