The Service Department

THE SERVICE DEPARTMENT

JODY NICHOLAS

BRIDGESTONE OILER

My Bridgestone 350 GTR is giving me a slight problem, and from what I’ve seen, it is the common curse of owning any two-stroke.

I use Sta-lube, and the oil pump is cut back about 1/8 in. from specs. It only smokes at starting and low speeds. It runs very hot to the touch but does not seize, and it is very, very quick.

My problem: how can I keep the plugs clean? I run 120 main jets and have tried both B8H and B9H NGK’s with little difference. A full throttle plug check gives a brown glazed look, which I interpret as plenty hot with the 120’s. If I could set the oiler to deliver less at the 3000 to 6000 range and the same on up, it would be OK. But how? I don’t dare cut the oiler back anymore, but I don’t care for the hesitation I get in the lower gears until it clears itself.

Iam really happy with the GTR, but I would like to clear up this one small flaw in her personality.

Robert Schulze Council Bluffs, Iowa

Your problem is common to twocycle motorcycles and especially to those with an automatic oiling system. Most automatic oiling systems are geared directly to the engine and are regulated both by engine rpm and by throttle opening. Thus, when the engine is turning over at high rpm at a slight throttle opening, the engine is still receiving an adequate supply of oil.

Since you have cut back your oil supply and are experiencing no problems with engine seizures, we can assume that the engine is receiving enough oil for the operating conditions you are subjecting it to, and you can leave your oiler set where it is.

The plug fouling/dirtying you mention is most likely caused by a combination of the type and brands of oil and gas you are using. It isn’t generally known that most two-cycle engines will run extremely well using a name-brand regular grade of gasoline, and it’s certainly worth a try in your case. Regular grade gasolines generally contain a lesser Continued from page 78

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amount of tetraethyl lead which is a major cause of carbon build-up.

You might also consider trying another brand of oil in your injection system. There are many low-residue high-performance oils available for motorcycles with oil injection systems. The problem won’t be completely cured, but its effects can be reduced.

B-B AGAIN

I just read the letter to Service in the July issue from Fred Schwartz complaining about whiskering or having small balls of lead build up between the electrodes on his plug.

Maybe I can pass a tip on to those with similar problems. I had a brand new Hodaka which did exactly the same thing, and after trying many heat ranges of plugs, many different two-stroke oils, different gasolines, setting the timing and pressure, testing the bottom end twice, not to mention jetting and also putting on a new carburetor, I finally found a small casting pit about the size of half a B-B in the combustion chamber of the head. It had carbon in it and would create a hot spot and pre-ignite the engine when running at full throttle, but would act normal at slow speeds. After replacing the head, the bike ran wonderfully and could be run flat out, and it would never skip a beat. It is something to look into when having this problem and the usual methods don't cure it.

Barry Cooney West Linn, Ore.

Thank you very much for your letter, Mr. Cooney. I have heard of similar problems, but I think Mr. Schwartz’s problem was not pre-ignition but rather the lack of any spark because of the bridged electrodes. We are publishing your letter in hopes that other readers may derive some benefit from it.

PRESSURIZED TRIUMPH

I have a 1968 Triumph T120R. Although all gaskets and plugs are tight, it leaks, and there is a large oil foam runoff from the breather pipe. I put a 750-cc kit on it, and the problem became worse. Since the 1970 T120R has improved crankcase breathing and is reportedly more oil tight, I would like to know if I can adapt my engine to have better crankcase ventilation and possibly eliminate the oil seepage. The harder I run the bike, the more it leaks. If I wash it and let it stand there is no leakage to be seen.

SP/5 Robert W. Smith Ft. Devins, Mass.

The pre-1970 Triumph 650s feature a crankcase breather located at the left-hand end of the inlet camshaft. As the camshaft rotates, holes in the breather unit uncover to allow excess pressure from the crankcase to escape to the atmosphere through a metal tube.

The 1970 Triumph 650 uses a completely different system for breathing the crankcase which was first successfully used on their racing 500s a few years ago. The breather at the end of the inlet camshaft has been done away with, and the engine now breathes through the crankcase into the primary chaincase and from there into the atmosphere.

This modification has been accomplished by leaving out the oil seal on the drive side of the crankshaft; three 1/8-in. holes are now located just below the crankshaft and extend through the crankcase to maintain the proper oil level in the primary chaincase^ There is also a breather outlet, and a baffle behind the clutch to keep dirt out.

Modifying your machine to the 1970 specifications would require dismantling the engine to do a proper job, but it would probably be worthwhile. First, the old breather pipe must be brazed closed and the seal behind the engine sprocket must be removed. Then the three 1/8-in. holes should be drilled on a line corresponding to the normal oil level line in the primary chaincase.

