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Discussion Starter · #1 · (Edited)
Hey guys,

I'm that's_incentive, check out my intro for pics.

I just picked up a 71 cb350, and it runs well, I'm just planning on going through it to get it on the road. One thing I noticed was the petcock would leak in reserve, so I let out the gas and took it off-

IMG_3939.jpg IMG_3930.jpg

Found the problem!

But it would turn out to be only the start of my problems. While the tank was off I removed the rust, which turned out to be quite the ordeal. One good chunk of change, one episode of flash rust, and three days later, the tank was clean, finally. I poured my first gallons of fresh fuel into my spotless tank. I breathed a short lived sigh of relief.


Everything looked good for all of about fifteen minutes before the petcock started dripping. I tried to snug up the lever plate and heard a snap as gasoline began to gush profusely from the lever. I quickly removed the petcock, to find that the threading had been stripped from one of the holes that holds on the lever plate. The other is 100%. I pushed on the screw and it just ripped out what was left of the threading, wrapped neatly around the screw. Neat!


Anyway, I'm currently trying to plug the hole, so I can leave the gas in the tank until I can get a new petcock- I *really* don't want to do the rust thing again.

TLDR- couple questions.

Best way to plug petcock hole to stop gas? I've tried a few ideas but this thing is going to have to hold for maybe a week until I can get my wretched hands on a new petcock. I'll try to source one locally when I get back Monday, but not counting on it. Only Walmart is open and I leave for out of town at 6am so I'm in a pickle.

I might just dump the tank and coat it with oil for the time being.

And WTF? Evaporust vs Aluminum? It says clearly on the box it's safe, so I just left the petcock on so I wouldn't have to make a seal. Jokes. on. me.
 

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Oil coating is a good way to go. I'd use 2 cycle oil if you have it but any oil will work. Then put a piece of tape over the petcock hole.
 

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Discussion Starter · #3 ·
Thanks. I ended up going with that, just had normal 4 stroke oil, gave it a good coat and checked a few hours later and there was still a nice oil slick coating everything I could see at least.

Can you speak on the medium term efficacy of the oil used in this way? 3-4 (business) days hopefully.


I was able to find a thread here in which a user had been known to plug the hole with an old tube stem. Genius. I just didn't want it to dissolve in the gasoline but that's what I've got in the hole now just to minimize air exchange and whatnot.
 

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That petcock was garbage before you put anything into the tank. It is missing the main tube that feeds the ON position and the screen for the reserve is pretty messed up a well. The gasket is probably hard as well.

I've gone through several gallons of evapo rust and clean carbs with it. Never have had any issues with it other than it leaving a light line where a part wasn't totally submerged.
 

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Discussion Starter · #6 ·
Boomerz, good to know, I was wondering why the ones I was finding online had second tube. Thoughts on OEM vs Chinese? $40 price difference, only difference I can see is plastic looking main tube on the replicas, brass on OEM.

Sweet on the oil J-T thanks.
 

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I can't really speak to comparison of OEM and replica petcocks but there are plenty of the latter in use. Most of the usual vendors sell them and plastic is probably more prevalent than brass in most new fuel system components - though "plastic" can cover a whole lot of materials! That said, I would always prefer brass but for forty bucks... :rolleyes: I wouldn't be afraid to take a chance if it was from an otherwise reputable vendor. If it is from an ebayer shipping from Asia (or an address in CA) I might exercise a bit more caution. ;)

For whatever reason, delivery times have become more of an issue for me on parts orders lately. I've found myself leaning more toward closer vendors or promised delivery dates than price. Something to consider since it sounds as though you are in sort of a hurry.
 

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Discussion Starter · #8 ·
Nice yeah I can get a replica from dime city so it should be alright. Yeah I'm waiting for shops to open here so I can call around and see if I can order one through them and see if it would be quicker/cheaper on shipping. Idk if you can do that but skate shops etc. will order random stuff for you if they don't have it so worth a shot maybe.

I am in something of a hurry, I'm excited about this bike, and don't feel comfortable with it sitting for any amount of time. But if I learned anything from my (mis)adventures with the gas tank (aside from a bunch of other stuff) its that it's better to go slow and do it right, first time. Like I don't know what I was thinking even working on the tank if I wasn't ready to button it up. I mean the petcock had to go anyway. Stupid, but a valuable lesson for me.

However price is also a concern, so I'm just going to slow things down a bit and try to spread out my cash and really focus on what needs to be done and in what order. I'm a novice so I'm going to need a clear head for all this, and a state of hurry isn't conducive to such a state of mind, I'm finding out quickly.

