Topic: Gradual loss of power and surging ('78 550 Four)

[fivefiftyfour]

Hi all, been on here since '98 but forgot my old login so I'm a "new member." I've searched the forums for gradual power loss and surging, but didn't find quite what I have going on, so please forgive me if this is covered in another thread.

I have a '78 550 that has been running reliably and revving great for years. It may have been running a bit lean, since it tended to crackle when I let off the throttle and backfired when cold. This week, it started a subtle power loss/surge at steady throttle, which became worse within 20 minutes. When I got back on it a day later, it started normally, but I could tell the throttle was a bit rough. Within 5 minutes, I had to keep the throttle steady around 2500-3000 to keep it running, and the power was surging up and down at steady throttle in neutral. Power loss in gear was getting much worse and I barely made it back home, where I just let it stall by letting off the throttle.

The lack of power and surging seems that it's likely a fuel issue, but just want to get your take on it in case I should consider testing the ignition first. If it's a fuel/mixture problem, why did it increasingly get worse? Is a jet getting blocked slowly, or is it a part that's gradually failing? All of the "why's" aside, seems I need to clean and inspect the carbs and go from there. I appreciate any recommendations if these symptoms are clearly a mixture or other issue. Maybe a sticky float or needle?

I'm pretty sure the carbs are stock, but have been rejetted for the funky 4 into 2 pipes on my bike. The original air box is gone, but the air setup is mainly stock with a single filter under the seat feeding all carbs through the stock air manifold. There have been some cracks in the air manifold that I've caulked, and I think it's sealed off but will check if there are any new leaks.

Thanks all.

[scottly]

Inspect your spark plugs; they are the windows to what is happening inside the combustion chambers. Post pics.

[fivefiftyfour]

The plugs are all much the same: wet and black around the end of the threads (I really hope that's unburned gas, not oil...), sooty deposits on the electrode, the insulator is dry or partially dry but dark gray. Maybe the #1 and #4 plugs are a little more wet throughout. The last time I started it, it was only for 20-30 seconds, so much of the wetness could be due running it cold. I adjusted the timing and cleaned the plugs about two weeks ago, so the soot and buildup is new.

Posting pics of the plugs here, hopefully they'll upload for me...

[fivefiftyfour]

Given that all four plugs are showing the same symptoms, maybe it is an ignition problem? Any recs on where to start? It has the original points ignition, with new condensers installed about a month ago.

[TwoTired]

Been a spate of recent posting where new condensers were faulty.  Do you still have the old ones to try out?

Cheers,

[scottly]

Specifically Daiichi brand condensers are known to fail in a short amount of time. If your new condensers have the three-bladed propeller logo on the end, get rid of them.

[fivefiftyfour]

The new condensers don't have any markings on them and came in generic packaging. I do still have the old condensers, so I'll swap 'em back and report the results. Thanks

[fivefiftyfour]

I think you nailed it, TwoTired. I switched back to the old condensers, cleaned the plugs, and it’s running fine now. Ridiculous that these things failed in about 20 hours of riding.

I got the condensers along with points on eBay, thinking they were OEM. They showed up in generic packaging and no markings or print on the condensers, so I can’t say what make to avoid, just buyer beware.

Thanks for the tip! I would be deep into the carbs by now otherwise.

[TwoTired]

Glad you tracked the problem down.

Ride safe!

[dave500]

too many carbs have been removed/cleaned over and again because of an ignition problem,allways be sure your ignition is spot on first!its a lot easier!