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Author Topic: 1989 cb1 for parts  (Read 1097 times)
a_morti
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« Reply #15 on: June 16, 2017, 07:07:45 PM »

Back to plug leads, lets dole check it. People paint numbers on things and aren't always right.

The plug leads from the left coil go to 1&4, from the right coil to 2&3. Doesn't matter if you mix them up within that framework but if you try to connect the left coil to 1&2 and the right coil to 3&4, you'll only be getting sparks at the right moment in two cylinders, and that is seldom if ever enough to start the bike. But (if the plugs aren't already fouled) it will potentially get the exhausts hot on cylinders 1&3 if you crank it a little while on the starter, but this may also foul the other two plugs (if not already fouled).

CB-1s really like clean plugs.
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ModerateFkr
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« Reply #16 on: June 16, 2017, 08:08:21 PM »

When mine was doing similar. I sat in frustration holding the starter in 10 second bursts for a good minute or so. All the time it wanted to fire but couldn't do it. That got just exhaust downpipe #2 hot, so I knew the fuel pump was fine and the safety circuit wasn't faulty. Had to be spark related, whether plugs, leads, caps, or coils.

Similarly, you are getting spark and fuel as you are getting backfires, so the fault can't be in the safety circuit unless weirdly intermittent, or the fuel pump.

As above, I cleaned the plugs and that solved it, they didn't even really look dirty in fact plug 4 may have been brand new, I am ofc unsure of the bike's history for the period I didn't own it so that plug may have had 0 miles on.

I'd say you are down to spark or carbs, and more likely spark since you seem to have had a good root through the carbs already.

Clean the plugs and plug caps (again), and see if it helps. While you are there, stick a screwdriver in the caps and you can disassemble the resistor for cleaning, also consider cutting back 1/2" of Ht lead and screwing it into a fresh end. None of this stuff costs anything but time and may even work.

That's a good one a_morti. My Dad told me that one 40 years ago. He wasn't well at the time, but had a great instinct for problem solving engine issues - one step at a time. He learned on a succession of Velocettes before he joined the REME and had to fix American tanks as part of Monty's lot. I should have helped him write a book on his time in the western desert.

TV aerial leads improve from similar treatment.
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Drew m
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« Reply #17 on: June 17, 2017, 03:19:07 AM »

Can the coils go faulty giving a weak spark, or do they usually just pack in completely and give no spark,I've had the resistors out of the plug caps before and cleaned them, I will cut a bit of plug cable back and try that as suggested, cheers,
Drew
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a_morti
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« Reply #18 on: June 17, 2017, 03:33:15 AM »

Coils typically fail under load and/or when hot as a precursor to completely giving up the ghost.

You did say it wanted to fire, try holding it on the starter and see which pipes are hot. Might be able to point the finger at a coil.
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Drew m
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« Reply #19 on: June 18, 2017, 04:31:52 AM »

I marked the ignition leads myself before I noticed someone else had marked them with paint so all good there, tried cutting a bit of the leads and then continually trying to start in bursts but it's not firing enough to heat any pipes, still popping out the carbs and an occasional back fire from exhaust, there's quite a bit of vapour (exhaust fumes)coming from exhaust when turning over, I expect this is normal though, checked that diode that's next to ecu seems ok only reading one way, I did have it nearly running on easy start,.
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ModerateFkr
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« Reply #20 on: June 18, 2017, 08:55:31 AM »

I marked the ignition leads myself before I noticed someone else had marked them with paint so all good there, tried cutting a bit of the leads and then continually trying to start in bursts but it's not firing enough to heat any pipes, still popping out the carbs and an occasional back fire from exhaust, there's quite a bit of vapour (exhaust fumes)coming from exhaust when turning over, I expect this is normal though, checked that diode that's next to ecu seems ok only reading one way, I did have it nearly running on easy start,.

That's a small improvement isn't it Drew? It suggests an electrical issue.

But have you got good compression on all cylinders? Are the carb boots in good condition and tight?
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Drew m
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« Reply #21 on: June 18, 2017, 09:06:58 AM »

Carb boots look ok and are a good tight fit, you need a fair bit of force to seat them, so much so that I've not bothered to tighten the clamps, I'll clamp them up try again, I've arranged to borrow a compression tester just to make sure their ok.
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Drew m
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« Reply #22 on: June 22, 2017, 02:39:51 PM »

Cb1 burst into life today, after downloading the Manual and checking all the electrics with a multimeter which all read ok, took carbs of again and gave them a good clean, before I put the carbs back on I sprayed ether directly into cylinders while cranking and it fired up,ruling out electrics fitted carbs back on and away it went, don't know where the blockage was if any carbs looked very clean,may have disturbed a wire into contact again not a 100 percent sure, anyway main thing is were up and running so thanks for all the help and suggestions  Grin
Cheers drew
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VintageHunter
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« Reply #23 on: June 22, 2017, 02:41:12 PM »

Congrats!............Now..........ride the piss outta her.
 Grin
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a_morti
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« Reply #24 on: June 22, 2017, 03:11:44 PM »

Woohoo!

Another -1 running Cheesy

Glad we could provide some inspiration even if none of us seems to have correctly guessed the  fault
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ModerateFkr
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« Reply #25 on: June 23, 2017, 12:04:24 AM »

Cb1 burst into life today, after downloading the Manual and checking all the electrics with a multimeter which all read ok, took carbs of again and gave them a good clean, before I put the carbs back on I sprayed ether directly into cylinders while cranking and it fired up,ruling out electrics fitted carbs back on and away it went, don't know where the blockage was if any carbs looked very clean,may have disturbed a wire into contact again not a 100 percent sure, anyway main thing is were up and running so thanks for all the help and suggestions  Grin
Cheers drew

That's great news Drew. Really pleased for you bro. Just a few days ago you were ready to break your baby!! If we CB-1 owners were psychopathic by nature, we would have thought only of what we could get out of your (happily limited) misfortune.

Air leaks are a bugger to detect, but your description of the carb boot situation sounds like the culprit to be honest. Don't they have to be fitted over a flange? The stiffness will be experienced in pulling off and pushing back on. But the air gap will be a real thing, even if you can't see or feel it. Had that experience many times on just one carb. The same situation on all four caused by no clamps, inadequately tightened clamps, or kinks, could have been the issue all along.


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