Oh yeah and boomer re the evaporust- that's weird, I wonder why the threads were so weak, something else must've gotten to it at some point.
 

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Nice yeah I can get a replica from dime city so it should be alright. Yeah I'm waiting for shops to open here so I can call around and see if I can order one through them and see if it would be quicker/cheaper on shipping. Idk if you can do that but skate shops etc. will order random stuff for you if they don't have it so worth a shot maybe.

I am in something of a hurry, I'm excited about this bike, and don't feel comfortable with it sitting for any amount of time. But if I learned anything from my (mis)adventures with the gas tank (aside from a bunch of other stuff) its that it's better to go slow and do it right, first time. Like I don't know what I was thinking even working on the tank if I wasn't ready to button it up. I mean the petcock had to go anyway. Stupid, but a valuable lesson for me.

However price is also a concern, so I'm just going to slow things down a bit and try to spread out my cash and really focus on what needs to be done and in what order. I'm a novice so I'm going to need a clear head for all this, and a state of hurry isn't conducive to such a state of mind, I'm finding out quickly.

Oh yeah and boomer re the evaporust- that's weird, I wonder why the threads were so weak, something else must've gotten to it at some point.
Good idea to slow down and try to prioritize future plans. ;)

It's way too easy to get excited and anxious on projects but as you've already discovered, slow and sure is the best way. All those TV shows and youtubes where they're rushing to finish a build in 72 hours or something to win a trophy at some show is... well, it's TV. :grin: It's entertainment. It is also usually a bunch of experienced well financed guys who've done this before. :cool: No. Take your time. Learn about what you're doing and enjoy the challenges. Above all else view every challenge as an opportunity to gain a new skill or knowledge. It is amazing how many processes and skills can transfer to totally non-related tasks later in life. Observe your limits, but never be deterred from trying something new simply because it's new!

"Made in China" (or Malaysia, Taiwan, etc.) is not the mark of cheapness it was just recently. As with anything, there is good and bad stuff produced anywhere. We live in a global market. Might as well get used to it. My best advice is to stick with reputable vendors who will honor a bad part or lost shipment rather than the cheapest guy on ebay. It's no guarantee of quality but it does save some of your hard earned cash when things go wrong.

I seriously doubt your threads were stripped by any chemical action. Those are tiny screws with VERY fine threads. Worse is that the screws are much harder/tougher than the metal they are tapped into. Best guess is the seal started leaking somewhere in the bike's history and someone tried to "fix it" by simply tightening the screws. Those threads were stripped by too much torque, not chemicals. ;)
 
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Discussion Starter · #12 · (Edited)
Yeah anxious is probably a good description of how I feel! I agree with your thoughts on the interplay of learned skills in all areas of life. Pretty cool.

Ah well in that case it was probably me! I'll have to be more careful about that. Also broke a small piece of the right choke plate trying to turn it from the inside :p oops.

IMG_3966.jpg

You'll notice the tips of the little wings on either side of the flap were missing too, kinda nervous about where those may have ended up.

Speaking of the carbs, I pulled them to take a look and put them back on the bike dry, will they be ok for now or should they be filled?

Looks like a shop here (Limey, ATX) can fix me up. He was pretty cool on the phone, tried to sell me on an OEM but said he'd see if he has any aftermarket in stock. Said if not, he could usually order one in a couple days tops or said we probably could piece together a good one from parts around the shop. That would be awesome, didn't ask about price though. Hopefully he'll hook me up if we do it that way.

He's out today, so I'm going into the shop tomorrow. Wish me luck, I'll update, I just know you all can't wait to find out how it ends.
 

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Threaded connections are more complex than we often think of them. As they tighten, only one side of the thread is making contact. Assuming the red is your steel screw and the blue is your aluminum petcock you can see how the threads were sheared off. The inclined plane of the (screw) threads is still pulling against the threads of the hole even as the inward movement has ceased. As the head bottomed on the surface of the petcock, it transferred increased pull on the extremely fine threads in the aluminum. It doesn't take much. They used to call this "mechanic's feel." In the absence of a torque wrench (and sometimes despite one) an experienced mechanic develops a feel for just when it's tight enough. ...and frequently still shears bolts. :grin: You're in good company. Don't fret over it. At least it was a trashed part instead of a screw sheared off in a necessary part!
bolt-10-32-fine-mesh-detail-zoom.jpg

This is why extra caution is advised when re-using fasteners. The smaller the screw, the more critical each stretch (tightening) of the fastener is to it's remaining shear strength. If in doubt, use new fasteners! If you buy a part that comes with new screws/bolts, USE THEM! Many parts on motorcycles use steel screws in aluminum housings. Look up the torque recommendations in the manual and err on the side of caution if in doubt.

