Author Topic: Cb650, Carbs Blowing out Air, Exhaust sucking in air (Read 28130 times)

wdmcdonald · « **Reply #100 on:** April 16, 2013, 08:19:38 PM »

Waiting for my phone battery to charge so I can take a picture. But the pin on the advancer is fine. Registers into the crank and is in the correct position. Put the ignition plate back to the correct stock location and lined up the 1.4F mark. Pointer on the lobe is pointed straight at the pickup on the pulsar. Everything is lined up correct but its still not starting. Tried switching the coil wires as well. It sounds like its so close to starting but just puffs and pops a bit. Nothing consistent. One weird thing is that the closest I get can get to it starting is right after I let go of the button after cranking the starter. Dunno if thats of any significance, just something I noticed.

scottly · « **Reply #101 on:** April 16, 2013, 08:37:54 PM »

Quote from: wdmcdonald on April 16, 2013, 08:19:38 PM

One weird thing is that the closest I get can get to it starting is right after I let go of the button after cranking the starter. Dunno if thats of any significance, just something I noticed.

Yes, that may be a clue; the electric starter draws a lot of current, which lowers the voltage to the ignition coils. Letting off the button takes the load off the battery and ignition switch, and allows the voltage to the coils to rise.

wdmcdonald · « **Reply #102 on:** April 16, 2013, 08:41:52 PM »

Just seems weird that it would start right up with no hesitation when the ignition was out of place.

scottly · « **Reply #103 on:** April 16, 2013, 09:15:39 PM »

Quote from: wdmcdonald on April 16, 2013, 08:41:52 PM

Just seems weird that it would start right up with no hesitation when the ignition was out of place.

Yes, it does. If the advancer was indeed properly indexed to the crank, the ignition would be 50 degrees before TDC.

wdmcdonald · « **Reply #104 on:** April 16, 2013, 09:35:10 PM »

Here's another thought... seemed like the bike was only running on 3 cylinders because the number 3 head pipe was cold when running. Could it be that the spark isn't strong enough to run all 4 when properly timed? I really dont know what else could be goin on. Everything is timed right. Got spark in all four. Gas goin in... Im stumped.

scottly · « **Reply #105 on:** April 16, 2013, 09:37:19 PM »

Quote from: scottly on April 13, 2013, 10:03:32 PM

Quote from: wdmcdonald on April 13, 2013, 09:59:08 PM
One thing I did notice though when I took it apart is that the spark plugs in cylinders 1 and 4 were black and 2 and 3 were toasted brown. or maybe it was 1 and 3 / 2 and 4 respectively. I'll take them out tomorrow and have a look.
Black plugs are a big clue; almost always caused by a carburetor issue...

trueblue · « **Reply #106 on:** April 17, 2013, 02:59:51 AM »

If you remove the outer tappet covers and look at the cam it will tell you where the engine is. Providing the cam is correctly timed that is.

Don't worry about your carbs yet, with your timing being as out of whack as it is you will without a doubt have black plugs. You know you have an issue with the ignition, sort that out before you start chasing rainbows. Double check that you're coil wires are the right way round, yellow should feed 2-3 coil and the blue should feed the 1-4 coil. Then make sure you have a fully charged battery.

wdmcdonald · « **Reply #107 on:** April 17, 2013, 11:25:27 AM »

Here is a pic of what I have. Coils and plugs are all correct. So at this point all physically wiring, connections, and static timing are correct. Cam is set correctly and I checked the pistons through the spark plug hole, they are at TDC when the advance unit is at the 1.4 Mark. Still it doesnt want to start.

So now that I have verified everything is stock and correct... now what? Weak spark? Carb problems?

scottly · « **Reply #108 on:** April 17, 2013, 11:48:47 AM »

Have you replaced the black spark plugs with new ones?

wdmcdonald · « **Reply #109 on:** April 17, 2013, 11:59:03 AM »

No not yet. They were brand new when I put them in last week. I didn't think that was an issue since the bike has ran on them.

scottly · « **Reply #110 on:** April 17, 2013, 12:35:11 PM »

Once blackened with carbon, the plugs may be shorted out, preventing a good spark. You might try burning the soot off with a propane torch. If the bike starts, but doesn't run well, pull the plugs and see if they are turning black again.

