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Author Topic: AUXILIADORA 1981 HONDA CB750K BUILD  (Read 3860 times)

Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #30 on: Sep 01, 2017, 23:50:48 »
Dumb question but are they leaking from the overflow or could it be very bad gaskets, cracked bowls or if they have drains, from leaking drains?

They were leaking from the bottom of the bowls where that nipple is for a hose.

So, do you have a stock airbox? If so then your simplest plan will be to keep it.  If not, getting it to run well with pods may not be too dreadful (some bikes are evidently).  Replacing the carbs altogether will be dreadfully expensive unless you get used, and whether stock replacements or from an alternative bike, you either are where you are now (you already have stock used carbs) or will likely see plenty of jetting work to get it to run properly - of course you could get very lucky - but it's not usually how it goes.  The vacuum valve itself is not a bad thing.  If it works, it's fine.  If it has issues (this is not your carb leaking problem) then fix it.  Just because others say it has problems does not mean it is terminal.  Of course you can simply eliminate it as long as the petcock works properly manually so you can turn off the fuel when you are parked.  If you bought aftermarket rebuild kits it is very possible that this is an issue.  If you kept your old parts put them back in.  The assembled height of the needle/seat assembly is CRITICAL, and aftermarket assemblies often are not correct.  You can "fix" that problem by adjusting the tang that sets the float height, but you trade one problem with another, which is screwing up the kinematics of the float mechanism by having the tang not meet the needle's tensioning pin at 90o when the fuel level is correct.  While you're thinking about this, make sure you have the correct washers under the seats as this will hugely affect the resulting assembled height of the parts.  Another reason to have the OEM factory gasket, seat and needle.  For the record, these parts almost NEVER need to be replaced unless mechanically damaged by corrosion or stupidity.  I've seen some wear on 2-stroke race motors, but otherwise consider them to be lifetime reliable only needing cleaning and polishing to be good as new.  As previously mentioned, it would be good to know EXACTLY where the leaks are.  I reckon everyone is presuming it is from the bowl overflows.  Assuming that to be the case, you should take off the bowls and fill them up with gas on the bench almost to the top of the overflow tube.  If no leaks, you can go back to troubleshooting the floats, mechanism and need/seat assembly.

I do have the stock air box and I'll likely be using it. Maybe I'll try out the pods and fiddle around with carbs to see if it can run half decently but we'll see. Luckily regarding the carbs, I still have all the original parts I replaced so before reinstalling the carbs I'll put the OEM parts back in and see if I have any issues. (Sigh never did I realize how big of a pain these were but I guess that comes with the glory of owning this beauty).


Dude I'm totally enjoying reading through your build - anyone working on '81 CB750K is cool as f*** as far as I'm concerned.  Might be a bit biased, but hey.

If you're still having issues with your carbs, there's a dude called Mike Nixon (he has his own website, you can google the guy) - he knows a ton about Honda carbs.  I got a ton of help here on the forum with mine, and spoke to Mike a load as well. Got mine running like champions, yours will too mate. 

Keep on keepin' on, high fives from Montreal

Thanks man! I really appreciate it ! Appreciate the tip. Hopefully I can get her done before winter comes but I live in Winnipeg so you never really know when the snow is going to hit around this time.

Current list of things to do:
1. Order a braided brake line. Old one was filled with a bunch of gunk and I don't want to fill my new master cylinder with any of it. Also the old brake line was to long so I need a shorter one.
2. Wire (You better Believe Im going to have a million questions). I got a Motogadget M unit and the only thing I feel like I'm really confused about is wiring in the components that orignially came with the bike aka spark generator, reg/rec, etc).
3. Install carbs with some new gas and see if she starts!!
4. All the other shit thats just for looks aka a seat and a colour for the rear cowl and tank

Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #31 on: Sep 07, 2017, 00:02:05 »
Small update!

ordered a new front braided brake line



Also got a new ignition to replace the old massive one and relocated it to the side of the tank where a side cover would normally attach for a super clean look (in my opinion atleast)







Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #32 on: Sep 11, 2017, 09:44:46 »
So close yet so far.

Got the controls wired. Now just to install them and run them to th m unit. Also stripped my clutch leveer and polished it to match the front end of the bike (pics of it later).

