Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your “Service” letters to technical subjects only, and keep them brief as possible. Send them to: “Service,” CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
BIG TIRE TIPS
In your July issue Michael Shelton asked about a bigger tire for his 1977 XS750D. You were right about the 16 in. tire not fitting, but you advised a 4.00-18 with a higher load rating. Most tires ofthat size are rated between 615 and 660 lb. The stock Bridgestone is rated at 670 lb.
I had a '77 XS750D and used a 4.50-18 Goodyear AT, with a 770 lb. rating. I had 1/5 in. clearance between tire and driveshaft and it never rubbed. I used a 3.50-19 Goodyear GT II in front. It's rated higher than the 3.25-19, so even with fairing and bags a large man will have nearly 300 lb. of load capacity on reserve.
When I bought mv 1979 XS750 Special, those tires went right on. E. Ostrowski M.P.O. Soo, Mich.
SERVICE FOR THE CX500
I own a '78 Honda CX500. Due to the unavailability of service manuals at this time, I'm in the dark about some aspects of it. Are there earb kits for this machine? What’s the procedure for taking care of the swing arm bearings? Clark Hestland Grandview, Mo.
BY the time this appears, you'll have a choice of manuals. We have Honda's own guide for most work and the latest complete CX500 manual from Cl voter Publications. We haven't yet had a question on our longterm CX500 that we haven't been able to answer.
FILTERS, STACKS OR STOCK
I own a Kawasaki KZ650. I want to put a set of Kerkers on it. I went to different dealers and found they recommend different changes. One says use velocity stacks. Another says individual filters. Another says to keep the stock air box. What will each do with the headers? Patrick Johnson Willingboro, N.J.
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The Kerkers will work with stacks, with filters or the stock air box, depending which Kerker core YOU want to use.
It's a matter of degree. The velocity stacks will flow the most air and you ma)' even get a little ram tuning from them. But they'll let dirt and water into the engine, meaning more wear. They'll make noise and because they flow more air, you may need rejet the carhs.
The filters, good ones, will flow nearly much air. They protect the engine and they'll make a hit more noise.
The stock box and filter will he quiet and give maximum protection at the price some restriction.
So first, how much power do you want, what price? We'd not he willing to run without filters on the street, hut we know people who do. The middle ground would individual filters. What we'd suggest is that you get the exhaust system you want and then mate the intake to the exhaust. Tor norma! street use the Kerker DBA-E nearly as quiet as stock and it will he the quickest if you keep the stock intake. The DBA (not E-model) is a little louder and will work best with careful rejetting and perhaps individual air filters. Finally, there's the standard core. It's very loud, enough to get you in trouble with the law if used indiscreetly, and it will take full advantage velocity stacks and different jetting.
GAS GUZZLER
I just purchased a used full dress 1975 Suzuki 750GT. I am getting only 27 mpg. have cleaned ¿tnd reoiled the air cleaner, cleaned the exhaust baffles, and in reading the plugs they are what I would say is perfect brow n color. Why. then, am 1 getting such bad gas mileage? Tom Pappas E. Providence. R.I.
Your mileage is way out of line for normal use on a Mater Buffalo. Highway mileage should he m the 40s and even around town they wilt run mileage in the high 30s. The GT750 came with a treated dry paper air filter, so it 's curious to hear you 've cleaned and reoited the air fiter unless there is a replacement foam filter installed. Other items to check include the gearing (stock is a 15-tooth countershaft and 47-tooth rear sprocket) as a used machine could have had a smaller countershaft sprocket or larger rear sprocket installed for more acceleration. Unless your 750 will he used for drags the gearing shouldn 7 he lowered.
Then there's the curbs. Unlike many other bikes, the GT750s use three curbs but with the center carh set differently than the end curbs. Main jet size f or the end curbs is a 102.5 while the middle curb should have a size 100. The needle should be set in the 4bird position in the center curb and in the fourth position (from the top) in the end curbs. Even though your plugs look acceptable, it can be difficult to read a plug accurately and unless you are taking your plug readings after shutting off the motor while it's been running on the main jet or yieedle jet, your readings could be misleading.
