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


Commando Recommendations and Slipping Clutch: Q and A

tech-corner

Recommended Commando

Question: I’ve been a fan of Motorcycle Classics since the premiere issue, and your column is always the first thing I look for. I really love my 1979 Suzuki GS1000E, and I’ll never give it up, but a friend had a bright yellow Norton Commando in college, and I’ve always wanted one ever since. Strictly from the standpoint of performance and the joy of riding, what year, model, and upgrades would be the best choice? Do you know of any shops on the west coast or in the Midwest (I live in Alaska) that specialize in Commandos? Other than eBay, where should I be looking for one? Thanks for your advice.

Doug/Anchorage, Alaska

Answer: The Roadster models seem to be the most numerous, with the Interstate models scarcer and the HiRider model the least liked (and perhaps less expensive as a result). The early Fastback model is beautiful, but suffers from a fiberglass tank that is problematic with ethanol-laced gasoline. I’ve got a 1974 Roadster model and with the Colorado Norton Works electric start upgrade (see story at bit.ly/cnwstarter) it’s as easy to use as any modern bike. Since you have a Suzuki as your favorite ride, you might be best served looking for a 1975 model Commando with electric start. After 1974, U.S. safety standards required all motorcycles to have left-foot-shift/right-foot-brake, so there wouldn’t be any control confusion between motorcycles. As I mentioned above, I’d avoid any bikes with fiberglass tanks due to fuel issues. As for where to look, Craigslist, Facebook Marketplace and word of mouth are all options to add to eBay.

Clutch issues

Question: I have a 1966 Yamaha YDS3C with a slipping clutch. When I purchased the bike it had three 3.5mm friction plates and three steel plates. The owner’s manual I have shows a diagram with four friction and four steel plates. I ordered new friction plates (3.6mm) from Barnett and an extra OEM steel plate. I installed everything and put it back together. It still slips when kicking it over. I noticed as I tighten the nut that holds the clutch in it slips worse. I’m stumped and at a complete loss of what to look for. I’ve heard from Facebook forums that there should be five plates but it’s impossible to fit five plates into my clutch housing.

Luke/via email

Answer: I’ll start with the simplest solution first and then move to more complex measurements. Make sure you’re not using a modern automotive oil, often rated a low 5W or even 0W. Those have friction modifiers in them that can cause wet plate clutches to slip. Use an old formulation oil such as Castrol GTX. Next, measure the clutch friction plates and springs to make sure the right parts are installed. The friction plates should measure .169 inches or 4.3mm thick and the springs should have a free length of 1-inch or 25.5mm length with a tolerance of .08-inches or 2mm. Note: I heard back from Luke and he replied: “I ended up fixing my slippage. My plates were for the later year with the 3.5mm clutch plates. I resolved the issue by adding an extra steel plate to get the right stack height, my springs were all 25.5mm.”

Wet sumping problem

Question: I have a 1974 Triumph Trident T150 that drains oil into crankcase after a few days. I have read a few articles on the problem and was hoping you might have an easy replacement or repair strategy where I don’t have to take the engine apart for a proper fix. Many thanks!

Bryan Domachowski/via email

Answer: The Trident engine has an anti-wet sumping valve built in that works fairly well. Yours could have a bit of debris holding it off the seat. On the underside of the engine, on the left side near the oil sump plate you will find the bolt holding the ball and spring. Place a pan under the engine to catch any oil and parts that may fall and loosen the bolt. A spring and steel ball should fall out when the bolt is removed. Clean both and replace the parts, ball first then spring, then bolt. If your setup has a copper washer used to seal the bolt, don’t forget to anneal it with a propane torch to soften the copper before reusing the washer. If, after this procedure you still have wet sumping there is one more thing you can do to try and stop it. Repeating the removal procedure, place the ball back in the cavity and, using a brass drift on the ball, give it a tap with a hammer. Don’t overdo it. A light rap should be enough to conform the seat and ball to each other. Then replace the components as before.

Slave cylinder issues

Question: I have an 1985 Suzuki Madura GV700, and it has lost all its clutch fluid. I’ve been told it’s the clutch slave cylinder because of the fact I’m not leaking fluid. I’ve watched videos of replacing them but never on a Madura. I have found that the head of the bolts holding the cylinder are not on the left hand outside. They’re on the inside. From what I get from the owners repair manual, I have to take the back wheel off, then the driveshaft, then remove the secondary gear set before I can get at the bolts. Let me know if I’m headed in the right direction, and if you have any tips to doing the repair. Thanks!

