Topic: 1973 CB350F "Modest Original" build

[sbeckman7]

Jetting is the only part I am slightly concerned about, only because I haven't done it before.  Plus the fact that everyone says tuning with aftermarket parts is an uphill battle

[iiAtlas]

Jetting is the only part I am slightly concerned about, only because I haven't done it before.  Plus the fact that everyone says tuning with aftermarket parts is an uphill battle

It'll be new to me too!  Eager to learn.  After tearing the carbs apart it all starts to click somewhat.  I'm no longer that worried, and I feel like I have a better understanding of what my actions in changing the jets will do re: fuel.  Get in there!  You'll feel better about it in no time.  The smart minds here will be able to guide you (and me!) in the right direction.

[iiAtlas]

The carbs live again!



The remnants of my organization.  All the remains bagged is some left over gaskets and fuel line.  I'd like to replace the fuel lines, does anyone know the sizing off hand?



There are way more parts in the throttle body than I'd imagined.  Again, pictures pictures pictures!  I wish I'd taken more.  It was a whole load of trial and error to get this thing back together, but after going at it about five times I'm confident it's all correct.  I was able to verify to the best of my ability correct alignment and placement of all pieces using a few pictures I had of the unit before I began disassembly.  Once you understand the concepts behind each piece everything begins to click somewhat.  An example, the link arms.  I knew from the throttle slides that each "ball" was sandwiched on either side by a spring (or screw) and a black pin with a divot in the top.  The pin sits in the spring, which is compressed onto the ball.  The ball sits in the divot allowing the arm to rotate but keeping it in place.  Very cool mechanism!  Here is a picture of the "pins" and "springs" I'm talking about.



Learning and making sense of these complex little things helped me feel confident that I'd put them back together right, but it certainly didn't prevent me from going through my fair share of bad ideas!  Some of you more experienced rebuilders will know immediately whats wrong with this picture...





Problem?  Yep.  Turns out you need to build all four carbs BEFORE placing the throttle body on.  D'oh!  I had assembled two of the link arms already and began tightening everything down.  Off they go!  I think I built the whole thing at least four times before I got it right!  Here was the most devastating realization...remember that small brass between carbs 2 and 3 which I thought was a "spacer"?



I put that o-ring on and assembled it thinking the o-ring was a buffer to prevent the carbs from clanking around.  Turns out, it's where the throttle spring mounts!  Another d'oh moment.  I desperately did not want to take the carbs apart again, especially not all four.  I used an exacto blade and some safety pins to destroy and remove the o-ring.  This took about 40 minutes of finagling - almost as long as it would have been if I just disassembled the whole thing!  Here it was before I removed the o-ring.





And after I managed to get the spring back in.





Much better!  A quick test and everything looks to be actuating properly.  I adjusted the four butterflies slightly so that they open at the same rate and to the same height.  The throttle slides appear to raise and lower at the same rate, all resting at the bottom and raising to the top.  I set all four air screws to a default 1.5 turns out.  There are a few places which seem like there is room for adjustment.  I'll run through them below.

1.  Throttle link arm adjustments.  There is a slotted screw which increases and decreases pressure on the link arm ball.  I set these to a what I thought was a somewhat standard place.  I tightened them until the arms looked to be even and straight.  Enough so that there was pressure, but not wrenched to the max.  I also simply screwed the top nuts on finger tight.  There doesn't seem to be much room for adjustment here, should I just snug them up with a wrench?





2.  Choke throttle stop.  There is a screw here which looks like it can be used for adjustment.  The throttle slides appear to bottom before this comes into play.  What is a good base for this position, and what does adjusting it do?





That should be it for now!  Any other adjustments you think I may have missed please let me know!  This was a really fun project and I'm happy with how it turned out.  Next step: engine!

[grcamna2]

Nice work, whew      I think the fuel line is 6mm i.d.

[iiAtlas]

Nice work, whew      I think the fuel line is 6mm i.d.

Whew is right! Thanks for the fuel line diameter. I'll attempt to verify with my current lines, hadn't thought of that for some reason...

[sbeckman7]

Looks great man!! Much better thank mine with those shiny bolts and linkages.  I just spent today sand blasting so finishing the carb's is on tomorrows list.  Although I did get the first one pretty much rebuilt

[grcamna2]

That last pic you posted is the high idle cam adj. screw for when your choke is fully engaged;you can adjust it precisely when you initially start up your engine after the work you're doing here.The idle should be just fast enough to keep the engine(2-2500rpm?)revving while it warms up.

