Author Topic: 1975 Honda CB400 Four Project - Rookie  (Read 317446 times)

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Offline jessezm

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #450 on: January 30, 2012, 06:24:04 PM »
It's just so hard to say, Rick.  I know the frustration of buttoning up your motor only to have an annoying leak when all you want to do is ride!  These small fours are tricky when it comes to the head gasket, but most people's problems are with the leak at on the ends at the oil feed jets rather than those sealing washers.   The good thing is that the top end is relatively easy to to pull apart and rebuild, and you get better at it each time you do it!  I would think that the extent of your leak would determine whether you ride on with some rolled up paper towels between the fins or pull it apart to redo the gasket.  But I guess the first step is to determine if the leak is at the gasket or at those washers, and if it's the washers, I hope someone else will chime in with a fix cause I haven't had a problem with those myself!

Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #451 on: January 30, 2012, 08:18:23 PM »
Jesse,

Thanks for the tips, I'll take a long hard look at the area of the leak, take some photos and report back what I find.

Ok so I finally got my seat upholstered. It came out better than I had hoped! Real brown leather, removable plywood base, just enough padding.











The fibreglass is starting to crack. Or rather the gel coat paint. Regardless, the whole thing should be re-made in alloy at some stage. Until then, I had tremendous help from my mates dad, Simon, with some last minute fabrication of an improved aluminum mounting plate. I'll take some more photos of how exactly that works another time.





I think it looks fantastic. Currently it's only held down at the rear under the hump via an aluminum plate that runs the entire length and width of the seat and mounts to the read inner fender holes.

I think I'm going to find a cool leather strap to hold down the front of the seat across that flat section of fibreglass in front of the leather. The strap would mount on some pegs or something on the frame uprights directly below it. Anyone have some ideas on this? Some vintage tank strap type thing I'm thinking.

Rick.

Offline Kwality

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #452 on: January 30, 2012, 08:51:44 PM »
Looking good Rick - hard to believe it's the same bike!  Well done.  Upholstery looks great... and matches your riding jacket!

Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #453 on: January 31, 2012, 03:43:57 PM »
Thanks mate, appreciate it!

Ok next up, carbs.







So I followed the first stage of Doctorlumen's advice above and replaced my #40 Keihin idle jets (aka slow jets) with Honda #38 idle jets. While I was at I also followed HondaMan's advice (always a good idea in my opinion  ;) ) and replaced the Keihin float valves with the old Honda float valves that I pulled out of the bike originally. I also purchased the 4 tube Morgan Carbtune and was able to sync the carbs in a couple of minutes. More on that later...

So results. Now whilst my lag hasn't entirely gone away, it has certainly improved. The 'stutter' on take off has gone, although it is still far from responsive in terms of take off. Although in good news, the rough idle at higher temperature issue is gone completely which is just fantastic. It idles great now which is such a relief.

So now I'm thinking of changing the float height from the 21mm recommended in the manual to 22mm or 23mm as I've heard and read that float height can help with that low end richness.

I do have various sized main jets that I can also try, although I really don't see an obvious need to as the bike seems to behave fantastically everywhere else but at take off. What does a bigger main jet really do? Would I get any sort of performance advantage out of increasing it from stock? The main jets I have are #78 (Honda), #80 (Keihin) and #98 (Keihin). I couldn't find anything for the CB400F inbetween those sizes at the time hence the big difference.



Here's how I was able to get the carbs back on with minimal frustration. Getting them off was much harder. I don't want to do that more than I have too!


Rick.
« Last Edit: January 31, 2012, 05:37:05 PM by RickB »

Offline Shade Tree

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #454 on: February 01, 2012, 07:33:37 AM »
Rick, Just thought you should know I recently started bringing back a 1975 cb400f. I was browsing around for information when I found this page. I've read every post and it has been a great help to me. I just wanted to say thanks for all the detailed postings and great pictures. My bike is in pieces at the moment with half of the bike off to the powder coaters. I was wondering if you ever looked into LED turn signals/ H4 headlight change over? I would like to do them but lack the knowledge. Thanks in advance.
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Offline jessezm

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #455 on: February 01, 2012, 08:29:42 AM »
Thanks mate, appreciate it!

Ok next up, carbs.

So I followed the first stage of Doctorlumen's advice above and replaced my #40 Keihin idle jets (aka slow jets) with Honda #38 idle jets. While I was at I also followed HondaMan's advice (always a good idea in my opinion  ;) ) and replaced the Keihin float valves with the old Honda float valves that I pulled out of the bike originally. I also purchased the 4 tube Morgan Carbtune and was able to sync the carbs in a couple of minutes. More on that later...

