testy

Author Topic: CB550 high rpm power loss  (Read 1014 times)

0 Members and 1 Guest are viewing this topic.

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
CB550 high rpm power loss
« on: January 21, 2019, 11:18:48 am »
Hi all, you may have seen my other post about trying to get this 1977 CB550f to idle with any semblance of consistency. Well I took a break from this project for awhile and finally came back to it this past weekend. I took some advice from a coworker and leak down tested it, the results came back perfect, 98 to 100 percent holding in the chamber. So I took apart the carburetor and cleaned it for the billionth time. This time I moved the needle clip position down to the last spot, and when I put it all back together I decided this time to run the velocity stacks instead of the pods I've had on since I bought it. Well to my surprise it not only idles great with no choke but also rides! (Sort of) I was able to take it down the driveway and I had no mid range. I came back and cut out some cloth to slip over the stacks and when I test rode it after that it was doing really well. The only issue was that at 5000 rpm it had no power, just bogs down. Also the 4Th float bowl Lets  glass out the overflow when at a stop sometimes, but not while riding. So now I come to you with a new problem to work out. Ill label below the specs and what's been done, I appreciate any advice guys.

Cb550F with velocity stack intake with cloth over stacks on stock carbs and a 4into1 exhaust.
Carb setup: 115 mains and 40 pilots
Needle clipped at last position at top of needle
Floats set to 22mil awhile back but carbs have been messed taken apart a few times since.
Carbs thoroughly cleaned and slides set with 1/8 drillbit  a few times
Ignition system has been changed to Dyna S ignition coils and wires.
Timing has been set following dyna s instruction.
Valve clearance has been adjusted to recommended spec

Offline hsas.69

  • Enthusiast
  • **
  • Posts: 226
Re: CB550 high rpm power loss
« Reply #1 on: January 21, 2019, 12:11:19 pm »
Vaccum sync the carbs and then do a plug chop.

Sent from my LG-LS993 using Tapatalk

78 CB750 F3
78 CB550 K4

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #2 on: January 21, 2019, 12:23:02 pm »
Head.69 Will do, hopefully I can get this thing tuned up and completely road worthy. Thanks

Offline Tracksnblades1

  • Hot Shot
  • ***
  • Posts: 414
Re: CB550 high rpm power loss
« Reply #3 on: January 21, 2019, 02:44:00 pm »
Can you breathe normally through the cloth you used to cover your velocity stacks..?
Age Quod Agis

Offline Tracksnblades1

  • Hot Shot
  • ***
  • Posts: 414
Re: CB550 high rpm power loss
« Reply #4 on: January 21, 2019, 02:47:53 pm »
Clip at the top of needle is as lean as you can go without making changes....
Age Quod Agis

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #5 on: January 22, 2019, 07:21:15 am »
Can you breathe normally through the cloth you used to cover your velocity stacks..?

From what I’ve seen yes it seems to breath pretty normally, it’s not very thick cloth.

Offline PeWe

  • Really Old Timer ...
  • *******
  • Posts: 7,854
  • Bike almost back to the 70's 2015
Re: CB550 high rpm power loss
« Reply #6 on: January 22, 2019, 10:54:04 am »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to stock K2

Offline sixthwisconsin

  • With an 1855 Springfield, I'm a
  • Hot Shot
  • ***
  • Posts: 516
Re: CB550 high rpm power loss
« Reply #7 on: January 22, 2019, 12:11:34 pm »
You are leaking gas at stop signs? Sounds like you need to do the clear tube method for float bowl levels. You can measure all you want but it will never be right until you do the clear tube method. (ask me how I know!) imbalance also causes poor idle.

You have leaned out your needles for less fuel AND added high flowing velocity stacks for more air. At higher RPMs you are probably running out of fuel. So if you really want to run the stacks you'll need bigger mains.