John Eberly · « **Reply #111 on:** April 17, 2013, 12:52:01 PM »

Try charging the battery.

You need lots of amps to get things spun up if your tune-up is off.

That and new plugs might get you going.

wdmcdonald · « **Reply #112 on:** April 17, 2013, 01:27:09 PM »

Ok I guess Ill try new plugs. Could be the battery but again, doesn't make sense that the bike was running fine under the same conditions with a different ignition position.

wdmcdonald · « **Reply #113 on:** April 17, 2013, 01:36:26 PM »

Lets assume its the battery, should I be able to jump start it? I will double check all connections and grounds but Im guessing if all the plugs are sparking when testing them outside the engine then weak spark is not the problem.

trueblue · « **Reply #114 on:** April 17, 2013, 02:04:39 PM »

It may be weak spark still, it takes approximately nine times the power to fire the plugs under compression on one of these engines. If your battery is run down from repeated attempts to start the bike then it should start with a set of jumper leads.

crazypj · « **Reply #115 on:** April 17, 2013, 02:09:49 PM »

I had similar problem with a CB900 DOHC, the ignitors were either wrong for bike or they were wired backwards, forget which (it was around 1985)
The CB650 uses similar ones to the 750/900, could be someone has swapped them for something that looks the same as they are known to burn out pretty regular if ignition is left on
I just can't remember if the part numbers matched from year to year or bike to bike?

Coldsmoke · « **Reply #116 on:** April 17, 2013, 04:52:12 PM »

I haven't read every single post but a cam 90-ish degree's off will do this. good luck

Vinhead1957 · « **Reply #117 on:** April 17, 2013, 07:01:58 PM »

Oh oh here we go again

wdmcdonald · « **Reply #118 on:** April 17, 2013, 08:34:44 PM »

Quote from: crazypj on April 17, 2013, 02:09:49 PM

I had similar problem with a CB900 DOHC, the ignitors were either wrong for bike or they were wired backwards, forget which (it was around 1985)
The CB650 uses similar ones to the 750/900, could be someone has swapped them for something that looks the same as they are known to burn out pretty regular if ignition is left on
I just can't remember if the part numbers matched from year to year or bike to bike?

They are from a DOHC CB900 I believe. But I was under the impression that they were the same. Still seems irrelevant since the bike has ran with them before.

trueblue · « **Reply #119 on:** April 18, 2013, 02:21:56 AM »

As far as I know the ignitors on the 650's are the same as the DOHC bikes.

Just so we have covered all bases:
*the battery is fully charged
*plugs are clean and correctly gapped
*pulsers are timed and gapped correctly
*advancer is free
*plug caps measure 5k ohms
*you have good clean spark that will jump a 10mm gap in open air
*cam is timed correctly
*valves adjusted correctly

Quote from: Vinhead1957 on April 17, 2013, 07:01:58 PM

Oh oh here we go again

A cam can be 90 out but it can't be 180 out

dave500 · « **Reply #120 on:** April 18, 2013, 02:41:49 AM »

thats it,,youve started me off again!!!a cam can also be one degree or 179 degrees out,,but not 180.

raymond10078 · « **Reply #121 on:** April 18, 2013, 07:18:09 AM »

Are you using a CB900 or a CB650 advancer? I'm asking because the two have different lobe placement.

dave500 · « **Reply #122 on:** April 18, 2013, 12:39:25 PM »

i havent seen those advancers side by side,from the top it looks like it has the lobe placed differently,thats to the top plate etc,,but turn them over and see if the alighnment pin is in a different spot to the lobes,thats the important thing?the pin hole in the crank often represents the tdc mark as well.

raymond10078 · « **Reply #123 on:** April 18, 2013, 01:04:15 PM »

Agreed. Just trying to put forth an idea/something to check. So much of this ordeal just doesn't make sense . . . .

Bailgang · « **Reply #124 on:** April 18, 2013, 02:08:06 PM »

Quote from: dave500 on April 18, 2013, 02:41:49 AM

thats it,,youve started me off again!!!a cam can also be one degree or 179 degrees out,,but not 180.

Hey don't look at me. I'm gonna keep my mouth shut this time I promise.

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Author Topic: Cb650, Carbs Blowing out Air, Exhaust sucking in air (Read 28130 times)