Topic: 75 CB550 carb help... searched... found nothing... PLEASE HELP ME Im lost!

[adamlwvdc36]

ok guys and gals.. Recently did a top end rebuild.  Tappets set, points cleaned and set, timing strobe set, ohmed out ignition coils, REBUILT carbs (stock [im assuming] jets, needles shimmed all the way up [to try to correct this lean condition], screws 1/2 turn out [also to correct lean], new plugs.  The airbox is installed, the exhaust is unmodified but Im still running lean... I KNOW this because when Im cruising at any speed i have to have half choke, and at times bike wont run correctly unless im full choke.  Ive checked for leaks in boots in the air path.  My question(s) [this may become more questions as a type] is/are: If I rejet, should I just go up one size? or 2?  Is there something else I may be missing? 

I wouldnt have posted a new topic, but all of the carb/lean mixture/running like crap threads are pretty obvious as to why they are in the condition they are in (things like pod filters, open headers, and the like) but on MY bike, in MY situation everything is stock.  I really dont want to have to ride around fiddling with the choke all the time... crazy little things like sometimes it wont idle without being fully choked, but then wont pull from a stop without being either no choke or half choked (this is pretty hard to do, but ive been able to get through the last few days by using my left foot to kick the choke down, left hand to work the clutch, right foot to stable the bike until i get enough momentum, and of course the right hand both does the brakes and throttle   I must look like a circus clown doing this in traffic (which i dont care how I look)  I JUST WANT TO RIDE MY DAMN BIKE ALREADY!!! please folks, help

[DJ_AX]

How are the rubber parts? Really? Leaks don't always so easily reveal themselves...

[DJ_AX]

I also recommend reading about "plug chops"
Then you'll "KNOW" this for sure AND which part of the carbs is causing your lean condition.

[adamlwvdc36]

the rubber is good and flexible and well seated...ive smoked a cigarette next to the boots to see if there is any suction (watch the smoke) anywhere, none.  The plug chop makes sense, but i guess i dont understand i know the basic principle of how a carburetor works, and i am mechanically inclined, and have better than average technical ability.  Am I to do this chop at different rpms? I know that there is the main jet, slow jet and the idle air mixture screw... so (if im thinking through this problem correctly) if im lean at idle then adjust the air screw,  if lean at low (in town) range then thats the slow jet? and if im blasting balls to a wall then that would be the main jet? is this correct?

[adamlwvdc36]

depending on what i need to do here i plan on using this tool pictured to "adjust" the jets i tested it out on an old jet from the bike before the rebuild.  basically its a set of file like thingys that correspond to certain orifice sizes.... says "AmeriGas" on it so i think maybe propane orifices.  anywho, its a cleaner type tool and if i go one step up at a time i can ream the jets to whatever size i want.  but i need to know what im doing before I do it.

just wanted to share the pic

[TwoTired]

Well, I'm wondering if you are operating the choke correctly or have a backwards understanding of it.
If the lever is down, the choke is off = inlet butterflies open  = Normal operating condition when at operating temperature.
If the lever is up the choke is on = inlet butterflies closed and only used during starting/warm up operation.

The lever is marked if you look at it closely.

Are you working it the right way?

[dave500]

that tool is for cleaning gas torch tips,dont jam them in any of your jets they will be way inaccurate,you dont ream jets,if your savvy they can be drilled but a complete new jet of the size you want is the best way,,dont try those gas reamers on those jets!!i forgot to add for  #$%*s sake!!

[adamlwvdc36]

Im working the choke correctly, ive been driving this bike for 6 years.  only since rebuilding the carbs have I had this problem.

[dave500]

re build them again maybe?

[phil71]

Before you get too crazy, maybe you should get a vessel to drain the bowls into.. Then, a measuring cup or graduated cylinder .  See if you have roughly the same amount of gas coming from each. If so, pull the line from the petcock and turn it on. Is it flowing fast, or trickling ? Overly advanced timing will also create a lean condition . Modern ethanol fuel, left sitting even for a month, seperates into hard, dry crystaline junk in  no time.
 Everyone thinks they cleaned their carbs well, but are you SURE you properly chased all the crap from your circuits? Thats what I thought.
  See you back here after another pull of the rack.

