Triumphrat

xardoz · 04-24-2007, 10:15 AM

My dad has a 1978 Honda CB-550 we picked up years ago that just has never run right. We can get it started easily enough, and it revs fine in neutral or with the clutch engaged, but it sputters and stalls under load.

We've done some carb work (drained and cleaned) and replaced the gas more than once, and we've replaced the rusted out tank and exhaust system. My dad thinks it may be electrical, but that doesn't make much sense to me.

I've asked this a few years ago at sohc4.net, but no one was able to help, and my dad wants to get his project bike running. Does anyone here have any thoughts or advice?

(other than sell it for parts and buy a Triumph)

97sprint · 04-24-2007, 11:14 AM

Try a plug chop.

What color are the plugs ? Nice tan ? Or black and sooty?
Tan is good, black/sooty is rich.

In any gear it "dies" or no power?

Who cleaned the carbs? With it running spray some wd-40 or water on the carb boots, does it change idle?
If yes you have a leak, causing it to go lean and sputter.
The leak is cause the carb boots are either not seated correctly or the yare old and cracked.

Or run some sea foam thru it to clean the internal passages in the carbs. Were the jets pulled and cleaned?
MAybe they are not seated correctly.
Check the flaor levels in the carb bowls

xardoz · 04-24-2007, 02:42 PM

Thanks for the reply. It loses power, then dies if you don't pull in the clutch and give it some revs. I can't say if it will do it in any gear, since we couldn't get it fast enough to warrant shifting up out of first. The tranny does shift smoothly in centerstand tests.

The plugs were a bit black, so it's a bit rich, but I've seen worse. My dad cleaned the carbs - removed the bank from the bike as a unit, drained the float bowls, cleaned with carb cleaner, a tooth brush and compressed air. We did not pull the jets - they're press fits for the '78 and we didn't want to risk screwing them up further - but we did check the float levels (they were OK).

I honestly don't recall if we ran carb cleaner through it while it was running, but I suspect we did. At this point, it probably wouldn't hurt to do it again. We did not perform a leak test on the boots - that's a good idea and I'll pass it on to him. I'll also recommend we try the Seafoam treatment.

Thanks again.

doodledog · 04-24-2007, 05:21 PM

Coils breaking down under load? as usual without being there its so hard to say but it does sound electrical to me as it it mechanically runs on tick over and revs in nuetral then it sort of points at electricals, a 78 still had points run from the end of the camshaft did'nt it is the advance retard plate ok? its got the weights and little springs on it, if again my memorie is correct, spray it with WD40, apart from that go back and check everything again.

danf_florida · 04-24-2007, 08:41 PM

Try to check gap of spark plugs. And if you can, do a compression check on the cylinders. Also, if the silencers are plugged, this could affect the same way (mouse nest).

[ This message was edited by: danf_florida on 2007-04-24 20:48 ]