Topic: New here, need help with cb500f.. seems to run on 2 cylinders

[FfejCB500four]

Hey im new to this forum.  I got a cb500f  a month ago that ive been cleaning up and turning into a mild cafe. i havent had it running since i got it as it needed the carbs cleaned.. Im new to these types of bikes..
ive cleaned out the gas tank, petcock, changed oil and had the carbs altrasonic cleaned, rebuilt and adjusted to spec..
I put it all together and i can only keep it started if im on the throttle and choke turned just a touch from closed position.. it wont hold idle unless i give throttle.
This is the thing, it was running on 2 cylinders, the right side (of bike) headers were hot but the left side were cool
so i replaced all the spark plugs with fresh ones and now the left side (of bike) headers are hot and the right side are cool??  what should i be trying next?
I would love to take this bike for a ride..

thanks
JP

[vern401]

Well lets try trouble shooting it.
  Odd that it switched sides on you. I'll be thinking about that but for now>
Pull a non firing plug and lay it on the block someplace connected to the coil. turn it over and see if it is sparking.
ummm back up... Pull int air filter side boots off the carbs.
Start the bike have some one with you to help since you hafto keep into it to keep it running.
Spray some WD-40 or carb cleaner into one of the cold cylendars carb. If it speeds the engine up then you have a fuel delivery problem. Let us know......

[FfejCB500four]

So i think i have found the issue.  i was staring at the bike when it came to me that when i replaced the plugs i took of the gas tank,  when i reinstalled the tank i connected the fuel lines back to the petcock the opposite way of how they were connected the first time i tried to start it.. which would make the cylinders switch  sides from the first attempt to the second attempt .. so im  thinking one of my petcock lines is clogged.. that could make sense right?
now assuming i didnt foul up my carbs.. im going to clean and replace the petcock, filter.. and hope im right..
ill keep you posted..

[vern401]

Put new lines on the petcock to carbs too.
If your petcock has a small screw on bowl on the bottom I would shut the fuel off and remove the bowl looking for anything in it. It was used as a sedement bowl on some of the older bikes.

[Scott S]

 The outlets on the petcock shouldn't matter. Each hose goes to a fuel T; one for the two left carbs, one for the two right carbs.
 The coils each fire two cylinders. One for 1 and 4, one for 2 and 3. Since you're having two adjacent cylinders acting up, I would think that points to a carb issue.

 If it were a coil, either the two outside or the two inside cylinders would be affected, 1&4 or 2&3. Same thing for a points problem.
 Check your carbs.

[FfejCB500four]

Hey Scott, my petcock has two outlets i dont have any T's in the system..  two carbs share one hose the other two carbs share the other hose..  when i switch the hoses back and forth the one set of cylinders work..
I know its wishful thinking but im trying not to think about having my carbs re cleaned after they went in for the ultrasonic cleaning.. i guess ill find out soon  im going to put a T in between the fuel lines and run one tube through  an inline filter into a bottle of gasoline to see if all four cylinders will catch..  if that works then i know what to do..  if not then it looks like im going to be taking my carbs back for a re clean..

wish me luck..
Jeff

[Scott S]

So you're saying if you move the hose from the left bank of carbs to the right bank, the problem follows it? That doesn't make sense. The right two carbs get fuel from one hose. The feed cylinders 1 and 2. Cylinder 1 is fired by one coil, 2 by the other. If those two cylinders aren't firing (or vice versa) it's got to be a carb problem.
 It's my understanding that both barbs on the petcock are fed from the same supply. Check you're hose for obstruction. Do you have an inline filter? Check that for obstruction.

[FfejCB500four]

Ok.  so bypassing the clogged nipple on the petcock ( towards back of tank) solved the problem.  i put a T on the fuel hoses coming from the carbs and up into the first nipple ( front of tank) and all four cylinders fire..  the headers feel equally hot now...  so a new petcock and fine tuning is in order..

i have to get the carbs synchronized because it runs rich..  that should smooth out the idle.. I hope, as i have to play with the choke to keep idle..  when its fully closed she dies out but just a touch open and it holds idle at between 1600-2000rpm
if not. the next step i will be taking of the carbs to have them cleaned some more..

thanks for the replies..  any more tips to watch out for would be great
Jeff

[vern401]

  Yup.. get the petcock installed.
  Make sure the floats are set to the right height.... Take your time and get them all right... it's that important.
  Increase the idle screw when it is warmed up so that it idles at about 1,000 + - 100 RPM.
  Set your pilots as per the books instructions.
  Then do the sync on the carbs. Take your time and do one carb at a time. reset the idle after each carb has been adjusted. I get picky about this and try to get them all to be +- 1 on the guages from eachother.
  One of the carbs is the baseline carb as I call it. its the one that the idle speed is set from. On my 78 CB750F it is cylendar #2. I try to get the other carbs to match it's reading.

[FfejCB500four]

I set the idle screw to idle around 1200rpm and the choke is open just a touch.. and it idles decent.. even went for a spin around the block since i never road the bike until just now..
now that i know it runs fairly smooth although rich... im going to fine tune the rest as what was mentioned in this thread.
I also sent the 750 supersport  tank out to get cleaned and lined.. and awaiting the petcock to be delivered..
so i guess i have to choose the cafe seat i want as stock seat wont fit with SS tank unless i cut it down.. im thinking a BCR seat
though expensive they seem to fit perfect...

thanks for the help..
hope to keep the progress smooth
Jeff