So results. Now whilst my lag hasn't entirely gone away, it has certainly improved. The 'stutter' on take off has gone, although it is still far from responsive in terms of take off. Although in good news, the rough idle at higher temperature issue is gone completely which is just fantastic. It idles great now which is such a relief.

So now I'm thinking of changing the float height from the 21mm recommended in the manual to 22mm or 23mm as I've heard read that float height can help with that low end richness.

I do have various sized main jets that I can also try, although I really don't see an obvious need to as the bike seems to behave fantastically everywhere else but at take off. What does a bigger main jet really do? Would I get any sort of performance advantage out of increasing it from stock? The main jets I have are #78 (Honda), #80 (Keihin) and #98 (Keihin). I couldn't find anything for the CB400F inbetween those sizes at the time hence the big difference.

Rick.

Wow those are some clean carbs, Rick!  Seems like our adventures are always running parallel--I'm now in the middle of carb tuning myself, and was just doing plug chops last night.  I think in your case since you've got the stock airbox and exhaust there's no reason to bump up the main jet.  If anything, use the 78.  I'm about to go the same route with lowering the fuel level in the bowls 1 or 2mm to deal with the soggy low end.  I get better response with the needle dropped a notch but in my case that gives me too lean a midrange.  In your case, though, dropping the needle may help and you can probably get away with it.  But I'm curious what changing the fuel level does.  Our set ups are quite different, so unfortunately it's hard to compare (I've got a 466cc kit, cam, bored carbs, ported heads, velocity stacks, and a free flowing exhaust...)

Offline -CB-Jamie-

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #456 on: February 01, 2012, 04:02:44 PM »
Rick, Just thought you should know I recently started bringing back a 1975 cb400f. I was browsing around for information when I found this page. I've read every post and it has been a great help to me. I just wanted to say thanks for all the detailed postings and great pictures. My bike is in pieces at the moment with half of the bike off to the powder coaters. I was wondering if you ever looked into LED turn signals/ H4 headlight change over? I would like to do them but lack the knowledge. Thanks in advance.

Gonna jump in here and let you know you can get a 6 3/8'' (162mm) headlamp from candlepower that takes a h4 bulb and is pretty much a direct swap for the standard sealed beam, just recently put one in my 400f.
Jamie

Here's a link
http://store.candlepower.com/638inhe.html
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Offline Shade Tree

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #457 on: February 01, 2012, 07:20:35 PM »
Thanks Jamie
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Two wheels move the soul."
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Offline -CB-Jamie-

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #458 on: February 02, 2012, 01:43:30 AM »
No problem.

Oh and that seat is looking pretty sweet Rick!!
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Offline malcolmgb

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #459 on: February 02, 2012, 08:59:56 AM »

Gonna jump in here and let you know you can get a 6 3/8'' (162mm) headlamp from candlepower that takes a h4 bulb and is pretty much a direct swap for the standard sealed beam, just recently put one in my 400f.
Jamie

Here's a link
http://store.candlepower.com/638inhe.html

Does this lamp have an opening for the pilot1 light, can't see one in the picture.
Malcolm

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Offline dagersh

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #460 on: February 02, 2012, 11:18:52 AM »
Rick,

The bike is looking fantastic.  The shapes and color scheme really scream Vintage British!  Amazing to see what you started and finished with!

Keep up the great work!

Gersh
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Offline -CB-Jamie-

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1975 Honda CB400 Four Project - Rookie
« Reply #461 on: February 03, 2012, 04:35:23 AM »

Gonna jump in here and let you know you can get a 6 3/8'' (162mm) headlamp from candlepower that takes a h4 bulb and is pretty much a direct swap for the standard sealed beam, just recently put one in my 400f.
Jamie

Here's a link
http://store.candlepower.com/638inhe.html

Does this lamp have an opening for the pilot1 light, can't see one in the picture.
No doesn't have a space for a pilot light
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Offline Hush

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #462 on: February 05, 2012, 05:25:04 PM »
She's really looking great Rick, love the colour scheme and the slight variations on the original Honda look without detracting from her factory styling. ;)
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #463 on: February 05, 2012, 05:31:41 PM »
@ Jesse: Thanks for the carb pointers. If you change your float height before I do, let me know how you go. I'm going to get to mine this week I hope. I may try that larger main jet to if you think it'll help.

@ Jason: Thanks for the encouragement mate, I appreciate it. Glad my trails and tribulations can help someone else. When I started out, I knew nothing about motorcycles or mechanics in general for that matter. As for your question about LED lighting, no I didn't really look into it. I didn't feel I needed it and when I begun, I didn't want unnecessary issues with my electrics.

@ Hush: Thanks so much mate, that's exactly was I was going for. Something not detracting from the original look too much. Appreciate the kid words.

