CB550 Help

mothgils

mothgils

Coast to Coast
Having some idling issues with my 74 CB550. It has a 4-1 Kerker with no baffles and individual Uni foam pod filters. I upgraded the main jets from 100-110 and left the others normal. I believe the clip is on the second setting up from the the bottom on the needle jet ( haven't looked in there in a while).


It doesn't want to hold an idle at 1k very well. Especially if I get the choke to fully open. Are adjustments on the air/idle mixture screw going to do anything to help this?


Also, in between carbs 2-3 are 2 brass fittings that look like vacuum lines. should they be connected to anything?




Please help if you can. I am really trying to get this thing dialed in before next weekend. Thanks!!
 
Mthgils,


Your problem, or at least most of it, is the pods. It really doesn't matter who's pods you are using either, they are all the same in one critical aspect. Pods do not have anything even remotely resembling a velocity stack prior to the carburetor throat. This has all sorts of ramifications but worst of them is that it makes it impossible to ever tune the carbs properly, or even so that they will work reasonably well - it simply can not be done. Pods look good to some folks, but they degrade performance in every case.


As for those idle screws, in the early 500s and 550s (everything before 1977) the screws are adjusted to effect fuel flow. The effects they have disappear into the clutter at about 1500~2000 RPM, where other carburetor circuits take over as being primarily responsible for performance. On the later model carbs (PD-46, either A or C models depending on the year of manufacture) that same screw has a different function. In the later model carbs the screw effects air flow at low RPM and because of the design of the screw's tip its actually not adjustable, its just an On/Off valve, either open or closes, with nearly no adjustable range in between.


So, if you want to improve your performance the first thing you have to do is get rid of those Pods. Almost any system that uses some sort of air box will work but keep in mind its essential that there be something that acts as a velocity stack in the system. The air entering those carbs must be straightened out and the flow coming in smoothed out; carburetors can not be tuned if their intake airflow is chaotic.


As for your jet choice and needle position, they sound about right. Maybe a little rich on that main jet, maybe not.


On Edit: I forgot something; you aren't doing yourself any favors having that baffle out of the exhaust system either. Put it back in and deal deal with one tuning step at a time and you will be a lot better off than making a bunch of modifications and then trying to sort out the whole package at once.
 
Kong,


Thank you very much for your informative response! Would switching to individual velocity stacks be a better idea than the pods?


Also, I don't have a pic of the baffle but it is a bolt in piece that mates to the Kerker. When I got the system from the PO, the insulation around the baffle was just taped. Should I refit it with new baffling material? I will try and post a pic later on today.


Any ideas on what would cause cylinder 4 to be about 50-60 degrees less than cylinders 1-3?


In regards to the Air/Idle screw, I read (obviously may not be true) that if the screw was situated on the backside of the carbs (closer to intake point), that when you screw it in it enriches the mixture and leans it when backed out. Is this the case with the 022A carbs on my bike?
 
As a rule, if the screw is on the filter side of the body it meters AIR and out = lean. On the motor side it's always the mixture, so out=rich. You can check on your crabs to see where that screw taps in.

Fuel comes in through the pilot jet, so if the screw is on the intake (open air) side of that jet position, it must be air that it meters. If teh screw is after that jet it meter mixed air and fuel. It's simple.
 
Well, just plain velocity stacks would certainly work well, they always have on any Honda 4 I've put them on, and you've got it jetted about right for a set. The problem with bare stacks is that they don't protect your engine from ingesting stuff - bugs, rocks, dust, small children.
 
Any ideas on where to find the "socks" that go over the ends of velocity stacks? That would prevent it from taking in anything but air.
 
The people who make the stacks may make some sort of filter cover for them. You also see a lot of them with screens over the end. Screens will keep your keys and small change from falling in the carbs but they don't do much for dust.


Here's the problem. I know this sounds nerdish, but its just one of them good old facts of life. The most common substance on earth is silica. Most of its in rocks but rocks break down into stones and stones break down into sand and sand eventually becomes dust. Lots (though certainly not all) dust is at least in part silica. Silica is remarkably hard. In fact its almost harder than anything. Its way harder than pistons or cylinder walls. That's why virtually all engines have air filters, its not the bugs and small birds they are trying to keep out, its the dust.


That's why the factory went with a big airbox, it allowed them to use a large filter. Then inside of the airbox you'll notice that the factory used rubber stacks to straighten out the air flow. That's why so many guys swear that the stock airbox/filter system is the best. It really does work well, but any combination of stacks and a box to contain filtered air will work well too.


Now if you're planning on keeping the bike for years and put lots of miles on it you'd want to filter the bejesus out of the air. However if you're building a zoomy zoomy bike just for fun (I've got 5 bikes, so the Cafe version Honda is just for fun riding) then you might just as well get yourself a (good looking) set of screened stacks. You'll find your tuning problems go away and the bike will become pretty straight forward to get running real well. Do that and knock one tooth off the front sprocket and that 550 will scream.
 
