Topic: me again...carbs back on, but will only start full throttle full choke

[brockj]

And usually dies shortly after! (78 CB550K, just went through and cleaned out slow jets and reassembled)

I am not sure what I am doing wrong!  Basically with full throttle and full choke it will start, sometimes, then it will shoot up to about 6000, I let up on the throttle quick, sometimes it dies, a few times I have been able to keep it around 3000 for a bit and it shoots up occassianly.  I know something must be set incorrectly, but I am not sure where to begin.  This is my first bike and I am fearing I am in for more than I bargained for!!

Thanks for all your help
Joe

[TwoTired]

What setting did you use for the idle mixture screws?
Did you verify all four holes into the slow mixture system were clear and flowing throughout?

Do you have any air leaks in the couplers between carb and cylinder head?

Did you check your float height?

Did you put the floats in upside down?

Did you verify the fuel level in the carb bowls?  (Clear tubing outside?)

[brockj]

What setting did you use for the idle mixture screws?

I started at 1.5 out and adjusted all the way to original which was 3.75/4.  I found that it seemed best about 2.5 out.

Did you verify all four holes into the slow mixture system were clear and flowing throughout?

Yes, I was able to blow through the jets when they were out and I was able to spray cleaner from the passages in the carbs out through the jets (main and slow)

Do you have any air leaks in the couplers between carb and cylinder head?

Not that I am aware of.  I know the boots in between are on very tight and are in good conition

Did you check your float height?

I did not do this, I left it as it was originally.  This is one of my concerns, however I was not able to track down a tool to measure with.  I believe the correct height should be 12.5 mm, is this correct?  I did eyeball to makesure they were all the same.

Did you put the floats in upside down?

I am pretty certain that I did not do this, but I can only think of one way to check....

Did you verify the fuel level in the carb bowls?  (Clear tubing outside?)

I only checked the number 4 to make sureit was getting fuel.  I have been able to have it running for up to 45 seconds, after which time I checked to make sure all pipes were hot (they were).

Let me try to explain what exactly is happening (this may seem like rambling at some point, I apologize).  Upon getting the bike to run, it WANTS to die.  I give it gas and it usually bogs down, if I give it quick shots I can keep it running, but eventually my timing will be off and I kill it.  Usually the only way I can start it is by giving the bike full choke and full throttle, it fires and I try to drop the throttle quickly to prevent it from hitting 8K RPM's.  At this point in time it usually just dies as the RPM's drop, if I can keep it running, it is not running good, usually slight backfires and sputtering til it dies.  I know the carbs will need to be synched, but I thought you should be able to get it running then sync (in fact I thought that was the only way to do it...but like I said I have been riding for all of 3 weeks!)

Any other thoughts?

Thanks for all your help!!

[Bob Wessner]

This is one of my concerns, however I was not able to track down a tool to measure with.  I believe the correct height should be 12.5 mm, is this correct?

Can't help with the correct height measurement, but as far as a tool, in the absence of a model specific float gauge, go to a decent hardware store and look for a small sliding "T" ruler. I used this on the floats for an early 750 and it proved quite accurate. I later acquired a gauge to verify the height. The ruler is only a couple of $'s.

[brockj]

I will have to pick one up this weekend...I guess the carbs are going to have to come off again!  Oh well, maybe this nice weather will stick around for a few more days

[TwoTired]

Your bike's symptoms are STILL indicative of a slow jet system blockage.

The slow mixture system has four holes in it not counting any other metering systems within the carb.  It has it's own air jet, slow jet, Idle mixture screw opening, and a delivery hole into the carb throat.  A blockage at any one of these, or the interlinking passagways, will prevent the entire slow system from working.

This fits your bike's symptoms.

The slow jet fuel supply tube does not go to the bottom of the carb bowl. If the fuel level is too low, the slow system starves, and only the mains gets supplied.

This fits your bike's symptoms.

 If you put a piece of clear tubing on the nipple at the bottom of your carb and then route that tubing upward next to the float bowl, turn the gas on from the petcock and open the drain screw at the bottom of the carb bowl, the tubing will fill with gas to match the level inside the carb.  This level should be 1/4 to 1/2 inch below the mating surface of carb bowl to carb body interface.