[iiAtlas]

Looks great man!! Much better thank mine with those shiny bolts and linkages.  I just spent today sand blasting so finishing the carb's is on tomorrows list.  Although I did get the first one pretty much rebuilt

Nice job!  Super satisfying to have them cleaned up.  Good luck on the rebuild!

That last pic you posted is the high idle cam adj. screw for when your choke is fully engaged;you can adjust it precisely when you initially start up your engine after the work you're doing here.The idle should be just fast enough to keep the engine(2-2500rpm?)revving while it warms up.

Thanks grcamna, ADW (who visits this forum) has been schooling me on those two adjustments over on ADVRider.  I'll quote his post below as I think it has some good info (hope you don't mind me doing this ADW)

1. The nuts on top of the slotted screws are locknuts to prevent the slotted screws from moving. No need for more than just a titch past snug on these. They aren't holding anything together, they're just keeping the adjuster nuts from moving. These nuts and the slotted screws are what you'll be fiddling with when you set the carb sync with the engine running.

2. That is the fast idle screw for when the bike is on the choke. It determines how fast the fast idle is when the choke is in the fully-actuated position, and moving toward choke fully off it gradually drops the fast idle speed (that's what the little cam is for). The spec is for the little screw with locknut to be between 0.000-0.012 when the choke is fully OFF/NOT actuated. I'd set it toward the biggest setting, 0.012. Small changes in the screw make big changes in choked idle speed, which is supposed to be about 3500-4500 RPM. You can't adjust this "forever" until after you've gotten the carbs synced and everything else set just right. It's a #$%* to get to the little screw and especially the locknut once the carbs are on the bike. It can be done, but it'll piss you off when you finally do get the carbs synced and want to dial it in. I suggest setting it to the largest spec because my bike needed to be backed off quite a bit/was idling too high with mine in the middle of the spec, which is where I set it when I was at the point you are now. Hopefully once your carbs are synced the fast idle speed will be OK and you won't have to fiddle with it.

Motion Pro makes a very useful tool for syncing the carbs on this bike. It has a nice long screwdriver going down through a locknut wrench (the screw and nut in #1). Here's a link for it on Amazon. http://www.amazon.com/dp/B001DDH2ZY/ref=pe_175190_21431760_cs_sce_3p_dp_1 Worth every penny IMHO. It can be done without it, but damn...I wouldn't wanna do it without it!

I had a minor misunderstanding of what choke on and off meant, so I wasn't adjusting the fast idle screw properly.  I've posted a more in depth write up on my misunderstand over on ADVRider (link) but it doesn't feel too relevant here so I won't bother cross-posting the whole thing.  In essence, I mixed up what "choke on" and "choke off" was, which led me to adjust the stop screw in the wrong position.

For double, triple, quadruple verification (or at least to embarrass myself further)...with the choke lever down, "click"-ed into position, in the "off" / regular riding position the butterflies are fully OPEN.  With the choke lever up, in the "on" or actuated position, the butterflies are CLOSED.  Is this correct?

[grcamna2]

yes,I never touch that screw    you can possibly try to find the orig. position of the threads and just return it close to that..

[sbeckman7]

Right on the choke: when its on, the butterflies are closed to "choke" the engine. This causes a very rich fuel/air mixture inside the engine which is easier to ignite when the engine is cold. If you already knew that please disregard my comment!

[iiAtlas]

yes,I never touch that screw    you can possibly try to find the orig. position of the threads and just return it close to that..

Ha, if it aint broke don't fix it - good strategy  ADW over on ADVRider told me between 0.000" and 0.012" with the choke off (butterflies closed) was factory.  I set mine to 0.012" and will adjust as need once I get everything else dialed in.

Right on the choke: when its on, the butterflies are closed to "choke" the engine. This causes a very rich fuel/air mixture inside the engine which is easier to ignite when the engine is cold. If you already knew that please disregard my comment!

Makes sense to me!  Nice concise description, thanks for the schooling.


