Author Topic: CB650 Urgent I think cylinders 3 and 4 are not firing!!! (Read 8202 times)

checkflag · « **on:** July 17, 2009, 12:24:33 AM »

I was riding home last night and at a stoplight I looked back at the smoke
that was illuminated by a cars headlights i'ts only smoking on one side. When I
got home a put my hands in front of the exhaust and the side I saw smoke from
is warmer than the other side, and accordingly, the headers were also hotter to the
touch. (ouch) on the same side.

The smokey/hotter side is the left side.

Please tell me, What the heck is going on? should I be worried?

checkflag · « **Reply #1 on:** July 17, 2009, 02:06:38 PM »

Please .. anyone..

IainC · « **Reply #2 on:** July 17, 2009, 03:42:48 PM »

If you could get a video with sound I'm sure someone would be able to tell if it sounds okay. Does it seem to be driving odd, or just a couple cooler pipes? Have you done any work recently that could have affected how it runs? May be in need of a tune up, have you gone over the bike and adjusted all the basics this year?

cb650 · « **Reply #3 on:** July 17, 2009, 04:21:22 PM »

It could be a number of things. I have a hard time sorting my own bikes out sometimes. One ? though. Do you let it idle on the sidestand?

checkflag · « **Reply #4 on:** July 17, 2009, 04:43:18 PM »

Quote from: IainC on July 17, 2009, 03:42:48 PM

If you could get a video with sound I'm sure someone would be able to tell if it sounds okay. Does it seem to be driving odd, or just a couple cooler pipes? Have you done any work recently that could have affected how it runs? May be in need of a tune up, have you gone over the bike and adjusted all the basics this year?

Heres a video I took just 10 minutes ago. I had just replaced all 4 spark plugs.

Quote from: cb650 on July 17, 2009, 04:21:22 PM

It could be a number of things. I have a hard time sorting my own bikes out sometimes. One ? though. Do you let it idle on the sidestand?

Yeah.. like to warm up and stuff. It never idles for very long on the sidestand though.
I rarely use the centerstand because I have a hard time getting the stand all the way down.

manjisann · « **Reply #5 on:** July 17, 2009, 05:02:34 PM »

I could be wrong but it sounds like your cylinders are fighting eachother. Have you checked your float heights to ensure that they are the same height and also to the correct height? I had messed with mine on my 500 and had the floats at diff heights and at idle it was pretty rough, once I adjusted them to the correct height it idled much better. This could also explain some cylinders being hotter than others, the ones getting more fuel will be hotter than the ones being starved (I think, could be reversed.)

Also, if you haven't vacuum synced your carbs during a tune up that could also be a cause.

Are 3 and 4 getting warm at least? It didn't sound to me like you were only running on 3 cylinders, as I've also experienced this, and it is extremely rough at low rpms.

HTH,

Brandon

checkflag · « **Reply #6 on:** July 17, 2009, 05:06:46 PM »

Thanks Brandon.. All I know about these carbs is that they sat for 25 years.
The guy i bought the bike from said he cleaned them and vacuum synced them.

I personally think he may have gotten most gunk out, but didn't do a real
thorough cleaning.

It seems that the right hand exhaust is not even exhausting.. I only see exhaust smoke coming from the left. only cool air
comes out of the right

Brandon, did u happen yo get a shipping quote?

manjisann · « **Reply #7 on:** July 17, 2009, 05:10:49 PM »

Just pm'd you with some info, just wanted to make sure it will all work before I box it all up.

You could try running some Seafoam through it, but in all honesty it really sounded like the carbs needed adjusting. Hopefully someone else will come along and be able to give you a more definate answer, this is just what it sounded like to me. Were pipes 3 and 4 warm but just not as hot as 1 and 2?