Lastly, (and this may sting a bit) your answers lack detail and indicate a lack of attention to detail toward your maintenence operations.  The details are what separates you from success in this repair, I think.
Yes, I know, you just want to ride the bike.  Too bad.  The bike doesn't care.  Until you address it's needs, it won't care to make you happy.

From here, it seems like you rushed through the carb cleaning without spending the time or paying attention to the details needed during a carb overhaul.  If I'm wrong about this, then I apologise.

Seems a shame, your reports show you are clearly talented enough to perform the work...

I know, I know, "shut the F**K up"!

Good Luck!

[brockj]

Thank you for your help TwoTired, I would guess that my missing something could be more linked to not knowing the carb than anything.  I have rebuilt the carbs on my old cars several times, and I know them.  These ones are different so I am know I am missing something.

That aside, I will check the gas levels this weekend.  I am going to be pulling the carbs off again, so we will try it again.  My fiance's father will hopefully be coming over, and he has worked on his own bikes for years.  So hopefully having someone around with a little more experience than myself will help. 

It just seems odd to me that after cleaning them this last time, it is running much worse.  My buddy helped me soak them before (not paying much attention to the slow jets) and it was running pretty well after that, just no low idle.  That is when I figured out that it must be the slow jets.  I can believe they are still not getting gas (float level) and that would be the explanation for nothing below 2500 RPM range, but you would think it would still run fine in the higher range, as it did before.  I guess it just goes to show how sensitive these buggers are.  Would it make sense that if no fuel is coming in the slow jets, but now that they are unclogged it is possible getting more air, throwing off the mix?

The positive to all this, is by the time it is running good, I should know quite a bit about my bike, which is always a good thing!

Thanks for all your help, I appreciate it!!

Thanks
Joe

[Buffo]

Pay some special attention to the passages that are involved with the slow jets. even though the slow jets may be clean the passages may be full of gunk...are you sure the jets are 100% clean...I had to clean mine like 4 times...each time saying to myself..."they are clean now!"

radio shack sells a T slide ruler that I use to check/set my floats it is awsome and costs about 2 bucks.

are you running an in line fuel filter...a new one?

Are you running it with the COMPLETE stock air filter assembly installed?

The first time I reassembled my carbs I put all the floats in upside down...mine fit nicely untill I put the bowl on...then it shut off the fuel supply

Buffo The Magnificent

[brockj]

It sounds like I will have someone coming over today to help make sure I have done everything correctly.  Hopefully by the end of the day, I will know more.

Thanks
Joe

[brockj]

Alright, update time.  Today I pulled the carbs back off and went through them again, before really doing anything I checked to make sure I could blow carb cleaner through the jets, all were open!!  I pulled out the idle mixture screws and soaked them, as they were the only things I had not touched yet (aside from adjusting).  Put the bike back together, fired right up!!  I can tell it really needs to be synched, but at least it is running.  I think the number 2 carb is still having issue, as I noticed the #2 pipe not as hot as the rest.  Also, the bike will run kinda choppy from 1000 - 3000, but it stays running.  I think I am going to be doing a rebuild on at least number two, but we will see how well it runs once the carbs get synched.

Thanks for all your help!
Joe

[written_black]

My 73 CB500 did the same thing after I rebuilt the carbs. I was baffled. I just blasted them with carb cleaner. I had a set of parts carbs that I dunked in the carb cleaning solution, I cleaned my jets out of my old carbs and put into the clean bodies. It ran like night and day. The part that holds the main jet on my old carb had erroded away and I think fuel was getting sucked up from around the 0-ring causing it to run rich. So you may look at that, they may be your problem. Just my thoughts... 

[TwoTired]

fired right up!!  I can tell it really needs to be synched, but at least it is running.  I think the number 2 carb is still having issue, as I noticed the #2 pipe not as hot as the rest. 

Great to hear things are going better.
My 78 Cb550 had the same colder pipe issue on #2.  Turns out that's the only one you cant change the slide position during syncing, and it was way off.  After tuning the other three to match #2, all the pipes heated the same it ran MUCH better.
Cheers,