The Service Dept.

THE SERVICE DEPT.

JODY NICHOLAS

PLUG FOULING

In the March issue you tried to help a poor 350 Yamaha owner to overcome the old problem of spark plug fouling. His Yamaha’s symptoms seem identical to those of my previous bike, a T125 Suzuki. The problem of chronic misfiring at high rpm and plug fouling seems to affect all T125s; mine could manage only 300 miles between plug changes. No dealer could tell me what was wrong, though one did suggest using American plugs. I ignored this advice; nearly 60,000 miles on two-strokes have taught me that if the thing won’t run on NGK plugs there’s something wrong with it. I tried everything-nondeter-gent oil, hotter plugs, new coils, the works.

Eventually I tried lead-free gas and the problem was solved; the bike was smoother, went faster, was more tractable and drank less. With new B-7H plugs I did 1000 miles before a gas station attendant put in supreme when I wasn’t watching (“Your cycle won’t run on that lead-free crap. ”). Fifty miles after this incident the misfire returned, a thin veneer of lead had formed over the whole inside surface of each plug; they were useless. The next plugs (B-8HCs) stayed in the engine for 7000 miles before I decided I ought to change them. They were still in excellent condition.

So if you have a two-stroke with plug fouling problems and everything (especially ignition timing) is correctly adjusted, clean the plugs and inspect them. If the ceramic insulation has a metallic glaze, throw the plugs away, drain the gas out of the tank, and try again with new plugs and lead-free gas. Trying to clean glazed plugs is a waste of time; after a lot of effort they may look reasonably free of the glaze but fire up the engine and it will probably start coughing after a few seconds. Obviously lead-free gas cannot be used in a really high compression engine as it is only available in regular grade. In this case use low-lead gas with the lowest octane rating the bike will run happily on. The compression ratio of my Suzuki was 7.3:1. I believe the c.r. of the 350 Yamaha is 7:1, so it should run well on lead-free gas.

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Gerard Fryer, Honolulu, Hawaii

WARM THE ELECTRODES

/ own a Honda 305 which gives good service, but is a devil to start after coming out of winter storage. I usually am exhausted before the bike begins to sputter. Today a veteran motorcyclist, Don Len, showed me a trick that had the engine running in three minutes. All that is required is to remove the plugs and warm the electrodes with a match. Probably more seasoned motorcyclists know of this trick, but please print this letter to save much exhaustion for other novice cyclists.

John W. Pinnella Eggertsville, N. Y.

CRANKCASE REPAIR

I own a Honda CB 750 on which I broke the chain last week, as so many others have done. The chain went through the crankcase. Both cases were broken; however, all the gears are undamaged. Cases are $1 75 and the Honda shop said nothing else could be done but to buy the cases.

Could I patch the hole or maybe have a machine shop try to mend it? The hole is about 1 in. by HA in. Would the cases be weakened too greatly?

Stan McConnell Birmingham, Ala.

Thankfully, not many of the latest Honda CB 750 models are experiencing chain failures. American Honda Motor Co. and Honda of Japan have been working feverishly to end the chain breaking problems experienced by several owners of early CB 750 models. Stronger rear chains of the “endless” variety (without a master link) are fitted to the latest models and with a reasonable amount of care in keeping them well lubricated and adjusted not many failures occur.

When the right person is located to perform the work, any piece of aluminum can be repaired. If the hole in your crankcase is located entirely above (or below) the seam between the horizontal crankcase halves the job will be relatively easy for a person equipped to do heliarc welding. If the hole has broken the area where the crankcase halves mate, care will have to be taken to carefully machine the mating surfaces to avoid oil leaks.

Because the crankcase area just in front of the countershaft sprocket is relatively far from the transmission shaft bearing support bosses, the "patch" area will not be subjected to really heavy loads and should give no trouble if the welding has been properly done.

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SMOKY KAWASAKI

Owning a very "smoky" 1971 Kawa saki F5 Big Horn (4000 miles), I am most interested in the new oil pump that supplies less oil at lower engine speeds as described in CW's February issue. Set full lean, the bike smokes outrageously enough when warm in street traffic to get a citation for "ex cess smoke." Can my stock pump be brought up to F9 specs or must a new one (about $30) be installed? Otherwise it runs like a good thing and will start on the first kick every time.

Also, I'm using - two head gaskets (one originally from the factory) as advised by one dealer, supposedly to prevent self-destruction, but the only result of note is slightly less top end speed on the freeway. As the engine is never pushed to the limit except for a very rare short blast, please advise about the gasket(s).

Alfred N. Pearl North Hollywood, Calif.

The new oil pump as suppliedon the 1972 model F9 Kawasakis has been changed quite a bit and will fit your F5 with no modifications. Basically the two pumps are the same, but the newer pump has a redesigned cam which sup plies the. engine with less oil at any throttle opening below full throttle. It was found that the F9 (as well as the earlier F5) would run reliably on a "weaker" oil pump setting. Attempting to modify your old pump is not recom mended and I would suggest buying a newF9 pump.

Unless there is a problem with excess carbon formation on top of the piston and in the combustion chamber, there is no reason to use two head. gaskets. I suspect that you might now be experi encing `excess carbon deposits, but the new pump should cure this. The mini mum octane requirement for fuel speci fied by Kawasaki is lower than even most of the cheapest regular gasolines sold in the United States and you might want to try a good regular gas instead of high test. If a pinging sound develops, switch back to high test.

Try installing a new F9 oil pump, remove the cylinder head and carefully scrape away all traces of carbon from the combustion chamber and top of the piston, using a suitable carbon scraper that will not gouge the aluminum, and reinstall the cylinder head using only one head gasket.