Author Topic: 550 shutting off (Read 1624 times)

Bastaldo · « **on:** May 24, 2020, 05:18:26 AM »

‘76 cb550, recently rebuilt top end and carbs. Drove it around for about an hr and it started dropping (not sure what word to use but no or slow power) while going into second. Then it died. I wait a couple of mins and put the idle screw in all the way and was able to get home no problem. A couple of days later (yesterday) was about 5 mins into a ride in 3rd and going about 50 and lost the same power. Then the bike just shut off. When to kick it over and nothing. Waiting 5 mins, idle screw in, and it started and I got home.

Between the two rides, I found my clutch cable was very loose, so I tightened it. But I figured since I was driving along fine and it didn’t feel like anything slipped.

It could be electrical. I installed a new m unit blue but that didn’t record any problems.

Anyone have any thoughts before I start diagnosing?

bryanj · « **Reply #1 on:** May 24, 2020, 05:27:22 AM »

Flat battery from not charging.

Bastaldo · « **Reply #2 on:** May 24, 2020, 06:48:30 AM »

I did just change the battery to a new one. Maybe it’s bunk. That said, when it turned off it had a 13v charge on it.

Johnie · « **Reply #3 on:** May 24, 2020, 12:23:21 PM »

Process of elimination...when it happens again open the gas cap and listen for rush of air. Maybe the cap vent is plugged. If that is okay we move onto the next idea.

Bankerdanny · « **Reply #4 on:** May 24, 2020, 12:59:58 PM »

Points or electronic ignition? When I experienced similar problems a couple years ago on my 550 it was the electronic ignition failing, but it only showed up when the bike was hot.

Take it for a ride and bring a small bottle of water. If the power starts to drop again, pull over and squirt some water on each exhaust pipe and see if any are colder than the rest. Ignition problems generally impact cylinders in pairs because the points and coils each run 2 cylinders, 1-4 and 2-4.

Bastaldo · « **Reply #5 on:** May 24, 2020, 04:50:59 PM »

Thanks for the great ideas. Re the ignition- did you have an electronic one? If so did it fail? I installed a Dynatek that’s about 5 years old. That would be interesting.

carnivorous chicken · « **Reply #6 on:** May 24, 2020, 04:54:43 PM »

second plugged cap vent, or pinched fuel line.

RickThomas · « **Reply #7 on:** May 24, 2020, 05:12:28 PM »

+1 Fuel Delivery
I have a 1974 CB550 and experienced the same problem. I had to disassemble, clean, and reassemble the gas cap to fix it. I'd start with the gas cap vent then check the fuel filter if your tank has one.

As a simple check, on a warm day you should hear air moving through the cap when you shake the tank by rocking the bike.

Bankerdanny · « **Reply #8 on:** May 24, 2020, 05:57:34 PM »

Quote from: Bastaldo on May 24, 2020, 04:50:59 PM

Thanks for the great ideas. Re the ignition- did you have an electronic one? If so did it fail? I installed a Dynatek that’s about 5 years old. That would be interesting.

Yes, I had an older Martek 440. The Dyna is known to suffer from the same issue as my Martek. It gets hot under the points cover and there is no airflow over the EI unit. On my bike I was riding through the desert, so heat was unavoidable. Ultimately I had to remove the points cover and expose the ignition unit so air could flow over it to keep it cool.

So another way to diagnose is to ride it until the symptoms appear, then pull the points cover and get back on the road. With my bike, it ran on 2 cylinders for about 10 minutes, then the airflow cooled it enough that it started to work right again and I was golden.

Deltarider · « **Reply #9 on:** May 24, 2020, 10:54:56 PM »

Any inline fuel filters present?

Bastaldo · « **Reply #10 on:** May 25, 2020, 08:16:34 AM »

Yep- there is a fuel filter. Looks clear. Been in there for a long time.

It sounds like most people think this is a fuel issue and not a electrical one. Is that bc I’d the dead spot when adding load? Or that it starts up after dying?