Ok so updates.



Got my cut down upper triple tree clamp painted by a friend after the powdercoaters wouldn't do it because of the body filler I used (said it would bake off, fair enough).





If I'm honest, this was more work than I thought it would be. Lot's of things to undo.



Once I got the old upper triple tree off, I had to install the clips on. I bought a set here in Melbourne from a store called Modern Motorcycle Company. However after a quick mockup on the bike I realized that there was no way they were going to work without significantly hitting my tank. So I bought a set of the same style clipons from Airtech that has recessed bolts. I would prefer that there weren't hex head, but I can't imagine finding a phillips head bolt that works (not to mention getting it tight enough might be impossible). Anyway, you can see the difference in profiles of the two clipons here.



Regardless of the Airtech tank saving clipons, they still hit. Both here at the neck and also the switch gear hitting near the tank emblems.



You can see it's not much on the steering stopper lug. I've read various ways of remedying this. From using small hose clamps or rubber hose on the lugs, to tapping a screw into the lower triple tree. Trouble is, on the CB400F, there really isn't much 'meat' on the stopper lugs. I'm not sure a hose clamp or hose would stay on the lug. Likewise I doubt there would be enough 'meat' in the lug to tap a suitable diameter screw in there. Maybe I could come up from underneath the lower triple tree. Does anyone have some experience on a CB400F with stopping clipons hitting the tank?





So this whole process got harder. The modified triple tree didn't fit right away. So I loosened the front axle clamps, the lower triple tree fork bolts and then lifted the front of the bike up. Once I had done all that, I used a rubber mallet and massaged it all into place. Chipped some paint on the modified upper triple tree in the process, but it was only minor. I was surprised at the lack of durability of paint when compared to powder coating.



Then I installed the switch gear. Getting it all out of the clubmans was a pain. In the end, it was easier to just cut it out of the bars. Clubmans cost $30, the switches $100's. I didn't want to damage any of the wires when I had no intention of using the clubmans ever again.

I'll take more photos of the completed setup as I need some second opinions on shorter throttle/clutch cables and gauge placement.





Ok, the other day I was syncing the carbs and I did the inevitable for a novice like me and dropped my tank. Well rather it rolled off the bench and landed square upside down on my tool set. Miraculously it didn't scratch anything, it 'just' pushed in the filler cap area. I was devastated as you can imagine.

However, the following day my mate Rhys, who is considerably more manly than I, was able to pull most of the damaged area out by pulling firmly up on the filler neck. There are some small dimples left, but with some sort of hook I can insert into the tank I think I can pull the rest out enough that I won't really notice it. So not a bad save I reckon'. I've read you can get dents out with a heat gun and a can of compressed air too.



Last week I came close to blowing up the engine! I was racing my mate Rhys off of a stoplight and didn't pull up hard enough from first into second. The bike clunked into neutral and me being the rookie that I am, I then dumped the throttle. I don't know what the engined revved too before I realized what had happened but I immediately heard a loud 'clacking' sound coming from the tappet area on the number 1 cylinder.

I limped the bike home. It didn't behave any differently, just the clacking sound. So I left it over night and in the morning, pulled of the tappet covers. I discovered the number 1 inlet tappet nut was almost undone completely!



You can see here were it was impacting the tappet cover!



I was expecting damage to the adjusting screw but it was fine.





Of course this near catastrophe was entirely my fault. When I pulled the rocker cover last week and consequently had to adjust the valve clearances, I must not have tightened the lock nuts down hard enough. Will the high revving from the missed gear change, it must had rattled it lose enough. Had it loosened a tiny bit more, I might have done some serious damage.

So this time, I was determined to do it right. After some research here on the forum, someone mentioned that using a 'Robinson' screw as a tool. A quick call to a tradey mate with 'what the hell do we call a Robinson screw here in Australia?!' lead me to the square drive decking screw isle. The guy at the hardware store gave me one for free and with a masonry plug as a handle, the job of adjusting the valves clearances got so much easier!

Ok, that's a big enough update for today.

Thanks again lads,

Rick.

Offline hondamatteo

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #464 on: February 05, 2012, 11:38:31 PM »
Very nifty idea with the robertson screw!! Will definitely have to steal that idea! The robertson screw was invented in Canada might i add ;)
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Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #465 on: February 06, 2012, 12:38:33 AM »
It certainly makes adjusting those valve clearance a lot easier.

However it wasn't my idea. That goes to HondanutRider's son:

http://forums.sohc4.net/index.php?topic=44938

Rick.

