Bypassing CV carbs vacuum controlled petcock

[idorsey]

Hey guys, what's up?

I bought a 1981 cb650 earlier this summer and I've been working hard on getting her in shape. I just finished with the carbs, and tried starting but no fuel got to the carbs. It escapes the tank fine and the hose is good, I think the problem is at the automatic fuel shutoff on the carbs that requires vacuum. I have 2 different parts for this, I bought some spare parts with the bike. I have tried both with the same result. Here is a picture of what I'm talking about: http://imgur.com/0gtURRt

From all the advice I've gotten it seems like a good idea to just bypass this. I already have the habit down of turning off the petcock when parking. How do I bypass it?

Thanks!

[cb650]

Take it off. Run new fuel line. Plug the #2 carb vacum port. And you might as well clean the tank out!!!!!

[idorsey]

Awesome, I'll do this tonight. So I won't need either of the parts in the picture? I just connect the tank line to the port between carb 2&3?

[cb650]

no There shouldnt be 2 on the bike. Dont know the story on the pic. Make sure you petcock works good and get in a habit of shutting it off at nite.

[idorsey]

no There shouldnt be 2 on the bike. Dont know the story on the pic. Make sure you petcock works good and get in a habit of shutting it off at nite.

Only one is connected to the carb, I just put them next to each other for comparison. I actually have no idea where the part that is connected is from, based on the manual the roundish vacuum petcock is stock on this bike.

(Edit I just realized its the same part, but one was put together wrong.

[idorsey]

So I took of the vacuum petcock and routed my fuel line directly into the center port. Only issue now is that my hose is too long. I have to turn my petcock, which leaks in this orientation, but not when facing the right direction. Is this normal? Here is what it looks like: http://imgur.com/R4qUcKv

So now I need to cut the fuel line. I was wondering if anyone had suggestions for how one might do this with a laymans tool set. I have box cutters, scissors, straight razors, but I'm thinking I might need more than that to get a clean cut. Should I just take it to an auto parts store and have them cut it?

Thanks!


Also, before I forget I have another question. My connection from the carbs to the airbox does not seem airtight. Even with the fasteners tightened I can slip them off with a small bit of effort. The rubber overlaps the carb but I am not sure if it is 100% air tight. The engine boots are air tight. Should I be concerned with this?

[cb650]

If you took out the vacuum shut off youll need to replace the fuel anyway.It should be to short if I remember right. study a diagram closely. there are 4 lines going to the shutoff. Be sure you hook up the right ones. sharp scissors work well on fuel line.

[idorsey]

If you took out the vacuum shut off youll need to replace the fuel anyway.It should be to short if I remember right. study a diagram closely. there are 4 lines going to the shutoff. Be sure you hook up the right ones. sharp scissors work well on fuel line.

I ended up using the fuel line from the tank to vacuum shut off as the line from the tank to the port between carbs 2 & 3, which is why it is too long.

In other words, using this image for reference : http://www.cmsnl.com/honda-cb650-1981-u ... ml#results
I replaced part 3 with part 7. As for the 4 lines, one goes to the vacuum port between 3&4, the other was just an exhaust line (part 5) that got routed to the air box, and the other two lines are part 3 and 7. Given that I plug the vacuum port (removing part 4), that should leave me with one fuel hose (part 7) after removing the vacuum shutoff, because the exhaust line (part 5) and part 3 have been eliminated.

Does this sound right? thanks again for all of the help.

[cb650]

Yes thats right. just cut the line. Been a long time scene I did it and replaced the line anyway. FYI the vacuum is between 1&2. Cyls are numbered as you sit on the bike going left to right.

[Volker_P]

Welcome here!

So now I need to cut the fuel line. I was wondering if anyone had suggestions for how one might do this with a laymans tool set. I have box cutters, scissors, straight razors, but I'm thinking I might need more than that to get a clean cut. Should I just take it to an auto parts store and have them cut it?

I would just cut it with a sharp knife on a piece of wood.
But if you really need a really clean cut: wrap it with some layers of tape and cut it together with the tape.

If also the inner side should be important, you may just cut it some millimeters too long.
Then insert some fitting plastic tube/stick and again wrap it outside and cut the whole thing. Best cut one can do.

Getting out the inner support without making the tube bad again is the remainig task left for exercise.

[idorsey]

Okay I've got it cut to a good length. I thought the reinforcement on the fuel line was metal but it turned out to be fabric so it was easy to cut.


I'm waiting on a battery to try starting her, at which point I think i will have more questions.

In the mean time, I was wondering if anyone might know where to get a new choke cable? Bike Bandit doesn't seem to offer a size that fits the 650, according to the compatible bikes on all of their cables.

Last question(s): What is a good process for starting a bike that hasn't been started in a while? How much time is too much on the starter button? How much should the throttle be pulled? Is starter fluid a good idea? Should I use choke, and if so, should I pull it before the start or during/after? In a clean environment what are the implications of not having an air filter in the bike?...actually my last question is what kind of air filter do you use/recommend?

thanks a lot! I think I might have a running bike by next weekend.

[cb650]

good battery and turn of the the kill switch. Get oil pressure before it starts.

[idorsey]

So I found a video that shows a cb650 start up after a long hiatus.

http://www.youtube.com/watch?v=nY60C_nv4pk

I've tried starting it before, but I definitely didn't do it as long as he attempted it there for two reasons, 1. a fear that I would burn up my starter and 2. the fact that my battery is close to death and is only good for x number of start attempts while being jumped by a shut off car before dying. (I'll have a new battery by next fridayish)

Anyways....it seems based on the video (and I don't know if this is best practice or not) that I should try 3-5 second intervals on the starter button and make sure the red oil light is not on if it begins to idle?

Edit: Also, I'll be cleaning my tank out this week
...Another edit...What if my vacuum port seems to be on the opposite end of everyone else's that I'm seeing online? See second picture down for an image: http://imgur.com/a/Ok7IO

[entropy]

Hmmm. My '81 CB650C (which is 99.8% identical to the CB650) shut-off has the vacuum port on the rear and a completely different shape. It looks more like the one on the right in this earlier picture you linked, but with the port facing rearward instead of coaxial with the fuel lines. For all I know, though, the one on my motorcycle could be a part from another bike just as easily as yours could. I can post a picture if you like, but sounds like you're pulling yours off, anyway.

[Volker_P]

Last question(s): What is a good process for starting a bike that hasn't been started in a while?environment what are the implications of not having an air filter in the bike?

See viewtopic.php?f=4&t=727&start=9

actually my last question is what kind of air filter do you use/recommend?

A clean one?
Beyond that, a stock filter avoids jetting problems although CV carbs are not that susceptible to that.