Topic: Senior project for high school - 78 CB750K

[Restoration Fan]

Went to put the front brakes on today and I think something may not be right.  We double- and triple-checked the part photo, as well as the manual and we have the pieces in the correct order.  But there's no room on the back side of the rotor between the rotor and the spokes.  Certainly not enough for the brake caliper to fit on that side of the rotor.

[Retro Rocket]

Rotor on back the front....

[Restoration Fan]

Sorry.  This is the front rotor.  Mine is a K model so there's no rotor on the rear; that uses a drum brake.

[mystic_1]

I believe he's suggesting that you have the rotor on backwards, which seems plausible to me, although it's difficult to tell in that photo.

Unbolt it and flip it over.

mystic_1

[Restoration Fan]

Well that would certainly explain it.  Thank you both!

[martin_uk]

Does this help

2015_0214frame0042 by nitram2010, on Flickr

[Restoration Fan]

Does this help

2015_0214frame0042 by nitram2010, on Flickr

Thank you, it does.  But it also makes me jealous of how beautiful and shiny yours is! 

[martin_uk]

Does this help

2015_0214frame0042 by nitram2010, on Flickr

Thank you, it does.  But it also makes me jealous of how beautiful and shiny yours is! 

Ah but what you cant see is that front mudguard is all bumpy

[Restoration Fan]

 Does anyone know what the thread pitch is on the rear brake arm rod?  It's the one with the spring that goes through the little cam that sits in the brake arm.

One of the POs had "made his own" version of the cam and nut that goes on the end of the rod.  And it appears he stripped the threads pretty well.

[Retro Rocket]

Sorry.  This is the front rotor.  Mine is a K model so there's no rotor on the rear; that uses a drum brake.

I'll forgive you, your still learning....

[Restoration Fan]

Sorry.  This is the front rotor.  Mine is a K model so there's no rotor on the rear; that uses a drum brake.

I'll forgive you, your still learning....

LOL, you're too kind.   
Looking it up in the 69-78 manual, it says that 6mm will have a thread pitch of 1.0, so I'm assuming the thread pitch should be 1.0 on this rear brake arm thread?

[calj737]

6mm/1.0 pitch is correct

[Restoration Fan]

6mm/1.0 pitch is correct

Thanks, Cal!

[Restoration Fan]

Where do you guys get your carb rebuild kits from?  I really only want the gasket and o-ring sets.

I see 4-into-1 carries it but they're out of stock for the kit that fits the 78.  VintageCB750 carries but it will be almost $100 to get the kit for all 4 gaskets, which seems REALLY high to me.  (I could get the OEM parts for that price from Honda).

[martin_uk]

Where do you guys get your carb rebuild kits from?  I really only want the gasket and o-ring sets.

I see 4-into-1 carries it but they're out of stock for the kit that fits the 78.  VintageCB750 carries but it will be almost $100 to get the kit for all 4 gaskets, which seems REALLY high to me.  (I could get the OEM parts for that price from Honda).

I bought mine from Cruizin image, but used original jets and needles. General consensus is that if the original Honda metal parts look good (check with a x10 magnifier) then dont change.

I also bought their accelerator pump diaphram as mine very hard

http://www.ebay.co.uk/itm/78-Honda-CB750K-CB750K8-Carb-Repair-Kits-4-Repair-Kits-Include-CI-CB75078CR-/141305419069?pt=Motorcycles_Parts_Accessories&hash=item20e675953d

[martin_uk]

Forgot to mention, take great care to get small O rings out of idle mixture screws orifice and assemble tiny washer and spring correctly (washer goes against spring)

Most of mine came out by inserting a small carb jet cleaning brush and when withdrawn the O ring came too.

I guess you could also use a tiny dental brush that you use for cleaning between teeth

[Restoration Fan]

Forgot to mention, take great care to get small O rings out of idle mixture screws and assemble tiny washer and spring correctly.

Most of mine came out by inserting a small carb jet cleaning brush and when withdrawn the O ring came too.

I guess you could also use a tiny dental brush that you use for cleaning between teeth

Thanks for that advice. 

I considered using cruzinimage after your post but I just placed the order with PartsNMore.  It was more expensive but time is the issue for me at this point more so than the extra $45.  Coming from Japan, they may not get here until the end of the month.

With Logan having his presentation potentially on the 15th of April, we definitely need them prior to that. 

[Restoration Fan]

The list of "TO DO" items is shrinking. 

Front brakes are on; fender now aligns properly.  Brake lines connected; just need to add the brake fluid and bleed them tomorrow.  Got the controls reworked, back together and on the bike.  New grips arriving from Amazon tomorrow.

