Topic: '77 CB550 Over revving (Carb issues)

[ATZ]

Could running lean cause this over revving issue? Based on the research I'v done it seems like an air leak but I just can't seem to find one.

[TwoTired]

Could running lean cause this over revving issue? Based on the research I'v done it seems like an air leak but I just can't seem to find one.

It can contribute, yes.
Are the carbs vacuum sync'd?

[ATZ]

I tried vacuum syncing but I really can't get it to run well enough to validate synching. When I hook up the gauges they all seem to be decently close

[harisuluv]

What did you do to "go through" them?  Also this might be silly but I saw no mention of the idle screw adjustment. That has no effect?

[dave500]

The first issue I noticed is that the #4 cylinder doesn't seem to firing. It's sparking outside the engine regularly

please read my post #6
umm?checked those plug caps yet?everyone seems to want you to chase your tail through the carbs over and again?im surprised this thread has gone this far without another ignition trouble shoot.

[ATZ]

I made sure all the jets passages were clear, I set the float height, sprayed Carb cleaner through each one. If I turn the idle screw in the bike will idle but certainly not around the recommended 1000k It will at about 2000k.

@dave500: I swapped the plug caps and have the same issue. And which one is your #6 post?

I appreciate the input

[KB02]

I have two things for you on this:

#1.) I was working on an old Kawasaki once ('80(ish) KZ550). The only way I could #4 cylinder to run was if the bike was leaned over at a substantial angle. Otherwise the running condition was very similar to what you describe. The problem turned out to be an issue with that carb itself. When building the carb, there were several passages that were drilled into the body at the factory and then were blocked off. One of the blocks had come out causing a HUGE vacuum issue within that carb. Hence - no gas was going into the cylinder unless choke was pulled or bike was tipped over enough to cover that hole. Most motorcycle carbs I have seen are built the same way. Might not be a bad plan to just give it a close once over, right next to another carb, and look for any holes seem out of place.

#2.) This also sounds a lot like the problem I had with my current CB. As TwoTired says, any change in the configuration throws things out of whack - Your exhaust might be part of the issue. With MY CB, I have a VERY altered set up (big bore, ported, exhaust, pod-like filters). For over a year and a half I chased a hanging/racing idle very similar to your issue. What the final answer to the problem was turned out to be the idles jets were too small. Basically, I had everything else turned up so much that the gas for my "Idle" was coming right out of my main jets. Hence when I revved up to the 4-5000 rpm range, it would just stick there. I COULD get it back down to a normal-ish idle, but as soon I opened the throttle the revving came right back.
   Take the specs, set your carbs to stock, and start from there. Like TT ssaid, you may need to open your slow circuit to get more gas from your idle.

[harisuluv]

Oops, wrote something relevant to cb750.

[ATZ]

KBO2, great advice, I'll look into the possible hole, I like the idea of the too small idle jet, I will go through everything again, ignition timing, valve clearance, etc, and then I might try upping the idle jet size. Thanks for the info, its much appreciated

[ATZ]

So I figured some things out today, I learned that the PO had raised all the slide needles to the last notch accept, for the 4th carb which was on the middle notch. I matched them all so the clip was on the second to last notch on all of the needles.
    I then reassembled everything and tried to start the bike. It wouldn't start. I realized this must be because the slow jets aren't giving the engine enough gas, as KB02 had suggested. The bike would start before because the needles were all the way up allowing more gas to be sucked through the main jet. Now that the needles are lowered one notch there isn't a significant amount of gas being drawn through to all the bike to start and idle.
    So if I'm correct the next step is to order slower jets that are a few sizes bigger, correct?
I think I might be finally close to narrowing this thing down, what do you think?

[my78k]

If it doesn't even start I'm guessing (still) that the idle jets are dirty....

But lord knows I have been wrong before....

