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Author Topic: 1 & 4 Cylinders Not Firing: FIXED  (Read 2402 times)

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Offline burmashave

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1 & 4 Cylinders Not Firing: FIXED
« on: June 16, 2011, 05:47:19 AM »
A few weeks back, my '77 750k (Dyna 2k ignition, 3 ohm coils, CR carbs) started cutting out on me. When it would happen, the bike would lose a lot of power but keep running. It would only happen after I had been on the road for 30-45 minutes, and it would last anywhere from a few seconds to a few minutes. Sometimes it would backfire once when it kicked back in.

Last week, it finally went into hard failure, but I was able to limp home. The 1 & 4 pipes were cold, so I started debugging the ignition. I had replaced the spark plugs the week before, and they looked O.K. Continuity and voltage to the coils checked out. I tested the coils, and the the 1 & 4 coil seemed to be bad: both coils showed about 3.5 ohms resistance on the ignition side. The 2 & 3 coil showed 14.5 k ohms on the spark plug side, while the 1 & 4 coil showed 308 k ohms on the plug side. It didn't seem that I could tease a spark from either the 1 or 4 coil. I didn't open the points cover; however, the LED on the Dyna 2k lights on both the 2/3 and 1/4 strokes. Voltage on the bike is rock solid. I have a mounted LED voltmeter, and it has never shown less than 13.8 volts when I've had this problem (usually, it's above 14v).

So, I thought this was easy. I replaced the coils, and while I was at it, I replaced the plugs and cables, but the 1 & 4 cylinders still wouldn't fire. I tested the plug wires to make sure I had gotten a good crimps, and they seem O.K.

Any thoughts before I go back to troubleshooting it? We've got some good days here, and I'm dying to put it back on the road.
« Last Edit: June 25, 2011, 09:03:36 PM by burmashave »
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Offline Bankerdanny

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Re: ! & 4 Cylinders Not Firing
« Reply #1 on: June 16, 2011, 07:45:59 AM »
Well, since you haven't opened the points cover yet that seems like the next step. If you still had points I would say you have a bad condenser or connection between the condenser and points.

Since you have an EI however, I would say you need to check the connections at the assembly.
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Offline wingman1946

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Re: ! & 4 Cylinders Not Firing
« Reply #2 on: June 16, 2011, 08:08:55 AM »
I had an old ford that acted lust as you describe and it turned out to be an new condenser I had recently installed as part of a tune up.
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Offline BobbyR

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Re: ! & 4 Cylinders Not Firing
« Reply #3 on: June 16, 2011, 08:53:17 AM »
It is unlikely that you have a fuel problem on 1-4. If you want to be completely certain, swap 2-3 with 1-4.  You wil probably find 1-4 come alive. If you are certain all is well with the coils and wires, the only thing left is the Dyna. Maybe you are lucky and the 1-4 pickup loosened and needs to be re gapped.

It is a stretch, a defective or broken plug could cause this problem since it is waste spark system.
« Last Edit: June 16, 2011, 08:55:19 AM by BobbyR »
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Offline burmashave

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Re: ! & 4 Cylinders Not Firing
« Reply #4 on: June 16, 2011, 09:30:55 AM »
Thanks, all. I'm gonna go back through and recheck everything, working backward from the sparkplugs. I'll pull the points cover and see if anything looks amiss. I'll try to figgur out if there's a good way to test the Dyna. I'm guessing that testing output from the Dyna would be a good test. I have a digital multimeter that does min/max, so I may be able to compare to the 2/3 ignition.
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Offline scottly

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Re: ! & 4 Cylinders Not Firing
« Reply #5 on: June 16, 2011, 10:19:39 AM »
Hmmm. This is the third or forth suspect DYNA 2000 just recently...
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Offline Bankerdanny

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Re: ! & 4 Cylinders Not Firing
« Reply #6 on: June 16, 2011, 11:42:35 AM »
If nothing works you can try reinstalling the stock poins and condenser and see what happens
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline wrenchmuch

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Re: ! & 4 Cylinders Not Firing
« Reply #7 on: June 17, 2011, 06:34:36 AM »
Its strange that the led's come on for both triggers and the coils check out . In the original post I would have voted for a heat related failure in the triggers or the coils .
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Offline burmashave

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Re: 1 & 4 Cylinders Not Firing
« Reply #8 on: June 20, 2011, 07:03:19 PM »
If anyone's still following this, I'm ready to shoot my bike. I used to be confident of my electrical troubleshooting ability, but I don't know now, and in my haste to get it back on the road, I think I've been too quick to repair before I had the problem completely isolated.