Still have to fix the threads on the rear brake arm.  Mike is bringing his metric tap & die set to fix the messed up threads. 

The carbs are all cleaned and waiting on the arrival of new gaskets to go back together.  Air box is cleaned, new air filter is in and it's waiting to go on the bike once the carbs are ready.

Started hooking up the wiring; taking care of regulator/rectifier/alternator and other big items that are easily identifiable and matched up.

Also, stripped most of the paint off the tank and was very pleasantly surprised at the shape it's in.  Only one tiny place up top with bondo in it.  There a few low spots that will need a skim coat and sanding but nowhere near the amount of work the original tank was going to take.

It was a very slow week for work on the bike last week due to a super crazy work schedule for me.  Unfortunately, we weren't able to take advantage of my wife being out of the country in Hong Kong to get a lot done.  We did get the paint stripping done before she arrived back home so that we didn't have to worry about triggering her asthma.  As it stands right now, I think we'll get the carb rebuild kits by Wednesday or Thursday.  If we do, then we should have everything on the bike buttoned up by the time the kits get here.  Give it a few days to get them reassembled and on the bike....and we get to hear if Stella can sing or not.

[calj737]

Did you leak test that tank after stripping it? And how's the interior? I have found many times that after stripping, small weep holes will become exposed after the paint and interior rust is removed. Yours shows a little sign of rust on the left side, down low, along the seam running towards the rear of the tank. Curious as to its cause...

I've go one I'm doing right now in the exact same condition  Soaking in rust remover after welding up the rotten bottom.

[Restoration Fan]

Cal,
Thank you for that suggestion.  I hadn't thought of that.  No, we haven't tested it yet but that's now on the docket for this afternoon. 

The interior of this one has very slight signs of surface rust inside but looks pretty good all things considered.  We're going to fill it with white vinegar today and let it soak for a few days to get any rust out before we begin the coating process.  Before we do that, I'll have Logan fill it with water so we can see if there are any pin hole leaks.

I don't think that's rust you're seeing though.  There are still patches of black paint on the tank in various places.  We've applied aircraft stripper to it 5 times but there are still a few stubborn patches of black paint remaining that we still have to address.  I just went and confirmed that what we're seeing on that tank in the photo is actually black paint that remains on the tank.  There is a bit of surface rust forming since the paint has been removed since about Wednesday now but there don't appear to be signs of serious rust.

The bottom of the tank itself though is in pristine condition, FWIW.  Still has a bit more paint to be removed, but it's in really really good shape.

[NobleHops]

Ron, when you get to reassembling those carbs, definitely wet-test them on the bench for a bit before you mount them. Mine had a split in one of the overflow tubes I had to repair and another has a slightly sticky (new) float assembly that is also allowing a bit of fuel to weep. It would have saved me some time if I had tested and discovered these leaks on the bench, and not on the floor :-).

Also, not sure what the wicked smaht guys use, but my carbs did not leak with water in them, but did with gas. Perhaps there's something similar to test with that won't mess with rubber, haven't got to Googling that question yet myself.

[Restoration Fan]

Ron, when you get to reassembling those carbs, definitely wet-test them on the bench for a bit before you mount them. Mine had a split in one of the overflow tubes I had to repair and another has a slightly sticky (new) float assembly that is also allowing a bit of fuel to weep. It would have saved me some time if I had tested and discovered these leaks on the bench, and not on the floor :-).

Also, not sure what the wicked smaht guys use, but my carbs did not leak with water in them, but did with gas. Perhaps there's something similar to test with that won't mess with rubber, haven't got to Googling that question yet myself.

Great idea.  Glad you mentioned it because I would have just stuck em in and turned it on, lol.

Hmmm...so would you recommend just testing them with gas?  I think I'm going to purchase one of those small IV-bag looking type tanks from Amazon today and have it shipped in for the carb synching process anyway.  I could hook up the petcock in between that and the carb lines and let it run gas into the carbs...and see if the floats do their job or let overflow happen.  Think that would work?

[strynboen]

i used a lavn mover tank for leak test..and a old one  kosts less

[martin_uk]

Dont fix the temporay tank too high above carbs when bench testing as can cause pressue to be too high.

[NobleHops]

Dont fix the temporay tank too high above carbs when bench testing as can cause pressue to be too high.

Is that so? Wow, news to me. Interesting.

Ron, those aux fuel tanks are invaluable, damn near essential for carb sync. I think you'll be glad to own one. My shopmate also has a full-on used IV stand to hang it from (on wheels) also highly useful for us.