Topic: Sudden Loss of Power

[KMR]

Hello all,
Until now I have been reading and learning from all the great info on here.
Thanks, you have all helped with every one of my common newbie bike questions.

Ok, 1974 Honda CB550Four

Once the bike is warmed up it will suddenly loose power and stall out if the throttle is not kept revving. when this happens it seems that it looses spark in the 1-4 cylinders. Once this starts happening it will come and go with no rhyme or reason.
I have a DynaS ignition installed that I have been very happy with but I am still running the stock coils. I ordered new Dyna coils and plug wires and plugs that will be here soon but in the meantime I thought I would swap out the coils for a spare set and keep the bike driving.
With the swapped in coils and plug wires (clean plugs as well, not new) The problem still exists, but rather than the 1-4 cylinders causing the problem it seems to be the 2-3 cylinders. After I discovered this I took the coil from the set that was sparking the 2-3 and combined it with the one that was sparking the 1-4, process of elimination, but still no luck, the problem persists.
Now I am worried that this may not be a coil problem. What else should I check?
I stripped the bike down and checked all the battery/ electrical connections.
I pulled the carbs and gave them a thorough cleaning and balancing about 300-miles ago, did the valve clearances at the same time, and the bike has been running great since then. This was an intermittent problem at first but know it happens every time the bike gets up to temp.
Any other ideas would be much appreciated, thanks for all the info and help so far.
Kevin R.

[kettlesd]

Hey Kevin,

Assuming u are correct in that your valves are adjusted, carbs are prisitine, balanced and therefore not running grossly lean (and therefore grossly HOT!!!!), one place to look for the cause that won't cost you any money (just your time), is to check to see if time and/or excess heat have degraded either the insulation or the actual wire core on some of your key ignition wiring components.

I had a machine do the same thing a few years ago - damn near gave me a stroke tryin to figure it out too! Turned out the wires from the points to the coils had degraded. Makes sense if you stop and think about it - Honda ran them right along the frame lower an inch from the right exhaust. Time, crud and intense heat had broken down the insulation to the point where the blue & yellow points wires were shorting intermittently to the frame - causing very mysterious igniton issues!!!! They would work fine when the machine was stone cold, but as soon as it heated up - the metal in the wire starts to expand..... well, you get the picture.

Easy enough to check though - check the wire (unplugged from both the harness & the points) with a Ohm-meter for resistance when cold. Check again after your igniton acts up when hot to see if the resistance value changes significantly.

Hope this helps....

Awesome site by the way - im new to the site and back on board the SOHC bandwagon with a pair of 750K's after suffering a lapse of mental judgement for a few years and not having at least one 70's Honda-Four in my garage.

Sean

[bowhunter]

Sounds Like the Dyna S is having a probem with heat. If you had a 2nd Dyna, you could try a swap, or go back to the points setup and try it with that.A second option would be to run it without the points cover until it acts up, then hit the Dyna S with some freeze spray from Radio Shack or other electronics store. If it behaves then, you know the problem is wth the Duna S.

Bowhunter

[kettlesd]

Nice idea on the cold spray.........

[KMR]

Great ideas, thanks guys.

The wires seem to be in really good shape on the entire bike (storage for 20 years) and the wire you mention is replaced with the new Dyna wires, I will definitely check the continuity to ground on all of them.

I had the ignition cover off trying to figure out how the heck to trouble shoot the little black box. I guess that is the good thing about the old points.
Awesome idea on the freeze spray (never heard of it before) I did notice that one ignition module was a bit warmer than the other and that was suspicious to me.

Oh, and I will double check the balance and mixture to be safe.