PS: I nearly forgot the most important part. You really have to concentrate on getting the ignition right on that bike before you venture into carb land. The Honda 4's can be a bit of a pain in the butt with their dual points and worn our coils. The wires go bad too of course (as do the resistor caps) and they are not easily replaceable. My own recommendation is that you just pick up a Dyna S magnetic pickup and a set of their coils (5 Ohm, not 3 Ohm) and stick them in. Get the Dyna right one time and you've done with it. The charging system of a 550 can handle 5 Ohm coils with ease too.
 
The main problem with fitting mesh screen is the restriction it gives.
The finer the screen the more restriction.
check out link (McMaster Carr)
It's for plastic mesh but principle is exactly the same.
you may fit a bellmouth 2"~3" at entry diameter but, fit mesh and area can get reduced by 76% with finest mesh
scroll down to bottom of page
http://www.mcmaster.com/#mesh/=dpi0mp

Went back and looked for stainless steel mesh, the finest has 36% 'open' area as the wire is only eight tenthousandths of an inch diameter
http://www.mcmaster.com/#wire-mesh/=dpi4wa
 
Kong said:
PS: I nearly forgot the most important part. You really have to concentrate on getting the ignition right on that bike before you venture into carb land. The Honda 4's can be a bit of a pain in the butt with their dual points and worn our coils. The wires go bad too of course (as do the resistor caps) and they are not easily replaceable. My own recommendation is that you just pick up a Dyna S magnetic pickup and a set of their coils (5 Ohm, not 3 Ohm) and stick them in. Get the Dyna right one time and you've done with it. The charging system of a 550 can handle 5 Ohm coils with ease too.
Click to expand...


I went through the 3k mile checklist and did the valves, cam tension, and ignition/timing. I actually replaced the points plate with a new.


I guess I could take a look at the coils as well to see if they worn or not. As much as I would like, I can't afford to get a Dyna S and new coils. What's the easiest way to test the coils?


I know that pod filters aren't the greatest but I know of people who have them and have got their bikes tuned with them. I just don't want to spend $75 plus covers for pods if that isn't exactly what is wrong.


I am just trying to get this thing semi-roadworthy for MotoGP next weekend and then can rip into it deeper before Barber in October.
 
Call me crazy, call me impulsive or obsessive but I purchase these this morning from DCC and am praying/hoping/crossing my fingers, that they get here within the next few days.


http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetor-parts-polished-aluminum-honda-cb500-cb550-velocity-stacks-bell-sd-cb500550-pos.html


I hope this will help my issues. They come with screens too.


Still looking for any ideas on the cause of cylinders 1-3 running hot and 4 not as hot. Compression of 1 & 4 are withing 10% of each other.
 
mothgils said:
Call me crazy, call me impulsive or obsessive but I purchase these this morning from DCC and am praying/hoping/crossing my fingers, that they get here within the next few days.


http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetor-parts-polished-aluminum-honda-cb500-cb550-velocity-stacks-bell-sd-cb500550-pos.html


I hope this will help my issues. They come with screens too.


Still looking for any ideas on the cause of cylinders 1-3 running hot and 4 not as hot. Compression of 1 & 4 are withing 10% of each other.
Click to expand...

OK, your crazy. ;D
Praying isn't going to help.
You have checked valve adjustment and carb sync?
Did you even read my post about mesh screens?
It's going to look cool, restriction may help with lean mixture by restricting airflow as rpm goes up but it's still going to be worse than stock
 
PJ - I did read your post. I will run them and see what happens. I know its not going to be optimal but hope it will be better than the pods. I can build a better system over the winter. Just looking for something to get me by until then.

I appreciate your input. Would the screens cause it to run rich from the restriction?
 
well I set the idle/mixture screws to about 1/8 turn out and it improved it but still seamed lean.




I took the carbs off to look at the needle jet and realized I put them all at the second notch down from the top. I am moving them all down to the center notch on each needle and going to tr that first.
 
I forgot to snap a side shot last night but they are the 022A Carbs with the Idle Mixture screw located on the intake side of the carbs.


I moved the clip down to the middle position on the carbs and went to bench sync them but the slide on #1 is open a lot more than 2-4. When I adjust it, it's adjuster holder is not level with #2. See the pics:


Before adjusting the 2 adjuster holders are approx. the same height.
6075739805_f9b0402b41_z.jpg



Slide opening gap before adjustment:


6075739805_f9b0402b41_z.jpg



After adjusting the slides to an even height using a .040 drill bit, the adjustment holder arms are not level. If I replace the dust cover, it won't be level. Is this an issue?


6076275634_d1b7922bd4_z.jpg



Could the arm coming off of the rail be bent on the left side on the ball mount to the adjuster arm? Or something be bent inside the carb? I opened those 2 carbs and things did not appear to be bent.
 
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