Topic: 30% loss of power, any ideas?

[1977_cb550k]

Hi, took my CB550k3 out for a ride today and it started raining 😔.

After about 10mins into the rain I lost about 30% power and it started running rough. It cut in and out of full power all the way home.

The spark plugs and timing were done last week, and the battery also tested ok last week.

 Any suggestions appreciated. I’m not very technical, but suspect it’s a common problem.

What do you think it is?

[Don R]

 A wet plug cap if you have a stock air box. If you have pod filters, wet pod filters. There are also documented cases of carb overflow hoses sucking water.

[1977_cb550k]

Thanks Don. I’m running a stock air box (bike is stock everything). I reckon your wet plug cap theory might be right.

Will wait for the weather to clear and re-try.

I had just taken off from some lights and got it up to 7,000rpm so wondered if something had possibly failed. It does feel like a spark issue if I had to guess.

[dave500]

if the caps are old replace them all,if water caused it to cut out theyve gone high resistance,a bike should be able to handle some rain.

[Deltarider]

Can't stress it enough: the plugcaps and -leads are the CB500/550s #1 troublemakers. Good thing is, an issue here is about the easiest to diagnose and cured.
When in doubt, one could start by checking the total resistance from one plugcap via the coil to the other plugcap. Realise that new resistor plugcaps are around 5kΩ each. The coils secundary itself is around 14-15kΩ, so with both plugcaps attached, you should read 24-30kΩ in total. In the test, wiggle the wires somewhat to find out whether connections are firm. When you read over 30kΩ in total, unscrew both plugcaps to be tested individually. Over time the plugcap's resistance tends to increase. When over 8kΩ, replace. Do not run and resistor caps and resistor plugs. When you have the choice, I'd prefer resistor caps over resistor plugs. Verify plugcaps are firmly connected to the wires and there's no arcing. Be aware this may occur intermittently. It's best seen in the dark.

[Erny]

A wet plug cap if you have a stock air box. If you have pod filters, wet pod filters. There are also documented cases of carb overflow hoses sucking water.

I got this issue on my CB750K K7. It uses same style carbs as CB550K3 (PD type).

There were really sucking water via overflow hoses. Reason is simple, vents in bowls (very tiny holes!) were clogged, carbs were vented via overflow hoses. As they are terminated close to rear wheel, water spray was sucked inside carbs...

To verify if you have the same issue, disconnect overflow hoses from carbs and check if behavior will change after short ride (when remaining water in carbs is consumed)

[Deltarider]

A wet plug cap if you have a stock air box. If you have pod filters, wet pod filters. There are also documented cases of carb overflow hoses sucking water.

I got this issue on my CB750K K7. It uses same style carbs as CB550K3 (PD type).

There were really sucking water via overflow hoses. Reason is simple, vents in bowls (very tiny holes!) were clogged, carbs were vented via overflow hoses. As they are terminated close to rear wheel, water spray was sucked inside carbs...

To verify if you have the same issue, disconnect overflow hoses from carbs and check if behavior will change after short ride (when remaining water in carbs is consumed)

Good point, it's been a typical K3 thing. Now I learn the K7 is also susceptible. Chances are little remaining water will be consumed however. It takes a tiny droplet to hamper carburation long time. Drain the bowls.

[BenelliSEI]

Is there a proper, working gasket under you points cover? Often left out. Water gets in there and can also cause your symptoms too.

[Erny]

Gasket on points can be causing it too.

But in my cas if was clear, since I rode on dry road for 1-3mins issues disappeared completely. (means no water sprayed from rear wheel)

It was enough to ride again on wet road issues were back almost immidiately.

[Erny]

BTW there is simple test to do, take 4 clear tubes, connect one side to overflow outlets and dip other sides into glass with water, start engine, rev it for while and see what is happening in tubes..

[1977_cb550k]

These are all great suggestions to check. Thanks.
Rain has stopped today so I’ll do a dry-run and report back.

[1977_cb550k]

OK< so took the bike out in the dry today, and the problem has completely disappeared. I'm guessing it was moisture in the plug caps.

However, in looking around, I noticed the stator cable looks a bit exposed and has some crappy tape around it. It's right behind the front wheel, so possibly taking some moisture in that way?

I've attached two photos
1. Side view pointing out the possible problem area
2. Upwards views, looking up from the ground

Does that cable need more heat shrink around it?

[bryanj]

As long as its electrically insulated its fine mechanically just naff visually, the 550 generator runs dry so no chance of leaks

[BenelliSEI]

Did you check under the points cover? Gasket?

[1977_cb550k]

Benelli, didn’t get a chance to look, but will inspect today and let you know.

[BenelliSEI]

Curious. I always like to start with the easiest fix.

[1977_cb550k]

Yep, there’s a gasket but it’s completely deteriorated!
Good tip Benelli.

I’ll need to buy a new one. Anyone got tips on where to buy? I’m in Australia. 

[bryanj]

They come in gasket sets but should still be available individually from Honda as it fits all the fours

EDIT part number 30372300300

[dave500]

make one its only a circle.

[1977_cb550k]

What material do you make them from Dave?

[Deltarider]

There are also documented cases of carb overflow hoses sucking water. I got this issue on my CB750K K7. It uses same style carbs as CB550K3 (PD type).
There were really sucking water via overflow hoses. Reason is simple, vents in bowls (very tiny holes!) were clogged, carbs were vented via overflow hoses. As they are terminated close to rear wheel, water spray was sucked inside carbs...

Honda eventually found out that this problem occurred - be it a bit late - and fitted a second nipple next to carb#2 to accomodate a TUBE, AIR VENT (4.5X6X350) , PN: 16143-404-600. 'Late' meaning: CB550K4-A, VIN# CB550K-2100001 TO CB550K-2122082. Nipple is shown on p.38 of the parts listl Honda CB550K3/K4 (difficult to see) and the tube is #11 in the pic. http://www.honda4fun.com/pdf_parts_list/pdf_spac500-550/CB500-550_K3-K4.pdf Don't know if Honda did the same modification on later CB750K7 models.

[dave500]

some gasket paper should work.

[bryanj]

Paper is a bit thin, cork or rubber would be better

[dave500]

the stock gasket looks like .4mm

[1977_cb550k]

Thanks fellas.

I doubt I will ever be able to give anywhere near as much advice as I receive on these forums, so I will give a donation to keep it going. All your input is really appreciated.

[Deltarider]

I'd start with looking after your plugcaps and -wires. With 30% loss of power, most likely the problem is there. At least that's my idea. When caps and wires age, they become dirty. In rain deposits like salts will become conductive. When the weather is dry - hey, a miracle! - the problem is gone. Not so. If you keep the same plugcaps and -wires, bring a can of WD-40 when expecting rain.