1973 CB350... (she's getting there! new PICS!)

Re: 1973 CB350... my first bike build

been busy with other stuff lately and haven't had a lot of progress to report
replaced the headlight brackets to lower the profile a bit, but the gauges are still up higher than i'd like. i was thinking about just putting the bracket under the triple tree. does this work? i didn't really examine how its put together closely.
also ditched the bars in favor of some Woodcraft clipons. my dad helped me drill them for the internal wiring and anti-rotation pins. it was a a bunch of work, but it looks really clean and i'm very pleased with how its turning out.
had to wrap my forks since they're pitted really bad though :( i am keeping the gaiters. right now i just have some hose clamps to hold them up until i come up with something better.

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Re: 1973 CB350... my first bike build

'nother update for ya.
-Driven Gel grips installed
-new turn signals and taillight installed
-stock turn signal relay replaced with electronic flasher since the new signals would just stay lit with the relay
-reused part of my GSXR fender to mount the turn signals on either side of the plate. stock ones were mounted to the huge grab rail which had to go

it starts easily, normally only taking a kick or two (sometimes alot if i forget to flip the kill switch to 'run' duhhhhh). its running on both cylinders now and the slow return to idle isn't as bad as it was, but i have new floats and rebuild kits ordered.

i also put insurance on it and received my title and plate back, so i'm street legal now. i got antique plates so no annual registration fees or inspection.

took it on a 23 mile run tonight, just running around town. the brakes suck and the slow return to idle means there isn't alot of engine braking, but it's a blast to ride.

it was great just wringing its neck and hearing it scream. sounds pretty mean with the new pipes too. still haven't got the seat done yet though

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Re: 1973 CB350... my first bike build

installed new floats in both carbs yesterday and found out that i have a torn diaphragm. also ordered some stainless steel brake lines and i need to get new pads too since i'm not happy with how it stops now.
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Re: 1973 CB350... my first bike build

Looks good Greg! Tough luck on the diaphram.
 
Re: 1973 CB350... my first bike build

Big Rich said:
Looks good Greg! Tough luck on the diaphram.
Click to expand...
been a while since i updated this, but a lot has happened in that time.
i replaced the torn diaphragm, but unfortunately that wasn't the cause of it not dropping down to idle.

theres a local guy that is really into old bikes, so i took it to him to see what he could make of it. he synced the carbs and adjusted the tension on the cam chain and it seemed to be running fine. it would, however, slowly die if it was idling for an extended period. i was leaning towards it being the rectifier and was going to replace it.

i had put about 200 miles on it since picking it up on tuesday of last week, including a few short (<20 miles) trips on the highway and a long cruise on backroads yesterday. it was running great. even checked my gas mileage and it came out to about 70mpg.

went out again today around noon. i was less than 10 miles from homeway going up a hill on the highway at about 60mph when it started breaking up really bad. i had the throttle turned all the way so i could get off to the shoulder, but it was still dying. i pulled off on a very convenient exit and coasted to the side of the road. looked down and noticed that my turn signals weren't work. hit the starter and it didn't even make a noise.

so i lifted the seat and sure enough the bolt had vibrated out of the positive terminal. luckily i was wearing a set of ear plugs that had the string connecting them, so i tied the cables to the terminal and road it back home.

i scrounged around and found another bolt, put it in and went on my way again. i was back on the highway now, a little further than i had made it before. i was cruising along at 60-65mph, which is around 6,000-6,500 rpm in 5th gear on the CB, well short of the 9k+ redline. starts breaking up again, losing power, AGAIN.
OK, well this sucks. take the next exit, coming down to the stop sign and it starts popping and backfiring. i limp it down the road a couple hundred yards to get to a good place to pull over and shut it down.

checked the battery, but sadly it wasn't the problem. no easy fix this time. i had only ridden it a couple times and was too dumb to put together a proper tool kit like i had been planning, so i couldn't do anything. called my dad, told him what happened, so he came in the truck with some tools, thinking it was probably just a fouled plug. we pulled the plug and sure enough it was wet and a tiny piece of carbon was lodged between the electrodes.

cleaned it up, checked to make sure we had spark, and put it back in, but it wasn't running on that side. exhaust coming out of that side was cold and now there was hardly any compression. still not running on that side and occasional backfiring.

and to think i thought i was only a seat and some paint away from having this thing finished :(

crap.
 