Dennis

[ATZ]

The idle jets are not dirty

[KC3]

I would highly recommend a thorough carb cleaning. A full cleaning involving either boiling the bodies or a good soak. I have had the similar issues with 550's in the past and after I cleaned them it ran 100 times better.  Have had no problems since. How is your gas tank btw? Rust can definitely cause some weird problems...Also, you might consider keeping the slow jets the way they areand stepping up the main jets a size or two for the exhaust...you shouldn't need bigger slow jets just for your exhaust mod...plus, I don't think those slow jets even come out...correct me if I'm wrong, but I thought everyone drilled them out bigger...?!

[Mighty550]

For what its worth, on my CB550F i was having trouble with cylinder 4 not firing, i cleaned the carbs and fired it up, ran fine, but still no cylinder 4.  I then replaced the points and condensers, and tried to set the timing.  Fired the bike up and it immediately slammed 4k rpms.  Im guessing i did something wrong with the timing.  My points are set correctly.  Still trying to figure it out.

[TwoTired]

For what its worth, on my CB550F i was having trouble with cylinder 4 not firing, i cleaned the carbs and fired it up, ran fine, but still no cylinder 4.  I then replaced the points and condensers, and tried to set the timing.  Fired the bike up and it immediately slammed 4k rpms.  Im guessing i did something wrong with the timing.  My points are set correctly.  Still trying to figure it out.

Probably need to back off the idle adjust knob.  Or, you may have skewed all the individual slide adjusters so the slides can't close far enough to achieve low idle.

[KB02]

So I figured some things out today, I learned that the PO had raised all the slide needles to the last notch accept, for the 4th carb which was on the middle notch. I matched them all so the clip was on the second to last notch on all of the needles.
    I then reassembled everything and tried to start the bike. It wouldn't start. I realized this must be because the slow jets aren't giving the engine enough gas, as KB02 had suggested. The bike would start before because the needles were all the way up allowing more gas to be sucked through the main jet. Now that the needles are lowered one notch there isn't a significant amount of gas being drawn through to all the bike to start and idle.
    So if I'm correct the next step is to order slower jets that are a few sizes bigger, correct?
I think I might be finally close to narrowing this thing down, what do you think?

Sounds to me like you are on the right track (It was running before and now it's not and THIS is the right track??   ). What is the position of the mixture screws on the carbs? And (like TwoTired said) where is your idle adjust screw at?

[Mighty550]

For what its worth, on my CB550F i was having trouble with cylinder 4 not firing, i cleaned the carbs and fired it up, ran fine, but still no cylinder 4.  I then replaced the points and condensers, and tried to set the timing.  Fired the bike up and it immediately slammed 4k rpms.  Im guessing i did something wrong with the timing.  My points are set correctly.  Still trying to figure it out.

Probably need to back off the idle adjust knob.  Or, you may have skewed all the individual slide adjusters so the slides can't close far enough to achieve low idle.

Dont mean to highjack your thread here, but after i cleaned the carbs and put them back on, the bike was idling fine, then i replaced the condensers/points, reset the timing, then when started it spiked high RPM.  Ill check the idle knob, how would i check the slide adjusters?

[TwoTired]

For what its worth, on my CB550F i was having trouble with cylinder 4 not firing, i cleaned the carbs and fired it up, ran fine, but still no cylinder 4.  I then replaced the points and condensers, and tried to set the timing.  Fired the bike up and it immediately slammed 4k rpms.  Im guessing i did something wrong with the timing.  My points are set correctly.  Still trying to figure it out.

Probably need to back off the idle adjust knob.  Or, you may have skewed all the individual slide adjusters so the slides can't close far enough to achieve low idle.

Dont mean to highjack your thread here, but after i cleaned the carbs and put them back on, the bike was idling fine, then i replaced the condensers/points, reset the timing, then when started it spiked high RPM.  Ill check the idle knob, how would i check the slide adjusters?

