Author Topic: cb650 wont stay running (Read 2860 times)

Thor0812 · « **on:** June 12, 2009, 07:23:01 PM »

Finally got the bike started tonight. 79 cb 650, pod filters, 4 to 2 straight piped with drag baffles. Jets have been changed to 110. When it finally started it will stay running with choke on. When I hit the throttle it bogs and sometimes dies. The short time it will idle without the choke on, any contact with the throttle and it immediately dies. Any ideas guys??

Frankenkit · « **Reply #1 on:** June 12, 2009, 07:50:53 PM »

probably your transition from the notoriously lean idle jets to the running jets. Part of it could be dirty idle jets, part of it could be the fact that 650s honestly just love being choked like hell for quite awhile. I start mine up with full choke, even in the summer. It takes a couple minutes, then the idle starts to climb to 2k. I nudge the choke in a little until rpms drop to 1.5k. When it makes it up to 2k again, I drop it down another nudge until I'm ready to go, and everything is sounding warm enough. I leave with the choke out just a bit to improve throttle responsiveness immediately after leaving, but once I'm on the road far enough that I know I won't have to stop for lights within a mile or two, I can put the choke knob all the way in and not worry about it dying on me at a light.

I'd give it a good five minutes, nudging the choke down the way I described and see if it takes choke better for you.

Thor0812 · « **Reply #2 on:** June 13, 2009, 06:01:16 AM »

Cleaned all jets when I reassembled. I will try a long choke run today to see if that helps. Any other ideas?

Inkscars · « **Reply #3 on:** June 13, 2009, 06:10:02 AM »

What jets were in there to begin with?

Frankenkit · « **Reply #4 on:** June 13, 2009, 08:46:24 AM »

unless I'm wrong, the '79 has press-fit 35s that you pretty much can't replace, (although someone, somewhere online actually drilled and tapped the hole it pressed into to accept screw-in jets, but I don't know that I'd that hot to try it...) and I think 95 (?) or 98 mains. I dunno. my bag o' parts is out in the garage.

Inkscars · « **Reply #5 on:** June 13, 2009, 08:58:36 AM »

It's gonna be bad, I'm gonna be used to the PDs. They aren't so bad once you've been in there 7 times.

Frankenkit · « **Reply #6 on:** June 13, 2009, 09:02:20 AM »

my feeling exactly, Ink.

I've actually put allen head bolts in the bottoms instead of phillips so I can a) take them apart over and over again without stripping the head b) unscrew them with a bent allen key without even taking the buggers off the bike. In fact I just did that to put the spring in my accelerator pump. (who forgets that?!) oh wait... I did.

Thor0812 · « **Reply #7 on:** June 13, 2009, 01:28:16 PM »

Made sure everything was nice and clean when apart. The original mains were 90's. The idle jets are press in and i dont know if I can get larger ones. Don't know how much larger I can go on the mains

Inkscars · « **Reply #8 on:** June 13, 2009, 01:34:32 PM »

Did you adjust your needle height to compensate for the pods and exhaust?

Thor0812 · « **Reply #9 on:** June 13, 2009, 04:03:13 PM »

Ok feel like a retard now. How do I go about that on these carbs?

scunny · « **Reply #10 on:** June 13, 2009, 04:23:26 PM »

I'm running 105's with pods and 4into 1, no problems with this set up(79 650)
EDIT have you over oiled your filters, and check your float heights.
the 650's don't have adjustable needles but I'm sure they could be shimmed

Thor0812 · « **Reply #11 on:** June 13, 2009, 04:57:56 PM »

ok so what do i do about the float height?

?

Thor0812 · « **Reply #12 on:** June 14, 2009, 12:53:27 PM »

elp me with how to properly set the float height???

Hush · « **Reply #13 on:** June 14, 2009, 01:59:56 PM »

OK you have a 79 650 like mine so you will have the brass tongue between your floats, this is the thing you are going to adjust.
If you don't want to remove the carb rack (and who does) you are going to be doing it while they are hanging in space so it's a lot of eyeometry.

I drop the bowls off all the carbs (replacing those crappy cross head screws with allan/hex screws helps and makes you less worried about dropping the bowls off again) lift the float with your finger and see where it begins to push against the float needle valve (wee pointy thing that shuts off the gas flow).
I set mine just as the brass tongue contacts the spring loaded end of the float needle valve as the pressure of gas pushing up the floats will shut it off from there once they are all back together.
Setting them simply means bending the wee tongue up or down to find the right height, this is a very unscientific way of setting them but I have yet to find a book/manual that covers this proceedure.
I guess the Japanese didn't expect us to have to fiddle that deeply with their carbs.
If they all "LOOK RIGHT" when you take the bowls off and all seem to contact the float valve at the same point then you should probably leave them as they are more than likely correctly set and your problem lies elsewhere.

Thor0812 · « **Reply #14 on:** June 15, 2009, 04:17:53 AM »

Quote from: Inkscars on June 13, 2009, 01:34:32 PM

Did you adjust your needle height to compensate for the pods and exhaust?

How would this compensate for my add on's? Allow more fuel in the bowl?

Hush · « **Reply #15 on:** June 15, 2009, 04:36:25 AM »

There's a formulea for this somewhere, when you add pods you need to move the needle valve up or down, can't remember which but should be in the FAQ's section.

http://forums.sohc4.net/index.php?topic=5410.0

Thor0812 · « **Reply #16 on:** June 15, 2009, 04:22:12 PM »

Adjusted the floats and the mix screw. Started and idled better but still bogs down. Is there anyone who has found a way to open up the idle jets?

Frankenkit · « **Reply #17 on:** June 15, 2009, 08:38:28 PM »

There's some discussion about it, but with the stock settings it should still start and run okay for you unless it's bitter cold.

Hush · « **Reply #18 on:** June 16, 2009, 03:56:47 AM »

What are your carb isolators like, those are the rubberish tubes that run between the carbs and the head, if they have leaks or are not tight the air mix will be too lean.
Have you pulled out your advancer unit, most 650 ones are rusted and dry and need taking apart and greasing to improve acceleration after years of neglect.

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Author Topic: cb650 wont stay running (Read 2860 times)

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