Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because oj the volume of mail received, we cannot return any personal replies. Please limit your “Service” letters to technical subjects only, and keep them asr' brief as possible. Send them to: “Service,” CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
CB PING
I own a 1980 Honda 750F that knocks like crazy between 2000 and 3000 rpm when the throttle is twisted open. I am running the highest octane fuel available and have had the timing checked by two different Honda dealers, who both found it to be set correctly.
The shop manual states that full advance occurs at 2000 rpm. Would changing the advance curve to get full advance at 3000 rpm cure this spark knock problem? If so, how could I obtain the parts to do this? I am more interested in engine life than all-out performance and am afraid this knock will damage the engine.
B.R. Love Lancaster, S.C.
According to Honda, the 1980 750F should not reach full advance until 6000 rpm, full advance being 40° BTDC, and it should go to an initial advance of 10° BTDC at 1000 rpm with the rest of the advance curve spread out between 1000 and 6000 rpm. Some movement of the timing plate is possible with the 750F, so you can delay the initial advance a little bit by retarding the spark, but you will also lose some power at the upper end along with the slight decrease in pinging problems. The only way to change the actual curve, of course, is to lighten the weights or strengthen the springs on the centrifugal advance mechanism. We don 7 know of any aftermarket spring and weight kits for the 750, so it’s probably up to you and your timing light if you want to experiment.
While the low end ping problem can be annoying on late CB750s (especially in hot weather) it isn’t too hard to keep it to a minimum. The simplest way is to use the highest octane fuel available, leaded or non-leaded, make sure your timing is set to specs, and then ride around the worst ping area in the rev band by keeping your rpms up. The 750F makes most of its power high on the tach and can be kept cooking along well above 3000 rpm without any heat or reliability problems, or much reduction in mileage.
BETTER BRAKES
I am the owner of a Bultaco Sherpa with bad brakes. The brake linings are worn out and were never much good. Could you produce a name and address for someone who could reline the brake shoes with a better material?
Ed Oldroyd Cedar City, Utah
Al-Jo Brake, 388 Grand Street, Patterson, N.J. 07505 [phone 201-278-0258) specializes in the relining of drum brakes for enduro and motocross use. They use a Ferodo flexible lining material that gives good performance on dirt bikes and most street applications. Al-Jo performs such services as turning drums and blueprinting brakes by turning your brake shoes mounted on your backing plate to match your drum diameter.
As a side note, w hen roadracing bikes still used drum brakes, Ferodo manufactured very fade resistant rigid linings. Because of their stiffness, these linings had to be molded in different radii to match different brake drum diameters; this led to the need to maintain large inventories of linings of the various radii in the different compounds offered. As disc brakes became more common, Ferodo’s sales of drum brake linings fell, and they could no longer justify production of the large range of rigid linings. However, their inventory of rigid linings was acquired by one of their distributors, Performance Research Organization (RD #/, Dreahook Rd., Lebanon, N.J. 08833, phone 201-236-6947). Performance Research is offering these linings on an availability basis, and anyone restoring an old roadracer, or looking for better brakes for their drum-braked Norton Dominator, might want to give them a call. There are surely other brake shops around the country that do good work on motorcycle brakes. If anyone has some experience with one of these shops and wants to recommend it, drop us a line and we’ll publish a list of them in a later issue.
TURBO KIT
I own a 1980 Yamaha 850 Special. I would like to know where I could get some information on a turbocharger for this motorcycle. I would also like to know how a turbo will affect dependability. How are they to install and tune properly? How do* they adapt to a Triple?
Robert Lawrence Fairmont, Minn.
Blake Enterprises, Rt. I, Box 403, Muskogee, Okla. 74401, manufactures a turbo kit for the 850 Yamaha. Any turbocharger-^ imposes higher loads and adds more heat to its host engine. In the case of an aftermarket kit, the engine was not designed to operate at these loads and temperatures, so reliability will be decreased. If the turbocharger is set to operate only at low’ boost pressures, the load and temperature.y increases will be minimized and reliability may not be significantly affected. Of course, the dramatic power increases seen in some turbocharger applications require high boost pressures and often involve> ’ thorough strengthening of almost all ' yengine components.
We tested a XS750 Triple with the Blake turbocharger kit in our January, 1980, issue. Installation of the turbo hardware was no problem, taking about eight hours. Some fiddling with the jetting was required and the carburetion was never as spot-on as with the stock XS750. The ' "turbo improved the quarter tuile time from 13.44 sec. to 12.63 sec. and increased the top speed from 114 mph to 125 mph. Despite the increase in performance, the bike was not as pleasant to ride as a stock XS750, possessing none of the civility of the recent factory turbos. Unless you must ’ have the fastest Yamaha 850 on vour block, you would be better off using the approximately $1500 a turbo kit costs to trade up to a faster stock machine.
JUMP START
V Can harm be done by jump starting a motorcycle from a car battery of the same voltage? 1 jumped my Suzuki a year ago, and afterwards some one told me I could have hurt the battery.
Lee Moore
Lincoln City, Ore.
[pYes, it ’s certainly possible to do damage to a motorcycle battery by connecting it to a car battery. The car battery is big enough to charge the motorcycle battery at an overly rapid rate, leading to overheating and plate war page. The Yuasa battery company recommends charging the battery using a low amperage charger, and simply being patient. If you have to jump tstart the bike, the chance of damage can be minimized by leaving the batteries connected no longer than absolutely necessary, but again, this is not a recommended procedure.
CUSTOM TIRES
I’m trying to improve my stock 1979 CM400T Honda in handling performance with better than stock quality tires and shocks. However, I can’t find the correct size for my bike. It requires a 3.50S-18 front and 4.60S-16 rear tire and narrow, clevis mounted shocks. Are there any better quality tires and shocks for my bike?
Barb Gore
Aurora, 111.
Dunlop is now offering K181 tires in 120/90V-16TL and 100/90V-I8TL sizes, which are metric equivalents of your curèrent tire sizes. Your stock shocks could be replaced by S& W models designed for the Honda CM400, such as their SS-4 Street Stroker. Your local dealer should be able to order both the tires and shocks for you. IS
