Author Topic: Ignition Skipping  (Read 1296 times)

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Offline Smitty057

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Ignition Skipping
« on: June 20, 2011, 06:19:34 AM »
Guys,

Recently my 750F starting skipping at what seemed like random intervals.  It will begin slightly and progress to where you can barely make it back to the house.  I have checked out the fuel delivery, points and plugs and everything looks good.

I have a brand new battery in it that reads 12.8V charged.  If I charge the battery with a tender at 2 AMPS/hr then the bike will run fine.  About 5 - 10 minutes of riding, it starts to skip.  The battery does not get lower than 12.5v, it can spin the starter fast and the headlight is bright enough.  It appears to me a bad connection to the ignition system is the culprit because the battery must be 100% and fresh off a charger in order to fire off the plugs.

Has anyone have advice on where to start looking for a failure point in the ignition system or anything else I should check out?  Thanks for the help
CB450 K7
CB750 F

Offline Skunk Stripe

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Re: Ignition Skipping
« Reply #1 on: June 20, 2011, 09:30:56 AM »
Have you checked the voltage after riding while the engine is running?
Do you have an aftermarket points plate or the stock plate?
Have you checked your plug wires for cracks and made sure your plug caps have good connection?
How clean are the wire connections for your coils?

bollingball

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Re: Ignition Skipping
« Reply #2 on: June 20, 2011, 09:42:51 AM »
Check the batt.vdc with the engine at 2500 to 3000 sounds like it is not charging or dirty connections. Look at FAQ electrics.

                    Ken
« Last Edit: June 20, 2011, 09:45:42 AM by bollingball »

Offline Smitty057

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Re: Ignition Skipping
« Reply #3 on: June 20, 2011, 10:32:26 AM »
These are some good starting points.  Charging system is around 13.5 @ 3000 RPM.  Not sure about the points plate because it looks new to me but I didn't install it  I will test out other possibilities noted this evening and report back.
CB450 K7
CB750 F

Offline camelman

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Re: Ignition Skipping
« Reply #4 on: June 20, 2011, 01:03:36 PM »
Skipping after it heats up sounds like condensers to me. Take a look at your points with the engine running. If you see sparks, then the corresponding condenser needs to be replaced. Another typical symptom of failing condensers is that the skipping can become less apparent at higher RPM.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline TwoTired

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Re: Ignition Skipping
« Reply #5 on: June 20, 2011, 01:07:31 PM »
Can you describe the spark plug deposits?

How old is your air filter?

Does your gas cap vent correctly?
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Skunk Stripe

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Re: Ignition Skipping
« Reply #6 on: June 20, 2011, 01:33:07 PM »
A point about arcing, even with good points, you can have arcing. It happens and so you have to base it more off of how much arcing you have. Very minor sparks, no big deal. A good light show, then you may have bad condensers

Offline camelman

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Re: Ignition Skipping
« Reply #7 on: June 20, 2011, 02:13:29 PM »
A point about arcing, even with good points, you can have arcing. It happens and so you have to base it more off of how much arcing you have. Very minor sparks, no big deal. A good light show, then you may have bad condensers

Well said. I should have clarified.
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline Smitty057

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Re: Ignition Skipping
« Reply #8 on: June 20, 2011, 07:51:11 PM »
I have a fat blue spark across the 1:4 gap. Nothing like 2:3.  Tonight I cleaned all the connectors associated with ignition - got some improvement.  Noticed that the ign switch was warm so I took it apart and cleaned it.  Ill throw it back together tomorrow and see if I can dig up a condenser.  Thanks for the replies.
CB450 K7
CB750 F

Offline camelman

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Re: Ignition Skipping
« Reply #9 on: June 20, 2011, 09:51:12 PM »
Just to clarify, you don't want a big spark across your points.  Replace the condenser for the 1/4 coil.

Good luck and let us know how it goes.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline Skunk Stripe

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Re: Ignition Skipping
« Reply #10 on: June 21, 2011, 10:17:55 AM »
Yeah, small arcing right between the points(think sparkplug with close gap and faint) is normal.

Offline Smitty057

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Re: Ignition Skipping
« Reply #11 on: June 27, 2011, 03:44:56 PM »
Guys,

It was the 1:4 condenser.  It would stop working properly when the bike got warmed up.  I put new ones on and things are good.  Thanks for everyone's input.
CB450 K7
CB750 F