Ed Shaver/via email

Answer: Unfortunately you’re right, you have to remove the driveshaft first, then the secondary gear set. Only then can you remove the clutch actuating cylinder from inside the secondary gear set. This is another bike I have no experience with so I don’t have any shortcuts to share. Again, maybe our readers can help out.


Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an email with “Keith’s Garage” as the subject.

Rita Ignition, Tire Tubes and Carburetors Q and A with Keith

wheel

Lucas Rita ignition

Q: Hi Keith. I read your article on Triumph T140E wiring and the Lucas Rita ignition. My 1976 Triumph T140, which has been heavily customized, has this system fitted. The bike is being recommissioned, very slowly due to time, but I’m working on the electrics at the moment. I noticed when I was testing the ignition that when a spark is triggered both plugs spark each time. Is that correct? Thanks.

Michael Atkinson via email

A: Both coils firing is normal for the twin Rita, as it is a wasted spark ignition. One cylinder is on the compression stroke ready to fire and the other is on the exhaust stroke with nothing to fire. I wanted to check my memory so I just looked at the wiring diagram and the giveaway is that the coils are wired in series. The first time I see the Rita show up in the parts books is for the 1979 range of twins so yours was indeed added later.

Triumph carburetor issue

Q: Hi Keith, you are my “go to guy” for British motorcycles, so here are a few questions for you. My 1965 Triumph is winterized every year, but I still start it up every few weeks. I use a fuel stabilizer and have never had any problems. This year, I had trouble starting it. When it did start, it backfired and ran rough. Eventually, it smoothed out and I took it for a ride. After a few miles, it died and wouldn’t start. Fortunately, I was only a couple of blocks from my shop so I pushed it there. While checking it out, I noticed the battery was weak. The battery was several years old so I wasn’t going to waste my time with it. I installed a new one and it started right up. I drove it several miles and it was fine. When I returned, I left it running on the side stand. As I walked away, it loaded up and died. It acted like it ran out of gas. I started it back up, and when I leaned it over to put on the side stand, it died again. I started it back up. Every time I leaned it over to the left, it started sputtering. When I returned it to upright, it lined out. I then leaned it to the right, and engine speed increased. OK, what’s going on? I looked both carburetors over, and remembered that it had two identical carburetors on each side. They are both left hand carburetors. Same numbers, float bowl cover installed on the left side, ticklers on the left side. Do you think this bike left the factory like this, or do you think someone might have changed the right carb out and replaced it with a left one? I was going to check the float on the right carb, but would have to remove the carburetor as the cover is on the inside. Have you ever heard of anything like this? Could the wrong carburetor be part of the problem? I know you’ll have the answer for this, you’re the best! Thanks in advance.

John Botts/Ponca City, Oklahoma

A: On the Monobloc, the jet is on the right side of the carburetor, while the bowl is on the left. If leaned over to the left, it is possible to reduce the fuel flow to the jet, leaning it out and causing your stall. They were both left hand bowls from the factory.

Tires and tubes

Q: Hello sir, I just read your excellent article in response to a guy with an alloy rim. I just bought a 1972 Triumph Tiger and I need to know if tubeless tires will work on there with a tube installed and what I should know about this combo. I tried putting a tube in a tubeless car tire once and it blew out on the freeway during a 300 mile high-speed trip the next day. I figured it was heat build-up. I’d hate to have that happen on a motorcycle. I’m not 19 anymore. Thanks.

Farley/via email

A: It’s not ideal, but it is often necessary due to a limited choice of tires in the right size. I’m using Avon tubeless with tubes in many of my classic bikes. It’s probably safest to consider that putting a tube in a tubeless tire drops the speed rating one whole classification.

Carburetor adjustments

Q: Hi, Keith, I’m working on a Mikuni carburetor. Does it have just one adjustment screw? If there are more, where are they located?

Jimmy Webb/via email

A: Mikuni carburetors, and many others, have two adjustment screws, one controls the air/fuel mixture at idle and the other controls the throttle opening at idle. You use both to achieve the optimum idle, smooth and not too fast. I’m going to describe the common VM series. The first screw is closer to the air intake side of the carburetor, which makes it an air bleed screw. This controls the air relative to the amount of fuel, the amount of fuel being metered by the idle jet inside the carburetor. A common starting point from which to make adjustments is 1½ turns open from lightly closed. The second screw is located right at the midpoint of the round slide and is the throttle opening screw. That one is usually set to one turn in from the slide bottoming out in the carburetor body. Start the engine and adjust the throttle screw to achieve your desired idle speed, then turn the air screw in and out in ½ turn increments to see where the idle is smoothest. This may raise or lower the idle speed, so you may again have to manipulate the throttle screw to get to your desired idle. A few times going back and forth between these 2 screws will give you the best idle speed. If the bike hesitates accelerating off idle, you may have to compromise the mixture by richening it to accommodate the sudden increase in airflow from opening the throttle. With an air screw like the Mikuni, richening it means turning it in, about 1/4 turn at a time to find the sweet spot. Adjust the idle speed screw again to achieve your desired turnover speed.