You're doing good. Every experience is a learning opportunity. Especially the bad ones! ;) "Keep your gratitude higher than your expectations." - Ray Wylie Hubbard
 

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Good idea to slow down and try to prioritize future plans. ;)

It's way too easy to get excited and anxious on projects but as you've already discovered, slow and sure is the best way. All those TV shows and youtubes where they're rushing to finish a build in 72 hours or something to win a trophy at some show is... well, it's TV. :grin: It's entertainment. It is also usually a bunch of experienced well financed guys who've done this before. :cool: No. Take your time. Learn about what you're doing and enjoy the challenges. Above all else view every challenge as an opportunity to gain a new skill or knowledge. It is amazing how many processes and skills can transfer to totally non-related tasks later in life. Observe your limits, but never be deterred from trying something new simply because it's new!

"Made in China" (or Malaysia, Taiwan, etc.) is not the mark of cheapness it was just recently. As with anything, there is good and bad stuff produced anywhere. We live in a global market. Might as well get used to it. My best advice is to stick with reputable vendors who will honor a bad part or lost shipment rather than the cheapest guy on ebay. It's no guarantee of quality but it does save some of your hard earned cash when things go wrong.

I seriously doubt your threads were stripped by any chemical action. Those are tiny screws with VERY fine threads. Worse is that the screws are much harder/tougher than the metal they are tapped into. Best guess is the seal started leaking somewhere in the bike's history and someone tried to "fix it" by simply tightening the screws. Those threads were stripped by too much torque, not chemicals. ;)
Well said oupa. I'll add though, try not to get ahead of yourself and order parts for parts of the project down the road. I can't tell you how many times I've got stopped on a project and when I got back into it, forgot parts that I ordered in advance and either re-bought them or found that they had aged so much I had to order new ones. Money wasted.
 
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OEM fuel tap is zinc based, don't know if that makes a difference to Evaporust? Sucks to have put gas in though and found the leak still there. You did fit a new 4 hole washer'?
 

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Evaporust is harmless, really not going to mess up anything on your motorcycle at all. Don't worry about flash rust, use a filter, rust never sleeps.
You can start worrying when you've dumped 3 gallons of muriatic acid in your tank and your petcock gives out...
Lots of petcock issues in the forum lately.
 
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Discussion Starter · #17 ·
Hey cool stuff oupa thanks. Can't seem to find the torque specs, I was looking for them the other day. I was looking in the shop manual for -250-350, I'll have to look around more.

Sorry crazypj do you mean the rubber one? I really didn't think to do a kit beforehand since I thought it was at least water tight. whew.

South Wales huh? That's sweet, must be some place to ride when it isn't drizzling. Hell even when it is.

That's good to know about the evaporust and the flash rust, though I got the tank looking real good for now at least and hopefully I can fill her up tomorrow. You can't use that stuff on the o-ring chain can you? Won't it clean out the grease too much?
 

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Discussion Starter · #18 ·
Well said oupa. I'll add though, try not to get ahead of yourself and order parts for parts of the project down the road. I can't tell you how many times I've got stopped on a project and when I got back into it, forgot parts that I ordered in advance and either re-bought them or found that they had aged so much I had to order new ones. Money wasted.
I couldn't even if I wanted to, unfortunately! On a bit of a budget.
 

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Boomerz, good to know, I was wondering why the ones I was finding online had second tube. Thoughts on OEM vs Chinese? $40 price difference, only difference I can see is plastic looking main tube on the replicas, brass on OEM.
So technically not a motorcycle, but had a petcock in a Honda NA50 that leaked. Replaced it with the cheapest one I found online, doubt it was OEM. Worked fine all last year. I could verify this because the carb needle loves not to seat in that thing, and leaving the petcock on would result in a nice puddle of gasoline all over the floor.

Suspect if it isn't the same replacement part as on motorcycles, it's similar.
 

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It's similar enough although 350 has a left/right threaded nut with an o-ring to seal it. Works well when you figure out how to adjust/install it (one end of nut has extra thread) I wouldn't worry about a cheap aftermarket fuel tap, I've used them without issue. The only downside I found was the delivery time from China
 
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