Brandon

checkflag · « **Reply #8 on:** July 17, 2009, 05:17:13 PM »

thats right.. 3 and 4 were warm.. but 1 and 2 sizzle! (saliva on finger)

manjisann · « **Reply #9 on:** July 17, 2009, 05:21:54 PM »

Have you checked to see if you get really good spark on those cylinders? Something you could try real easily to check to see if it's electric is switch the wires on 1 and 4, 2 and 3. If 3 and 4 suddenly heat up and 1 and 2 are suddenly cool, you'll know it's your coil. I am still thinking it's the carbs, but lets try the easy stuff first. obviously when you are done switch them back, label them so there is no confusion if you think it would help.

Brandon.

cb650PK · « **Reply #10 on:** July 17, 2009, 07:36:20 PM »

I see pilot jet cleaning in your future, but first make sure your spark plugs are not fouled.

checkflag · « **Reply #11 on:** July 17, 2009, 07:55:41 PM »

i installed new plugs today. some of the old ones were fouled, but #1 looked like it was burning good.
One other thing I noticed was a slow gasoline drip from one of the waste tubes by the swing arm. I think
its from carb #3

Hush · « **Reply #12 on:** July 17, 2009, 08:03:39 PM »

Sounds like your floats are either hanging (jamming) or are set slightly too high.
Carbs are a #$%* on all the SOHC4's and one thing I can reccomend is that when you get around to removing your carb bowls (and most of the skin on your knuckles) that you replace the wee evil cross head screws with allen key screws (do you call them hex key screws in USA?).

Makes removing them in the future really really easy.
A good habit to get into when stopping your 650 is to turn the gas off, sounds funny I know but it's a habit that will save you much grief in future when the tank decideds to empty all over your shed floor or the main street in town, for some reason (usually time to replace float valves) these things just let go every now and then, so good habit...turn to the "off" position when stopped.

manjisann · « **Reply #13 on:** July 17, 2009, 08:04:44 PM »

It sounds like your carbs need a cleaning. If you've never done it before it seems scary, but carbs really aren't that bad. Drain the gas. Working on one at a time, remove the float bowls, remove the floats and float needle, then shoot carb cleaner into every hole you can find until it comes out clean (I'd wear safety glasses for this.) Follow that by compressed air if you can. If you feel up to it, remove the jets and soak them in carb cleaner until they are clean and all the little holes are unblocked. An exploded diagram helps. This is the bare minimum I'd do.

Brandon

Hush · « **Reply #14 on:** July 17, 2009, 08:08:27 PM »

Also I agree totally with Brandon on this.

I could be wrong but it sounds like your cylinders are fighting eachother. Have you checked your float heights to ensure that they are the same height and also to the correct height? I had messed with mine on my 500 and had the floats at diff heights and at idle it was pretty rough, once I adjusted them to the correct height it idled much better. This could also explain some cylinders being hotter than others, the ones getting more fuel will be hotter than the ones being starved (I think, could be reversed.)

Also, if you haven't vacuum synced your carbs during a tune up that could also be a cause.

A decent tune up of the carbs will give you a much quieter idle and better accelleration, I'm crap myself with carb syncing so get my mechanic to do it, always a different bike when they are done.

manjisann · « **Reply #15 on:** July 17, 2009, 08:15:46 PM »

Quote

Also I agree totally with Brandon on this.

I always knew you were an agreeable fellow Hush

I bought an inexpensive vacuum guage from Z1, it's not the best, but after using it on my 500 it ran TONS better, idled like a top at approx 1000 rpm's once it was warm. Not saying it was racing synced, but for riding it was great. Personally I don't find carbs all that intimidating, the biggest key is a good diagram and taking lots of pics as you remove stuff. But that is just my opinion, and I've been considered crazy for quite some time

Brandon

checkflag · « **Reply #16 on:** July 17, 2009, 11:15:34 PM »

a little gas. (like a drop every 30 seconds) form the discharge tube

Hush · « **Reply #17 on:** July 18, 2009, 01:42:07 AM »

It's probably unburnt gas then because the carbs are out of sync, I can't reinforce enough the need to get them well balanced, it makes a massive difference to inline 4's.
If one cylinder is getting too much gas it wants to rev, if another is not getting enough it will want to slow down, so you see this concept (which took me forever to grasp) is vital that all cylinders recieve the same amount of gas at the same time or they will pull against each other and ruin the good running of your bike.

checkflag · « **Reply #18 on:** July 18, 2009, 09:07:17 AM »

I certainly hope it's just the carbs. I will call my friend
and see if I can't get him over to sync these for me.