Norton Commando Q and A with Keith

Commando revival

Question:

Hello, Keith, maybe you can help me. I bought an all original 1975 Norton 850 Commando from a woman whose husband had passed away. The bike has 2,750 miles and is a one-owner machine. It appears to be 100% original and was last inspected in 1995. I have cleaned it up, replaced the fluids and some gaskets, cleaned the carburetors and more. I did all the things that I thought should be done to a bike sitting for so long. It was in very good condition for its age, sitting in a dry garage with little heat. I cleaned the gas tank, put a new battery in it and it fired right up. All the lights work. That was a month ago. It idles great, but above that, it misses constantly with dry sooty plugs, both are exactly the same condition every time. I must have pulled the carbs 5 times just to check again and again. It has new coils, condensers and points, and the timing is dead on. I ran it without the mufflers on and there was no difference. I must have read the shop manual a couple of times. I was about ready to give up until I saw your posts. Please help.

 Mike Glessner/Levittown, Pennsylvania

Answer:

Well you’re probably not going to like hearing that I think you need to pull the carburetors off, yet again, just to check that the jets and needle haven’t been changed over the years. The recommended settings changed from 1974 to 1975 and the main jet and needle clip were specified leaner. Make sure you have the correct needle. The Commando needle has 4 small grooves above the 3 needle clip grooves and the needle clip should be in the top of those 3 grooves (leanest setting). The main jet went from a 260 in 1974 to a 220 in 1975, again a leaner jet. The reasons for these changes were to meet emissions standards and to accommodate the more restrictive airbox and exhaust.


engine

Coughing Commando

Question:

Hi, Keith, I’m stumped and thought maybe you could offer some guidance. I have a 1972 Norton Mark V 750 Commando. The bike runs great with me aboard, but not as well with a passenger. Adding a passenger causes the engine to sporadically “tug” coming through first and second gear. It almost feels like the engine is all the sudden not getting a steady flow of gasoline. It takes a half mile or so of riding for the phenomena to show itself and begin coughing and shuddering. It actually continues to get worse the further we ride. Within 3-4 miles of stop-and-start neighborhood riding, it’s time to head home and drop the passenger. Off I go again (alone) and the bike is back to running great. The tank has plenty of gas, the rider’s foot is not on the brake or brake cable, the chain tension is good, loaded or unloaded, and the tire does not come in contact with the rear fender. I’m stumped. Thanks!

Pat Long/via email

Answer:

We may as well make it a mostly Norton column this time around. It sounds to me without testing that your bike is running too rich. The old adage is running worse when hot is too rich, running worse when cold is too lean. If you have a patient passenger, drag along your spark plug wrench next time and when you hit that less than magic moment in your ride, find a safe place to stop and read your plugs. If they’re black and sooty you’ll have your answer.


Using a Twinmax

Question:

Hi, Keith, I was reading the subject article about fitting Don Pender’s carb gantry in Motorcycle Classics with interest. In the article for carb synchronization a TwinMax was used. Would it be possible for someone to explain how this is done?

Chris/via email

Answer:

The Twinmax was originally marketed for use on BMW airhead twins, but I’ve found a use for it on many other machines. It measures the difference in vacuum between two carburetors, a good indicator of throttle opening. To use it, you first have to have a vacuum port on either the carburetor or the manifold. On the Norton Commando, I remove the balance tube and plug the Twinmax tubes in there. Turn on the Twinmax and adjust it to the most sensitive setting, then zero out the meter. Turn the sensitivity knob back to least sensitive. Start the engine and see if the needle is deflected to one side more than the other. Adjust the sensitivity knob higher to highlight any deflection. The needle deflects to the side with less vacuum. Using the throttle slide stops, adjust until the needle is centered. You may then have to reduce or increase the idle by adjusting the throttle stops equally. Once done, your carburetors are now idle synchronized. With the gantry, you synchronize the slides with the nut and locknut on the top of the carburetor. The old throttle slide stop serves no purpose. If you have cables instead of a gantry you’ll need to check to make sure the cables are also synchronized, pulling the slides up simultaneously. Slowly increase the throttle to about 2,000-3,000rpm via the twist grip and check for needle deflection to one side over the other. Again the deflected side is being pulled up sooner and you’ll need to adjust the cable slack on one or the other cable to balance the carburetors. When you’re done you should be rewarded with a smoother idle and acceleration.


