Service

SERVICE

BSA OCTANE DEFICIENCY

I am the proud owner of a 1970 BSA Thunderbolt. I have more than 27,000 miles on this beautiful dinosaur and figure it has at least that many left in it, if I can overcome a problem that must be common to most pre-energy crisis machines. The owner’s manual states that the cycle must have at least 98 octane petrol. Unfortunately, the highest octane on the market (that I am aware of) is 95. This is rather bothersome but I have temporarily overcome pre-ignition problems by retarding the timing about three degrees. What is more bothersome is that I recently pulled into a nationally known gas station to fill up with high test. When I examined the octane rating posted on the tank I found although the brand name has not been changed, the rating was now only 92, something called “mid-premium.” The trend being increased price and decreased quality, I’m afraid this type of gas may replace the higher ratings.

What can be done to make this machine run on low-grade gas? Retarding the timing further will not only cause a loss of performance, but will likely cause overheating.

I noticed a part number for 7.5:1 compression pistons. Would lowering the compression ratio in this manner help?

I can’t sit back and watch my dinosaur become a victim of its environment.

M. W. Robinson Rockville, Md.

We recommend YOU retain the stock components, limiting timing advance to a point just shy of pinging. Install a step colder plug, and try to gas up at stations having higher octane ratings.

You may also wish to try some of the commercially available octane boosters, but that could be one obvious hassle worth avoiding.

If you are still dissatisfied with your Beeza's response to available petrol, those 7.5:1 pistons might be the answer. But although your engine would run cooler than with the 9.0:1 stock compression, you'd probably lose just as much power as if the timing was severly retarded.

CYCLE WORLD staff' members who own a '71 BSA Thunderbolt and Triumph Bonneville, same vintage, offer their sympathies. But that's progress for y a!

HONDA EXHAUST

I am looking for an aftermarket exhaust system for my 1976 Honda 750 Super Sport. I'm trying to find one which will not only increase horsepower and gas mileage, if possible. but still allow access to the oil filter and stands. I would hope to find one which requires no carburetor modification,

and is not too loud.

Also, I seem to have a problem with gas mileage—compared to other Honda 750s. As nearly as I can figure, I’m getting 25-30 mpg. Is this the nature of the bike or is something out of whack?

Mike Ruck Mt. Prospect, 111.

There are quite a few good exhaust sy-s1tems for the 750-4 available. Included are 4into-4, 4-into-2, and 4-into-l configurations, and replacements for the stock mufflers.

In an area as popular as aftermarket exhausts, we would be doing the readers and manufacturers a disservice by playing favorites. We'd rather you do some shopping armed with a list of your own needs and priorities, then make a selection.

As to your fuel consumption problem, here 's what one reader related:

HELPFUL HINT FOR HONDA 750F OWNERS

To the owners of the notoriously thirsty Honda 750F, 1976 vintage, I have a helpful hint on how to increase gas mileage and range. I have logged many hundreds of miles of the open road so range is important to me. The previous 39 mpg from my Honda really hindered me, so this is what I did:

I drilled a series of V^-in. holes in the rear portion of the breather box, thus relieving the breathing. I invested in an 18-tooth counter sprocket. This had the effect of lowering my rpm approximately 450-475 at 60 mph. I then removed the carburetor assembly. Remove the gas tank and disconnect the throttle cables. Remove the breather box and disconnect the gas lines. Loosen the bolts that hold each carb to the rubber intakes. Loosen the bolt closest to the carb, not at the heads. Once the carbs are off, take out the eight Phillips-type screws holding the carbs to the rack, and one at a time remove each carb. Take the slides out of the carbs by loosening the large threaded ring at the top of each carb, then remove the slide needles. Raise the horseshoe-clip on each needle valve one notch. Then reassemble the carbs.

The end result of this modification was a whopping 52-55 mpg and with no discernable difference in performance. My plugs still obtain a good burn and the exhaust cleaned up from the sooty black to a nice ash-brown.

This operation was performed on two of my friends bikes with equally good results. One of these bikes was a Kawasaki 900— the mileage increased from 42 to 51 mpg, again with no discernable difference in performance.

Jim Lamb Manhattan Beach, Calif.

Len Vucci

RD OVER OILING

Last spring I purchased a new 1975 Yamaha RD350 and have had plug fouling problems right from the start. One dealer soldered all the electrical connections to prevent voltage leaks. This seemed to help, but did not cure my problem. The bike currently has run over 5000 miles and has fouled out at least two dozen plugs, usually the right cylinder, but more recently the left. Some plugs don’t even last 100 miles.

I’ve tried riding it hard (over 5000 rpm) most of the time but it only fouls out as soon as I take it easy. The engine runs best from 3500 to 5000 rpm but won’t accelerate over 5000 rpm without bogging and coughing. Also, after keeping it under 5000 rpm, the exhaust pipes are dripping with oil. I generally get 225 miles per quart, which is considered normal.

