Topic: New 75cb750 owner....bunch of questions

[new2novas]

Hey guys, just got my first bike, had it out a few times and have some questions....its a 75 750 with a vance and hines exhaust and pod filters....i will just list out my questions (and i have tried searching but its real late and searching for more than an hour tends to fry my brain, so don't waste your time telling me to search, sorry some forums are like that)

the rear brake locks up almost instantly when applied (in combination with the front) and it doesn't just lock it squats the rear and kicks out to the side, so needless to say i haven't been using it, i assume thats not normal? also there is only one front caliper but two front rotors, the left side is there....i tried looking around to find a caliper but it seems like they didn't make a dual disc front until 77?

I think i need to ditch those filters, bogs really bad (almost can stall it if i keep on it) if i don't roll into the throttle real smooth, but i can zing it with the clutch in, it backfires too while it does that and blows a bit of black smoke....the backfire seems to be coming from the exhaust so that makes sense, but when it bogs it feels lean (if that makes sense), almost the same as when i ran out of fuel earlier today.....but i can usually back it off a hair and its ok.....i am a mechanic/fabricator so having to pull this thing apart to mess around with it is no big deal...the thing is it hauls up top, from like 6500 on up it pulls hard and without hesitation at WOT, but until then i have to really work the throttle to get it to accelerate briskly

what manuals should i get and/or is there a place to download them from? There is a sloppy chain type of noise in the motor and it seems like an adjustment on the chain may help that

also is there a worthwhile ignition upgrade, i think i saw one electronic ignition upgrade but wanted to hear from some enthusiasts, but my points were just replaced by the previous owner so i can work with them for a while....

is there a diagram or can some post a pic of the proper way to route the fuel line coming right off the petcock, because the PO has it coming off right at the bottom at a 90 and its kinking the line (thought originally that could be the running issue, but since it clears up at the top i don't feel its related, but i still want it right)

phew, sorry, if your like any other forum i'm on i'll get #$%*ed at for not posting pics of the bike....i'll get to it asap..thanks

[Gordon]

Welcome!

That's a lot of questions in one post, so I'm just gonna start off with the first part and see who else wants to chime in.

That's definitely not normal behavior for the rear brake.  Is the brake arm adjusted properly?  Are the shoes worn past their limits?  If you haven't yet, it's probably a good idea to take the wheel off and get a good look inside the drum to see what's going on and what you're working with. 

The second disc may have just been a cosmetic add-on by a PO, or maybe there was a plan to convert to dual disc brake that didn't get finished?  Adding a second caliper can be done, though, but it does require some extra work.   

[martino1972]

welcome to the forum.....you will find that we will not #$%* at ya but will try and help ya wherever we can....

First off,it's recommended to do a full tune up on the bike before you start trying to fix things...not knowing the history of the bike it would be wise to:set valves,CLEAN CARBS..!!! ,new sparkplugs,clean oil+filter,check ignition advance,clean air filters etc. 
That way you set up a good base for later trouble shooting,nothing is worse then spending hours on setting carbs right while your valve clearances are way out of spec and causing you the trouble your trying to fix...


okay,you got a few questions here,let's split them up:

the rear brake:
I assume you have drum brakes in the back..you will have to remove the rear wheel and inspect the brake shoes for wear,most likely they will be worn down far and the key that spreads the shoes is in almost 90 degree angle before it brakes......or brake lining has separated from shoe etc..  It will tell ya when you take that apart....

the pod filters:
first thing i would do is do a plug chop....that means putting the engine  at WOT for a few seconds and then pull in clutch and kill the engine..engine has to be under load though,when you do that.....and then pull the spark plugs and look at the color of the tip...this will tell you if the main jet's are lean or rich or dead on... here is a link with a sparkplug chart so you can compare your settings...
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
I'm kinda guessing she will be reading lean....if so you will need bigger main jets...
after you got your main jets right you can play with the needles to set up the mid-range....
pod filters can work fine,just a matter of jetting the carbs right...

downloading a manual for your bike you do here: http://forums.sohc4.net/index.php?topic=17788.0

hondaman, a member from this side makes upgraded ignitions for these things....you can find that here:  http://forums.sohc4.net/index.php?topic=50269.0            just send him a PM with questions about that...

the fuel line coming from the petcock to the carbs should be as vertical as possible without loops etc..

oh,and we LOVE pictures,the more the better.....

most of these bikes have spend a long time collecting dust in their life,but are very rewarding to work on....

welcome to our insanity....

[seaweb11]

When you do pull the carbs off for a good cleaning, take a look and see what size the main jets are.
There will be numbers on them.  Do a search for "Pods" sorry but there is a ton of info.................

Sounds like you got a bike from someone who wanted a cool dual break bike with pods, but never added the other brake caliper, and I would guess never changed out the main jets in the carbs for the extra air you are now getting in there with the pods.  As martino1972 has said, they can be re jetted to a larger main jet size and run great.  I have 2- 750's with pods and no ill experience

[new2novas]

hey thanks guys....i'll start with the brakes and come back on later and read up some and ask more questions

the rear brake is disc and the right front fork where there is no caliper looks like it has the same attachment points, like all it needs is a caliper pads and line with a longer banjo bolt to double up or a "T" on the fender to split....i assume there is really no adjustment you can make to the rear short of changing the lever geometry to provide less leverage, but i think that would be a band aid to the true issue

oh and i seriously apologize, i am completly retarded, there is definetly a sticky that says HONDA MANUALS on the top of this section....give me hell for that at least

[martino1972]

oh and i seriously apologize, i am completly retarded,

you will fit in nicely with the rest of us then......

