New to site and a 79 CB750k

[klapool]

Hey All, Newby here, first post!

My son just traded his 1988 Honda NX125 for a 1979 CB750k.

Its got 11000 on the clock and a few dings and stuff.

Many years ago I bought a '93 750 nighthawk new. Never messed with anything so this is my second inline 4.

I know nothing about them. Is there a CDI or is it points. I know that one of the coils is dead.

The tank has a small bit of rust in it but I think I can get it cleaned and sealed pretty easily.

I also saw some of the carb overflow tubes are leaking when the gas is turned on so I guess I am going to get familiar with carb cleaning a quad.

Also, somewhere in the dusty recesses in my mind I remember some of these older bikes have air pressure on the front forks. Am I correct?

So I hope you dont mind me asking questions I think we can get a pretty cool bike for my kid.

Take a look...

 

[dirtdigger]

This is cdi type ignition. Only if it has the air valves on the top of the fork tubes are they air adjustable forks. But yours is not

 

[klapool]

This is cdi type ignition. Only if it has the air valves on the top of the fork tubes are they air adjustable forks. But yours is not

COOL!! I like CDI!! THANK YOU!! Any suggestions on this endeavor? What to look for what to replace. I surmise being that it only has 11000 miles it should be in good shape, just needs a good cleaning.

 

[Steve P]

Looks good, you should be fine, watch out for engine rattles but i'm guessing you will be ok. I'm just restoring one that had almost 40k miles on the clock, the internals were great apart from a broken ring, they are great bikes.

 

[klapool]

Looks good, you should be fine, watch out for engine rattles but i'm guessing you will be ok. I'm just restoring one that had almost 40k miles on the clock, the internals were great apart from a broken ring, they are great bikes.

Thanks!

The first task is to clean the rust out of the tank.

I am thinking maybe a handfull of BB's and shake it up till its clean. Then seal it but not sure what is best to seal it with.

 

[tommycarl]

Is the tank leaking? I'm guessing so, otherwise, why seal it.

Rust in the tank, could be the same rust that has your carb float seat not sealing and gas coming from the overflow tubes. Gas should be turned off when it's parked anyway.

Assuming that he bike runs okay, before messing with the carbs I'd make sure it has a clean inline paper fuel filter and run a can of Seafoam through it... mixed as on the instructions, of course. Maybe you'll get lucky.

If you do have to get into the carbs, here's a link to a nice carb cleaning manual: http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

 

[klapool]

HOLY MOLY!! Thank you!! That is AWESOME info!!!

 

[klapool]

So I followed the PDF file and got the bike to run. It is scarey fast.

It seems to starve for fuel when the engine gets to 7000 rpm. I dont know if the rev limiter is set lower than the 9500 red line.

I dont know if the carbs are synched properly but is does run and it runs pretty well.

One thing I did notice was the #4 carb "Puck" and needle slide seemed to want to stick open. I polished the slide with some soft brillow pads and it seemed to slide up and down easier.

Anyway thank you for the help its been a cool project!!

 

[tommycarl]

If I were you and wanted to get rid of your "starve for fuel" issue, and you're satisfied that the #4 puck is freed up, I'd clean the jets again. When I did my 900 I kept telling myself I had them clean, and kept looking for issues that ended up not being issues... I was in denial! If I remember correctly, it was the 6th cleaning that finally got mine over the hump. I got pretty good at getting the carbs off and on! On the other hand, if 7k rpm is fast enough for you, and it sounds like it might be, I'd try some Seafoam in hopes that it might get "that jet" clean.

Just a reminder and in case I'm wrong about the jets needing re-cleaned... make sure you have that inline paper filter in place because you sure don't want any of that rust from the tank messing up your freshly cleaned carbs!

 

[klapool]

I did get the inline filter but may just go after the jets this winter. It would be a good winter project.

I ride a Honda VTX 1300 and my wife has a Heritage Softail and both of these V twins are nice cruisers but this 750 is insane...

I had mine dyno tuned and its generating about 62 horse power and my wife's is somewhere about the same and this 750 according to the info online is capable of 79 horsepower. Insane speed...

 

[tommycarl]

It sounds like you have a good head on your shoulders... and know fast enough when you feel it.

You've apparently made some good progress in a short time... congratulations.

 

[klapool]

Well, the learning curve has been straight up..

I had the laptop out on the work bench and followed the PDF file on carb dis-assemble and re assembly line by line. I would never have known how to go about this until I found this site and was directed to the how to.

I am indebted to this site and its members!! Thank you!!

 

[rexnz]

Hi there I have the exact same model
Im in New Zealand but mine is tagged with australian motor vehicle certification
Only difference I can see is mine has duel front discs and speedo only has KPH
Forks are not air filled they have hydrolic oil I refilled mine a while back
CB750-900 dohc fours
Haynes
Owners work shop manual
Front fork damping is governed by the viscosity of the oil in the fork legs
Normaly ATF (automatic transmission fluid) and by the action of the damper assembly
Each fork leg holds 172.5-177.5 cc of damping fluid

Hope this helps

 

[klapool]

Thanks Rex, taking the forks off and cleaning them along with the brake fluid (which is filthy) are all on the winter project list. Thanks for the amount of ATF needed that will come in handy!!!