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72 CB750 Project

Patterson0922

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I'm new to the forum, just got my first CB750 off a friend before he sold it and it needs a lot of TLC. I've done engine rebuilds on cars like my Volvo S60 and have wanted to get into motorcycles, so I figured this is my chance. Anyways I got this 72 CB750 off my friend who got it from a storage unit auction. I don't know how long it's been sitting there, I would guess about 10 years, and it doesn't run but it kicks. I don't know where to start with this bike, but it looks like the carbs are a little gummed up so I'll probably start there. Does anyone have any tips or advice to help me through this project? I don't know much about working on motorcycles so anything and everything is appreciated.
 
Best advise is first search the forum, has been discussed many times about bringing bikes out of storage. But I guarantee the carbs will be plugged and will need at least a cleaning. Put a little of some type of oil in the cylinders and let that sit while you work on the carbs. turn the motor over once in a while with the oil in there, you want to get some oil on the rings and on the cylinders after setting for so long. Do a good tuneup and go through all the adjustments. Get a manual if you dont have one.
 
Once you get the oil around the rings get a battery and spin the starter a little bit, let it set a day or so and then compression test to make sure you aren't wasting your time. There's often a reason why something like that gets left behind. By oil we mean only a few drops, a teaspoon is fine.

It never fails to get me how so many pick up 'projects' like that with no checking any deeper into how sound the basic motor is before they throw scads of money at it trying to get it to run well when it is never going to even at best. Yes, the carbs will need rebuild but wasted if motor is junk.
 
Well the bike was out in storage along with 5 or 6 other bikes. An old man owned the unit and passed away so the unit went up for auction. I know at least 4 of the other bikes were stored properly and are in full gunning condition so I'm hopeful that this bike will too.
 
Means literally nothing. Why you run the compression. It could also mean somebody who stored them because he was a pack rat, we used to buy them all over town like that. Everybody swears they are in good shape and commonly not. A 50/50 thing at best.

Certainly not trying to blow your bubble and luck, but I find that at least good luck is actually mostly comprised of looking out for oneself ahead of time.

I have an identical situation like that now except a 550F. Bike has not started since maybe 2013, rolls over easy with a kick but unknown to others is the fact there will be tensioner and valve work needed in the close future, nobody EVER addresses that when selling and what commonly tears them up. Here in Texas the tensioners are cracking up in pieces at 30K miles even though rest of engine is in fine shape. Honda camchain tensioning systems were flimsy even off the showroom floor. The valves guaranteed to be fairly shortlived as we are in 100% no lead fuel now and the nitride coat on them going through pure hell as they were intended for leaded fuel. The 550 is beginning to show that, the slight rough idle (most people would never pick up on it but I do having worked on them for years) that no one can get perfect even if carbs taken apart again and again. Compression reading tells you that instantly but nobody wants to know that, too depressing. I could have that bike back up and running in say 30 minutes and I daresay most people would think it runs 'perfect', little do they know. With that one a moron PO never adjusted camchain and it rattles too easy since chain was allowed to run long periods dead loose. I can get the noise to stop for a month or two but then it comes back, tensioner wearing rapidly now. Any buyer would think it's perfect though since at the time sold it would be quiet. So easy to fool the public if one chooses to do so. That bike is most definitely in 'full running condition, it will still run over 100 mph and 9000+ rpm. I did so with it the last time it ran in 2013. Before that it had sat another couple years. It would be fine for short pleasure jaunts but if one committed to drive it 100% all the time? No way. Break city.

See how that can work? There is a whopping amount of gray between the black and the white. 'Full running condition' can mean they will blow up in the next 5 minutes. Seen so many DOHCs do that I can't count.

Screw all that. Run the valves, most never do that. Stay toward the loose side with the exhausts, it allows them to seal a bit better. They are the ones that flaw the most with unleaded fuel, the intakes fare better. When you get it running, it can be helpful to go out and do the Amish speed test thing, or run the living crap out of it, for a bit. It can beat any carbon off the seats to seal better. Then run valves (at least the exhaust) again to see if anything changed. If so watch that one in the future.

Run the bike first a small bit THEN change the oil. Changing oil first leaves any sediment and trash in place from the sit. You wanna stir that up to come out.

As far as being a motorcycle, don't let that put you off. Engines all work the same, consider M/Cs to be finer more precise cars, they are simply pickier about tune because they work at higher load levels than cars. The more hp. per cubic inch thing.
 
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