Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

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ArrowOfTime
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Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby ArrowOfTime » Sun Jan 14, 2018 9:56 pm

Hello Everyone, first post! Been enjoying lurking around the forum so far (so awesome there is a cb650 forum!) and see I have a pretty common complaint but I have some specific questions about my situation hopefully you could help me with.

I have an 81 cb650c I've been riding around for about 3k miles to its current 21k. It's been running okay (loves the choke) but is a bit weak until 2.5k rpm. I figured it's an old bike and the first owner let it sit for 9 years so I'd try to clean the carburetors.

I got them off yesterday, opened them up (but kept them together), cleaned out the main jets, saw they were 120s (bigger than stock I think) and the float needles looked new so I'm guessing some work had been already done on them. Besides some gunk on the slide bores everything was looking pretty good.

Get to carb 3 though where the fuel accelerator pump is adjoined and find the o-ring sitting there was disintegrated, held together with some kind of yellow sealant. Also the boot for the diaphragm rod fell apart basically as soon as I touched it. Without replacement parts on hand I ended up putting it back together without the o-ring or the boot, figuring they weren't doing much before in the shape they were.

I now think this may be why I can't the bike to start. I turned it over until the battery died, then got a jumper and turned it over some more. I opened the release valve on bottom of the bowls to find just a smidgen of gas in carb 1, the others dry. I suppose this means that o-ring I removed was really critical? What do you think? Any other checks I should do? There is also the vacuum stop between the tank and the carb, I don't know how to check if fuel is flowing through this but it was pristine inside. Fuel seems to leave the tank just fine until then.

By the way, even at full tightness, the boots from the airbox don't make a good seal against the carburetors. Should I be worried about this?

Thanks!

ArrowOfTime
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby ArrowOfTime » Mon Jan 15, 2018 1:03 am

I just gave it a go with some starter fluid. The engine sputtered to life until the starter fluid ran out. Still no fuel in the bowls after that. I'm going to try bypassing the auto shut off valve tomorrow.

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GeorgeSweety
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby GeorgeSweety » Mon Jan 15, 2018 2:49 am

ArrowOfTime wrote: I figured it's an old bike and the first owner let it sit for 9 years

Get to carb 3 though where the fuel accelerator pump is adjoined and find the o-ring sitting there was disintegrated, held together with some kind of yellow sealant. Also the boot for the diaphragm rod fell apart basically as soon as I touched it. Without replacement parts on hand I ended up putting it back together without the o-ring or the boot, figuring they weren't doing much before in the shape they were.

I now think this may be why I can't the bike to start. I turned it over until the battery died, then got a jumper and turned it over some more. I opened the release valve on bottom of the bowls to find just a smidgen of gas in carb 1, the others dry. I suppose this means that o-ring I removed was really critical? What do you think? Any other checks I should do?

By the way, even at full tightness, the boots from the airbox don't make a good seal against the carburetors. Should I be worried about this?

Thanks!


Hello ArrowOfTime and welcome to the forum :) Wow!, where do we start?.........I'd start by stopping what you are doing, you won't get anywhere trying to start a bike with parts missing from your carbs :shock: And another thing, stop cranking the motor until you sort out your carb problem or you are going burn out your starter motor or destroy your starter clutch.
The first thing you should do is to sort out a work area because you are going to have to remove the carbs, strip them, clean them, clean them some more and then find out exactly what is missing and what needs replacing. By the sounds of it, all rubber parts are going to need replacing.
You are going to have to forget about trying to start the bike until you have sorted the carbs or you'll be wasting a whole lot of time.

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Folsoml
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby Folsoml » Mon Jan 15, 2018 6:44 am

Welcome here!

Everything George said and more. First, just so we are on the same page when we are describing things, the carbs are numbered from left to right as if you were sitting on the bike. That being said, the accelerator pump SHOULD be on carb #2, not 3. Double check your's, as if it actually IS on #3, we have a whole new thing to try to figure out.

ArrowOfTime wrote:I have an 81 cb650c I've been riding around for about 3k miles to its current 21k. It's been running okay (loves the choke) but is a bit weak until 2.5k rpm. I figured it's an old bike and the first owner let it sit for 9 years so I'd try to clean the carburetors.


You were able to take the bike and start it after it sat 9 years without first cleaning the carbs? That is amazing!

ArrowOfTime wrote:(but kept them together), cleaned out the main jets, saw they were 120s (bigger than stock I think) and the float needles looked new so I'm guessing some work had been already done on them. Besides some gunk on the slide bores everything was looking pretty good.


Sadly, you cannot truly clean the carbs on these bikes without separating them. A 120 main jet is stock for this bike.

ArrowOfTime wrote:Get to carb 3 though where the fuel accelerator pump is adjoined and find the o-ring sitting there was disintegrated, held together with some kind of yellow sealant. Also the boot for the diaphragm rod fell apart basically as soon as I touched it. Without replacement parts on hand I ended up putting it back together without the o-ring or the boot, figuring they weren't doing much before in the shape they were.


