New and looking for some help..

[anthony8488]

So I picked up an 82 CB750sc about three weeks ago, i am taking my MSF course this weekend so i can start riding. Bike looks to be in great shape, 24k miles on it, i've been polishing paint, cleaning and just looking over the bike since i cant ride it yet.

The problem I'm having is i am getting fuel leaking from the SOS, aft hose. My searches keep bringing me back to carb bowls leaking instead of finding out why it would be leaking from that specific hose. I saw a parts break down on here and it was hose #5. Would it just be better to take off the SOS and remember to shut fuel off or is this an easy fix?

I also took the bike out today and stayed on back roads in my neighborhood and occasionally the bike would stall when i pulled the clutch in to start downshifting then would be alittle hard to get it started again, does this issue sound like its related to the SOS or what else should i be looking into.

I don't mind searching more, just need some help in the right terminology to search for, to fix my troubles.

thanks for any help!!

[TOOLS1]

I would remove the SOS. Also I never, repeat never turn the gas petcock off, unless gas is running out onto the floor. My thinking is that as long as the float bowels are full of gas; the needles are seated and nothing is getting in between the needle, and seat. Not dirt, not varnish, and the carb is not going to dry out.
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BTW my buddies know I don't turn the gas off, and only once has one turned it off on me, and he, or anyone else will not do it again. 

[FastCletus]

If it were me I would pull carbs off and clean and or rebuild.  24K miles is alot and who  knows if/when they were rebuilt.  lots of pics on this site to help with carbs, and many people on here are excellent in their experience on rebuilding them.  I am a novice now considering how many times I have tinkered with mine.

[seestheday]

I would just pull the SOS if I were you.  I turn my fuel off every time, but TOOLS and I disagree over this minor point.  Suit yourself.

Your issue with it stalling could be related to a fuel starvation problem caused by the SOS, but it could be other stuff.  Only way to know is to start by pulling the SOS and seeing if it fixes your problem.

It is probably the easiest mod you can do to the bike.

Cheers,
Simon

[anthony8488]

"So let it be written, so let it be done" I can pull it off this afternoon if i can find the 1/8" plug/cap needed for carb #2. So in theory with SOS off and the petcock on, bike off, then i could test my floats for leaks..

thanks for the quick replies!

[TOOLS1]

I will often work on these old carbs, and get them to seal. I like to keep them around for a few days to make sure they are sealed. Then when I send them home the owner will start turning the petcock off and on, then after a few weeks of sitting they are leaking.
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[anthony8488]

Yea, i know im the third owner and the second owner only mentioned that the carbs were synced in march of this year along with tires changes, clutch work, battery swap, plugs(its all on a hand written receipt from a small town shop he went through).

I was hoping they would be okay long enough to research re-jetting and learn more on syncing the carbs myself. With that though practice makes perfect so would only make it easier for the next time i pull them off to look at them.

[anthony8488]

The reasoning sounds good to me, enough so to try it and see how it goes. Worst case my garage will smell like fuel a bit and i have a bit of a mess to clean.

[anthony8488]

So pulling of the SOS fixed the issue i was having with it stalling out, have taken the bike out three time now and she rides good. My next issue is a bouncing RPM needle and i notice that when the bike is above 5k rpm i get a noticeable vibration.

Im going to check the cable tomorrow to make sure its seated inside the valve cover but would a new cable fix the issue?

For the vibration i feel is this normal for these bikes? When i did a google search for vibration above 5k the article that pulls up is on a 2013 cb1100 that honda released. If this is not the norm what should i start looking at?

[TOOLS1]

A cable might cure the tachometer problem. As for a vibration, is it only while riding, or does it do it while sitting still and revving the engine?
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[anthony8488]

I only notice it from about 5k and up ive only taken it up to around 8k when the needle bounced on the high side.

As for sitting still, it is a noticeable change in vibration/bike noise (feels and sounds like a rattle) when you gas it up in the higher rpms. (needle starts to bounce at 5k RPM, under 5k is smooth)

I'm not getting hesitation in power that i notice, just the noticed vibration feel. So with that i find my self shifting at around 3k then riding 5th gear up to speed.  

[motogrady]

On the vibration,
Check all the motormounts, make sure all is tight, same with exhaust pipes.
I get some vibs also, but nothing like a vtwin.

There's a place in Maryland, The House of Balance, I've heard they can
get pretty much anything spinning without shaking.
That takes a motor teardown tho, maybe just get some thicker gloves for a bit?

[anthony8488]

its not so much an issue, its lack of knowing. It's noticeable that i feel it at those specific times but i don't know if its suppose to be that way since this is my first bike and first time riding a cb750.

So if vibration is normal when i'm feeling it then its nothing i cant live with (will check engine and exhaust mounts), just mentally right now i think something is wrong. So if it is wrong then of'course id rather fix it now then let it get worse.


Probably dumb question, When i search for like carb rebuild kits for my model and year it seems to be lost somewhere ill see up to 81 and then 83 and up. So is the 82 the same as the 81 or the 83? Also when i search for CB750SC or nighthawk i notice CB750K populates in the search does the K series have the same motor?

[anthony8488]

I swapped the spark plugs out today just because i didn't know how old the previous ones were, the plugs all had black on the bottom of the threads but #1 and #3 the curved tips were white and #2 and #4 were dark like the threads.

 I think i read white tips are a lean and dark are rich condition? Since i dont know how old the plugs are are they even a good source to go by?