Author Topic: cb550k4 PD overflow tube cracks  (Read 1321 times)

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Offline BigAl

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cb550k4 PD overflow tube cracks
« on: October 20, 2024, 05:23:18 AM »
Hi All, The bike is back together and running well, other than a constant drip out of the #2 (and a tiny drip out of the #3) carb.  I initially thought the floats were bad, but they were not.  Pulled the carbs out yet again and closer inspection shows some small cracks at the bottom of the overflow tube.  I looked around a bit on the forum and dug my solder and flux out and attempted a fix.  It worked a little bit, but I am having a hard time getting any uniformity of solder application.  I'm no expert, but neither am I a novice at soldering.  To me, nothing felt like it got hot enough to let the solder flow the way it wanted to.  It would ball up and roll out, or ball up and just stick.  Even with a torch.  So, I can pull the carbs out yet again and give it another go.  Any suggestions on doing this well?

I also looked around the inter webs for a float bowl, but they seems hard to find.  One thing I found that did peak my interest was a clear blue float bowl sold by 223cycles.net that looks like the correct bowl for my PD46s.  It is not advertised for these carbs, but it looks correct to me.  It would be nice to see the level of fuel across the bowls in real time, although I could also see it resulting in me pulling the carbs again and again making tiny adjustments to float levels.

For background, I rebuild the carbs on this bike that sat for an easy 20 years.  Replaced everything brass (mains, slows, etc).  Floats are set at 12.5 with a gauge, I think they are correct as I really took my time on them.  Running the stock airbox (which really makes the carbs a pain in the butt to pull).  New but stock main jet (90 I think), but did raise the needles up a bit as my understanding was that they were a bit lean at factory setting.  My next question will be to get my idle to be a little less finnicky, but maybe that will come with fixing the leak through the overflow.  Only unusual think is that my tank was bad and I am using a tank off of a 74.  That shouldn't make a difference though.
1978 CB550K4

Offline BenelliSEI

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Re: cb550k4 PD overflow tube cracks
« Reply #1 on: October 20, 2024, 05:55:48 AM »
I’ve repaired a few and they can be tough. The “balling up” you describe is usually because the pipe is not clean enough. You need to get in there with a Dremel tool, sandpaper, or even a make a small, sharp scraper and really get it clean. I assume you used a propane torch? And lots of flux paste? The other bit I keep aside for really tough soldering jobs is a roll of 50/50 solder (lots of lead), which you’ll never find. But, do make sure you are using “plumbing solder” not “electrical solder).

Offline BigAl

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Re: cb550k4 PD overflow tube cracks
« Reply #2 on: October 20, 2024, 06:40:58 AM »
Thanks Benelli, cleanliness could have easily been an issue as I did nothing as invasive as you describe.

I also feel kind of dumb.  Yup, I used electrical solder.  I do see 50/50 out there to buy, even on Amazon.  Is this the same stuff?  Or did the components change over time to make it less effective than it used to be?  At least I got the propane torch part right.....
1978 CB550K4

Offline BenelliSEI

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Re: cb550k4 PD overflow tube cracks
« Reply #3 on: October 23, 2024, 01:32:38 PM »
Thanks Benelli, cleanliness could have easily been an issue as I did nothing as invasive as you describe.

I also feel kind of dumb.  Yup, I used electrical solder.  I do see 50/50 out there to buy, even on Amazon.  Is this the same stuff?  Or did the components change over time to make it less effective than it used to be?  At least I got the propane torch part right.....

Go for the 50/50 and get it really clean and fluxed. When using a propane torch heat the pipe from underneath the bowl. That will tend to draw the solder to the bottom. Good luck.

Offline fire113

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Re: cb550k4 PD overflow tube cracks
« Reply #4 on: October 25, 2024, 12:13:13 AM »
...You can solder it but You can use shrinking tube too.
I fixed several broken small pipes with soldering  but the last I did with shrinking tube and still no more leaking.

Have a good one...Georg
Honda CB750 K0 & K0 & K1 & K1 & K2 & K2 & K6