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Modest '78 CB750 Build

Pabeye

Older than Dirt
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Long Island, NY
I recently bought a 78 CB750, for which I am planning a modest cafe build. Nothing too radical, mostly low budget, with the focus on being a comfortable rider with a bit of style! For starters as of now the bike runs but not well, choke must be on all the time, but I will be addressing that carb issue ASAP, and hopefully will get sorted out. Of course will do all the other stuff this 35+ year old bike needs......cam cham adjust, valve adjust, carb sync, new hoops, etc etc.

Since I am anxious to get started on the build I was snooping around eBay and found a seat that I thought would work well. Bought it and after a little fiddling got it to mount to the stock locking device. Will address the hinge side shortly.

I plan on lower bars.....4 into one exhaust....new headlight, new turn signals..........all that cafe "look" stuff" MAYBE pods, although I hear a LOT of bad things about them........( but the look so COOL!) Here's a couple of pix ........wish me luck......
 

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No problems with pods on these carbs, you will just have to do some jetting more then likely when you put them on along with the 4 into 1.
 
The pods 'bad thing' is generally with using them on CV type carbs, in that application they pretty much truly suck. If you can jet and motor in good shape they run well on direct lift type carbs all day long.
 
A little premature, but I was window shoppin on ebay and found a seat I liked so I bought it. I really wanted to get to work on the carbs, but this seat sort of "presented itself" With a little home brewed engineering I was able to mount it nicely with out modifying the frame in any way. Now, the question. As you can see from the photo with the stock fender removed there is some frame sticking out form under the seat. I would like to remove some of it, but how much? I do not want to compromise the strength of the frame in any way. And yeah I have a Lincoln welder which I can use but have marginal skills using it! IMG_0852.JPGIMG_0853.JPGIMG_0847.jpg
 
Looks like you got a top joining hoop raising up there joining the two sides, it would be nice to see a pic with the seat off to see how that is shaped.

Any extension past the top joiner can come off and maybe even 1/2" to 3/4" of the lower part of the joiner depending on how the plate is shaped. You do not want to remove the entire hoop that connects the two sides. Or remove it and weld another slightly further forward. You need connection there of the two sides to force the two shocks to work more together and evenly.

IMG_0852_zpsyczxtilf.jpg


You may want to preserve some of what's under there (hoop) to mount a stub fender to not load the seat with having to deflect all water there.
 
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AMC49......thanks for taking the trouble of drawing cool red cut lines on the frame pix! ........soon as I get a chance I will take a pix of the frame w/o seat.
Mean time, your help is appreciated!
 
IMG_0878.JPGHere is a pix of the frame w/o the seat. The gray thing on top of the top joiner is a piece of high density foam that supports the rear cowl.
 
Just installed the "superbike" bars which I purchased on eBay.......OH WHAT A DIFFERENCE!

How the heck do people ride with those high bars???..............and those "ape hangers"??? WTF? accident waiting to happen!

Now have to work on getting a shorter clutch cable, brake lines, throttle cable etc.

bars 2.jpg
 
I mount that type of shorter lower bar and simply reroute cables and such to take a little longer to get there and looks fine with OEM cables. Those bars and some shorter sport type rectangular mirrors change the whole look of the machine.
 
Ahh, AMC, the hunt for mirrors has yet l to take place. :)

The cable I played with a bit and I do believe you are right. With a little creative re routing it could work. That being said I have to buy a new throttle cable anyway, as the one the bike came with broke. The clutch cable is also in need of replacement as even when it is not attached it is difficult to move! The wires and such I think I'm going the re route route. The brake line is a bit funky right now, but I'd like to upgrade to stainless anyway. Thanks as always for your input.
 
Standard length cables should work fine with those bars, they aren't hugely different from stock bars so you should be able to make them work.
 
A couple of pix.....cut the frame in a "safety Zone" put a couple of LED's in the frame tubes that light with the tail light ( my favorite touch on the build so fat ...:)......fitted a new tail light. Today I got it registered and inspected too! It WAS A GOOD day.

IMG_1068.jpgIMG_1070.jpg
 
My "modest" cafe build CB 750 is progressing........as usual keeping it low budget.....rattle can paint job and so on.

New tires......(Metzler Lasertech F & R ) tried "superbike bars" which provided a very comfortable ride position but lacked sex appeal. A good friend passed along slightly used clubman bars, which fit the bill perfectly. Have a 4 into one SS exhaust by Delkevic (ebay) cheapo pods and a bunch of weight taken off.......here are the results so far, still have to clean up the entire front end new signal lights and so on. She idles great........starts instantly...........she accelerates wonderfully...........BUT........here where I need help ....

When throttle is held steady between 4K to 5K rpm the engine seems to be "unhappy" searching a bit for the correct rpm, and just feels sluggish, Hit the throttle and all is OK again. I am running stock PD carbs, stock idle jets, and I think 110 main jets ( the ones that unscrew)..........HELP appreciated!!

IMG_1711.jpgIMG_1717.jpg
 
Carb sync or pod issue, may need some cruise jetting messed with.

Thanks for the input.......carbs were cleaned professionally but not synced. I'm thinkin she's running a bit lean in the mid range.......I GUESS that is what you mean by "cruise jetting".........appreciate the help!
 
A new "problem"...........bike has been running great in spite of the cheap Emgo pods and the 4 into one exhaust except for that flat spot between 4-5K rpm. So, I take her out today for a short spin today ( I have touched NOTHING mechanically!) and she's running like crap. Many backfires, refuses to idle and does not accelerate smoothly like it did just two days ago!

It's got me bugged! what could have happened while it was sitting in my garage???........PS: ambient temps were more or less the same 60 degrees or so......

Any ideas??
 
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probably got some trash in the carbs and you have some restriction in the carbs. I would say pull the carbs and heck the jets. Also these carbs are very lean and rely on the accel pump a great deal, pull the pods and open the throttle while observing the accel pump squirters, all four should squirt. If not you have issues with the diaphram or the check balls for the accel pump. These are very touchy and one reason I prefer the older carbs w/o accel pump.

Easy way to check if it is rich or lean. While riding get to the spot it runs worse then slowly close the choke...as you close it you will richen up the mixture. If it runs better and picks up power with the choke closing you are lean, if it bogs and pulls the engine down you were rich to start with. Normally lean the engine will surge, with it rich it will be constant bog feeling. You can do this at all rpm ranges while you are riding, I use this method all the time to tune, just be careful and try to pick a nice road with no distractions and low traffic. Jetting is available from jetsrus, the needle is adjusted with shims on these carbs and require partial disassembly, pilots are press in but are replaceable.
 
Dirtdigger and AMC, My THANKS!.......so,e very helpful advice there. Thanks for sharing your knowledge. I did replace the accelerator pump so unless some crap got in there I think I'm OK on that score. Will investigate the rest of your suggestions ASAP. It's getting pretty cold here in the North East....,.38 degrees out side my door this evening, so it may be a while :wink2:

Here's a couple of photos of the old beast so far....15110254_329745200738572_5152616563111442774_o.jpg

New clubman bars.....

IMG_1717.JPG
 
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