Topic: CB650 Only running on 3 cylinders.

[sloppydawg123]

I got this bike as a project, and cleaned up the brakes, and cleaned out the carbs thus far, not it stats a lot easier and revs up quickly, but cylinder 2 doesn't seem to be working. Cylinders 1,3,4 are all hot, and I can put my hand on cylinder 2. There is smoke coming out of the 1-2 exhaust side, but not really out of the 3-4 side. Also exhaust 1 seems hotter than 3/4. Any suggestions on why 2 isn't heating up? All sparks look the same, no oil around the threads on spark plus two, looks clean. Thinking hasn't been firing since I've started the project, maybe something to do with the gas accelerator pump? Still not sure on how that works. Any input would be great.

[Spanner 1]

First step would be to try a new plug in #2...or do two steps in one and swap #3 plug and plug wire into #2 cyl. and ( obviously! ) #2 plug and wire into #3. If the prob. is now the #3 cyl., then the plugcap and/or plug is bad....... more possibilities, but try that first....and welcome to the one-and-only SOHC/4 Forum !!

[sloppydawg123]

Tried switching boots, and it's the spark plug that was in cylinder 2 that doesn't seem to work. It sparks against the block, is gapped the same (~.027) as the others, looks fine. Is there some spark plug attribute that it could be missing? I mean besides model and spark what else could it be? Didn't matter which boot was on it, that plug was cold either way.

[Spanner 1]

A plug can spark in the open air quite happily, but not in the cylinder under the compressed air/fuel mixture....need to just change it...should be a NGK D7 as far as I know.
However, if the plug is coming out of #2 and is dry, then it's a carb issue.. but try a new plug first...shoot, change 'em all while your at it.....

[sloppydawg123]

Just cleaned all the carbs, and if cylinder 2 is fine with the plug from cylinder three, puts the focus on the plug, have to get some new ones tomorrow and see if it solves the problems of the world.

[Gorms]

How "clean" are the carbs?  Did you make sure the idle and main jets are  clear?  Sure carb #2 has gas in the bowl?  When I started my cb550 engine for the first time, cyl 4 wasnt firing even though I had spark.  Later that day it just started firing and has been fine since.  Has the engine been sitting or not run in a while?

[sloppydawg123]

Bike was stored for 28 years, only has 2500 miles on it. But since it works with the other plug, pretty sure it's the plug. And went through the carbs pretty well, soaked, scrubbed, sprayed, dried, sprayed again for peace of mind, dried again. Tested, retested.

[Gorms]

...missed the part about it working with other plug.

[Hush]

650 plug is NGK D8EA well tis in NZ.

[BVCB650]

Yes, an #8 plug is stock in a 650, but I am getting ready to install 7's since it is getting below the majical 41* now.

[Buber]

Save yourself troubles, and install iridium plugs. 7$/pc on ebay.

[sloppydawg123]

New plugs didn't solve the problem. Running out of ideas, if there a way to check the coil to see if it is good, or any ideas of what may be dropping one cylinder?

[BVCB650]

New plugs didn't solve the problem. Running out of ideas, if there a way to check the coil to see if it is good, or any ideas of what may be dropping one cylinder?

You can always switch coils to see if the dead cylinder changes with the coil.

[Frankenkit]

Save yourself troubles, and install iridium plugs. 7$/pc on ebay.

+1
I had a weird hiccup while the bike was starting/warming and it disappeared after the iridiums.  Beyond that, though, they warm up a lot faster than having to swap between 7s and 8s according to temp.

Does 2 seem to fire when you roll on the throttle and up the RPMs?  If so, then you're looking at a clogged idle circuit... but  if it's cold all the way 'round then (since we've explored a lot of our spark options) I'd look at the float level on 2.  They can be fiddly. Too high and you run rich, overflow, blah blah.  Slightly too low and it never seems to pick up gas on the idle circuit, but as the running circuit is 'taller' and scoops further into your float bowl, you can still get gas that way.  Really mimics a clogged idle circuit, too.  This is really only handy when you're low on gas and can get the last dregs of the bowls by opening 'er up all the way.

Beyond trying the plugs, did you try new plug wires?  If it just sat there, it might've oxidized the insides.  In a pinch nip off the leading 1/2" from either side to get to fresh copper and try again.  Once you get 'er figured out and working you're going to want to coat this bugger in dielectric grease.  These bikes have major electrical weaknesses, and a little di grease will go a long way in fixing and preventing them.

I wouldn't say this is a coil problem just bcause when a coil drops out, you lose two cylinders.  In this case, 3 wouldn't be firing right, either.

[sloppydawg123]

Seems like I may be incorrect in my assumption, don't think 2 is firing well when 3 isn't and vise versa. After all new plugs were put in, 2-3 didn't color up like 1-4 did, and if you disconnect 2 and 3 it doesn't change rpm/sound, anything really. also if you switch 2/3 coil to 1/4, 1/4 still run fine and 2/3 still don't. Maybe something with the pulse generator? Took the cover off looks like new. Trying to read up on how to test it now, or spark units? Connections, possibly plug wires on 2/3, seems a little strange both would fail like that

[cb650]

Along with the pulse gens you have the ignitors under the seat.

