Topic: 79 650 Poor Performance, Tried Almost Everything, Running out of options :(

[andy2108]

Hello, I'm Andy. I got a great deal my 79 CB650 (in really good, completely original, condition -- although not running)  this summer and I've enjoyed having it.  The great community around these bikes helped make my decision to get a CB.  I've used the knowledge here to learn about what I can do to get the bike running well but I'm running out of options so I'm going to go ahead and make my first post.  Lets get to it.

1979 CB650 15k miles, brown, all original barring deleted blinkers, looks to be taken care of and garaged
Previous owner in North Carolina said when he bought it it was smoking so he opened the engine down to the jugs to take a look around, this is how I bought it
Me and my engine friends did our own inspection, found one bad valve (seat or guide, can't remember), so we just got a used head from a known running bike
Slapped together, did cold compression test. results: 145, 95, 130, 145   (cyl 1,2,3,4)   Not great but rideable.

Got it running, but not very well. I've ridden it a couple hundred miles. Here's what I've done to try and fix it:

new battery (charging system seems to work great)
new top end gasket kit (exhaust gaskets too)
new plugs, oil, oil filter, air filter, other little small maintenance stuff.
tank is pretttttyy clean, flows very freely out of the petcock
tried driving around with the tank cap off, made no difference
validated timing seems to be correct with a light, and the advance is working, based on the shop manual
valve adjustment
checked for spark
moved wires around to different cylinders to see if it runs any different
new carb-to-head boots "isolators"
Thoroughly Cleaned (like three times) and rebuilt the carbs (did this very early on)
-new rebuild kits
-new idle mix needles
-unracked carbs, new accel pump diaphragm, fully blocked off the air cut off valve circuits, removed and cleaned slow and main jets
-set float height according to the shop manual
-yes still has stock airbox and jets, 95 mains, with a new filter and everything in order

I have not yet done:
a proper carb sync with gauges or water, although I did inspect the slides and they seemed to be close
another compression test, after riding it a couple hundred miles
checked ohms of plug wires and coils
check fuel level in the bowl with clear tube
check exhaust temperatures with IR temp gun
check plugs for color

Symptoms (which, for the most part, have always been true ever since I got the bike, despite all this stuff I've been doing to it):
Starts fine, 80% of the time
Doesn't Idle great, so I have the idle set a bit high, around 2,000 to be able to drive it around without stalling
pops and backfires on cyl 3 or 4 quite a bit, and sometimes 1 or 2. really under any conditions, starting, idling, driving, not ever on deceleration though
when removing one spark wire at a time while the bike it idling, some wires when removed make the bike stall almost immediately, while other wires sometimes can be removed and the bike will run basically the same. This is a bit intermittent though so hard to say. Upon visual inspection it might have been possible that some plugs had stronger spark than others, but hard to say using the method I was, while also trying to not get shocked.

THE REAL PROBLEM:
This bike is not performing as it should. Ever since I got it it never has performed as a 650 should.  It drives like its only got 125cc's between my legs  -- and I drove my buddy's GROM yesterday and it was a bit quicker because of the weight and gearing ect.  A 49 cc child's dirt bike walks me from 0-10 mph. The only condition where this bike feels like its not running bad is 75% throttle between 5-7k rpm.  I don't think that's right. 

So after all I've done I feel like I'm starting to run out of options. And yes, my carbs are clean. I'm tempted to spend the $70 on a new set of coils and wires but I haven't seen a lot of posts about how that's fixed a problem like mine for much of anybody. I'm still not in the bike for more than it's worth so I wouldn't feel too bad about throwing another $70 at it at this point.  On the other hand, it might just be that the compression is too low for this bike to be anything. In which case, I'll wait till winter, pull the jugs, do a quick dingle ball hone and re-ring it.  Or I could always just walk away from it and make money on it.

This has probably gone on long enough and it's late now. Please let me know if there are any more ideas out there.  Thank you! -Andy

PS: I'll post some pics tomorrow

[Bodi]

Agreed that if the bike doesn't run A LOT poorer with a plug wire removed, something is really wrong... pulling one plug kills two cylinders unless you ground the removed wire (actually it's a good idea to touch it to ground directly or through a spare plug, leaving it hang encourages HV arcing through the cable insulation somewhere under the tank).
And yes - the electronic ignition triggers and/or "black box" have caused lots of problems. Coils - not so much trouble, but you can swap the coils (probably you need to physically swap them so the plug wires will all reach) and see if a problem goes with a coil.
Carbs... it's been accepted wisdom here for a long time that aftermarket (Keyster etc) carb brass parts are NOT equivalent to the Honda/Keihin OEM parts. Jets basically do not wear and don't need replacement, just clean them thoroughly and reinstall. The needle and its emulsion tube orifice do wear from contacting each other - but very slowly in normal use. If replacements are needed for wear or to tune the carbs (for pods, big cam, overbore or freeflowing exhaust) you should use OEM parts if they are available. If you must use aftermarket jets or needles... expect to have issues with carburetion.