Whenever you omit an o-ring, you run the risk of the bike leaking, but this is not why the fuel is not filling the bowls.

ArrowOfTime wrote: I opened the release valve on bottom of the bowls to find just a smidgen of gas in carb 1, the others dry. What do you think? Any other checks I should do? There is also the vacuum stop between the tank and the carb, I don't know how to check if fuel is flowing through this but it was pristine inside. Fuel seems to leave the tank just fine until then.


I will usually remove the vacuum stop as they are finicky at best. The only caveat of doing this is you MUST shutoff the petcock whenever you park the bike. If you do not, and the float needles fail, you run the risk of filling your engine with gasoline (not in the normal way :lol: ).

If you choose to keep it, you can test it by applying vacuum pressure to the tube that comes from the nipple on carb 2 or 3 (I've seen them on one or the other). This should open the valve to allow fuel to flow. This tube could be the source of your problem. If it is dry rotted, you may have created a crack in it while you were working on the bank. This would then keep it from being able to create the vacuum pressure to open the valve.

Another way to diagnose what is causing your lack of fuel issue would be to trace the system back to the source. You are getting no fuel at the carbs, so go backwards through the fuel line at each component and see where the last place is that is getting fuel. This is easy with the fuel line, since there are not that many things between the tank and the carbs. You say you checked it at the float bowl drain screw, so now remove the fuel line at the brass tube where it connects to the carbs. Does fuel come out there? If not, remove the fuel line where it connects to the vacuum stop and check that. Then remove it from the petcock at the tank. This is the method I use for electrical problems as well.

ArrowOfTime wrote:By the way, even at full tightness, the boots from the airbox don't make a good seal against the carburetors. Should I be worried about this?


Yes. The VB carbs were designed very specifically to run with the original airbox and air filter. Any variations or modifications can cause erratic behavior. This is why these carbs do not work well with pod filters. Now I know that the lack of a good seal is not a "modification," but what it does is allow more air in than the carbs want--causing it to run lean. Running lean can cause burnt valves. One might think (much like folks do with pods) that you can change jets to make it run rich and this will compensate, but sadly, the amount of air the lack of seal (or pods) is (are) allowing in is not consistent.

ArrowOfTime wrote:cleaned out the main jets


What method did you use to clean the jets? I always have to ask whenever someone writes that they "cleaned their carbs." I was was communicating with someone who "cleaned their carbs several times" but was still having trouble. As it turns out, he was soaking the entire fully assembled bank in pinesol and water and considering that "cleaned." Go to this thread and check out the cleaning manual:

viewtopic.php?f=4&t=14053

As the thread says, this manual was written for DOHC Honda carbs, so they will not be exactly like yours, but they are similar enough that this manual will be extremely helpful. Follow it to the letter (as best you can given the differences).

Good Luck!
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

ArrowOfTime
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby ArrowOfTime » Mon Jan 15, 2018 1:56 pm

Thank you both for the quick replies! I have much to learn, and that's part of the fun.


Folsoml wrote:Welcome here!

Everything George said and more. First, just so we are on the same page when we are describing things, the carbs are numbered from left to right as if you were sitting on the bike. That being said, the accelerator pump SHOULD be on carb #2, not 3. Double check your's, as if it actually IS on #3, we have a whole new thing to try to figure out.


Ah yes, I meant #2... got it turned around in my head.

You were able to take the bike and start it after it sat 9 years without first cleaning the carbs? That is amazing!


I'm the third owner, I suspect the 2nd owner cleaned it and put at least new float needles, but probably no gaskets because they were a bit gunked.

Sadly, you cannot truly clean the carbs on these bikes without separating them. A 120 main jet is stock for this bike.


Good to know.

Folsoml wrote:

Whenever you omit an o-ring, you run the risk of the bike leaking, but this is not why the fuel is not filling the bowls.



Makes sense, vacuums just make me paranoid.


I will usually remove the vacuum stop as they are finicky at best. The only caveat of doing this is you MUST shutoff the petcock whenever you park the bike. If you do not, and the float needles fail, you run the risk of filling your engine with gasoline (not in the normal way :lol: ).



I've heard if I do this I should also install an in-line fuel filter between the tank and the carbs. My tank is pretty clean. Do you recommend a particular one?


If you choose to keep it, you can test it by applying vacuum pressure to the tube that comes from the nipple on carb 2 or 3 (I've seen them on one or the other). This should open the valve to allow fuel to flow. This tube could be the source of your problem. If it is dry rotted, you may have created a crack in it while you were working on the bank. This would then keep it from being able to create the vacuum pressure to open the valve.