I have tried various gasolines but there seems to be no difference between them. I’ve tried various oils too, but they seem to perform the same.

I would greatly appreciate any advice you might be able to give. Could you recommend both a gasoline and an oil that best suits my bike? What have other readers done to solve this problem with their Yamahas? I thank you for any help you could send my way.

Richard P. Belhumeur Cranston, R.I.

Even though your RD's oil consumption is within acceptable limits, I suspect the oil pump is not properly adjusted. Yamaha RDs have an adjustment for minimum oiling, in addition to an adjustment to sync the pump to carb opening. This “minimum ” adjustment is accomplished bv shims, and it's a good bet that it's the cause of your problems.

Just in case you'd like to beef your ignition, look for the article on the RD ignition hop-up elsew here in this issue.

KAWASAKI COMPRESSION

I purchased a Kawasaki Z1 in August, 1976 and noted shortly thereafter that the compression was 90-100 psi on all four cylinders. My dealer seemed unconcerned. I recently tested the compression again and three cylinders tested between 65-75 psi. One gave a higher reading of 100 psi. The clearances are correct on the valves. The bike runs well, but the mileage is low— usually around 36 mpg. Do you think I should be concerned?

Eligió Dela Cruz, Jr.

Edinburg, Tex.

In a word, yes. Normal ZI compression should be around 120 psi with the engine at normal operating temperature. And the difference between the maximum and minimum readings should be no more than 10 psi. Readings of65-75 psi are indicative of a

definite problem, most likely stemming from inadequate lubrication.

The low compression could be caused by poor piston ring sealing, worn valves, or both. There is an easy check for piston ring sealing which may reveal more of the problem.

Pour about a teaspoonful or so of 50 wt. engine oil into each cylinder before it is tested for compression. If the readings become significantly higher, then the problem is ring sealing. If the diff erence is minimal, the valves are most likely at fault.

Regardless of the components deemed to be at fault, don’t neglect the lubrication system. Have a competent mechanic check it out for possible obstructions or other malfunctions.

HONDA CB360 IGNITION

I would like to know if there is an electronic ignition kit on the market that will fit my Honda CB360T. If not, which make would require the least modification?

Albert W. Chau Seattle, Wash.

We assume you are looking for a product which will allow you to eliminate the breaker points. To our knowledge, several types of breakerless conversion kits are available, but not for your particular machine.

Depending upon your mechanical skills, we suppose one of the available units meant for another model could be adapted. But we would not recommend such a conversion as the expense and time involved would probably be unwarranted in terms of results achieved.

If your primary concern is elimination of the need for periodic maintenance of a breaker points system, we’re back to the original question. But the article on ignition modifications elsewhere in this issue may provide you with at least a partial answer.

XT500 GAS TANK

I have a 1976 Yamaha XT500 Single on which I’ve put 7500 miles, including a 3500 mile Toronto to Vancouver trip. I’ve had no trouble and have only two complaints: The stock fenders are woefully inadequate and the 2.2-gal. gas tank limits the range to about 110 miles. Preston Petty solved my fender problem but I’m having difficulty finding a long-range tank that will fit over the XT500’s large frame backbone and allows access to the oil filler cap.

Could you recommend a tank that would fit, the larger the better? Unfortunately, aftermarket goodies don’t seem to be as readily available here in Canada as they are in California. None of the local> dealers have been able to give any helpful hints.

Jon Anderson Alta Lake, B.C. Canada

Don Vesco Products makes a 3.1 gal. tank, in a choice of yellow, white, orange, silver, or red.

Malcolm Smith lists a 3.5 gal. tank in yellow, orange, red, or white.

Both are listed at a retail price of $49.95, and should be available through a local dealer. If not, they may be contacted at the following addresses: Malcolm Smith Products, 888 Marlborough, Riverside, Calif. 92507 (714) 686-1006. Don Vesco Products, 7565 North Ave., Lemon Grove, Calif. 92045 ( 714) 465-8256.

HONDA OILER

I own a Honda CL 125 which has about 5200 miles on the odometer. Lately it has been burning much more oil than usual. I plan on giving it the complete tune-up which it needs. Will this cure the oil problem?

Joe Souza Hollywood, Fla.

No. Oil consumption in a four-stroke is normally caused by excessive wear. Worn piston rings allow oil to pass into the combustion chamber. This results in blue-grey exhaust smoke, especially at higher rpm.

Worn valve stems and guides (and seals, where present) can allow oil to pass into the fuel intake tract, then into the cylinder. If the bike smokes badly after idling for any length of time, this is most likely the problem.

And finally, check to make sure the crankcase breathers are intact and functional. Clogged breathers can allow excess crankcase pressure to build up, increasing oil consumption. in