[BVCB650]

Save yourself troubles, and install iridium plugs. 7$/pc on ebay.

+1
I had a weird hiccup while the bike was starting/warming and it disappeared after the iridiums.  Beyond that, though, they warm up a lot faster than having to swap between 7s and 8s according to temp.

Does 2 seem to fire when you roll on the throttle and up the RPMs?  If so, then you're looking at a clogged idle circuit... but  if it's cold all the way 'round then (since we've explored a lot of our spark options) I'd look at the float level on 2.  They can be fiddly. Too high and you run rich, overflow, blah blah.  Slightly too low and it never seems to pick up gas on the idle circuit, but as the running circuit is 'taller' and scoops further into your float bowl, you can still get gas that way.  Really mimics a clogged idle circuit, too.  This is really only handy when you're low on gas and can get the last dregs of the bowls by opening 'er up all the way.

Beyond trying the plugs, did you try new plug wires?  If it just sat there, it might've oxidized the insides.  In a pinch nip off the leading 1/2" from either side to get to fresh copper and try again.  Once you get 'er figured out and working you're going to want to coat this bugger in dielectric grease.  These bikes have major electrical weaknesses, and a little di grease will go a long way in fixing and preventing them.

I wouldn't say this is a coil problem just bcause when a coil drops out, you lose two cylinders.  In this case, 3 wouldn't be firing right, either.

Did your bike fail to start when cold or was it just a little miss? I priced the Iridiums at NAPA and they will be the same as ebay with shipping. I about froze my fingers off today with just a short exposed ride to the store. It was 38* here today.

[sloppydawg123]

Does seem to matter what I do coil/plug/boot wise, 2 and 3 just don't want to run well. And if I swap coils they still don't has to be the signal coming in or something, since the 1 & 4 work on either coil. Any advice for testing pulse generator and spark units?

[BVCB650]

Does seem to matter what I do coil/plug/boot wise, 2 and 3 just don't want to run well. And if I swap coils they still don't has to be the signal coming in or something, since the 1 & 4 work on either coil. Any advice for testing pulse generator and spark units?

Look here for all your ignitor needs.

http://www.jasonkent.ca/cb650manual.htm

[sloppydawg123]

Checked the sparks according to the manual, put a plug on the engine, and touch the piece on the pulse generator with a screwdriver and they all spark strong. will bridge almost a 1 cm to the engine block if you hold it away. This supposedly means that the pulse/spark unit/ coils are all good. So still wondering why 2 & 3 just aren't firing, does it seem like it could be a timing issue on that side of the pulse generator?

[Spanner 1]

I think were back to carb issue....are 2+3 plugs wet ( with fuel ) when you take them out after running the bike for a min. or two ? Probably not. Are 2+3  idle/slow jets and their air bleed passages clear ? Are 2+3 float bowls full ( to correct level ) with fuel ?...some ideas.

[sloppydawg123]

I cleaned the carbs pretty well, be surprised if it was one of those issues, and just opened the drain screws on 2 & 3, both were full of gas. Also sounds like a chattering coming from the exhaust, would that be a valve issue? Also what would be the symptoms of a stuck valve or something that would result from 28yrs of storage

[Hush]

You can check your valves are opening and closing by removing the valve covers, turn the bike over by hand and watch the cam lobes rise and fall the valves.
Maybe a PO did a lousy job of resetting the valves, might pay to check.
Otherwise I'm wondering if the accelerator pump (since it is only attached to #2 is rusted or the diaphram broken, I bought a spare set of carbs and the diaphram was like biscuit, crumbled into dust.
But if you had that apart and it was OK ignore my last.

He has gas, he has spark......we've been down this track before and it was something really really basic that stopped the bike from running!?

[sloppydawg123]

I think I'll do a compression check tomorrow to see what it says. And originally it was not running on 2, then i switched plugs from 2 and 3 and now it's either doesn't run on 2 and 3, or just doesn't run on three, even though all plugs are new. Not sure what else can be, sparking strong, seems like all ignition stuff is correct, the accelerator pump seemed a little firm, but not sure what it should feel like, and given that it's not running on three doesn't seem like the culprit. Possibly poorly done float levels? Except they do have gas, and even when i hold it at 4-5k rpms cylinder 3 won't warm up. Running out of ideas. Does it seem like 2 & 3 could be timed incorrectly?

[Hush]

I remember now, 650 with same problem, turned out the PO had set the slides at zero clearance and the bike was getting nil air.
As you have pods this is a bit easier to check, slip the #2 and #3 off and check that the carb slides are not fully at the bottom of their travel, if they are, remove the tops of the carbs and wind them up a bit so you have about 3 mil (rough as I know) clearance from the bottom edge of the slide to the carb floor, now try startring it.
If you have recently paid good money to have them professionally synced, please ignore this as well.