CB750.org - Home of the CB750 Preservation Society

Ask the Expert

Our resident expert is Kurt Winter, Proprietor of Valleycycles, whose work has been promenently displayed at the Peterson Automotive Museum in Los Angeles, CA, as well as touring with the Guggenheim. Both motorcycles are pictured in this web site.

This page is the result of emails received to the site, and subsequently answered by our expert.

August 13, 2005

Q: Hi . my name is Justin. i just got my first bike , a 1980 honda cb650 sohc .
It has four keihin carbs . my question is how do I sycronize these carbs?
there are no vizable ajustment screws other than the idle speed screw. the
only way i can get the bike to stay running is by leaving the choke all the way
on . any help would be greatly apreciated ! i know your site is dedicated to
750's . but i figuerd you guys would know how to sync these carbs becaues
they came on 550's , 650's , and 750's also. well thanks for any help you can
giv. if u can please email me at drumguy16@yahoo.com . cool site . keep it
up ! and thanks again!

August 14, 2003

Q: Hi, My name is Eli, and I'd like to get any help I could. Here's my story, I'm working on my friend's 1981 Honda CB750 Custom (C model). It is not charging the battery. I have been a mechanic at a bike shop before, so I mostly know what I am doing. I am using a Clymer manual and Everything checks out fine except the reg/rec. But my friend has three of them, two used and one brand new and none of them work. According to the Clymer manual, the diodes in all three reg/rec are backwards. In other words, they have infinite resistance in the wrong direction. I think it is very possible that the manual is wrong, or maybe my friend has bought the wrong reg/rec. The only other thing I can think of is that possibly the stator is starting to fail, even though it tests ok, and we have tried two different stators in the bike with the same result. The other strange thing is that it will charge to about 12.5 volts at 5K RPM with the headlight disconnected. Of course I have checked everything simple, fuses, broken wires, etc. Any help you could give me would be great, I really appreciate your time. One more thing, I checked AC voltage at one of the yellow wires coming out of the stator and at idle it is at 14 volts. Thanks again. Eli

A: Eli, The charging system on your bike is made up of several components. The rectifier-regulator,stator, rotor,brushes and wiring connecting them. The diodes in the rectifier act as a one way gate. They should have continuity to ground in one direction only, and the same goes for continuity to the plus side which goes to the battery. The stator should be continuos to each wire with no continuity to ground. Both rings of the rotor should also be continuous to each other without being grounded. You also need to check the wear on the brushes to be certain that they make full contact. The cover is only held on by three bolts. If the bike has been droped on the right side while running the cover could move slightly causing the rotor to strike the stator damaging them. Good luck. Kurt

August 13, 2003

Q: I just purchased a 1972 CB750 from an Indiana Honda dealership. I have to have it shipped from there to western New York, so I won't be taking delivery until the end of this month. But it is a done deal. Questions: 1) I need a pipe. A 4 into 1 header preferably, although I'll settle for four good front pipes, sans silencers, un-bent and no corrosion if no new items are available. 2) I need sources for minor spare parts and tune-up items. The bike in question is basically stock except for some minor cosmetic jazz (you know, milk crate behind the sissy bar etc.) and 44k on the odometer. Motor appears to be bone stock. Can you help? Thanks in advance and I look forward to hearing from you, Tom Tibbils

A: Tom, I believe that I can find you a new Kerker pipe. This 4 into 1 is the first type of exhaust they produced and looks consistent with the age of the bike. It will require removing the original exhaust flanges and comes with the hardwhere you will need except the exhaust gaskets which are available from your local dealer. The pipe runs about $500. If interested, please give me a call at 818 9938640 Kurt

August 5, 2003

Q: Would you know if items such as R/C Headers, or equivalent might still be available for the good 'ol venerable 750 SOHC. I am currently in the hunt for an early 70's 750 and need some information as to what parts are still available out there, if any. I'd like to duplicate one of Russ Collins' Stage III bikes. 1000cc kit and all. Thanks in advance for any help you can provide. Sincerely, Tom Tibbils

A: Tom, RC parts are no longer available as are most hop up parts. I can get the early style Kerker and possibly an 836 kit. I do have a Tracy body 1970 CB 750 for sale.The body is one piece tank,seat, side covers, and tail piece .It has lester mag wheels and is lowered. The engine is stock with chrome covers.I am asking $3495. If you are interested please call me at 818 9938640. Thank you. Kurt

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