The slide adjusters position the slides in the the carb bore.  Therefore, they can be positioned such that they are unable to seat and fully close off the air inlet, thus defeating the big idle adjust knob domination of this function.  This is normally checked when the carbs are off the bike during the cleaning process.  But, if you are able to look into the carb throats while installed, can be checked on bike as well.
I mention this because you say you had the carbs apart, and don't know your familiarity with how the carbs work.
A dead cylinder via ignition issues would make the engine idle low (requiring more open slides), and when restored to operation, would instantly increase the idle dramatically.  If the idle knob can't dominate idle speed, then the slide adjusters are likely skewed from the prior cleaning process.  (You never said what was involved in the your specific cleaning process, and that varies widely from one person 's prowess to to another.)

Another possibility is that your mechanical ignition advance is stuck.

Cheers,

[Mighty550]

Well, I figured out why it was hitting high RPM..... you know that drain tube for the tank???  yea, that got stuck under the piece of metal where the carb sync knobs are.  Pulled it out and it idled just fine 

So that problem is solved, still need to figure out the misfire.  I noticed the pipe got a bit warm when it would hit high rpm for a few minutes, but when it was sitting idle, it was cold to the touch.  I know the needle is clean, gotta check the passage up to the intake now to make sure thats clear.  Really hoping thats the problem.

[TwoTired]

So that problem is solved, still need to figure out the misfire.  I noticed the pipe got a bit warm when it would hit high rpm for a few minutes, but when it was sitting idle, it was cold to the touch.  I know the needle is clean, gotta check the passage up to the intake now to make sure thats clear.  Really hoping thats the problem.

Carbs vacuum synch'd?
Pilot jets/circuit clear and flowing?

[Mighty550]

Thats on the menu for this weekend, ill let ya know how it goes.

[ATZ]

Okay, so I bought some pilot jets off of ebay N424-22 size #48 they are the threaded jets but they have the same outer diameter as the press in size so they squeezed in place just fine. I put everything back together and started the bike. It started really fast, alot faster than usual and idle MUCH better than it has before. I got it to idle well around 1100 rpm  with the idle screw turned all the way down. The fourth cylinder issue is all cleared up now as well. It is still doing the over revving thing but not as bad. I have to give it much more throttle to get it to spike but it still holds at 4k for about 3 seconds before dropping back down again. So I'm debating whether I should put in a bit bigger slow jets say #50 or whether I should step up the main jet. I'm thinking main jet but I'm not sure what I should start with? What do you guys think?

thanks

[ATZ]

Well guys I'm totally out of ideas. Just to summarize the problem again, when I try start the bike it starts and runs but terribly (sputters and small back fires). It can't idle well unless its at 2k and then when I give it gas it takes off to about 4k and stays there for a bit and then comes down well after the throttle is closed. Here is what I have done so far.

1. I switched the idle jets to a 48

2. I switched the mains to a 98, which seemed to help a bit, so I switched to a 110 and the problem seems to be back, I figure it was never really gone.

3. I've tried syncing the carbs but I can never really get a good reading on the gauges.

4. I noticed though when adjusting the screws to sync the carbs, it seems to make a large difference. If I turn it a bit all of a sudden the bike will catch up and revv to kingdom come, and then come down again.

5. I have also vigorously checked for air leaks.

6. I have checked out the plugs and they are pretty dark, some even have carbon building up so its not like I'm lean

7. The throttle cables are not sticking at all.

The fourth cylinder is firing now so that problem is over, but it is just so unpredictable and everything I do doesn't seem to help.

I have been trying different things for a month now and I really need some input.






HELP

[ATZ]

Also just a side note, when the choke is on it doesnt seem to make a difference

[TwoTired]

Also just a side note, when the choke is on it doesnt seem to make a difference

Is your choke at the bars or at the side of the carbs?   Cb550K had PD carbs, Cb550F has the older style carbs with a different choke arrangement.

In fact, you need to tell us about the exhaust and air filtration installed.