Author Topic: fire out the exhaust ..help (Read 3628 times)

cb650 bobber · « **on:** April 14, 2008, 12:07:25 PM »

Went out to start the bike for the first time this year...started right up but then it started acting funny....had the choke the whole way out and it wasnt picking up idle like is ussually does....then it shut off...so I started it agian this time reved it up a couple of times and it stayed running for a little while and still sounded real slugish so i revved it agian and it shot flames out the back...pretty nice size....and I dont have a spark plug in the exhuast...

Badger 5 · « **Reply #1 on:** April 14, 2008, 12:09:54 PM »

Sounds cool to me. I say go with it

my78k · « **Reply #2 on:** April 14, 2008, 12:12:05 PM »

Any chance a critter built a nest in the exhaust over the winter?

Dennis

cb650 bobber · « **Reply #3 on:** April 14, 2008, 12:15:10 PM »

that is why i was asking about the fuel filter it almost sounds like it isnt getting enough gas...maybe the exhaust is plugged. I dont think anything built a nest in the winter it was in my basement keep the ideas coming I am checking everything tonight.

Geeto67 · « **Reply #4 on:** April 14, 2008, 12:18:11 PM »

well if you are as young as I think you are, then you probably have no real expirence with carb'ed vehicles. Welcome to the stone age with your first real out the exhaust backfire.

Exhaust back fires (as opposed to carb backfires or intake backfires) are usually caused by an overabundance of unburnt fuel in the exhaust or a rich condition.

First I would check your plugs. Chances are they are fouled and you are not getting complete combustion, hence a buildup of unburned fuel.

If the plugs are not fouled then I would check the timing, it may have slipped and advanced. On the 650s they use a pulse controlled ignition and IIRC if one of the controllers goes bad the spark will be weak or inconsistent and you will get backfires.

If the plugs are fouled then I would check the carbs over. Perhaps your idle mixture is too rich and with the choke the bike is loading up with fuel.

cb650 bobber · « **Reply #5 on:** April 14, 2008, 12:50:44 PM »

could it be one of the spark plugs is gapped wrong....

cb650 bobber · « **Reply #6 on:** April 14, 2008, 12:51:04 PM »

I just changed them

Geeto67 · « **Reply #7 on:** April 14, 2008, 01:51:31 PM »

The problem is not in the plugs, the problem is either the timing or the carbs but the plugs will show you which one it is (it is part of the art of reading plugs). If the plugs are uniformily tan then you should not be backfiring out the exhaust. If all 4 plugs are wet looking and kinda sooty or blackish I would start looking at the carbs first. If plugs 1 and 4 are fouled and 2 and 3 are tan looking then the problem is ignition, if plugs 1 and 2 or 3 and 4 are fouled in a pair, then I would lean toward the problem being carbs.

cb650 bobber · « **Reply #8 on:** April 14, 2008, 01:55:09 PM »

it ran fine till i replaced the coils and wires and plugs this winter. and i had the tank off in my basement.

Gordon · « **Reply #9 on:** April 14, 2008, 01:59:54 PM »

Quote from: cb650 bobber on April 14, 2008, 01:55:09 PM

it ran fine till i replaced the coils and wires and plugs this winter. and i had the tank off in my basement.

And it also sat all Winter, too.

Follow Geeto's suggestion.

Geeto67 · « **Reply #10 on:** April 14, 2008, 02:25:49 PM »

Additionally I would check to see if you have one of the plug wires reversed with another. That has happened to me when I have done coil replacement and it makes a backfire. Also check how you wired the coils - my brother's DOHC cb750 (which shares an ignition with the cb650) was backfiring because one of the coil leads (2-3 cylinders) was shorting against the frame. I rewired it and put a sleve of heat shrink on it and the bike ran strong again.

cb650 bobber · « **Reply #11 on:** April 15, 2008, 06:04:21 AM »

I was looking in my manual for a coil and wire diagram and couldn't find one....I guess I will try and find a way to double check it...the one and four wires are marked....

736cc · « **Reply #12 on:** April 15, 2008, 06:03:35 PM »

I've had that happen w/ HM300 pipes w/o baffles. Only happens when cold after a reluctant start and lotsa fuel dumped out the exhaust valves; post-ignition. Makes a very impressive backfire, too.