I’m primed for it to always be electrical. if it’s fuel, that’d be great.

carnivorous chicken · « **Reply #11 on:** May 25, 2020, 08:27:27 AM »

Quote from: Bastaldo on May 25, 2020, 08:16:34 AM

It sounds like most people think this is a fuel issue and not a electrical one. Is that bc I’d the dead spot when adding load? Or that it starts up after dying?

The second. If there is a slowdown in the delivery of fuel -- clogged filter, pinched fuel line -- a bike will die but then simply restart a few minutes later when enough fuel has made it down to the bowls.

Korven · « **Reply #12 on:** May 25, 2020, 09:01:04 AM »

This might be a longshot but i have had two ignitions switches that arent 100% if you touch the key slightly it turns off/on, not sure how a issue like this could affect the m-unit or ignition. A issue like this could come and go but you should probs see lights flashing.

Deltarider · « **Reply #13 on:** May 25, 2020, 09:31:50 AM »

Quote from: Korven on May 25, 2020, 09:01:04 AM

This might be a longshot but i have had two ignitions switches that arent 100% if you touch the key slightly it turns off/on, not sure how a issue like this could affect the m-unit or ignition. A issue like this could come and go but you should probs see lights flashing.

This is serious and can become dangerous. Read my thread: http://forums.sohc4.net/index.php/topic,179776.msg2084881.html#msg2084881
On fuel. CB500/550s are very sensitive to the right size fuellines. The correct dimensions are for: the CB500 and CB550Ks with oldstyle carbs: 18 and 30 cm length for the models with the bowltype petcock and 17 and 28 cm for models that have the newer style petcock. You probably have the latter. Do not be tempted to have them even one cm longer. For the tube that supplies carbs 3+4 use the soft metal clamp in the middle front side. Ideal inside ⌀ 5,5 mm. Outside ⌀ will be 9-11mm. Have this and the lines CAN'T even kink ever. Abstain from extra inline filters. They can cause hazardous situations.

Bastaldo · « **Reply #14 on:** May 27, 2020, 01:29:55 PM »

This is all super helpful. The gasket was old and cracked so I ordered a new one. I don’t see any vent holes but they may have been painted over. Does anyone have a pic where the vent holes are supposed to be?

carnivorous chicken · « **Reply #15 on:** May 27, 2020, 01:48:25 PM »

The vent hole is a very small hole in the middle of your cap, on the underside. Have a look and you'll see it. It vents to the top part of the cap, which is on the other side of the rubber cap seal. It can get clogged from someone lining the tank and not keeping the cap on, or rust or gunk. But one way to diagnose it is to go for a short ride, then pull over and lift the cap up. If there is a shoosh of depressurization, it's a cap clog. The vent allows the gravity-fed fuel line to work properly. When it's clogged or obstructed, gas will flow but much more slowly -- meaning you can appear to run out of gas, sit for 5 minutes, and then it will start back up again. Fuel can't fill the bowls quickly enough for normal riding. You can also undo the cap so it's open (not wide open, just resting on the top of the neck) and ride around (carefully). If it doesn't stall, there you go.

Bastaldo · « **Reply #16 on:** May 28, 2020, 02:33:52 PM »

Sure sounds like my looonnngg running problem. My cap has a little triangle cutout that I assume is the vent. It looked open but maybe a touch clogged. Either way I cleaned it out. We will see. Thanks!

Johnie · « **Reply #17 on:** May 28, 2020, 05:21:40 PM »

Can't go by what it looks like from the triangle hole. I actually get my mouth on it and see if I can blow or suck through it.

Deltarider · « **Reply #18 on:** May 29, 2020, 03:02:59 AM »

Haven't met or heard of any SOHC Four that had it blocked, but that's just me. In hot weather tank on mine hisses like an alarmed snake when I hit it, like with my thighs.

dave500 · « **Reply #19 on:** May 29, 2020, 04:42:26 AM »

never hit snakes with your thighs!,it makes em hiss!

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Author Topic: 550 shutting off (Read 1624 times)