Topic: 1972 CB750 K2. ITS ALL OVER!! *Video link*

[Honda3]

Scroll down to see that the job has been completed. Video of the bike running with the new carbs, boots and switch can be seen here: https://www.instagram.com/p/B24NDjmprvY/

These are my adventures with my 1972 CB 750, changing a leaking oil pressure switch and removing/installing the carbs

I have learned:

1. Oil pressure switch leak will imitate a head gasket leak until you look really closely. The swap out is a challenge due to spatial/clearance issues. Vice grips worked for me, but some say channel lock pliers work as well. Im glad that part is over.
2. Airbox removal is vital to getting carbs removed. Removing the airbox is too easy. Took me 5 min
3. Removing the carbs is easier if you let the bike run just before taking off the tank and fuel lines. The hot engine heats the rubber boots making them more pliable; this makes pulling the carbs incredibly easy. Took me another 5 min to rock the carb body out after removing the linkages and airbox.

[Nurse Julie]

The carb manifold rubbers, of which there are 4 (obviously  ) come in 2 pairs of 2 and both pairs have a different orientation. When sitting on the bike, the rubbers need to be fitted from the left to right, in order 1,2,3,4. Because the 2 pairs are different, you turn the rubbers around to show the correct numbers in order, this ensures you have them fitted in the correct place.

[Honda3]

The carb manifold rubbers, of which there are 4 (obviously  ) come in 2 pairs of 2 and both pairs have a different orientation. When sitting on the bike, the rubbers need to be fitted from the left to right, in order 1,2,3,4. Because the 2 pairs are different, you turn the rubbers around to show the correct numbers in order, this ensures you have them fitted in the correct place.

Awesome. Clear, concise description. I think I had it right to begin with even though I was unsure. What about the Airbox to carb boots and the "pinched direction" which I mentioned?:

[Keith]

Check the intake boots carefully...one end is larger diameter than the other. That is the key! If reversed, you won’t be able to install or you will have a huge vacuum leak if you can get them installed. The carb to airbox boots should have no flat spots or misshapen areas. 

[Honda3]

Check the intake boots carefully...one end is larger diameter than the other. That is the key! If reversed, you won’t be able to install or you will have a huge vacuum leak if you can get them installed. The carb to airbox boots should have no flat spots or misshapen areas.

Yep. I can see how the lip slots into the box. I cleaned the entire airbox with simple green and soapy water. Its squeaky clean. Then I installed the boots as you see below. Notice there are no gaps where the boots meet the box.

I even filled the top part of the box with water, tilted it on the side, and NO water came out where the boots meet the box. Its tight. See below:

[Scott S]

 You need to rotate one of the inner boots. See how they're both angled the same way?

 And I think Keith is referring to the manifolds,  not the air box.

[Honda3]

You need to rotate one of the inner boots. See how they're both angled the same way?

 And I think Keith is referring to the manifolds,  not the air box.

Hmmm. He mentioned both airbox and intake.

In re the intake manifold, im assuming the BIGGER end connect to the engine and the smaller diameter opening to the carb?

Thanks for responding.

[Keith]

Yes, the manifolds!

[754]

put the manifolds on the engine  first , then visually line them up if need  be , straight line across , reason being the carbs are then a straight shot in.
 oil the lip, then start the carbs, get one side in first, then wiggle and push.

[Honda3]

put the manifolds on the engine  first , then visually line them up if need  be , straight line across , reason being the carbs are then a straight shot in.
 oil the lip, then start the carbs, get one side in first, then wiggle and push.

Thanks for this!

I was going to put them on the carbs first and force them onto the manifold, but now I'll do it your way. Ive got it now! Thanks!

[HondaMan]

If you put the little numbers on those intake hoses on the top, so you could read them from the seat, that's the right orientation. #1 on the left...the ones in the airbox orient so they tilt downward slightly to meet the carbs. All 4 are the same, but may be shrunken from the years, not sealing well into the upper airbox half. Honda still has them from time to time (usually in the Spring), PartsNmore has some aftermarket ones that work better than the Tourmaster's carb hoses do, too.

[Honda3]

Yes, the manifolds!

Yeh but you left out the important part which caused confusion. You mentioned the diameter on one side is larger than the other, but you didnt say WHICH part the larger diamter faces (i.e. larger diameter affixes to the manifold or larger diameter affixes to the carbs).

[Honda3]

If you put the little numbers on those intake hoses on the top, so you could read them from the seat, that's the right orientation. #1 on the left...the ones in the airbox orient so they tilt downward slightly to meet the carbs. All 4 are the same, but may be shrunken from the years, not sealing well into the upper airbox half. Honda still has them from time to time (usually in the Spring), PartsNmore has some aftermarket ones that work better than the Tourmaster's carb hoses do, too.

Thanks. However I may have mentioned I ordered and now have new OEM boots all the way round - nice and soft!!

Today I took a break and played with the kids when they got home from school. Such amazing weather in NYC these past few weeks. NO rain for nearly 2 weeks and nothing but Sun!

The only thing i DID do today is take the oil pressure switch out and replace it with the new one (using thread sealer, and also making sure not to  over-tighten it).

Tomorrow is the big day when it all goes back together.