DRam · « **Reply #13 on:** April 16, 2008, 08:49:46 AM »

Quote from: cb650 bobber on April 15, 2008, 06:04:21 AM

I was looking in my manual for a coil and wire diagram and couldn't find one....I guess I will try and find a way to double check it...the one and four wires are marked....

If the 1 & 4 wires are marked you could be okay at the plugs but still have them mixed up at the coils. The 1 & 4 cylinders fire as a pair, the 2 & 3 fire as a pair, so wires 1 & 4 go to one coil, 2 & 3 to the other. Putting wires 1 & 2 on one coil and 3 & 4 on the other means you'd be running on two cylinders, letting the two non-firing cylinders fill the exhaust with fuel. From experience I can vouch that the bike will run on two cylinders, but won't idle. Since the problem started when you changed wires I'd check that out first.

Geeto's explanation and advice is good - go with it.

cb650 bobber · « **Reply #14 on:** April 16, 2008, 12:13:07 PM »

are you saying ...just wondering that you can put 1 and 4 one side and 2 and 3 on the other side. and it doesnt matter which side as long as they are paired just wondering...or is there a distinct order all four must go in..ex..1top right 4 bottom right 3top left 2 bottom left...just wondering ...thanks guys for all your help as always...only been riding one year and you guys drive me to ride till the end.

heffay · « **Reply #15 on:** April 16, 2008, 12:29:22 PM »

you can flip flop the coils but they still must be connected correctly (wires would not match anymore)... for some reason that's how mine was wired by the PO and i just followed the his lead the other day and put it back together the same way. $:-\$

when wiring bikes LABEL EVERYTHING.

i think what geeto said was you may have swapped one half of each pair of plugs... making it run on 2 cyls.

check your wiring... i just had this trouble because of what i just told you and i had the EXACT same symptoms... only mine never actually ran for a moment.

DRam · « **Reply #16 on:** April 16, 2008, 03:32:39 PM »

If your bike is a '79 or later 650, as one would assume from your signature, the left hand coil hosts plug wires for cylinders 1 and 4. The right hand coil hosts those for cylinders 2 and 3.

cb650 bobber · « **Reply #17 on:** April 17, 2008, 07:11:54 AM »

just as I thought they are right does it matter top and bottom should 1 be on the top and 4 on the bottom.

cb650 bobber · « **Reply #18 on:** April 17, 2008, 07:12:30 AM »

I checked my wires last night and 1 and 4 are going to one coil and 2-3 are going to the other coil...so I am still in a pinch to why it is missing and shooting flames.

heffay · « **Reply #19 on:** April 17, 2008, 07:22:48 AM »

ok... but are the right wires going to the right coils?
not plug wires.

just for narrowing it down's sake... flip flop the coils. its either gonna start right up and purr or it won't. if it doesn't want to start, don't sit there and crank forever, i wouldn't think any damage could really come from giving it a shot. others may disagree but about all i see happening is a spark at the bottom of the piston travel instead of the top... would be likely not to start if it is sparking at bottom dead center.

754 · « **Reply #20 on:** April 17, 2008, 07:29:40 AM »

Exactly...

cb650 bobber · « **Reply #21 on:** April 17, 2008, 08:48:14 AM »

someone else just told me that 1 and 4 go on the left and 2 and 3 on the right...i am assuming this is orientation of sitting on the bike.

Gordon · « **Reply #22 on:** April 17, 2008, 08:56:46 AM »

Quote from: cb650 bobber on April 17, 2008, 08:48:14 AM

someone else just told me that 1 and 4 go on the left and 2 and 3 on the right...i am assuming this is orientation of sitting on the bike.

Yes, that's correct, but you've already confirmed that you have the spark plug wires from the proper coils going to the proper cylinders. What's in question now is whether or not you have the wires from the ignition hooked to the correct coils. It's possible, and fairly easy to accidentally hook them up opposite of the way they're supposed to go, which would cause the exact same problem as hooking the spark plug wires up backwards.

cb650 bobber · « **Reply #23 on:** April 17, 2008, 09:17:22 AM »

ok well i guess I will just have to switch them and see.

cb650 bobber · « **Reply #24 on:** April 17, 2008, 09:20:10 AM »

once agian thanks for all the help at least with your guys help I stay semi positive about getting it running right no matter what.

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Author Topic: fire out the exhaust ..help (Read 3628 times)