Topic: Help - Carb question

[ddmcnair]

Thanks in advance for any help you can give.

1982 CB 650 in great shape (<2000 miles)

If she sits for a week or so she's hard to start and doesn't fire on all four (two cylinders on the right are missing).  Feels like gunk in the carbs so I've pulled them off and cleaned them twice.  Seemed to be clean both times and she started right up after the cleaning.  Same problems again after sitting.  Will start with lots of choke but is only firing on two cylinders most of the time.  If you give her throttle the other two cylinders will fire but only sporadically.

Happened again two days ago and I just kept trying to start her.  Drained a little off each carb.  After a several hours (trying every 15 minutes or so) she finally started to kick in all cylinders and smoothed out to run great.

Has a new petcock and the tank has been treated with PR-15.  In line filter shows no sediment.

Thanks for any suggestions.

Doug

[OldSchool_IsCool]

Welcome to the forum, Doug!

I'm afraid I don't know much about the '82 650 as far as carbs, fuel lines & petcock are concerned.  does the petcock have 2 fuel lines or just one?  You mentioned an in-line fuel filter.  Do you mean in-tank?  I've had the unfortunate experience of fuel starvation caused by an air bubble caught up in and in-line filter.  If you have a dual fuel line setup, maybe this is a possibility.   The remedy was to make sure the in-line filter was mounted vertically and not horizontally.

Hopefully some of our 650 brotheren/sisteren can offer you more 650-specific ideas.

[ieism]

And if the petcock has two lines, does one go to the 2 cylinders that are not firing?

[ddmcnair]

Petcock has a single line.  In line filter is outside the tank.

I'll check positioning of the filter but I would think this would effect all cylinders.

Thanks

[OldSchool_IsCool]

True, one fuel line would affect all cylinders similarly.  Since the two cylinders affected don't share the same coil, ignition issues are unlikely.  I think your initial suspicions of the carbs is probably correct.  but why after sitting a week plus??    Hmmmmm.

Maybe leaky rubber seals allowing condensation to mess with the fuel mixture on those two carbs?  Just spit balling here.

[Klark Kent]

whats the history on the carbs?  could those two carbs be gummed up? float levels to spec?  i think you should take them apart and clean them either way.  its fun to do and its good for you.  less than 2k miles is a lot of sitting for those 25 year old carbs, if any part of that was done with fuel in the carbs all that not running could leave you with carb issues.  Post pics

[Gordon]

Have you checked, cleaned, or replaced the spark plugs recently? 

[eurban]

Your 82's carbs probably have a vacuum operated safety device that only alows fuel to flow from the tank to the carbs when the engine is producing vacuum.  When the bike sits for a while, fuel evaporates from the bowls leaving you with a low supply.  It may take a while of cranking the engine before enough fuel will flow into the bowls to replenish the supply and allow the bike to start.  If the safety device is not functioning properly (bad vacuum hose, crudded up internals) then you can have fuel delivery issues. . . . .Its relatively easy to temporarily bypass the device by simply running the fuel line directly from the petcock to the inlet on the carb bank.  If things (hard starting in particular) improve then you probably will want to remove the device for good.  Just make sure to turn the petcock to the off position when you park the bike to eliminate the risk of a hung up float dumping your fuel on the engine/ground! . . .Overall, sounds like you may a have a few issues going on.  As the previous posters suggested, new plugs and a thurough carb cleaning and inspection would be advised.  Your carbs probably have plastic non adjustable floats btw.  I can't remember exactly what the pilot jets situation is in the CV carbed 650s. You should pay close attention to cleaning them out.  Pressed in pilots can often times be gently twisted out and properly cleaned.  . . . . Make sure that you don't have any intake leaks, that your air filter is clean and that the spark plug wires are in decent shape.  Probably would be wise to order up a set of NGK ends and some copper core wire and replace the old stuff.  It is easy to change the plug wires on the 650s coils.   

[ddmcnair]

Thanks to all.

I have completely cleaned the carbs twice but am planning another cleaning and will swap out the idle jets.

Good suggestion on the vacuum device.  I'll give it a try.

Thanks again,

Doug