A breather outlet will then have to be fabricated, preferably at the rear of the primary chaincase and fairly high up. Use the 1970 Triumph set-up as a guide.

Another possible cause of your oiling problem could be a worn plunger in the scavenge (return) side of your oil pump. If the oil quantity in the sump reaches much more than lOOcc, there is a good chance that a malady such as yours will occur. If in doubt, replace the pump assembly first.

HONDA CB350 OR CB450

I am planning to buy a Honda CB350, or 450, and would like to do some extensive travelling. For this travelling I would get a heavy-duty pair of plastic saddlebags. I like the indicator lights on the bikes mentioned and was wondering if there is a way to mount these saddlebags without removing the indicator lights. Perhaps there is a way of mounting the lights on the outside of the bags, or would this be too wide.

Excuse my curiosity, but in your motorcycle Road Test Annual you listed the Honda CL350 as 102 mph and in CYCLE WORLD, July 1970, you listed the Honda CB450 as also doing 102 mph. How could this be? Please explain or clear up, as many of us are confused as to these speeds.

Thank you very much for your attention, and I'm sure CYCLE WORLD will remain the magazine by which others set their standards.

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Sky Moore Los Angeles, Calif.

The turn signal indicators are a good safety feature, and you would do well to retain them. There are saddlebags available which incorporate turn signals in the rear of the bags themselves, but if the ones you choose don't, brackets are available which would allow you to install your present turn signals on the rear of almost any plastic saddlebags.

egaraing tue top speeus 01 tue Honda CL350 and CB450 models, I can only quote the road tests and make a few observations. True, the two ma chines' top speeds are almost identical, but there are many factors which enter into each and every road test. Different rider techniques could account for a sizeable difference in quarter-mile accel eration times, but as expected, the CB450 was over a full second quicker through the quarter than the CL350.

Conversely, it would generally be assumed that the CB450 would be faster through the top speed traps, but due to the state of tune of the machine or weather conditions, the top speed was down slightly from what was antici pated. Even fully automated production line machines vary from unit to unit and are faster or slower than other machines in the same batch.

Because of these differences, we try to describe the test machines as well as we know how, record all performance figures accurately and help the reader make up his mind, using our findings.

SHAKY LOBITO

First of all, congratulations for an excellent magazine. As far as we're concerned, it's the best cycle magazine on the market.

Having purchased a couple of Bul taco Lobitos, we were real happy with the clean bill of health your magazine gave them in the April issue, and just about wild when we read about the ease with which the 125cc could be jumped to 250cc. We're stationed in Spain where they make them, so we figured it would be no sweat at all to have them swapped over to 250cc. But when we went to the local Bultaco Service Agency with our plans of enlarging our little Buls, they gave us the sad look and said it wasn `t possible. We finally convinced them it was, but we ended up with having to mill out the transmission case a total of 4mm to accept the larger 250cc sleeve. Your article made no mention of this necessary milling, and we wondered if you had neglected to print it, or if possibly it’s new info to you as well.

Since the changeover we have had quite a bit of trouble with vibration. Our Lobitos came stock with a 14-tooth sprocket in the front and a 64-tooth sprocket in the rear. We changed the front to a 17-tooth (as large as would fit) and left the rear stock. All the rest of the running gear is stock including the 3.00-19 knobby in front and 4.00-18 in the rear. The vibration doesn’t seem to get bad until around 50 mph, and then it’s like riding over a bunch of railroad ties. Although we run the little Buis on and off the roads, we never had the vibrations before the changeover to 250cc. We’re out of ideas. Any suggestions to stop the “shakes?” ETN2 D.R. Wright RM2 J. W. Binns FPO New York, N. Y.

True enough, the CYCLE WORLD impression of the Bultaco 100 and 125 Sherpas did mention that many parts are interchangeable between the 125, 175, 200 and 250 machines, and that the crankcase assemblies are the same. I know of many people who have changed their 175s to 200cc and viceversa, but going from a 125 all the way to a 250 is a new one on me.

First of all, the area around the cylinder base is somewhat smaller, as you found out when you modified your own machines, and secondly, you should have taken into consideration the fact that the 250’s bore is 72mm, some 20mm larger than the 125’s 52mm. This is a bore increase of almost 4/5 in., and quite naturally, involves a heavier piston.

With a swap such as the one I mentioned above, the size differéntial between a 175 and a 200 is closer to 1/5 in. Although the balance factor is changed somewhat by substituting one piston/cylinder for the other, it isn’t that great a change and can be lived with without rebalancing the crankshaft .

Of course, there is a difference in the weight of the crankshaft between all the Bultaco models, although the connecting rod assemblies are interchangeable. In order to correct the vibration problem you have, you would have to substitute the flywheel assemblies from the 250 Pursang or Matador. ®