Another way to diagnose what is causing your lack of fuel issue would be to trace the system back to the source. You are getting no fuel at the carbs, so go backwards through the fuel line at each component and see where the last place is that is getting fuel. This is easy with the fuel line, since there are not that many things between the tank and the carbs. You say you checked it at the float bowl drain screw, so now remove the fuel line at the brass tube where it connects to the carbs. Does fuel come out there? If not, remove the fuel line where it connects to the vacuum stop and check that. Then remove it from the petcock at the tank. This is the method I use for electrical problems as well.



I'll check this today.

A question: the vacuum in the auto-stop valve is formed in the piston, right? So the engine has to turn over for fuel to flow through it?

EDIT: working on this assumption, I disconnected the fuel line from the auto-shut-off to the carbs and fed it to an aluminum foil tray I fashioned. I turned the engine over for a few seconds using the starter and with everything else connected and found no trace of gas in the foil tray. I think this must mean fuel is not getting through the auto-shut-off. Is this correct?


What method did you use to clean the jets? I always have to ask whenever someone writes that they "cleaned their carbs." I was was communicating with someone who "cleaned their carbs several times" but was still having trouble. As it turns out, he was soaking the entire fully assembled bank in pinesol and water and considering that "cleaned." Go to this thread and check out the cleaning manual:

http://hondacb650.com/viewtopic.php?f=4&t=14053

As the thread says, this manual was written for DOHC Honda carbs, so they will not be exactly like yours, but they are similar enough that this manual will be extremely helpful. Follow it to the letter (as best you can given the differences).

Good Luck!


Thanks for the link. I opened up the carbs and unscrewed everything I could. I soaked the jets and other metal pieces in some carb cleaner for a couple minutes, then blew it off with compressed air. The rest I rubbed down with carb cleaner and a toothbrush, followed by more compressed air to get the cleaner out.

ArrowOfTime
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby ArrowOfTime » Mon Jan 15, 2018 8:35 pm

The plot thickens. I bypassed the auto-shut-off to see if I could get fuel to the carbs and I had gas in bowl 2-4 but bowl 1 was dry... hmm

Guess they're comin' back off next chance I get.

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Folsoml
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby Folsoml » Tue Jan 16, 2018 6:22 am

An inline fuel filter is not a bad idea, but it is not the lack of a vacuum shutoff that makes it so. The vacuum shutoff does not do anything to filter the fuel. There is a filter inside the tank where the petcock screws in, but on nearly every old bike I've rebuilt, I've found that this has disintegrated over the years.

So the bike was running before you cleaned the carbs? So what is different with the carbs now? Did you use any kind of gasket sealant anywhere? Silicone RTV gasket maker products are not good to use--I was going to say on carbs, but they're not good anywhere on the bike (not sure what you DO use them for). They have a tendency to have pieces break off whatever you've put them on and go exploring in other places in the carbs/engine. A chunk of this can easily plug a jet/fuel line/oil passageway.

I see that you soaked the jets in carb cleaner and blew them out with compressed air. Did you do anything with the carb bodies?
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ArrowOfTime
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby ArrowOfTime » Tue Feb 13, 2018 7:57 pm

Hi everyone, I'm back with some good news... and more questions ;) .

I followed the advice and did things the slow and steady way, following that carb cleaning guide to the t. I finally got the carbs on again yesterday and was very unhappy when gas started to pour from the overflows... even from one of the throats. I let it sit until this afternoon and now not a leak to be seen! I guess those new gaskets and o-rings needed some gas to expand into position?

Anyway, I got the bike started and it sounds great. The response to throttle is much snappier. My only issue now is that it needs a bit of choke to idle. I suppose this means its running too lean. I'm running it with the air filter cover off. Maybe it could be as simple as covering that up? Or the sync just isn't right? I've only bench sync'd it. Possibly some playing with the idle mix screw is needed?

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Folsoml
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby Folsoml » Tue Feb 13, 2018 8:08 pm

Whenever you reinstall the carbs, have something like a large screwdriver handle ready. When you turn on the fuel, start tapping on the float bowls with the screwdriver handle. This will help the needles seat that first time (not a problem after that). The leaking you describe is pretty common, and nothing to be concerned about (once you address it).

Have you tried adjusting the idle using the black plastic knob on the bottom of carb 2? Ideally, it also needs the airbox cover as well.
Have a problem with your CB650? Have a technical question? Click here!


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GeorgeSweety
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Re: Just Cleaned Carbs First Time, Now Having Trouble Starting the Bike

Postby GeorgeSweety » Wed Feb 14, 2018 2:34 am

Folsoml wrote:Whenever you reinstall the carbs, have something like a large screwdriver handle ready. When you turn on the fuel, start tapping on the float bowls with the screwdriver handle. This will help the needles seat that first time (not a problem after that). The leaking you describe is pretty common, and nothing to be concerned about (once you address it).

Have you tried adjusting the idle using the black plastic knob on the bottom of carb 2? Ideally, it also needs the airbox cover as well.


This^. Don't try to fix a problem that may not even be a problem yet, put your airbox cover on before investigating if its running rich or lean because it will have an effect on the outcome.


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