[mrbreeze]

You have a rear disk...........I would thoroughly clean out the master cylinder.On the front cylinder of an earlier K bike,there is a small compensation port in the bottom of the reservoir...............when that port plugs up......the brake sticks. AS far as your mid range probs......needle setting but you should post as much info on the bike as possible and where you are riding it.

[BeSeeingYou]

Sounds like you have a 75 CB750F Super Sport.  There are mounting holes for two calipers up front but it only came with one on the left side.  Some one has added a rotor or you have a rim from 77 or 78.  Is it a spoked rim or cast aluminum?
It sounds like the piston seals in the rear caliper need to be replaced.  The 75/76 had two pistons in the rear.  The seals  act to retract the piston/pads when you let off the brake.  It is a common problem as they age.  The master cylinder should also be cleaned out and possibly rebuilt making sure the fluid return hole is clear.  You can access the two holes in the rear master cylinder reservoir by removing a bolt that is on the bottom side.  It does not do anything but provide access to these two holes.
    I found  the trick to getting the rear caliper apart is this.  Dismount the caliper and remove the pads but leave the master cylinder hooked up.  You use this to force the pistons out but there is not enough clearance to get them both out at the same time.  Using a small long reach C clamp to hold one one piston down and remove the other.  Replace the seal, making sure you clean the groove it sits in (very important) and replace the piston.  Do a quick bleed of the system it does not have to be perfect.  Clamp the other piston down and repeat the process.  It may be best to rebuild your master cylinder first and then do this.  It comes apart pretty easy with a c clip pliers or various modified tools that some of us have come up with.  Do a search the info is all here.

[new2novas]

i guess i didn't explain the rear brake situation properly....its not that it sticks its that it seems to work TOO well, locking up with not much pressure at all, but it does not drag as soon as i let off it stops grabbing....i'm gonna go take pics now so you know what i'm workin with

[martino1972]

um.....press less hard on it...   

[new2novas]

hahaha i know it seems like that would be the answer, but its hard to press less hard... if i had to use it in any emergency situation i wouldn't be able to use it less, should i just not use it at all....heres some pics

[BeSeeingYou]

It's a frankenbike   If it's a 75 then it has 77/78 rims and rear caliper.  The front caliper looks right for a 75.  The rear master cylinder is from a 75/76 but not the rear caliper.  The 77/78 rear caliper is a single piston design and the 75/76 is a dual piston design.  I wonder if it is possible that the earlier master cylinder is too powerful for the later caliper?  The carbs look right for a 75.  The 75/76 engine should be silver and the 77/78 should be black but it just looks like a bad paint job to me.

[new2novas]

i think your right about the frankenbike deal....i had a hard time matching up parts just by searching for year....the motor has had a crappy paint job that is flaking and needs redone...i just went for a ride to pick up a 6-pack and used the rear brake as lightly as i could and it seemed to work ok, but its not right....also the choke seems to have no effect (idleing, moving, etc..) i pulled a filter off and verified that the flaps are moving, it just isn't having an effect on it.

also it doesn't appear that there is an accelerator pump on these carbs (manual says otherwise, sure there is something not right here)...but i don't see anything that resembles an accelerator pump (thinking cars here)

also part 2....what "series" is my bike, i see K* defining the different years, why use the k rather than the years or does the k refer to the generation

[Steve F]

I was going to ask you where you found a Vance & Hines for the SOHC 750 (V&H never made a system for the SOHC) and after you posted the pics, I see it's just the megaphone part that is V&H which appears to be welded to the stock headers, which from what I can see, seems to be a better than average weld job.

[BeSeeingYou]

K,F, and A are  model designations.  You have a CB750F Super Sport possibly an F0. My 76 is an F1, a 77 an F2 etc.    The K is a different model and is referred to as a K0, K1, K2, etc depending on when it was built.  Accelerator pumps came on the 77 and later carbs and yours are earlier.  The 75 and 76 Super Sports are for the most part identical and the 77 and 78 are similar but there are many differences between these two "generations" of the Super Sport.  This picture is my stock 76F1.  At one time your bike looked like this though it was either orange or blue.

When running pods as opposed to the stock airbox rejetting the carbs is usually done.  The jets will have numbers stamped on them.  Pull off one of the bowls and remove the main and slow jet.  Stock is 105 main and 40 slow, yours should probably be something else.  What else...well that's the trick.  Plenty of info on that here by others who know more than me on the subject.  If you have running issues it is possible that they were never set up properly or you could have dirty carbs or a combination of both.  Hell you should pull all the bowls off and clean the floats, needle valves, and both jets and shoot some cleaner up into the jet passages.  The slow jets have a tiny passage and are easily plugged.

The cam chain may need adjustement.  Do a search plenty of detailed info on that. 

[new2novas]

you know what, this weekend i'll pull the carbs off and go over them....i have a question about the charging system....only getting 10v (or whatever bat voltage is when i start it, its been dead so i have been kicking it, having to kick up to or more than 10 times when it hasn't been run) and the voltage rises with rpm up to like 13, but thats above normal cruise rpm....i assume this is not correct although i was reading something about certain models and this being the norm for them..

could this be related to my drivability problems....BTW its a new battery so i guess it is discharging as i ride at low rpm?

[new2novas]

ok, so i decided to try and tackle the charging situation today and pulled the dynamo cover and trans cover to see what was going on with the generator(or alternator....or dynamo...or whatever) and found some stock looking bullet connectors and the stock bulkhead type connector for all that....rewired from the grommet in the stator back to a little before the fuse block getting rid of all the stock connectors and used weatherpack connectors so i can still take that all apart if needed and it looks like i solved the charging situation without having to buy anything....i did notice however that the bottom couple fuses were unnaturally warm (hot really, couldn't hold my finger on them for more than a second or two) looks like i still have some stuff to figure out