Today's mystery was that the wire from the ignition to the 1/4 coil seemed to be grounding out a bit, so I replaced wires, but no go. I had already replaced the entire wiring harness a couple of years ago, so it's all relatively new. I wouldn't have jumped to replacing the wires, but it seemed some heatshrink tubing had been melted by some battery acid.

Anyway, I have checked inside the points cover. The Dyna LED does light for each coil. If I still had my old points ignition, I would try that. I went through the Dyna troubleshooting guide, and all tested O.K. As soon as I can get some more time, I'll get the multimeter back out, do some testing and then likely call Dyna Engineering.
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Quote from: SOHC Digger, RIP
'Ere's whatcha do, Guvna', just throw a couple dookie logs in the hearth and bob's your uncle!
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Offline Lars

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Re: 1 & 4 Cylinders Not Firing
« Reply #9 on: June 21, 2011, 02:47:06 AM »
The black and white wires properly connected? If one of them has a poor connection, either 1+4 or 2+3 fails.

I was working on a Boyer Brandsted electronical system lately for a friend, no way we could make it work. Put back original points and coils, rund like a champ. ;)
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Offline burmashave

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Re: 1 & 4 Cylinders Not Firing
« Reply #10 on: June 21, 2011, 07:29:16 AM »
Thanks, Lars. Yup, the black wires are properly connected, and they get 12v when the ignition is on.
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Quote from: SOHC Digger, RIP
'Ere's whatcha do, Guvna', just throw a couple dookie logs in the hearth and bob's your uncle!
'77 CB750k

Offline Spanner 1

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Re: 1 & 4 Cylinders Not Firing
« Reply #11 on: June 21, 2011, 09:31:54 AM »
Those 3ohm coils place a heavier load on the ignition wiring and any corroded connections would show-up more readily than with stock coils ,including the kill switch......... and with a lowered power available one coil would be 'favored' over the other ( some folks won't believe that , I'm sure ) as no two coils will be the exact same impedance ( ohms ), the lower imp. one taking all available energy, especially in a rapid switching situation as our two coil ignition is.   I would try a temp. wire from the battery + to the black/white junction at the coils and see if that cures the prob...... for test only, you really need your kill switch in the circuit and a fused supply to the coils for safety... Good Luck.
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Offline wrenchmuch

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Re: 1 & 4 Cylinders Not Firing
« Reply #12 on: June 21, 2011, 06:31:39 PM »
When you get your meter out check resistance for the trigger pickups . Check resistance between leads on each trigger and from each lead to ground . Is there a discrepancy between 1-4 and 2-3 ? If triggers check out ,and wiring and coils are good the control box might be the culprit . The Dyna 2000 should have no problem driving 3 ohm coils . There have been other posts about Dyna failures and Dyna seems to be pretty good about replacing faulty products . How old is it ?
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Offline burmashave

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Re: 1 & 4 Cylinders Not Firing
« Reply #13 on: June 22, 2011, 03:32:02 PM »
I talked to tech support at Dyna today, and the guy there thinks it is the controller unit. The option for me is that I can send it back and get a discount on the replacement if it turns out to be faulty. The replacement would cost about $125, but I'd have to wait for it while the summer is passing me by. I'm pondering on ordering an entire new unit and having it shipped as soon as possible.

That said, both of you point to some things to check. I will try jumping the battery to the 1/4 coil to see what happens, and mebbe have another looksee inside the points cover.
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'Ere's whatcha do, Guvna', just throw a couple dookie logs in the hearth and bob's your uncle!
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Offline burmashave

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Re: 1 & 4 Cylinders Not Firing: FIXED
« Reply #14 on: June 25, 2011, 09:09:45 PM »
I didn't want to wait for Dyna to confirm that the unit was broken, so I ordered a new controller from Z1. I installed it, and now my bike runs stronger than it has this season.

I think the key was that the ignition wire from the controller to the 1/4 coil was actually grounding out just a bit.
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Quote from: SOHC Digger, RIP
'Ere's whatcha do, Guvna', just throw a couple dookie logs in the hearth and bob's your uncle!
'77 CB750k

bollingball

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Re: 1 & 4 Cylinders Not Firing: FIXED
« Reply #15 on: June 26, 2011, 06:39:59 AM »
Looks like another good reason to keep my points and add a HondaMan box :D :D


            Ken
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