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1975 Honda Cb550, help me troubleshoot?
1975 Honda CB550 K1, all stock engine (air box, carbs, etc, all stock)
Here are my symptoms:
- The colder the air, the harder to start and the more cranking it takes - won't start at all when colder than about 60degrees outside - starts fine after engine is warmed up.
- The warmer the air, the smoother it runs throughout the power band
- Runs very rough when cold - the colder, the rougher
- Choke on makes the RPM drop rather than rise
- Smells like it's running rich, but air/fuel mix screws are set as specified in manual
I'm just curious as to what these symptoms point to. I suspect it could be one or more of the following: vacuum leak somewhere, running rich, carbs out of sync. Let me know if any or all of these are valid or if there's something else it could be
Thanks!
4 Answers
- bikinkawboyLv 71 decade agoFavorite Answer
Your bike has a true choke, rather than the more common enricher circuit found on later carbs. A true choke reduces the amount of air and because of that, it will reduce engine rpm rather than speed it up like enrichers do.
With your rocker arm valve train, the valves tend to loosen rather than ttighten like bucket and shim valve trains. While it's true tight valves can make cold running lousy, the valve train on your bike tightens as it warms up, which is opposite of the symptoms of your bike.
The running better as it warms up does point to plugged pilot jets, but if the choke is operating properly, they'll have nothing at all to do with cold starting.
Were it me, I'd be looking at the ignition rather than the carbs because the starting and running better when warm points to that. A lot of carb problems have been cured by fixing the ignition. If the plugs aren't new, then install new plugs gapped at around .028". That's miniscule by automotive standards, but bikes the age of yours had really crappy ignitions when new and they haven't gotten any better with age. Adjust the points, check the plug cap resistance as well as the condition of the plug wire insulation.