Re: 1973 CB350... my first bike build

well, we found the problem tonight. i don't want to just tell you guys though, i'd rather wait and just post a picture of the carnage once i get it all apart.

almost got the engine out of the frame. i just need to disconnect the starter and lift it out. i was planning on taking it out this winter so i could touch up some of the rust on the frame and clean everything better, but i guess i'm doing it a little earlier than planned.
 
Re: 1973 CB350... my first bike build

it was the cam tensioner, wasnt it....



shit man, she was looking great too!
 
Re: 1973 CB350... my first bike build

Rocan said:
it was the cam tensioner, wasnt it....



shit man, she was looking great too!
Click to expand...
crap. could be.

it was loose and just had it tightened last week which could have been enough to cause it to fail.

all i know right now is i have a rather large hole in my left piston :(

i'll update this when i get in deeper tomorrow
 
Re: 1973 CB350... my first bike build

That was gonna be my guess - from the exhaust cold on one side.

If it was the cam chain, might have bent a valve. Do you know it's the piston? Could be snapped rings too.
 
Re: 1973 CB350... my first bike build

could be loose tensioner allowed the cam to jump around, allowing a valve to hit the piston. its a bit less likely, but a possibility.

oh well... see it as an excuse to overbore and modify! ;)
 
Re: 1973 CB350... my first bike build

Valve touching a piston won't usually make a hole, unless valve head snaps off.
Post a pic of piston, sound like lean mixture burned a hole or timing out caused detonation and broke it
 
Re: 1973 CB350... my first bike build

cb350greg said:
crap. could be.

it was loose and just had it tightened last week which could have been enough to cause it to fail.

all i know right now is i have a rather large hole in my left piston :(

i'll update this when i get in deeper tomorrow
Click to expand...

When you pull the top and post pictures of the head and piston we can determine what went wrong. I happen to like the broken tensioner/broken valve theory. We have had a few of those on other bikes. Detonation to that extent is relatively unusual on a 4 stroke but not impossible.
 
Re: 1973 CB350... my first bike build

i have the motor totally unbolted and disconnected, but since that little motor prob weighs more than me, i need to wait until i can get my dad to help lift it out.

i'll keep everyone updated. i really, really hope its just the piston. don't want to have to do valves, piston, AND cam chain tensioner :(

this was the side that i had a lot of trouble getting it to run on at all when i got the bike... wonder if there was already something wrong in there that lead to this? guess i won't know til i get it apart
 
Re: 1973 CB350... my first bike build

Ha! It's not too heavy - but lifting it out of the frame is a pita.

You can actuall lay down a thick blanket of something and tip the entire bike over. Once the motor is on the "cushion", just slowly stand the frame back up.
 
Re: 1973 CB350... my first bike build

Yeah dude! Shit this is worse than the season ending cliff hanger of LOST!!
 
Re: 1973 CB350... my first bike build

i'm back guys.... but not with good news.
i finally got around to lifting the engine out and yanking the top off to see what the damage is like.
so far it looks like it needs bored, new rings and pistons, new cam chain tensioner (and new cam chain i'd assume). valves look ok. probably need to tear into the bottom end to clean it out. hopefully the cam is ok.

ughhh this is not how i planned this. the freaking thing was running, and pretty decent too. i was going to do the seat and then just ride the thing. did not plan on dumping hundreds into the motor :(

any of the local guys have a running 350 engine they want to get rid of??
 
Re: 1973 CB350... my first bike build

Where are you located? I'm picking up a 350 today, not sure if its a parts bike or a project yet.
 
Re: 1973 CB350... my first bike build

i need to find some good prices for .25 over pistons, rings, a whole gasket set, and a new chain tensioner. who wants to help me shop??
 
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