Cycle World Service
CYCLE WORLD SERVICE
Honda 750F mid-range power
My 1980 Honda 750F is definitely biased toward top-end power; it comes on at about 6500 rpm with a real burst of acceleration. This may be great for racing, but many of us ordinary street
riders could use more mid-range power. There are a lot of performance parts available for twin-cam Honda 750s: big-bore kits, exhaust systems, cams, etc. In general, which of these, singly or in combination, could be expected to yield a decent mid-range power increase without sacrificing driveability or reliability?
Giff Nickol
Towson, Md.
More displacement will translate into more midrange. The simplest way to make the engine bigger would be a 3mm larger piston set with the same compression or slightly less than stock. This change by itself will have the desired effect without sacrificing either Tdriveability, or in normal street use, reliability.
10w-40 or 20w-50
i am in disagreement with a local motorcycle dealership that uses 20w-50 grade oil in its new motorcycles. I recently purchased a Kawasaki Ninja that has a tendency to run somewhat hot in town. I think that this bike would run cooler using a 10w-40 grade oil. Who’s right?
Bryan Nelson
Carson City, Nev.
Your dealer is right. We ran some carefully instrumented experiments a few years ago and determined that for a CB750F, there was no significant difference in oil temperature when either a 10w-40 or 20w50 oil was used. We fully expect that result applies to all other motorcycles as well. You can read about our oil test in more detail in the October, 1982, Cycle World.
Synthetic oil life
/ would like to know more about synthetic oils. From what I’ve read, a person can go 25,000+ miles before changing oil. I suppose the oil filters would be changed every 4000 miles, or whatever the motorcycle manual calls for. The 25,000-mile figure is used for cars, but the articles never mention anything about motorcycles. How often would a motorcycle need its oil changed if a synthetic oil were used?
Doug Hetrick
Tacoma, Wash.
Synthetic oils maintain their viscosity for much longer periods than do standard motor oils, and they're much more resistant to oxidizing into an unpumpable sludge. For those reasons, a bike using a synthetic oil might go 25,000 miles between oil changes, but such intervals are not necessarily recommended.
First, motorcycle manufacturers don’t accept extended periods between oil changes with synthetic oils as meeting warranty requirements, so you’d have to change at the recommended intervals during the warranty period. Second, while the properties of synthetic oil itself may be maintained over long periods with synthetic oils, the oil can become contaminated by combustion by-products that sneak past the piston rings. These can be harmful to long-term engine life.
So even though the motorcycle manufacturer recommended shorter oil-change intervals, following their guidelines would seem to offer peace of mind regardless of the type of oil being used.
Discolored oil
Ê ride a GSI 100G in winter weather, which is occasionally 30 to 26° F. The oil inspection window clouds up with a white substance that disappears after a long ride or a long warm-up. I use Pennzoil GT Performance 20w-50 oil.
What is the white stuff? Does it harm the engine?
Robert Marchus
Jackson, Calif.
The white stuff is probably an oil/water emulsion resulting from water condensing in the crankcase. If the bike isn’t operated long enough to heat up and boil the water away, you should change your engine oil more frequently than suggested in your owner’s manual. In any case, it isn’t a serious problem.
If you operate your motorcycle in predominately cold weather for months at a time, you should switch to a lOw40 oil for better low temperature lubrication.
Belt drive status
W hat is the current status of belt drive? I was planning on replacing my 1979 bike soon but originally wanted a belt drive. Should I settle for chain or shaft, or are any of the Japanese manufacturers working on a mid-size belt drive bike?
Tom Gates
Glendale, Calif.
We don’t have access to all the future plans of the major motorcycle companies, but we don’t expect to see many mid-size machines with belt drive in the near term. It’s not because belts don’t work well; the Harley Sturgis has proven that belts can offer exceptional lije and convenience. The problem is that belts are bulkier than chains for any given power rating. That’s fine jor small bikes with relatively lower power outputs, or for the Harley models that allow room for a belt of the required width. But a mid-sized motorcycle would almost have to be designed from the ground up to accommodate an appropriate belt, and that may not happen for awhile.
More on jerky clutches
I just read about Carl Anderson’s problem with a jerky clutch in the Service column of your June, 1984, issue. I think I can help him out so that his bike won’t have to spend any more nights with a steel ring holding its clutch lever in.
My 1982 CB900F and 1983 CB1 100F had the same problem that Mr. Anderson describes. Dropping the bike into first gear on a cold morning would usually result in a quick stall, followed by the bike lurching forward a few feet when I pulled the clutch in and restarted the bike while it was in gear.
I found that if I disengaged the clutch a few times, and then blipped the throttle a few times with the clutch disengaged before actually shifting into first gear, the problem stopped. When I pulled the clutch lever in and blipped the throttle, I could hear the clutch making noise for a few seconds before becoming quiet. The bike would then shift into first gear without so much as a clunk.
Kenneth L. Bird
West Chazy, N.Y. g)
