Author Topic: NO power in 2 & 3! Help! 78 550  (Read 203 times)

0 Members and 1 Guest are viewing this topic.

Offline BenjaminoLA

  • Full Member
  • *
  • Posts: 3
NO power in 2 & 3! Help! 78 550
« on: October 07, 2018, 11:28:54 am »
Hey team

I have a 78 550 that ive been restoring for the last month!

Sent my carbs out to Mike Nixon and have driven 220 unproblematic miles

then all of a sudden cylinders 2&3 will not fire

Checked spark in all 4 looks good if anything could maybe be inconsistent


What should I be checking to figure this out!

Help meeeee




Online 754

  • Really Old Timer ...
  • *******
  • Posts: 25,397
Re: NO power in 2 & 3! Help! 78 550
« Reply #1 on: October 07, 2018, 11:40:50 am »
 Has to be ignition problem..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline jgger

  • Hot Shot
  • ***
  • Posts: 711
Re: NO power in 2 & 3! Help! 78 550
« Reply #2 on: October 07, 2018, 11:44:40 am »
Points and condenser  are (place brand name here)?

Online calj737

  • Really Old Timer ...
  • *******
  • Posts: 19,141
  • I refuse...
Re: NO power in 2 & 3! Help! 78 550
« Reply #3 on: October 07, 2018, 12:55:04 pm »
+2 on condensers.
'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

*** Currently experiencing life at 60 WTFs per hour ***
I always thought getting old would take longer

Offline Bankerdanny

  • Eventually I will be old enough in reality to be
  • Really Old Timer ...
  • *******
  • Posts: 5,870
  • Endeavor to persevere
Re: NO power in 2 & 3! Help! 78 550
« Reply #4 on: October 07, 2018, 08:09:51 pm »
The coils fire in pairs 1-4 and 2-3, so as the others have said, if 2-3 aren't working then you have an ignition issue. Before I swapped the coil out I would first check the blue and yellow wires from the points where they plug into the wiring harness under the airbox right at the back of the engine and make sure both are firmly connected (I say both because I don't recall which color is the 2-3 points).
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F, '74 CB550k project bike, '77 CB550F basket case engine donor. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki 80 (K11 probably, it's been 30 years), '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline scottly

  • Really Old Timer ...
  • *******
  • Posts: 12,305
  • Humboldt, AZ
Re: NO power in 2 & 3! Help! 78 550
« Reply #5 on: October 07, 2018, 09:04:15 pm »

Checked spark in all 4 looks good if anything could maybe be inconsistent

What do your spark plugs look like?
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Online jakec

  • Hot Shot
  • ***
  • Posts: 398
Re: NO power in 2 & 3! Help! 78 550
« Reply #6 on: October 07, 2018, 10:30:24 pm »
I just started having this sameness problem on my 400. Spark on all 4 (plugs out) but when I run it it's cold on 2&3. Came out of nowhere after 700 unproblematic miles.
1975 CB400F
1972 CL175 K2

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 10,617
  • Saver of unloved motorcycles.
Re: NO power in 2 & 3! Help! 78 550
« Reply #7 on: October 10, 2018, 09:08:53 am »
 Condenser, points, wiring all could cause a weak spark. A spark that will fire in air may not fire in wet compression. A fuel fouled cylinder will also repeatedly wet the spark pug. Maybe just leave the plugs out for a while and try after it's had a chance to dry out.  Good luck and keep us informed.
If the things you own end up owning you, it's better to be owned by some cool things.

Online Deltarider

  • Really Old Timer ...
  • *******
  • Posts: 5,427
  • "Tremendous progress has been made... "
Re: NO power in 2 & 3! Help! 78 550
« Reply #8 on: October 10, 2018, 12:26:40 pm »
In case you have the stock ignition setup, I'd first check breakerpoints and condensers. Open the ignition cover. First check if breakerpointgap is still correct and also that the forked connectors at the back of the breakerpoints aren't accidently touching the plate. Breaker 2+3 in particular is prone do this as there's a crosshead dangerously near. Then, with engine running, see if there's excessive arcing at the breakerpoints. A tiny bit of sparking is normal, excessive sparking is not good. Check: 
In this vid left condensor (1+4) is bad, right condensor (2+3) is good. I'd also check plugcaps 2 + 3 and measure their resistance. Should be about 5 kΩ each. What plugs do you run?
« Last Edit: October 10, 2018, 12:48:28 pm by Deltarider »
Money is like manure. It's not worth a thing unless it's spread around.

 

;
Honda