First CB750

R

RebelSkyRot

New Member
Well I picked up my '75 CB750 yesterday ;D It's definitely going to need a top end rebuild, which I was planning on doing anyways. A couple of questions though: what type of oil should I be filling the tank with, and are all 750 clutch levers pretty hard to squeeze? I've ridden it less than 20 miles and I'm already starting to blister on my fingers from squeezing the clutch... Is it normal for the clutch to be that tight, or is it something that can be made easier?
-Kyle
 
Alright thanks guys. Also, I got the bike with two batteries, one a gel and one a traditional lead/acid. I rode the bike around last night for maybe a half hour, then went to ride it a couple hours later and it died after three blocks... I couldn't get it to start with the kick start and the headlight was pretty dim, so I pushed it home and switched out the batteries, and it started right up. I took it out today a couple times, starting it only with the kick every time and rode fine for a ways until I started it again to ride home and it died again at an intersection.... I got it to start with the kick and got a block before it died again, the headlight going dim again. The only way I got it home was to keep it in first gear with high revs. Any ideas on what's wrong? The guy I bought it from said he had the electrical system checked over by a mechanic, with a new rectifier installed, as well as the carbs cleaned and synched. I have all the documentation for this so I know it's not BS but what would it be? If it were an electrical issue why wouldn't it start by kick starting? But if it were a mechanical problem, what would cause it to go from running fine all day to cutting out at low revs suddenly while riding? Any help is much appreciated! It's starting to look like I might be starting my build a bit sooner than planned ;D
 
The big CB's, like the 500,550 and 750 need battery because they don't have a permanent rotor. The battery is needed to 'load' the coils for spark.
I'm pretty confident it's a battery loading issue. Mostly because when you ride in high revs it runs. In high revs the rotor produces enough electrical power to keep 'er going.

No power on the battery means no spark. You can kick it till your legs fall off.

The reason it has a kicker is that your starter system could get fouled. Also, the coil will load at 12volt-6amps while your battery can theoraticly give you 12 amps. When battery is down enough not to turn the electric starter you are still able to kick start her.

Good and fast way to check your system is to keep the bike at idle and put a multimeter to the positive and negative terminal of the battery. Set it on 'Volt' and check. It should be anywhere between 11v and 14v. Also check 'ampere' this way. Now rev the bike till 5000rpm and check multimeter. If readings barely change your battery does not get power from the rotor to load itself wich basicly means the bike drowns the battery till it dies. When readings go up you're ok on the loading thingy. But i doubt that.

I wonder why you got 2 batteries with the bike... ::)

BTW it's Bert Jan here, on my GF's account. Left my laptop in the shop last night..
 
Also the charging system, IF up to par, won't start really charging the battery until about 3500-4000 RPMS. If you were nursing the bike around town all day the battery never received the voltage needed to charge it. Most times new owners want to pussy the bikes, lugging along about 2000-2500 RPMs thinking they are doing a good thing by taking it easy. You need to stay in lower gears at in traffic speeds, let her breath. These bikes aren't Harley's with all that low end torque so they are built to be rev'ed .
 
RebelSkyRot said:
So if I check the battery with the multimeter and the readings don't go up I've got a problem with the rotor?
Click to expand...
First, make sure your battery is fully charged. 12V or more. Then start the bike and bring the RPMs up to 3000-4000 and you should see an increase to about 14V. If not, don't assume it's the rotor without checking, It could be the stator, regulator or even dirty connections.
 
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