Topic: CB500 Rough/Not Starting After Carb Rebuild

[Cleric40]

Hi Guys,

I recently cleaned and rebuilt my carbs  on my '73 CB500 with all stock jets and new gaskets and now she's having trouble starting. Floats were set properly, air/fuel screw set correctly, bench synched, the whole 9 yards.

I have to have it choked and wide open throttle to even get it to pop a little. It will then fire up, rev up to about 3k then die...


After this past rough winter I want to get out and Ride!!!!  Any help would be greatly appreciated

Thanks in Advance 

[harisuluv]

Where to begin?  Can't tell you where really, you need to provide information for us to help you with.

If your information for specs is just "correct" well, then I guess that's that.  Instead, things like "floats set to 26mm" helps, that is real data.

So you rebuilt your carbs and everything is set correctly, "the whole 9 yards."  What else changed, pod filters?  Exhaust?  If nothing else changed, then you didn't do everything correctly.

From what little info available, it sounds like you're lean, and that rev up before dying sounds like what happens when you run out of gas.  I'm not saying you're out of gas, I'm saying that what you describe is a symptom of running lean.  You might want to double check your slow jets.

[Stev-o]

Are you getting proper fuel flow out of the petcock? (Have gas?!)
Spark on all four?

[Cleric40]

My apologies for the lack of information, late night and wanted to get the ball rolling on a post.

Let me elaborate. I picked up the bike from craigslist and for the most part it is the stock setup. Stock airbox, but different 2 into 1 exhaust. (Not sure which one) I understand that this will most likely lead to needing to change the jets but figured I would start with a stock rebuild kit to see where the bike stands. 

The reason for the rebuild was rough running before, so I figured I would start with the carbs and boy were they nasty. The “specs” were based on the repair manual and certain information I have read in the FAQ section..

I am pretty sure I have proper flow out of the petcock as the bowls are full and almost certain getting spark to all four because I did have the bike running and idling fairly well, but now when I went to go start it again its being stubborn starting. 

[Stev-o]

If the current exhaust has a baffle, rejegging may not be necessary, it would as least run.

When diagnosing, "pretty sure" is not good.  I'm "pretty sure" your bike should run if you have fuel and spark!

[Cleric40]

When diagnosing, "pretty sure" is not good.  I'm "pretty sure" your bike should run if you have fuel and spark!

Stev-O, you are right "Pretty sure" is not good, but its the best I can say for now while at work 

I plan to check more tonight.

Taking a look at the stock petcock, it appears that there is only one fuel pickup hose? I am used to that if the petcock has a reserve it has a separate hose. Does the reserve just simply pickup from the body of the petcock? 

[iron_worker]

You say it's a CB500 and then you mention a 2-1 exhaust ... are we talking about a CB500 twin?!

Just checking because that would certainly change things.

IW

[Cleric40]

You say it's a CB500 and then you mention a 2-1 exhaust ... are we talking about a CB500 twin?!

Just checking because that would certainly change things.

IW

No its a CB500/4.  It has 2 header pipes into 1 on each side of the bike. I guess this is called 4into2?

Sorry for the confusion