[dave500]

how come everyone pulls their carbs multiple times?these carbs are piss easy!go over your igniton again first,i think im repeating myself again here?

[andrewk]

Did you change/adjust the float level?

[trueblue]

how come everyone pulls their carbs multiple times?these carbs are piss easy!go over your igniton again first,i think im repeating myself again here?

Don't you know Dave, the carbs are the only thing to cause an issue on these bikes

[adamlwvdc36]

I will run the checks listed here on the carbs, with some cleaner.  The floats were changed but to 22mm... the spec. Will repost with update after I go through all of this...more than likely today will be helping my friend swap out a motor in a bike.  I need to let him take the reigns on his own projects... this will give him that opportunity

[adamlwvdc36]

Ok, so today I didnt get to work on my bike as much as I wanted to... but, I got to do a plug chop at 5000 rpm the attached picture is of 2 and 4, 4 on left 2 on right... Im confused even more now... Lets add this little fact... last night when i was gassing up i put seafoam in the tank thinking maybe if while rebuilding the carbs I may have knocked some varnish (hardly any in there) loose and that could be causing the problem.  Well, today she ran great, never had to touch the choke for almost all day.  Then on the way home today she started acting up again so this time I left everything alone and drove home shifting to keep my bike at that rpm (5,000) during all speed ranges. The last half mile of doing this i kept it in 1st on my street to keep it at 5k and as i pulled in the driveway, killed and clutched... these plugs are from that chop.  I did notice that if I pull suddenly back to WOT the bike bogs down. this problem the last couple of days intermittently gets worse but then eventually ends up okish again.

[TwoTired]

can't get a detailed look at the plugs.  But, they seem rather sooty.


When it recovers from "bog" whatever that means, does it burble back to life or suddenly act normal?

[That 70s Bike]

Im working the choke correctly, ive been driving this bike for 6 years.  only since rebuilding the carbs have I had this problem.

It's my understanding that unless the carb parts are from Honda or Keihin the jets & needles are wrong, especially the "rebuild kits". I hope you saved your old needles & jets.

[adamlwvdc36]

If i hold WOT all power is lost, the engine almost dies minus the inertia of the bike keeping it running.  Only after I release the throttle will it come back to life.  I can gradually (over1.5 seconds) take it back to WOT but not in one quick snap.

[TwoTired]

If i hold WOT all power is lost, the engine almost dies minus the inertia of the bike keeping it running.  Only after I release the throttle will it come back to life.  I can gradually (over1.5 seconds) take it back to WOT but not in one quick snap.

These carbs will always make the engine wheeze/stumble from a quick snap to WOT from idle.  It's the way they were designed and physics that determines operation.
From idle, in any gear, you should be able to get smooth, reliable engine response with up to 1/2 of total throttle travel.

[adamlwvdc36]

Ok, well then i guess that part is ok.  checked the condensers in the ignition system both are at 266 nF.. so theyre good. Points are adjusted and cleaned... Ignition coil primaries are 5 ohms, secondaries are exactly 15Kohms. so the ignition system is ok.

[phil71]

wow, you have a capacitance tester! I'm impressed!

[adamlwvdc36]

I messed around with the Idle air mix screw...did like 5 plug chops in a row and eventually got the plugs to be nice and brown (spending a lot of money on plugs here) at idle rpms... now, I also (since previous chops came out black) shimed my needles back to factory settings and its running lean in the area between 1/4 rpm and full throttle.  should I just jet this thing wider now or what?

I have a lot of really cool tools that people borrow and come to my garage to work on their stuff

[adamlwvdc36]

just pulled my bowls... water in them.  drained them out and took it for a ride... still having the same problem.  but, the water in the bowls would explain why it gets intermittently worse since when it gets worse, its when im low on fuel.  going back out to bore the jets with my method i listed... i dont care if its not the "recommended" procedure, im doing it... Ill see you on the other side.

[adamlwvdc36]

well, i reamed the jets.. and you know what? the sky didnt fall, demons didnt come up from the ground, and the bike runs better.  Not saying its perfect yet, but its better.

[dave500]

if you have water in your carbs the tank should be drained and flushed out along with the strainer.