Also, where are your air screws set?
1974 cb550k0 with 1978 motor
https://lensdump.com/a/neo550.A9iak
1974 cb550k0 Custom
1975 cb750f0 Custom Cafe
https://lensdump.com/a/cb836f.A9rrc
http://forums.sohc4.net/index.php?topic=101126.msg1134620#msg1134620
2009 Kawasaki Concours 14 (Sold)

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #8 on: January 25, 2019, 06:10:48 am »
Sixthwisconsin, this bike has been giving me a hard time since I got it, now that I have set it up where it runs halfway decent I really don’t want to mess with carbs again in fear of messing it all up, but I am about to order new mains, I also have a vacuum synchronizer on the way to get them dialed in. The mix screws are out half a turn

Offline seanbarney41

  • not really that much younger than an
  • Really Old Timer ...
  • *******
  • Posts: 8,140
Re: CB550 high rpm power loss
« Reply #9 on: January 25, 2019, 09:36:20 am »
If your 550 only runs below 5000, you are really missing out. 5-9000+ is where the 550 makes acceptable power.  Your carb troubles are not over until this is fixed.
If it works good, it looks good...

Offline Bodi

  • Old Timer
  • ******
  • Posts: 4,869
Re: CB550 high rpm power loss
« Reply #10 on: January 26, 2019, 07:52:24 pm »
The carbs are a likely source of problems, yes. A plug chop will tell that tale (or a dyno with EGA...). I also wonder about the cloth, have you tried without that?
Ignition and valve timing affect performance progressively more as RPM increases, there is less time for intake/exhaust and spark events to happen so a few degrees out can make a big difference. I worked on a 550 with no top end power, wouldn't even rev up in neutral, but it started and idled just fine. Tracked it down to a cam chain one or two teeth out, plus the ignition was set a bit retarded. Fixed those problems and it was "a new bike!" according to the owner.

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #11 on: February 09, 2019, 11:42:44 pm »
Hello, sorry for the delayed reply, I have been a bit busy lately. But I did have a chance to do a little fiddling, I moved the needle clip down two spots and that made it a lot better still had a flat spot around 3000 rpm so I think I may be too lean still, but before chasing that down I’m going to check timing again and make sure everything is good to go, If so then I’ll go for the plug chop method to see where it’s running.

A bunch of parts came in for the front end that I ordered so the forks have been torn off and rebuilt, the new headlight assembly and clip on handlebars with new controls are in. So for the foreseeable future I’ll be figuring out the mess of wires I’ve got hanging off my front end. Speaking of which I need to make another post to answer a question regarding that. But once it’s all back together I’ll be back to getting it tuned in perfect and rollin through Seattle’s new viaduct before you know it!

Offline BomberMann650

  • Holy Cow! I'm an
  • Really Old Timer ...
  • *******
  • Posts: 5,248
  • Dr. Bovinestein
Re: CB550 high rpm power loss
« Reply #12 on: February 10, 2019, 03:59:01 pm »
Sweet seattle!

Greetings from the south puget sound.

When snowpocalypse is over maybe I could help.
75 CB550F codename Bloo
76/78 XS750 triple; trash can.
07 FJR1300; Longma
73 Norton Commando 850 Cafe Racer

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #13 on: February 10, 2019, 07:37:43 pm »
Ahh I’m about an hour north of the city, the assistance may be needed with how deep of a hole I’ve dug myself  :o

Offline BomberMann650

  • Holy Cow! I'm an
  • Really Old Timer ...
  • *******
  • Posts: 5,248
  • Dr. Bovinestein
Re: CB550 high rpm power loss
« Reply #14 on: February 11, 2019, 04:20:33 pm »
Tuning modified setups is a trial and error process if you don't have all the fancy gadgets a dyno shop does.  Went down lots of dead ends with the 750 triple project.  It was flat in the middle too.  It would rev to a certain point then begin making a blubbery sound with no throttle response.  Went up in jet size, got worse.  Went down in jet size,  Saw some improvement.  Got to a point that things were real close, but no adjustment would smooth the trouble spots.  That's when plug chop readings came to the rescue.  Even with the K&N pods the bike was over fueling at WOT.  Thanks to the forum I understood a bit about manifold air pressures.  A couple of minor mods to the mikuni CV carbs helped to deliver the extra air and keep the intake pressures up.   The bike runs smooth. 

