Topic: What did I do?

[olmy]

Hi folks

I'm having some trouble with my '75 CB550F, my 1st bike, which I bought last fall.  I had pulled off the float bowl covers and bought some new gaskets as the old ones had swollen up.  The guy at the parts store told me to put a little bit of silicon into the grove to keep them in place.  Extremely bad idea.  After I put them back on, the bike ran fairly well, but soon died after 20 mins of riding.  The plugs were black and a bit wet.  I pulled the bowls off again and found the silicon had swollen up and fallen into the bowls.  I cleaned them out as best I could and put them back on (using advise from old posts on this forum to get the gaskets in place ... thanks), with some new plugs.  The bike ran again initially and I took it for a short test ride but I had to put it way for a couple days.

When I came back to it, it was only running on 2 cylinders, #3 and #4.  The exhausts on #1 and #2 were barely even warm.  As they don't share an ignition coil, and given the silicon problem, I assumed I had clogged up the carbs.  I pulled them off, dissembled and cleaned them, put in new jets, a new needle valve and gaskets and put them back on (again using losts of great advise from old posts).  While it was off, I also checked the valve gaps and tried to clean the points up (I used a metal nail file as I can't find a points file so far).  When I put it all back together, it started immediately and ran better then it ever has.  I couldn't believe it!  I was thrilled as the carb rebuild was the most ambitious job I've taken on yet (I am a true newbie).  I took it out for another short boot and had to put it away for the night (work keeps interfering).

Sadly, the next day when I took it out, it was right back where I started.  Running on only #3 and #4.  ARGGGHHH!

Does anybody have any ideas as to what could have changed in a few hours sitting in my garage?  How could it run so well one day and be back to running on two cylinders overnight?

[Bob Wessner]

I'm assuming you have verified that the offending cylinders are getting air, fuel, and spark? What do the plugs look like in the two non-running cylinders? Dry, wet with fuel, sooty, what?

[TwoTired]

Clean carbs won't stay that way if fed from a dirty fuel source.

Any rust and scale in the fuel tank?

Have you checked the integrity of the in tank fuel filter?

Are your fuel hoses disintegrating on the inside?

Drain and catch the contents from the float bowls.  Is the fuel still clean?

Cheers,

[olmy]

Just got home and getting ready to get back at 'er.  The plugs look pretty good.  They appeared dry and clean compared to before I worked on the carbs, in which they came out very black and wet.  They spark but I am not certain how well, as I don't have a real frame of reference (1st bike).  My Clymer manual describes a "fat blue spark" but I see only a small spark, virtually colourless, but I did this check them in bright daylight.  What should I see?

I have the small in-line fuel filters installed between the tank and carbs and I had replaced all the fuel hoses when I did the job.  I'll drain the float bowls anyway and have another look.  I'll drain a sample straight from my tank too and see what I get.  It's been a good six weeks now since I refilled the tank.  I used some Sunoco 94 (thought it would help clean the system out).  It should still be O.K. should it not?

I'm going to try another set of plugs to see if that changes anything.

[olmy]

I finally had a chance to get back at this and I found the problem.  A pinched fuel line of all things.  I assumed it wasn't a fuel problem because it had been running the day before but sure enough, when I tried to drain the float bowls on 1 and 2, nothing.  I cut a new piece of fuel hose when I put the carb back on and it was a bit too long such that the geometry of the hose and the in line filter crammed between the intakes bent it enought to cut it off.

I don't know how it ran so well intially.  Surely I would have exhausted the fuel in the float bowls in a few minutes.  I'm thinking it wasn't kinked intially and that I must have taken the tank off one more time before I put the bike away and the hose got bent at that point.  Lesson learned.  Never assume anything and always do the basic checks first.  It should have been obvious.  What do carbs/cylinders 1 and 2 have in common?  They both are fueled by one hose coming directly from the tank.  Is there some way to learn to work on bikes without making endless stupid mistakes?

[Bob Wessner]

Is there some way to learn to work on bikes without making endless stupid mistakes?

Maybe, but this is as good a teaching method as any. I use this method frequently myself. 

[Dusthawk]

A mistake can only be stupid if you don't learn something from it. Therefore, your mistake was actually a smart mistake!

Peace and Long Rides,

Jeff