Decided it was time to get the engine going.  I followed my Clymer and began removing the bolts to get the head off.  Easy breezy!  One thing, I neglected to loosen them in any sort of pattern.  I'm not sure if this had any effect and my Clymer didn't make not of anything, but on the cars I am used to a sort of sequence to loosen and tighten so as not to warp anything.  Everything came off easy so I'm not worried, just thought I'd mention it.  I'll stick to a pattern when I torque them down to final spec.



When I looked inside I was pleasantly surprised by what I saw.  No visible pitting or rust on the cams or lifters.  The engine looks to have had oil in head for it's entire service and post-service life.  Of course this is all assumptions at this point, but nonetheless a good start to the project.  With the unknown history of the bike, it could've gone far worse.









That tachometer drive is so awesome.  What a mechanism!  At this stage I just snugged everything up.  Didn't have time to delve deeper and get a look at the pistons or valves, that will be the next leg of this journey.  I'm slightly less hopeful for the quality of the pistons as the exhaust and intake ports were simply plugged with a rag when I picked the bike up.  Who knows how long they sat with nothing.

One other thing to mention, as I was trying to place the camshaft cover back on (the big cover with all the bolts) I could NOT get it to sit right.  It would cock up on one side or the other, or sit with a 1cm gap all around.  Is it simply that the bolts snug it tight?  Or is it an alignment thing?  I didn't spend too long fussing with it so excuse the ignorance.    Thanks all!

[calj737]

You need to release the tension on the tappet adjuster nuts. These are the valve adjusters in turn, and to replace the cover, ALL should be loosened so as to not bend a valve as you bolt down the cover.

This is an idiosynchrasy of an SOHC motor with rockers attached to the underside of the cover.

[iiAtlas]

You need to release the tension on the tappet adjuster nuts. These are the valve adjusters in turn, and to replace the cover, ALL should be loosened so as to not bend a valve as you bolt down the cover.

This is an idiosynchrasy of an SOHC motor with rockers attached to the underside of the cover.

Ahh, interesting!  Just snugged them all hand tight for now, but I'll be sure to keep that tidbit in mind when I get there.  Hoping to continue down into the pistons tomorrow afternoon.

[iiAtlas]

Had some time tonight so I thought I'd mark the frame up.  This is tough for me.  I hate to take a grinder to something all original but I think it's keeping in vain with my vision of the bike.  Marked red is where I plan to remove.  Side cover mounts, battery and airbox mounts, seat hinge and clip.  I'll sit on this for a few days to let you all talk me out of it.  I'm working on that too...













When I see the frame like this I can visualize it though.  Clean lines, only what needs to be there.  Not ultra-minimal, just cleaned up to let the bike shine.  I feel like this is the right direction for me and for the bike.

[sbeckman7]

Two things I think you should consider (which you may already have). First, de-tabbing is more or less a one-way street.  Are you sure you won't ever feel a desire to change the bike again later on and wish you had kept some of those tabs?  Secondly, if you ever plan on selling it, will the future buyer want to restore it or feel like the bike is missing these tabs rather than benefiting from their removal?  I'm excited to see what you do with it. Cheers

[iiAtlas]

Two things I think you should consider (which you may already have). First, de-tabbing is more or less a one-way street.  Are you sure you won't ever feel a desire to change the bike again later on and wish you had kept some of those tabs?  Secondly, if you ever plan on selling it, will the future buyer want to restore it or feel like the bike is missing these tabs rather than benefiting from their removal?  I'm excited to see what you do with it. Cheers

These are the reasons it's taken so long to get this far on the frame.  My original vision for the bike is in the first post, a lightweight, well sorted, well performing CB350F while still maintaining the classic charm.  The only tabs I'm worried about removing at this point are the frame side cover mounts.  I think a set of these really adds to the "classic charm" I had in mind.  I don't want this to look like an overly modern bike, I want it to feel true to itself - a 1973 small displacement Honda.  The main thing which will sway my decision as to whether or not I want the side covers is mocking up my airbox.  Sadly that looks like it won't be here until later in the month.  Thanks for the input sbeckman.

[sbeckman7]

The main thing which will sway my decision as to whether or not I want the side covers is mocking up my airbox.  Sadly that looks like it won't be here until later in the month.  Thanks for the input sbeckman.

I'm in the same order as you  The anticipation is mounting!

[iiAtlas]

Engine time!  Step 1 - Camshaft.  She came out pretty easy after I worked out how to slip the chain off.  A bit of an angles game.  I used a rubber band and a coathanger to keep track of the timing chain.  This worked well throughout the project.