Well, as smooth as a non-counterbalanced 3 cylinder can.

On the other end, my 550/4 used to run up to about 2/3 of the throttle before there was no more response.  It didn't blubber out, just wouldn't go any further.  That's a sign of under-fueling.  Rebuilt the motor and restored some carbs with bigger 105 main jets, and it's got a little more spunk now.  This is with a stock airbox, 650 cam and port contoured intakes.
« Last Edit: February 11, 2019, 04:22:58 pm by BomberMann650 »
75 CB550F codename Bloo
76/78 XS750 triple; trash can.
07 FJR1300; Longma
73 Norton Commando 850 Cafe Racer

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #15 on: March 09, 2019, 03:06:30 pm »
Sorry for the delayed response, I’ve been focused on some other things. However to update you guys the bike looks great now, clip ons installed, new upper clamp with built in speedo, new headlight with built in turn signals as well as a new tach.

Now related to the problems I’m having with the carbs, my previous setup was 115 main jets with 40 pilots, needle clip in the middle with 4 into 1 exhaust and velocity stack intake. With this setup the bike backfired like a mofo and had a flat spot at 3k. Assuming I was taking too much air I upped the jets to 120 mains and 45 pilots. The backfiring has now stopped. I have great acceleration up to 5k rpm and then I hit a wall. Also my idle doesn’t like to be at 1100 rpm, it either stays between 2000 and 2500 or it drops so low it eventually kills itself, there is no in between.

My question to you guys is what should I do? I haven’t done a plug chop yet. I have 125 main jets and I can still drop needle clip position 2 more notches if it’s still a little lean.

Offline sixthwisconsin

  • With an 1855 Springfield, I'm a
  • Hot Shot
  • ***
  • Posts: 516
Re: CB550 high rpm power loss
« Reply #16 on: March 09, 2019, 03:47:13 pm »
You are fighting all kinds of problems here. Do yourself a favor and do ONE adjustment/jet change at a time. Go back to 40 idle JETS and see how your idle does. DO NOTHING ELSE and report back.
1974 cb550k0 with 1978 motor
https://lensdump.com/a/neo550.A9iak
1974 cb550k0 Custom
1975 cb750f0 Custom Cafe
https://lensdump.com/a/cb836f.A9rrc
http://forums.sohc4.net/index.php?topic=101126.msg1134620#msg1134620
2009 Kawasaki Concours 14 (Sold)

Offline BomberMann650

  • Holy Cow! I'm an
  • Really Old Timer ...
  • *******
  • Posts: 5,248
  • Dr. Bovinestein
Re: CB550 high rpm power loss
« Reply #17 on: March 10, 2019, 12:23:48 am »
It's really hard to do performance tuning over the internet ya know!

The idle fall from 2500 can be a combination of lean fuel or ignition advance issues.  If you haven't serviced the timing advancer mechanism already, it would be a good thing to do.  Rule it out as a culprit before upping the pilot fuel mix.

Without hearing the engine sound at 5-6k I can't comment on rich or lean condition.  An overfueled engine can turn into a shaky amateur tuba solo.  An underfueled engine simply won't accelerate as desired. 

Of course, you want to make damn sure the valves are clearanced right and the cam timing is good.

For posterity sake; raising the needle richens the mix, lowering the needle leans it.  If you're moving the clip towards the blunt end, thats reducing fuel delivery.

Whatever its worth, that particular mac canister is a weird design.  It's natural resonance felt a little off of what actually makes these engines sing.  Not to mention is baffled to hell inside. 
Thats why I cut mine off at the dome and had the yoshimura canister welded in.