What do u guys think about what I said about the gas
seepage from that single discharge tube? That can't be
normal. (carb 3 I think)

manjisann · « **Reply #19 on:** July 18, 2009, 09:18:07 AM »

Quote

What do u guys think about what I said about the gas
seepage from that single discharge tube? That can't be
normal. (carb 3 I think)

Desirable no, normal, pretty much

As Hush said, you have either a stuck float, a misadjusted float height, or there is some small bit of debris stuck between the float needle and the seat causing it to allow a small amount of fuel to always flow into the bowl even if it is full. You can try tapping it with a screwdriver and it might cause the stuck float to pop up, assuming that is what it is. Personally when that happens I just pull them off and clean all of them as I hate dealing with that.

Brandon

checkflag · « **Reply #20 on:** July 18, 2009, 10:45:10 AM »

uggh.. I had to jump start the CB today.. I left the key in the on position! what a fool I am.
Brandon.. Im pretty sure by concensus that it is most likely the carb's as well. I left a message
for a mechanic friend and am waiting to hear back.

I'm almost considering doing a CB750 carb swap (71-76). from what I have read.. it eliminates
the pressed in slow speed jet, and I suppose some other silly emission control thingamabobs.
Ultimately I want to delete the stock airbox system as well and get some UNI foam pods on there.

well, hey, This is my first motorbike, so its a slow process to learn and to improve.

tomsweb1 · « **Reply #21 on:** July 18, 2009, 10:46:51 AM »

did you replace your plugs before or after this problem? I replaced my plugs and it turned out that I had resistor plugs and caps. Apparently they weren't compatible. two cilynders wouldn't fire. replaced them with the proper ones, and all was good. Also, check your caps. Sometimes the resistors wear out, and cause non-fire issues too. YOu should have between 5k and 10k ohms. Yeah.

manjisann · « **Reply #22 on:** July 18, 2009, 10:49:10 AM »

Don't feel bad, I killed a battery a month or so ago because I left the key on. We're all new at some point (I keep wondering when that feeling will wear off

)

BTW, did you get the PM about the wheels?

Brandon

Hush · « **Reply #23 on:** July 18, 2009, 03:24:24 PM »

Just a suggestion Checkflag but that #3 carb that it weeping, take a screw driver and remove the drain screw, you can put a jar under the tubes to catch the flow of gas.
I've done this before and it has fixed that problem on my 650, probably was some junk in there causing float to catch, releasing the gas and emptying the bowl this way gives the float a chance to reset it self, as I said...just a suggestion but it costs you nothing and may work.

I also had a float puncture and sink on one carb, I ended up buying just an old float from a wreckers and that cured that too.

cb650PK · « **Reply #24 on:** July 18, 2009, 06:27:51 PM »

The 650 carbs are not really that bad in my opinion. Removing the pressed in pilot jets is not such drama, and once clean and sorted out, make sure you turn the petcock of, religiously. If I leave it on even for couple of days, there is a good chance, one of my pilot jets will be clogged. Also if your carb drain is leaking, make sure the drain screw is tight. If you are going to clean the carbs your self, I thing we all can provide some tips for easier carb removal and cleaning.

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Author Topic: CB650 **Urgent** I think cylinders 3 and 4 are not firing!!! (Read 8202 times)

Author Topic: CB650 Urgent I think cylinders 3 and 4 are not firing!!! (Read 8202 times)