Here's a bit of a teaser

Sent from my SM-G935W8 using Tapatalk


Offline CB MIKE

  • Posts: 91
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #33 on: Sep 11, 2017, 18:48:32 »
Man that rear end is low... no bumps lol. She looks great though keep it up!

Sent from my SM-G930V using DO THE TON mobile app

81 CB750C

Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #34 on: Sep 11, 2017, 19:43:35 »
Man that rear end is low... no bumps lol. She looks great though keep it up!

Sent from my SM-G930V using DO THE TON mobile app

I'll forsure be avoiding as many bumps as I can hahahaha

Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #35 on: Apr 23, 2018, 02:33:31 »
Welp, 7 months later and im back to working on the bike. After a very exhausting school year/winter, I finally have sometime to wire the bike. Expect updates.

Offline Ryan Stecken

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Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #36 on: Apr 23, 2018, 03:09:53 »
CanŽt wait!

Offline 88SS

  • Posts: 82
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #37 on: Apr 23, 2018, 18:51:31 »
Details when you wire the m-unit!!! Please!!


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Offline PRIMEWORKS

  • Posts: 21
Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #38 on: Apr 25, 2018, 02:22:18 »
Small small update.

So far I've done some very basic wiring to get the controls wired up to turn on the turn signals (front and rear), and the head light. So far it's not bad. I'm sure my wiring could be a million times better but given this is my first time wiring a bike, as long as it works, it's not a rats nest, and I can figure out which wires go where in the future I'm happy. I still need to wiring in the components from the original wiring harness which is what I'm most afraid of but so far it's looking good.

Once the wiring is complete I'll only have a few more things to really do before the bike is ride-able in my eyes. (Not saying done because I'm sure ill change things on the bike over time):

1. Install the carbs, start the bike and hope my engine doesn't blow up.

As of right now I really, really, really don't want to use the stock air box. Sue me. I know it's going to affect the way the bike runs, and it won't run 100% but I honestly think it ruins the look of the bike. I've recently looked into a different options for carbs and have seen a lot of people mentioning older GSXR carbs but I haven't found much info on them. I'll continue my research but if anyone has any info on this and would be willing to share, that would be greatly appreciated.

2. Determine if i want to paint the bike or not.

As of right now I LOVE the raw metal look the bike tank and rear cowl have. However, Even with clear coat the tank seems to be building up some small surface rust and the rear cowl isn't how I'd like it to be. There are small pits in the rear cowl and one side doesn't have as much of a body line as the other and I'd really love to fix this but the only way to do so is with paint. If i did paint the tank and cowl I'd likely paint it either black, a dark grey, or an aluminium silver (but i feel like an aluminium silver just wouldnt be the same).

Inspiration for colours

Black:

Dark Grey (Specifically Grigio Telesto):

or something along the lines of this


It's a tough call..

3. Make a seat.

This is the last thing on the list as it will bring everything together.

Until the next update, Here is a picture of the bike.





« Last Edit: Apr 25, 2018, 02:54:36 by PRIMEWORKS »

Offline The Jimbonaut

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Re: AUXILIADORA 1981 HONDA CB750K BUILD
« Reply #39 on: Apr 25, 2018, 10:20:50 »
Mate I really dig the brushed still look too.  Don't give up on it just yet!  I've done it on two bikes now and I think I'm learning a bit more about the process as I go along.  The rust you're seeing under the clear probably isn't from outside moisture getting underneath the clear, it could well be residual moisture that was in or near the surface of the steel when you cleared it. 

That moisture has now leached out from the steel and is what is causing the rusting underneath the clear.  At least that's what I found with my CB750 tank.  It's by no means bad, but a year later and there are small (very small - 1/4" tops) patches of spiderweb-like rust.  It's not spreading which is great, but it's there.  I have no problem with it.

So for my KLR tank I heated the tank up for 24 hours next to my shop heater before hitting it with the clear.  Two months later - sitting in a fairly damp garage in Montreal for the last two cold moths, and no signs of rust yet.  Whether or not the heat was enough to drive all the moisture out I guess time will tell.  But it's holding up better this time.

Worth noting - I hit both tanks with SprayMax 2K clear.  CB had a satin finish and the KLR has gloss.  I'll keep you posted.  Go Team Brushed Steel  8)
« Last Edit: Apr 25, 2018, 10:22:48 by The Jimbonaut »
"I'm telling you Donnie, nuthin' but nuthin' but right"