After that, the head came off.  It took me a while to find all the bolts.  I didn't realize there were those two hiding by the 2 & 3 cylinders.  I also spent way to long looking for an ulta-thin profile socket to get the bolts by the left and right oil manifolds before I realized they we're removable...d'oh!  Anyways, once I get everything lined up I loosed the bolts in the pattern described in my Clymer manual.  The head popped off without too much coercing.





It was at this point where I could first see the condition of the valves and pistons.  Sadly, they are not in the best condition...far worse than the rest of the head.  I guess the bike was outside with no carbs and no exhaust header for a fair number of years.









Significant build up.  I'm not sure what the call is on these, I'll definitely need some input from you all here.  We've done the head on an MG before but this is the deepest I've been.  Pretty amazing stuff, but will definitely need some help determining the extent of the piston damage!  Anyways - deeper and deeper we go...off goes the cylinder block.





This one took a fair bit more convincing to get off.  Some hits around the block with a soft mallet weren't making much of a difference.  Ultimately what did it was pulling UPWARDS while giving repeated wallops.  This allowed the gasket to release its death grip.  The cylinder walls looked good (to my eye and feel), as did the walls of the pistons.  There is some build up here but no noticeable scratching or scoring.  Will need to take a better look though.





Time for the pistons to come out.  I didn't want anything to fall down there so I punched a hole through a shop towel and pushed it over the cylinder.  I felt like a dentist!





The pistons came out relatively easy.  I used a very small flat head screwdriver to pry the retaining clip out of its groove, this worked well - I only launched one across the room... I found a sharpie to be the perfect size to drift the piston pin out.





I'll need one of you all to tell me whether that wear is normal.  I wasn't worried about it, it seems to be right at the points where the piston would be actuating, but of course you all know better than I.  With the pistons out I could asses the damage.  Here are all four in order 4, 3, 2, 1.











My next plan of action for these it to remove the rings and chem-dip them.  Thoughts?  I think once I clean off any of the surface level gunk I'll be able to make a better guess as to how damaged they are.  Maybe you wiser than I can already make that call. 

At this point I was more or less finished -- or so I thought...



After I took this shot I realized I could put the head nuts back one.  One less thing to loose. I began doing that when the unthinkable happened..... kerplunk

I dropped a head bolt into cylinder #2.  Gah, what a horrible feeling.  I'd made it this far averting disaster only to have this happen as I was cleaning up.  Of course!  I took out a flashlight and started looking everywhere for it.  Nada.  As far as I could tell she was in a black hole.  It was time to step up to the big guns.  A scope.



Amazingly, after a few minutes searching, I found it!  As it came across the screen my eyes lit up.  The treasure was in sight.  At this point I came up with a plan.  I saw the bolt was resting at what appeared to be a small pan, away from the crank gears.  I was worried if I moved the engine at all the bolt would snag something in the crank case and cause damage.  Luckily, it was resting clear of anything damaging.  I decided my best course of action was to turn the engine over slightly, moving the connecting rod, and giving me greater access to the bolt.  I used the kickstarter and inched it over, carefully watching on the scope to make sure nothing moved.  It worked!  I could now see the nut with my own to eyes.

I grabbed my bolt extracting rod (a coathanger...) and went fishing.  Amazingly, I got a catch.



Up, up, up she went - and of course I had to have my phone in one hand to document it for you all...



Voila!



Phew...that was a close call.  I cut out a sheet of cardboard and lay it over the cylinders to prevent that from happening again.  Here is how she sits now.

 



I had a great time taking this little girl apart and I'm excited to keep this project rolling.  Next up for me is checking each and every part for wear.  I have a dial indicator and a micrometer (though I will need to pick up some bigger ones).  For things like the pistons I will dip them in the chem-dip before using the micrometer.  Let me know if this is a bad idea, or if there are any other things you think I should dip while I'm at it.

I've also decided to go ahead with the detabbing on the frame except KEEP the four side cover hooks until I receive my airbox.  Then I'll mock it up with the carbs and airbox and make my final choice.

Hope you all enjoyed the read!  I look forward to reading your responses.

[grcamna2]

I hope you decide to keep the oem filter box;350's & 400F's hate pods.