Offline Hush

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #466 on: February 06, 2012, 02:37:17 AM »
Dang that's a clever idea to use a square drive screw to hold the adjuster, mint idea all right.
Gave some thought to your steering stopper problem, maybe if you looked at it from a different angle say like using some really thick plastic tubing/rubber innertube on the part that hits the lock stop rather than the lockstop it's self.
In a way sleeve the non moving part instead of the moving bits. :)
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #467 on: February 06, 2012, 03:16:25 AM »
Hush, yeah plus I think it would hold better on that tab anyway as there is more of it. I'd have to check how much clearance is underneath the tab but I think a thick rubber band would do it.

Offline jessezm

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #468 on: February 06, 2012, 05:23:54 AM »
@ Jesse: Thanks for the carb pointers. If you change your float height before I do, let me know how you go. I'm going to get to mine this week I hope. I may try that larger main jet to if you think it'll help.

Rick:   I did end up adjusting the carb floats and went for a ride, but didn't really do a proper plug chop.  One thing of note:  the floats are at an angle and I had already set them so that the lowest corner was at 22mm.  I changed that to 23.5mm, which puts the highest point at about 25mm.  That seems pretty high to me, but the bike did feel a little more responsive even after it was totally warmed up.  If anything, there is still a little hesitation, but not too much.  Plugs are still a bit sooty after rolling around from stop light to stop light.

Also, just to clarify, I can't see a reason you would benefit from larger main jets at this point--I was just suggesting that if you do try them out, go with the 78's rather than the larger sizes you mentioned.

Sounds like you had some adventures this weekend!  I myself pulled the carbs, set the floats, rechecked the valves, and went for a great ride yesterday!

Offline dmcgrego

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #469 on: February 08, 2012, 05:47:50 PM »
Wow, I'm wondering why Honda had the pilot jet set so rich on these bikes. I just got mine on the road this week and I'm having the same problem. I love how it runs when it cold, but when warmed up it it has a stumble when blipping the throttle on downshifts and it has a flat spot right off of idle. It's nice to see that it not just me! I've got the stock air filter and an emgo muffler on it so I thought if anything I might be a little lean, but no...I'm fighting a too rich problem instead.

Is it worth just doing the float height or should I just go for the 38's?
The fewer times I have to take off those carb's the better.

Rick, you build has given me lots of good info, I love the square screw trip!
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Offline jessezm

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #470 on: February 08, 2012, 05:52:45 PM »
Wow, I'm wondering why Honda had the pilot jet set so rich on these bikes. I just got mine on the road this week and I'm having the same problem. I love how it runs when it cold, but when warmed up it it has a stumble when blipping the throttle on downshifts and it has a flat spot right off of idle. It's nice to see that it not just me! I've got the stock air filter and an emgo muffler on it so I thought if anything I might be a little lean, but no...I'm fighting a too rich problem instead.

Is it worth just doing the float height or should I just go for the 38's?
The fewer times I have to take off those carb's the better.

Rick, you build has given me lots of good info, I love the square screw trip!

I know it's a pain in the arse, but you might even try lowering the needles a notch...  I got much better response that way, although with all my other mods it does run too lean that way now.  But you could maybe get away with it.

Offline Really?

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #471 on: February 08, 2012, 05:53:26 PM »
These Texans jut pop up out of nowhere  ??? ???
I don't have a motorcycle, sold it ('85 Yamaha Venture Royale).  Haven't had a CB750 for over 40 years.

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Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #472 on: February 08, 2012, 06:54:18 PM »
dmcgrego, thanks mate. I just saw your thread. Sounds like we are having similar issues. If you see my earlier post on my carbies, you'll see I linked too two different thoughts on float levels. That's the only reason I think changing my float level may work. I especially like what Timbo said about doing wheelies! That's where I'd like to be. I should get to changing it in the next couple days, so I'll report back with my results.

Now that I've changed from those flared larger British type grips to a slim GP style grip, I too have to re-grip when going full throttle. I've heard you can get quick turn throttle tubes, but have never looked for them. Not even sure how they work. Could be worth looking into though.

Offline Retro Rocket

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #473 on: February 08, 2012, 07:10:22 PM »
I have a quick action throttle in my shed, the "cam" part of the throttle is larger requiring less turn to get full throttle. Shouldn't be too hard to find one....
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Offline RickB

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Re: 1975 Honda CB400 Four Project - Rookie
« Reply #474 on: February 08, 2012, 07:45:18 PM »
Thanks for the advice,

In my mind I was thinking it was the throttle tube up on the bars. A quick search naturally took me to Rick Denoon's website and he makes a keep turn cam that has to be installed on the carb rack.

http://www.denoonsp.com/quick-turn-throttle.htm
http://www.denoonsp.com/prod02.htm

That means removing that pin that holds in the cam shaft on the carbs. The exact same pin that I broke off an extracting drill bit in. Hmm... For another time I think.

Rick.