[1976cb750f836]

With the boots on the head, i use a flat piece of scrap alum, held to carb side of boots, twist boots untill thay touch the flat evenly all way round. Then tighten clamp to head side.

[Honda3]

I finished the carb swap job this morning, starting just as the Sun came up.

Pretty simple but I had to go back and do a few thing:  I got over-excited and put the tank and fuel lines back on after putting the airbox, boots and new carbs on - and forgot to connect the throttle linkages. I was just eager to get it done:

Here are the photos of some of the process, a link to my instagram of the bike running.

Im quite pleased. No air of fuel leaks. Idles great

Video of the bike running after all was said and done.  https://www.instagram.com/p/B24NDjmprvY/

[MauiK3]

Are you leaving the boots off the carb rack lifters?

[Honda3]

Are you leaving the boots off the carb rack lifters?

Yeah. They werent on the bike when I got it with the old rack. The new rack has none too.

[PeWe]

Those rubbers are important to keep dust, water and sand away.

If you had old ones with the carbs you might need to buy new anyway.
These are a must and not cheap.
Mount them this winter so you'll get the bike complete.

[Buddhapie]

Dynoman Performance sells all the lil rubber booties you need for those carb banks, pricey tho, but man they have lots of good stuff!


Sent from my iPhone using Tapatalk

[Honda3]

Dynoman Performance sells all the lil rubber booties you need for those carb banks, pricey tho, but man they have lots of good stuff!


Sent from my iPhone using Tapatalk

Dynoman has already got a lot of my money. I bought 2 sets of CR carbs from them. One for my Kawasaki and the set you see here on my 1982 CB900F super sport:

[Honda3]

Dynoman Performance sells all the lil rubber booties you need for those carb banks, pricey tho, but man they have lots of good stuff!


Sent from my iPhone using Tapatalk

Do I have to take the carbs off to install?

[maxheadflow]

Well too me it sounds like the carbs are out of sync. Idle not that smooth. Could be something else.  Manifold leak?

[Buddhapie]

I don’t think so, I’m not around my bike right now, but might be easier. You should just have to detach the throttle gang from the individual carb shafts and slide the boot on and reattach.


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[Honda3]

Well too me it sounds like the carbs are out of sync. Idle not that smooth. Could be something else.  Manifold leak?

Nope.

All is well.

Carbs ARE synched and NO leaks anywhere. Made a stop by my local mechanic's  shop after I did the work. They were sad they didnt get the money to do the job, but excited to see I did a good job. They are rebuilding my 500F engine over winter AND making suspension changes to a 1979 CBX1000 I bought last weekend. So they try to be nice, knowing I have a lot of bikes aka potential biz.

They tested for leaks and didnt charge me. No air leaks anywhere;

They checked the carbs synch and didnt charge me. Carbs are synched.

Bike was running rough because the new carbs hadnt filled with fuel properly and I hadnt set the idle.

Runs like a top now.

[maxheadflow]

Sure not filling the carbs properly will do it.  I guess we aren't supposed to listen to nuthin' but the fact it's runnin'

[Honda3]

Sure not filling the carbs properly will do it.  I guess we aren't supposed to listen to nuthin' but the fact it's runnin'

Me no care.

Im pleased!

Never in my life have I done THIS kind of work on a bike. Took it for a 50 mile spin today after doing the work and having the mechanic check it. At speed Im reminded me how much the 750s still pull hard. Amazing bike!!

[maxheadflow]

Sure not filling the carbs properly will do it.  I guess we aren't supposed to listen to nuthin' but the fact it's runnin'

Me no care.

Im pleased!

Never in my life have I done THIS kind of work on a bike. Took it for a 50 mile spin today after doing the work and having the mechanic check it. At speed Im reminded me how much the 750s still pull hard. Amazing bike!!

I guess it's good to know your perspective.

[Honda3]

Sure not filling the carbs properly will do it.  I guess we aren't supposed to listen to nuthin' but the fact it's runnin'

Me no care.

Im pleased!

Never in my life have I done THIS kind of work on a bike. Took it for a 50 mile spin today after doing the work and having the mechanic check it. At speed Im reminded me how much the 750s still pull hard. Amazing bike!!

I guess it's good to know your perspective.

My perspective is ...  Im chuffed! I could upload a video i took of it idling at the mechanics and them saying 'shes so smooth" but Im not going to disrupt my instagram pattern by posting it.

Trust me, the bike runs great and Im happy.

[754]

 hmm.  strange .  we walk you thru every step of the way..
 and now it is, look what I did, don't need you guys,  I am outa here. 
 Jeepers. and I was just thinking.. hey he is going about this in a normal way, maybe he changed.. .

[Nurse Julie]

Bye bye

[Stev-o]

This guy needs to have forum name "Sybil", he has 12 personalities! And all are crazy!!

[my name is nobody]

This guy needs to have forum name "Sybil", he has 12 personalities! And all are crazy!!

I thought I saw the name of the wildeone in his video(?) , am I just late to the party and it's tongue and cheek? sorry if this is a dumb question I never met an oil sending unit I couldn't unscrew. his
other thread suggests the operation is quite complicated

PS. please disregard this post...I just got educated, I get it now, loud and clear.

[RAFster122s]

“Me no care”
He briefly channeled Jar Jar Binks...we all know how well loved a character he was!!!