[calj737]

Couple of tips: keep the pins, pistons and rings together by cylinder as matched pairs (if you haven't already figured that out). The piston skirts "look" good, but a soda blast of the pistons would help clean them up pretty quickly. A mic of the bores and pistons is best to determine the condition. I'd soak the pistons with rings in place before attempting to remove the rings. Before removing them, measure the ring end gap in place. If they're good, use extra care and eke them ordered. If out of spec, tear them off and replace.

A good hone of the cylinders after determining their spec is really a good idea. Should give you back full compression and a nice tight gas/oil seal.

Upon re-assembly, lots of lube to join up the hard parts saves lives...

[iiAtlas]

I hope you decide to keep the oem filter box;350's & 400F's hate pods.

Not running pods directly (don't like the look), but rather a Steel Dragon Performance intake box.  It looks like a combo of velocity stacks with an airbox.  I'm sure this will have some jetting concerns but I'm hoping to be able to dial it in.  I think the look of this box is really unique, and I'm happy to support an American manufacturing company.  This one isn't, but here is a link to someone else's here on SOHC/4 http://forums.sohc4.net/index.php?topic=118897.0

Couple of tips: keep the pins, pistons and rings together by cylinder as matched pairs (if you haven't already figured that out). The piston skirts "look" good, but a soda blast of the pistons would help clean them up pretty quickly. A mic of the bores and pistons is best to determine the condition. I'd soak the pistons with rings in place before attempting to remove the rings. Before removing them, measure the ring end gap in place. If they're good, use extra care and eke them ordered. If out of spec, tear them off and replace.

A good hone of the cylinders after determining their spec is really a good idea. Should give you back full compression and a nice tight gas/oil seal.

Upon re-assembly, lots of lube to join up the hard parts saves lives...

Sounds good!  Pistons and everything attached to them are of course being kept together.  When speaking in terms of piston 1, 2, 3, and 4, which side is #1?  I had assumed the left side is #1 if you were sitting on the bike facing forward.  Correct me if I'm wrong.  Are you saying if the rings are in spec I should keep them - even after the soak?  Excited to hear the prospect of full compression and a tight oil seal   Thanks for the tips.

[calj737]

Yes, yes and yes. Facing forward, leftmost is 1-4 while seated. Keep rings in place during soak, then measure end gap in place on piston, then again after removal. While on piston in not very accurate, but I use it as a relative expansion metric.

Here's another new entrant to the unibox with stacks: http://cognitomoto.com/collections/new-products/products/cb550-air-intake-box Though not yet available for your motor.

[iiAtlas]

Yes, yes and yes. Facing forward, leftmost is 1-4 while seated. Keep rings in place during soak, then measure end gap in place on piston, then again after removal. While on piston in not very accurate, but I use it as a relative expansion metric.

Here's another new entrant to the unibox with stacks: http://cognitomoto.com/collections/new-products/products/cb550-air-intake-box Though not yet available for your motor.

Nice uni-box!  I like the look of that.  Excited for mine to arrive!!  Any tips for ring removal?

[sbeckman7]

Yes, yes and yes. Facing forward, leftmost is 1-4 while seated. Keep rings in place during soak, then measure end gap in place on piston, then again after removal. While on piston in not very accurate, but I use it as a relative expansion metric.

Here's another new entrant to the unibox with stacks: http://cognitomoto.com/collections/new-products/products/cb550-air-intake-box Though not yet available for your motor.

I saw the Cognito offering, but in addition to not being available to our bikes they are also a good $75 more expensive    iiAtlas, that thread you found has some good baseline tuning information (albeit for a much larger engine).  Good to know about blocking off the top of the filter.

[iiAtlas]

Yes, yes and yes. Facing forward, leftmost is 1-4 while seated. Keep rings in place during soak, then measure end gap in place on piston, then again after removal. While on piston in not very accurate, but I use it as a relative expansion metric.

Here's another new entrant to the unibox with stacks: http://cognitomoto.com/collections/new-products/products/cb550-air-intake-box Though not yet available for your motor.

I saw the Cognito offering, but in addition to not being available to our bikes they are also a good $75 more expensive    iiAtlas, that thread you found has some good baseline tuning information (albeit for a much larger engine).  Good to know about blocking off the top of the filter.

Yes!  A good writeup for a not-oft-mentioned style airbox.  I know it will take some tweaking but I'm confident I'll be able to get this little girl running right with the Steel Dragon "unibox".