Do a plug chop run test at that 5k problem spot and let the electrode color tell you what the engine wants.
75 CB550F codename Bloo
76/78 XS750 triple; trash can.
07 FJR1300; Longma
73 Norton Commando 850 Cafe Racer

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #18 on: March 10, 2019, 02:07:29 pm »
Okay, so between tiling my bathroom today I had a chance to swap the pilots.
Sixthwisconsin, idle is good now, once it’s warmed up It stays around 1100. Riding it I found that acceleration is still good, it can go to about 5500 rpm and it hits a little bit of a softer wall than last time.

Bombermann650, valves have been checked a few months back and adjusted. I haven’t checked cam timing yet. Timing advance was set when I installed the dyna ignition maybe 5 months back. I suppose I could get some extra plugs and do a plug chop on it next.

Offline BomberMann650

  • Holy Cow! I'm an
  • Really Old Timer ...
  • *******
  • Posts: 5,248
  • Dr. Bovinestein
Re: CB550 high rpm power loss
« Reply #19 on: March 10, 2019, 06:26:57 pm »
Thats good the idle is steady now. 

Still wish I knew exactly what that "wall" was.  Its a term that gets abused so much it lost meaning
75 CB550F codename Bloo
76/78 XS750 triple; trash can.
07 FJR1300; Longma
73 Norton Commando 850 Cafe Racer

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #20 on: March 10, 2019, 07:44:21 pm »
Bombermann650, the wall in this instance is an odd engine sound and I can’t get my Toms or speed up any higher.

Offline Tracksnblades1

  • Hot Shot
  • ***
  • Posts: 414
Re: CB550 high rpm power loss
« Reply #21 on: March 10, 2019, 07:56:06 pm »
Sweet seattle!

Greetings from the south puget sound.

When snowpocalypse is over maybe I could help.

Farmer,

You poor soul. My daughter lived in DuPont for a year and half or so. Son-in-law is an US Army Captain then stationed at Lewis/McChord joint base. I visited and did the normal site seeing. Weather sucks up there, got wet everyday and saw the sun once, for a few minutes.
You poor soul,
😩
Age Quod Agis

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #22 on: March 10, 2019, 08:15:38 pm »
Yeah we’ve had sun the last few days. When the sun comes out spring/summer it’s beautiful here. Working in the rain can suck though 🤷🏽‍♂️

Offline sixthwisconsin

  • With an 1855 Springfield, I'm a
  • Hot Shot
  • ***
  • Posts: 516
Re: CB550 high rpm power loss
« Reply #23 on: March 11, 2019, 06:20:57 am »
Sticking with the idle, you posted earlier that your air screws were at 1/2 turn out. Have you tried adjusting these back out after swapping the idle jets? With the velocity stacks, I don't know what you will need but 1/2 turn is in beyond spec of 1 1/2 +- 1/2. So you are ramming lots of air in then choking it down.

Something else jumped out to me as well. You are running high flow velocity stacks and a MAC 4 into 1 exhaust that is not high flowing.
1974 cb550k0 with 1978 motor
https://lensdump.com/a/neo550.A9iak
1974 cb550k0 Custom
1975 cb750f0 Custom Cafe
https://lensdump.com/a/cb836f.A9rrc
http://forums.sohc4.net/index.php?topic=101126.msg1134620#msg1134620
2009 Kawasaki Concours 14 (Sold)

Offline Wyatt565

  • Full Member
  • *
  • Posts: 24
Re: CB550 high rpm power loss
« Reply #24 on: March 11, 2019, 07:00:10 pm »
sixthwisconsin, I practically forgot about the idle air screws, but I could take them out to spec and see what it does! First I think I’ll do the plug chop and see what that shows.
In terms of the intake exhaust, I noticed that, I did cut part of the baffle out but I don’t see much else I can do without spending a lot of money on a new exhaust setup.

 

;