Tech Corner
Technical Q and A for classic motorcycle maintenance and repair.


Suzuki TC185 Carburetor Jetting

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I have just acquired a 1976 Suzuki TC185. The bike starts easily and runs, but has some minor problems. It has a 71.5 main jet, but my manual says it needs a 130 main, so now I doubt any of the jets are correct. What is the correct carburetor setup for this TC185? I can't find any information, much less the parts. So far I've cleaned the carb, the air filter, the gas tank and the spark arrestor. I've replaced all the fuel lines and added an inline filter and a new spark plug. As I said, it starts and idles but then gets blubbery, like it's holding back. I think my top speed might be 30mph with the throttle wide open. I've tried the dual-range transmission and that works fine. My problem is in the carburetor, but I need to know what the right jets should be and where to get them.
— Dean/via email

A: That's a sweet little scrambler you found. That main jet size is correct for the 185 twin, but not the single. The main jet should be 130, as you found out. The pilot or idle jet for that model should be 17.5. You need standard Mikuni jets. If you have a local motorcycle shop that's been in business a few years, they may have what you need on hand. If not, Dime City Cycles has the jets. Just search on their site for those jet sizes.

Pinging Noise in a Kawasaki 350 S2A

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I recently purchased a 1973 Kawasaki 350 S2A triple. I'm using regular gasoline. The issue I'm having is a pinging noise coming from cylinder No. 3. This pinging noise is more noticeable at low rpm (below 2,000rpm). What could be causing this problem? — Mario/via email

A: I suppose there could be a carbon spike glowing and pre-igniting cylinder No. 3, but having it happen at idle makes me think it's something else, like a bearing rattle. Pinging usually occurs under moderate throttle while choosing a gear a little higher than conditions require. A mechanic's stethoscope, available at Harbor Freight or any auto parts store, is a handy tool for chasing down odd noises coming from your engine, but a long screwdriver held against the engine case with the other end pressed to your temple can give similar results. What you'll be listening for is the frequency of the sound. Is it every revolution or one in three? If you hear the sound on every revolution, then it's probably bearing related, but if you only hear it every one in three it would be specific to that cylinder.

Yamaha SR500 Petcock Challenges

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: My 1979 Yamaha SR500 has a vacuum fuel petcock. I've found no way to eliminate it for a simple gravity-style petcock. I installed an inline fuel shut-off in the fuel line below the petcock. When I'm done riding, since the stock petcock has no "off" position and relies on engine vacuum to allow fuel flow, I turn the inline one to "off" and let the carburetor run dry to eliminate any gas going stale inside the carburetor. My problem is, when I go to start it, it takes anywhere from 5 to 20 kicks to get it started. The engine is running a 1980 Hi-Per-Kinetics Stage Two 650 stroker with 97mm x 88mm bore and stroke, a Megacycle 5120HP cam, Mikuni VM36 and other goodies.

I've owned three Yamaha TT500s, and they all had the on/off/reserve manual petcocks and all started first kick, hot or cold. How can I eliminate the funky stock petcock without replacing the tank? Does it require a lot of kicks to get the fuel flowing from the petcock because of the engine modifications? Should I just not run the carb dry after riding? I use octane booster and fuel preservative. The bike had sat for over 25 years when I bought it in 2012. The inside of the carburetor was surprisingly clean, with no gum at all. — David Fruhling/via email

A: It is taking so many kicks because there would normally be enough gas in the carburetor to start, then engine vacuum would open the petcock and refill the bowl before it ran dry. There should be a "PRI" or prime position on the petcock that bypasses the vacuum and flows gas to the carb for those instances when the bowls are dry, such as after a carb rebuild. After a little searching I found a good option. It's an adapter that bolts directly to your tank and allows you to use a standard non-vacuum petcock. They also offer the petcock that fits the adapter, making it a one stop shop. Don't forget to plug the vacuum port on the intake manifold.

Kawasaki KZ1000R1 Engine Paint Codes

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I'm slowly restoring a 1982 Kawasaki KZ1000R1 and am having difficulty identifying the correct black paint to use on the engine and carburetors. I'm under the impression that the paints used in 1982 no longer meet regulatory requirements in the U.S. and finding a suitable replacement is difficult. Any chance that you have insight on this matter and a source for the paint codes and type of paint? — Drew Jones/via email

A: I've never worried too much about a correct match for black barrel paint; it's more important to get a heat-resistant paint. Most of the time I just use a quality brand spray paint made for BBQ grills. It's meant to take the heat and has worked well.

