Author Topic: 1975 CB400F -- decision time  (Read 766 times)

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Offline musiccity

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1975 CB400F -- decision time
« on: April 18, 2020, 08:50:47 PM »
Pulled the motor today to get the frame ready for the welder to repair the damaged tube (thanks for the advice on that, calj737).  It's decision time on how far I want to go on restoring her.  I am the second and fourth (current) owner of the bike.  I would like to get her as close back to stock as possible and be roadworthy for the occasional fair weather ride.  The bike was running before the frame issue cropped up and sidelined her, only 7500 miles on the odometer. The brake m/c has since rotted through its seals, so a rebuild there is mandatory. The tires are old and need replacing.  Beyond that, I face some choices.  This board is full of great info, some of which is making me reconsider what I originally planned to do. So additional input on my options welcomed from all.

1.  The engine has developed a slow oil leak between the upper and lower cylinder heads, probably a head gasket. It isn't blowing oil, just dribbling out onto the fins. Photo here: https://flic.kr/p/2iRPX8R.  I understand this is a somewhat common problem on these bikes, but there seems to be some disagreement whether its really avoidable or worth tearing down an otherwise good motor to fix.  But the motor is out to allow for the frame repair, so it's easier to do it now if it needs to be done. First decision: Take the motor apart to replace the gaskets, or live with the small leak as a cosmetic issue until something in there really needs fixing?

2.  Third owner left gas in the carbs when it was stored, gumming everything up. I've removed the carbs and gone through about a can of carb cleaner to get them ungunked (as best I can tell). Floats are eaten away in spots and gas would leak from the carbs when the bike was at idle.  I was getting some sputtering at high revs that could be the carbs or ignition.  Second decision: Send the carbs out for a rebuild by a pro or replace the floats and see if it was enough to just clean them out?  It's been too long since I rebuilt a carb myself to tackle a set of four.  The carbs are a PITA to remove, so I am leaning here to just dropping the dough on a thorough rebuild to eliminate them as an issue.

3. I was considering a Dynatek electronic ignition with upgraded Magna coils. But these coils do not fit the stock bracket according to 4into1.  Some debate about whether the Dynatek unit needs the upgraded coils, whether the Hondaman transistor ignition system gets you most of the benefit with less hassle/expense, or to just stick with the stock ignition if you aren't going racing.
Third decision:  Dynatek only, Dynatek plus Magna coils, go the Hondaman route, or do nothing now other than clean up and adjust points as needed?

4.  The main wire harness is fairly inexpensive and could be easily replaced given how much of the bike is disassembled now.  These are almost 50 year old wires and connectors.  Fourth decision:
 Replace the main harness to avoid going connection by connection to assure clean contact?

I'm trying to find the right "while I am at it" fixes.  I appreciate the wisdom of those who have gone before me on these decisions.  Thanks in advance.
« Last Edit: April 18, 2020, 08:55:20 PM by musiccity »
1975 CB400F Super Sport