Finally, check compression. With the plugs removed and the motor spun by the ■starter motor, there should be 106 psi cranking compression for a healthy motor. A large variation in pressures between cylinders means crank seals are bad and should be replaced. A reading below 90 psi in all cylinders indicates worn rings.
Finally, if your ignition isn't set properly the mileage will be hurt and so will power. Instructions for setting the three sets of points on the 750 are included in your owners manual.
WHEN THE LEAD IS OUT
1 always thought tetra-ethyl lead was used in gasoline to increase the octane rating and prevent detonation and preignition. I understood that because lead doesn't burn it can collect around the rings, contaminate the oil and (because it has an affinity for moisture) it will make for early deterioration of mufflers.
The current gasoline situation has led to discussion about damage to the valve train if unleaded fuels are used in engines designed to operate with regular or low-lead fuels. Would you be kind enough to explain the risks? ( I assume these are cases in which octane rating and compression ratio are not a problem.) Do manufacturers use different materials or design with no-lead engines, or is a lower compression ratio the only difference? Harry Ransone Helotes. Texas
There aren't as many hard and fast an swers to this as we'd like. When low-lead fuel first appeared, there was concern for valve life, because the lead in gas did provide some lubrication.
Currently, the oil companies are using other additives and the engines in most cases have better or different materials for the valve seats. Far as we know, assuming an octane rating compatible with the engine'st needs, no-lead will do no harm. And with an engine designed for low or no-lead, leaded fuel can leave deposits that reduce spark plug life.
FLOODED FLOATS
Since the purchase of my used Can-Am 175 T'NT. the Bing carb has been leaking whenever the engine is revved above idle. The needle and seat assembly and the float level have been checked and appear to be correct, yet the fuel still pours out the overflow pipe whenever the engine is running. R. Sedgew ick Oshawa. Ont.
My brother has a 1972 Honda CB750. The floats in two of the carbs sunk. He put new floats in and ever since he's had trouble with gas-fouled plugs. The carbs have been leaned as far as they can go, but the plugs last no more than 300 mi. and the engine blubbers on cruise. Alan Niemeyer Lena. 111.
One of the lessons taught by experience is that the last thing you fixed is likely to be the thing that 's giving you trouble now.
What we have here is carbs that are flooding. The needles and seats aren 't working, although they appear to be set right. Quickest cure here is to replace the needles and seats. Set the levels by the book and make sure the level is what it’s supposed to he.
While doing that, look for loose mounting flanges, clamps, nuts and bolts. Older engines tend to loosen up some, and both the above cases sound as if there's a vibration, anywhere from carb flange to engine mount, that 's allowing the carb to get rattled around and keeps the needle from getting the firm seal it needs to do its fob.
NO NON-LEAD
After reading your July 1978 issue decided the bike for me (and obviously not for you) was the Honda CB750A. And like the bike very much.
In your specifications, you listed recommended fuel as lowor no-lead. My manual recommends low-lead or regular with a research octane number of 91 or higher, or a pump octane number of 86 or higher. No-lead is not recommended.
What gives?
E.A. Conley Marietta. Ohio
Lead is put into gasoline mostly to raise the octane rating, but there's more to it than that. Lead also serves as a lubricant for the valve seats. When no-lead first appeared, there was some confusion over this, as early experience showed that the lack of this lubrication could cause problems.
Note we say “could. ’’ The different manufacturers have had different experiences with no-lead. Some say lead is useful, some say it doesn't make any difference.
Evidently, to be on the safe side, Honda would prefer you use lead and not worry too much about octane. Unless the lead fouls spark plugs, we'd say leaded gas is good insurance.
YANKEE PARTS
In the June issue, there was a letter from a man interested in the Yankee Z500. thought I’d pass along the address of the Yankee distributor:
Yankee Accessory Corp. 2910 Campbell Ave. Schenectady, N.Y. 12306
Guy Gallucci Schenectady, N.Y.