Seized Cylinder on a Suzuki GT550

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA, or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send your questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I have the chance to buy a reasonably nice Suzuki GT550. I believe it is a 1976 model — one of the later disc-brake bikes — but the center cylinder on this triple is seized and I wondered if you have any thoughts on the best way to free it up?
— Peter/via email

A: You can do a simple test to see if it is the piston seized in the bore (somewhat common and fixable) or a seized main bearing (unlikely, but probably a deal killer). If the seller will let you, take off the left side engine cover, and with the appropriate size wrench gently turn the nut at the end of the crankshaft back and forth. If there is some movement you can assume the main bearing is free. If it passes that test and you buy it, the next step will be to pull off the cylinder heads and have a look at the middle cylinder. If the piston is up you won't be able to tell much, but if it is down you should be able to see if the bore is scored or scuffed, indicating a seizure while running. If none of the transfer ports are visible yet there is some room in the cylinder to hold liquid, the shade tree mechanic fix is to pour in a mixture of ATF and acetone and let it sit. After a decent interval of several days, you can again try to turn the crankshaft with the wrench, looking to see if the center piston moves at all. If the center piston isn't at TDC you can also try tapping the center piston with a suitable sized wooden dowel and hammer. Easy does it. Repeat the solvent, wrench and tapping until you achieve success. Once it's free, you can confirm if you'll need a new piston or other work to get it running. Good luck!

Norton Commando Clutch Setup

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I have a beautiful 1975 Norton Mark III Commando that is nearly unrideable due to a clutch/shifter issue that my local vintage mechanic has been unsuccessful at fixing. The clutch does not fully disengage when you pull in the clutch lever. The 1 to 2, and 2 to 3 upshifts are very hard, particularly when the bike is warmed up. Downshifting is worse, as pulling in the clutch to downshift does not fully release the clutch (i.e., even with the clutch lever pulled in, the transmission engages immediately when you shift down). Sometimes on a 4 to 3 or 3 to 2 downshift it hits what seems to be a false neutral, but sometimes blipping the throttle gets a gear to engage from the false neutral. To stop this quirky Commando I need to pull in the clutch lever, apply the brakes, and blip the throttle to "break" the clutch loose. Otherwise I'm "power-braking," which is of course not ideal. Unfortunately, I lack the skills to troubleshoot and solve the problem. — Christopher Belling/New York

A: The Norton Commando clutch is usually pretty easy to set right, but there are a few things to check. First among them is the stack height, the total thickness of all the plain plates, friction plates and pressure plate. For your 1975 model the height should be close to 1.027 inches. If the height isn't correct, you'll notice it with either a dragging clutch like you describe or a difficult pull at the clutch lever. It's possible that over the years there has been some mismatching of parts between a 750 and 850 clutch. The diaphragm spring and clutch basket are the same across the models, but the number and thicknesses of the plain and friction plates is different. For the 850 the friction plates should be 0.121 inches thick and the plain plates should be 0.080 inches thick, with the pressure plate being 0.102 inches thick. The 850 has five friction plates and four plain plates, while the 750 has four and three, respectively. Another common problem is a notched basket or clutch hub. This will tend to keep the plates in contact with each other even when the clutch is pulled in. To complicate things further, the plates can build up oil residue and stick to each other. On the right side of the bike, you should open the inspection cover of the gearbox to make sure of two things. One, that the clutch release lock ring is in all the way and tight, and two, that the cable to the clutch rod actuation lever hasn't fallen out of position. It can fall down when the clutch pack and rod is removed. To make a long story boring, I think you'll need to tear down the clutch and check everything to see what's out of spec.

Triumph Trident Boyer Ignition Troubles

Motorcycle Classics tech expert Keith Fellenstein
Editor's note: If you're having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith's Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with "Keith's Garage" as the subject.

Q: I recently purchased a classic Triumph Trident with wiring problems. The biggest problem at the moment is that the Boyer ignition doesn't compute to hook the coils in series. When tested, there is a voltage drop until near nothing on the last coil. Do I have coil problems? The other problem is the flasher that is hot all the time, the left turn signal works but not the right. — Gene McKillips/via email

A: I agree, at first glance wiring coils in series just looks wrong. The difference between points ignition and electronic ignition on the Trident is that the three sets of points fire each coil in sequence, while most electronic ignitions fire all the coils simultaneously. That's called wasted spark ignition, since in the case of the Trident only one cylinder will be on the compression stroke while the rest are on some degree of exhaust stroke. If you are still using the original coils, the problem with wiring all the coils in series is the voltage drop becomes a problem; the coils don't fire properly or at all. Where you once had three 12-volt coils, each wired separately, now you need — ideally — three 4-volt coils wired serially in order for each coil to receive enough voltage to fire properly. The Boyer instructions call for using 6-volt coils. If you make that switch you should be OK. I have to say that of all the bikes I own, an electronic ignition makes the most sense on my Trident. As to your left signal problem, grounding those old Lucas stalks is a common problem. The originals back in the day had a ground wire running from the socket to the metal pipe connecting them to the bike frame. Modern copies rely on the chrome plating on the plastic to ground the socket. As you might imagine, this fails over time due to corrosion and flaking chrome on the plastic.







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