Topic: Doesn't run once warmed up

[sledder23]

hello.  Have a '72 CB5004.  Sorted out some issues and got it running today for the first time in a longg while.  Ran good last time it was out, but that's been 3-4 years maybe.

Now the bike starts ok, but as soon as it warms up doesn't run well at all.  I considered that it's running too rich, but carbs were fine last time out and I can't imagine running rich would make the bike totally die.

Thoughts?  Advice?

[Raef]

I'd check and see if it's getting gas and spark after it dies, if no spark i would check the coils, condenser and plugs. If no gas the filter then the float seat valves. if the floats are sticky drain the fuel, add fresh with some fuel treatment is worth a shot but they will probably need cleaned

Mark

[scottly]

Turn the choke off....

[GammaFlat]

I'm with Raef.. I'm gonna guess condensers.  When old, they can screw up when they get hot. 

[sledder23]

hadn't thought of condensers.  If they can go from good to bad like a switch, that may be it.  I'll get it going again and check for spark.  I have a stuck float bowl on the #3 carb, so I'm going to sort that out first.  Love carbs.

Turn off the choke: really?? 

[scottly]

Turn off the choke: really?? 

You would be surprised how many people get the choke operation mixed up.

[Spanner 1]

Slow fuel delivery due to crap in the petcock/ fuel system....... bowls eventually can't fill fast enough to keep-up with running the bike.... my 2c.

[scottly]

I considered that it's running too rich, but carbs were fine last time out and I can't imagine running rich would make the bike totally die.

Thoughts?  Advice?

What do your spark plugs look like?

[ron.cieri.313]

Can I chime in?...I have a similar problem...'76 CB750 with stock air box recently re-installed, timing good, slow jets replaced just to be sure...same thing in terms she sounds great when I start her, but she doesn't run the same after 20 minutes or so...have the keep the idle artificial high so she doesn't stall out at stops.

so condenser?...really?...why would that be?...I really don't understand the entire role of a condenser.

boy, clogged petcock...I better check that cuz it always seems like a fuel issue or like its being choked off...but I've played with the air pilot screws alot and the standard 1 turn out seems to be the best.  Their are drap pipes on my bike though.

don't mean to highjack but will be following along

[sledder23]

The plugs actually look really good.  To add a few more details, the bike runs well for only about 3-5 minutes max.  I'll check the petcock, but it seems to go fine when first started, even revving it up.  Of course that could also be gas from the bowl.  Which is the worse problem, I've got a #3 carb that was first stuck closed and after fixing is now stuck closed.  I need to get that sorted out before I come back to this issue.

On the subject of jets, what are people running in the 500's?  I know that's a broad question...  I have the OEM airbox and after market 4x2 exhaust but it's not a hi performance exhaust.

[TwoTired]

When was last 3000 miles tune up performed?

How old is the air filter?

Running rich puts black conductive soot deposits on the spark plugs and shorts them out.

What position is your choke lever in?  Describe.

[sledder23]

Tune up: very recent.  New plugs, oil change, air filter, and carbs got new jets and needles from kit.  Bike ran fine 2 years ago, ran great in fact.

Choke: once warmed off obviously (guess not!) in the full OFF position

I need to check the plugs, but as I said it ran fine last time it was run.  It has sat for too long, but started up pretty easily.  I can't imagine the fuel/air came far enough out of whack on it's own to account for this and all air/fuel screws were put back to the prior setting and carbs balanced.  Lack of spark due to condensor sounds right, but I'm trying to check with the former owner (my father) to see if/when those were replaced.