[Chamwow]

I had the same performance issues to a T of how you are describing them with my 79 cb650. I did most the upgrades and services you did also.

Long story short, one cyclinder wasn't firing on my bike (cylinder 2). The previous owner had wired aftermarket coils incorrectly (left and right coil wires switched) as well as run the spark plug wires incorrectly.

I ordered new coils (not knowing if one of my coils was bad before I realized they were wired improperly), installed them according to the shop manual, and run the plug wires in the proper firing order (1,4,2,3) as before they were wired (1,2,3,4).

Now she runs on all four, idles at 1.4k easily, and is nearly twice as fast.

Check out if all your cylinders are getting spark. What I pinned as carb issues the whole time I had my bike turned out to be ignition. Drop some water on all the headers and see if any are cold. You can test for spark with a $5 spark plug light like I did or simply take a spare spark plug, plug it into the wire, and hold it close to the head to see if a spark arcs. 

 Test all 4, check if your wires are run correctly, and eventually check if it's the coils. If it isn't a problem there you might have to go and replace your cdi.

[andy2108]

Hey  all, thanks for the replies so far.

I assume my ignition hasn't been monkied with much. Everything looks very original. HOWEVER. The previous owner reported some electrical issues which he repaired.  So he had done some electrical repairs. Unfortunately I don't know what these electrical repairs entailed.  Considering my #2 and #4 are both so cold, is it possible their wires are switched and my bike is running on only two cylinders? This would mean half the power strokes are receiving ignition and half are not...


After reading the suggestions this morning I went out and tried a couple more things, mainly measuring the continuity of pulser leads (blue and yellow).  Blue measured 491 ohms, and yellow measured 492 ohms.  Seems like that's checking out ok.

I then started it up and measured the temperature of the exhaust runners with a thermocouple. Results (deg F): 300, 90, 260, 75.   (1,2,3,4) (ambient temp of about 45f)

Cyl 4 was super cold so I pulled the plug boot to check for spark and got shocked a a few times as I tried to fit my automotive spark plug in to ground against the block, so there is some spark there.

Next I found a clear tube and connected it to the #4 bowl drain and raised the tube up to see where the fuel level was.  The level seemed pretty low, like almost an inch lower than it should have been. But fuel flowed freely out of the tube when lowered. Then I went over and checked the cyl 1 level and it seemed to be where it belonged. Then I got on the bike and moved it left and right and checked #4 again and still low. Maybe this difference describes why cyl 1 is running at operating temp and cyl 4 is cold. 

I just learned this clear tube trick last night before I posted, so tonight maybe I will drop the #4 bowl and bend the float up and see what happens?

EDIT: Thinking more about my clear tube check... I certainly shouldn't have done it with the bike on the kick stand because the angle the bike is at will change the apparent float level. I should probably try this again on the center stand.

[andy2108]

FANTASTIC NEWS!!!

I switched the #2 and #4 plug wires and now the bike is super fast! woo hoo!

I'm not entirely sure what's wrong, if either I had the wires wrong all along or if craiglist guy botched something in the harness, but in either case its seems to be running very well now.

Had it been wired like this all along I probably wouldn't have messed with the carbs at all 

[andy2108]

looks like four months ago when I first got the bike my engine buddy made an assumption about how the plug wires were supposed to be connected... and after double checking the manual just now... his assumption was wrong. dang. 

[seanbarney41]

thats one of those don't know whether to laugh or cry moments

[evinrude7]

good news.  it's always the simplest #$%*ing thing. 

[Chamwow]

This was the same thing that was wrong with mine.  My fault for not noticing until now. But man, what a sigh of relief. Good to hear you have it running on all 4 again. Check the float height adjustment as well.  I adjusted mine recently and it's running as good as I could have ever imagined.

[Chamwow]

Glad to hear you've got it sorted out!