Send questions to Motorcycle Classics, Keith’s Garage, 1503 S.W. 42nd St., Topeka, KS, 66609, or email keithsgarage@motorcycleclassics.com

 

Electrical, 2-Strokes, Misfire and Carb Issues Q and A with Keith

 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 email with “Keith’s Garage” as the subject.

1978 Triumph T140 Electrical issues

Q: I have a 1978 Triumph T140 with stock points ignition that has lost spark. I ran the bike a couple of summers ago with an old, possibly highly sulfated, battery. Since it’s a kickstart bike I didn’t need the battery for starting. Anyway, I started the bike and began a short ride. About 5 miles out, I lost spark and ended up trailering the bike home. I parked the bike, rode others, and haven’t done any troubleshooting since that incident but would like to get the bike going again this spring. I guess my question is can major damage be done, like stator damage, etc., by operating with an old discharged battery? Thank you for any assistance you can provide.

Mark/via email

A: It’s possible but unlikely to damage the generating side of the electrical system by running with a damaged storage side. If the battery has an internal short the alternator will run at full output all the time. In this specific case though, it’s unlikely. The Lucas charging circuit in your Triumph runs full tilt all the time anyway, and depends on the Zener diode to dump excess current to ground when the battery is charged. Here are a few ways to troubleshoot your electrical system. The first would be to test the alternator windings for continuity and short circuits. Disconnect the green/brown and green/yellow leads at the rectifier and use a voltmeter (if you don’t have one, get one, they’re essential) set to ohms or continuity. Place a lead on each of those wires and the result should be close to zero or a beep if set to continuity. Put one lead on a wire and ground the other one, the results should be 1 on a digital meter and no beep if set to continuity. If all this checks out all you’ll need is a new battery.

Reviving 2-strokes

Q: I did not like 2-stroke bikes when I started riding motorcycles in 1967, but after they went extinct I bought a couple of Yamaha RDs and a CT 175. My question is, at the time I bought them they started and ran OK, but after sitting for 12-15 years, I know I need to clean out the carbs. I couldn’t drain the carbs because they sit right on top the crankcases and there is zero clearance between them. But what about the auto lube system? Do I need to do anything to make sure they still work, like flushing the system and replacing the oil? I haven’t found a source for proper 2-stroke oil for motorcycles. Thanks for your help.

Bing Fong/via email

A: The oil won’t be ideal, but it won’t be as bad as the gas would be after all those years. I’d drain the oil reservoir and put in fresh synthetic 2-stroke oil. If you have access to the oil pump, most of the time there is a small screw backed with a fiber washer on the pump body that is used to prime the system when completely drained. You could remove that screw and let fresh oil flow down from the tank through the pump and then seal it up again. Modern 2-stoke oils are a vast improvement over the old formulations. Spectro Performance Motorcycle Oils makes several kinds of 2-stroke oil. Check out spectro-oils.com

Suzuki misfire

Q: Hi, Keith, I’ve acquired a 1982 Suzuki GS1100EZ that had sat for many years. All fuel and brake systems have been completely overhauled. The engine starts, idles and runs perfectly until 7,500rpm, 1,500 short of redline. At that point regardless of load or road speed there is misfiring and no rpm increase. The intake and exhaust systems are stock as is the carb jetting (110 mains). I have ohmed out the coils and wires as well as the pickups and all are within spec. After many years of tuning and repair I find myself stumped as to whether I have an ignition or fuel problems. The spark plugs show a white color indicating a lean condition but everything is stock. Any help would be greatly appreciated.

Joe Padula/via email

A: Thanks for the detailed background of steps you’ve already taken, that’s very helpful. The early ’80s bikes almost universally suffered from fueling issues due to attempts to meet California emissions standards. Since you’ve done all the leg work scoping out the ignition system I think your next step should be to buy a set of main jets one major size larger and see if that improves the wide open running. As a quick check to see if this might help, if you can do it safely, try using the enriching circuit at wide open throttle. If the bike suddenly surges ahead, you’ll know what to do.

More carb issues

Q: I have a 1979 Suzuki GS550L with low mileage that we rescued from a backyard in Amarillo, Texas, a couple of years ago. After a bunch of elbow grease, updates, new parts, etc., the bike has been returned to life. We upgraded to electronic ignition. My problem is that the bike runs great up to about 4,000rpm. It starts easily, idles evenly and has excellent power until about 1/2 throttle. The thing acts as if it had a governor. It just sort of stalls out and will not accelerate. It reminds me of a rev limiter at a shift point. The bike is timed correctly and the centrifugal advance mechanism is working correctly. At idle, about 1,000rpm the timing is at the “F” mark and will fully advance at about 2,500rpm. So I don’t think timing is the issue. The bike has a set of rebuilt carbs. It just seems like the main jets are allowing fuel to flow at the upper rpm’s. I need some help. The bike runs and rides great in the world of idle to around 4,000rpm, but will not accelerate beyond that. Help!

Mike Baker/via email

A: My answer here is about the same as above, a quick test would be to apply the enrichment circuit and see if that improves things. If so, try larger main jets.


Email questions to keithsgarage@motorcycleclassics.com

Oil-In Frame BSA Design Issues

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 email with “Keith’s Garage” as the subject.

Oil-in-frame BSA

Q: A friend has an oil-in-frame 1970 BSA. Are there issues related to this design? It hasn’t run in 20 years.

Jerry Gere/via email

A: The only mechanical issues I’ve run into with oil-in-frame (OIF) Triumphs or BSAs were caused by careless sandblasting, leaving sand in the frame oil tank. Having sat that long, the oil left, if any, will be sludgy at the bottom. Best practice would be to first drain the oil, then remove the four bolts holding the bottom cover on the downtube. Thoroughly clean the filter screen, looking for any telltale metal parts, then reassemble with new gaskets.

Suzuki TS185 Suggestions

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 email with “Keith’s Garage” as the subject.

Suzuki TS185 suggestions

A: A number of readers wrote in to help me with the question in the November/December issue about the Suzuki TS185. I’ll let them add what I missed in my troubleshooting. Thanks for the help, I appreciate it.

From: Gene O’Meara Jr. “I read the magazine cover to cover like most readers. I noted something that caught my attention in your column, regarding jetting issues for a reader’s TS185 and its tendency to blubber at 5/8 to full throttle. I just thought I would pass on my experience renovating a 1975 Suzuki TS250. It was having similar symptoms, and after removing and working on the carburetor more than a dozen times, I finally decided to buy a second carb from an eBay source. Sure enough, the bike exhibited the exact same symptoms and I was forced to open my thinking to other areas. Eventually I found the problem: a collapsed spark arrestor in the rear of the exhaust pipe, causing back pressure. The bike could not breathe properly. It was a little torpedo-shaped thing with twisted metal to deflect the sparks. The welds had broken after 40-plus years. So I tacked it back together and re-assembled it, and on the first test ride that bike took off like a scared cat.”

From: Tim Sickel. “In reference to the problem Steve is having, it could be that the spark arrestor in the back of the muffler needs to be cleaned or removed. Having owned three of these I found this to be a recurring issue. We would remove them and it did make a big difference in the way they ran.

From: Vincent Palazzo. “Regarding the Suzuki TS185 blubber above 5/8 throttle. I suggest checking and/or replacing the jet needle and needle jet. On old bikes these items wear due to the constant back-and-forth movement of the needle. The hole in the top of the jet needle is probably elongated, with corresponding wear on the needle jet. This causes a rich condition above 1/2 throttle that you can’t jet out unless you go so lean that you will cause the engine to seize.

Kawasaki GPz550 Carburetor Suggestions

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 email with “Keith’s Garage” as the subject.

Kawasaki GPz550 suggestions

A: It looks like I’m going to let my readers do the bulk of my work this issue. On the subject of the Kawasaki GPz550 from November/December 2019 issue, I heard from a few of you with helpful advice.

From: Vincent Palazzo. “It may not be carburetion. An ignition control module can fail in such a manner that you still get spark, but it won’t advance or retard. His bike is less sophisticated in that it still has a mechanical advance on the right crankshaft end. The weights and/or rotor may be rusted/stuck in the retarded position. Since it won’t rev, I’d be willing to bet spark timing is not advancing. This will cause all the symptoms Mr. Herchenroder noted.”

From: Tom Batchelor of Moto-Resto in Florida. “I think I have a suggestion for the other Keith (Keith Herchenroder) who wrote in about his GPz550 carb issue in the November/December 2019 Keith’s Garage column. I’m guessing you may still have his contact info. Please tell him he likely needs to shorten the CV carb diaphragm springs in regards to length. This was a mandatory operation on my Bandit 1200 Stage 2 setup from Holeshot Performance, and it’s required on a lot of other intake/exhaust modified CV carb bikes. Tell him I can’t give him an exact amount to cut them down to; however, what I’d do is start with 12mm off the length and try that; and go up to 25 mm. But I’d have to know the nominal length of the spring first to make an educated suggestion.”






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