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

1967 Triumph Bonneville Carburetor 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 e-mail with “Keith’s Garage” as the subject.

Carburetor issues

Q: I have a 1967 Triumph Bonneville with 18,000 miles on it. It recently started running with a rough exhaust note once it was warm. After sitting all winter it started with one kick, but from then on it ran very rough. The left cylinder exhaust ran hot on start. The pipe and exhaust were hot while the right side was cool. I thought maybe I had a tight exhaust valve, so I adjusted it. It was better, but still not right, so I readjusted it, and the left cylinder went back to running hot. It still starts on the first kick. I have also noticed that the carburetor ticklers take forever to flow, where in the past they filled more quickly. – Peter/via email

A:  When you say the right pipe was cool it sounds like maybe the right cylinder wasn’t firing, or did you mean that in comparison to the left it was cooler? Assuming you meant the latter, and knowing that it sat all winter, I’d suspect a restricted/clogged jet on the left carburetor leading to a lean condition for that cylinder. Just to be sure of the state of the fuel system, I’d pull the carburetors and clean them both. Since you mention difficulty in getting the ticklers to work well, double check the float heights. They shouldn’t change on their own; they are difficult enough to change on purpose unless you are using the new StayUp floats. Another possibility if the bike is still on points would be timing differences, with the left cylinder running with the timing retarded in relation to the right cylinder, but since you said it ran well enough when parked I’d check the fuel delivery system first.

Rear Brake Master Cylinder Found

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.

Master cylinder found

Q: Last issue, Dennis Ventura wrote in looking for a rear brake master cylinder for his 1983 Kawasaki GPz750. He recently sourced a cheap and effective replacement and wrote in to tell us about it. Well done! — Ed.

A: I wanted to give you an update regarding my GPz rear brake woes. I solved the problem by going to a nearby Japanese bike salvage yard and just plunking down the old one on the table and asking, “What do you have that looks like this?” The gentleman helping me came back with one that looked similar, complete with remote reservoir, from a late-model Kawasaki Ninja 250cc. Everything lined up. I used the 1983 mounting bolts and the line from the master cylinder to the rear caliper was the same size, as well. The reservoir even went into place using the 1983 hardware. It cost $50. I forgot just how much fun that bike is to ride. Dennis Ventura/via email

Hard-Starting Yamaha SR500

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. 

Hard-starting Yamaha SR500

Q: I’ve owned my early 1980s Yamaha SR500 since new and it has always been hard to get started when cold. Unless I get the kickstarter at the very top of its stroke by using the compression release and give it all the oomph I’ve got, it doesn’t even think about starting. Even then, if I’m holding my mouth wrong it won’t start and I have to try again, over and over. If I’m parked on any kind of a slope it’s much easier to just get it rolling and bump start it. Hot starts are a little more predictable. I’ll press that little white button up on the bottom of the carburetor (which cracks the throttle open a bit) and if I’m lucky it will start after a couple or so kicks. Is this a normal situation for these old thumpers, or did I just get a lemon from the get-go? Is it an ignition thing, timing, a mixture issue or what? It’s never kicked back on me. The bike runs fine once it’s started, and I really enjoy riding the SR500. In fact I’d probably ride it a lot more if it wasn’t such a recalcitrant B#$%@ to start. Do you have any ideas how I can get the old girl to start more easily on a more regular basis? — Mac/via email

A: I have a friend with an SR500 who is making a custom out of it. He will soon be bringing it to me to do the wiring and I’m looking forward to the chance to learn more about the model. Your mention of hot starts being easier makes me suspect you could go a little richer on the idle jet to improve your cold starts. What does your spark plug look like? White insulator or brown to black? If mostly white it’s definitely lean, a common condition with bikes of that era. MC

Engine Life for a 1984 Yamaha FJ1100

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.

Yamaha engine life

Q: Ten years ago I bought a 1984 Yamaha FJ1100 from the original owner — an old friend — with 25,000 miles on it. At that time the bike had been sitting for many years and it took a lot of TLC to get it back on the road. Over the years since, I’ve had to repair or replace a number of things that you would expect to fail after 32 years, but the bike has never failed to get me home from a ride. The engine is in great shape as far as I can tell and uses very little oil. When I first purchased the bike, my friend and I replaced the old clutch with one that would accept full synthetic oil, and I have run that in the bike ever since. At 40,000 miles I discovered three valves were tight and had the local Yamaha dealership adjust those. So this is my question: How long were these engines designed to run before needing major surgery? I read somewhere that the cam chain needed replacement at 50,000 miles and required the engine to be completely disassembled to replace it. Are the tight valves an indication that the heads will need to be rebuilt in the near future? Do piston rings last beyond this 50,000-mile range? It’s my understanding that the engine uses roller bearings on the crankshaft and transmission. I also read that these first year FJs were prone to having the second gear fail if the bike was abused (i.e., drag raced), but to date the transmission shifts fine. The bike currently has 42,000 adult-driven miles on it. Is it reasonable to expect another 42,000 miles on this engine, or am I just around the corner in needing a complete engine rebuild? — Tim/via email

A: Most of these questions don’t have a definite answer without some further diagnosis. For example, there is no way to know if the cam chain is worn out without checking it physically by pulling the valve cover and examining the chain. You can test for piston ring wear by doing a leak-down test or the more common check of watching for blue exhaust smoke on acceleration. Valve guide wear can be tested in a similar manner by looking for blue smoke on the overrun. Valve adjustment typically tightens up over the life of an engine with mechanical adjusters due to slow friction wear between the valve and valve seat. Several of the big Yamahas of that era had the reputation of jumping out of second gear if regularly abused, but it sounds like your bike wasn’t treated badly, so again you’re probably OK there. Overall, I’d say if you have been rigorous in your oil and filter changes and continue to inspect the used oil for unusual particles, you should just enjoy the bike and ride it for as long as it lasts, which is probably many more miles yet. MC

Norton Commando Roadster Idling Problem

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.

Norton Commando idling problem

Q: About two years ago I bought a 1974 Norton Commando Roadster that was  in excellent original condition, with one exception: The left cylinder doesn’t fire regularly at idle. I had the original ignition upgraded to a Pazon electronic ignition, but the problem remained. I replaced the original Amals with new ethanol-resistant Amal carburetors, and still there was no improvement. I also tried reversing the coil wires to see if the problem changed sides, and the left cylinder remained anemic at idle. I recently replaced both coils, plug wires and plugs, but the problem remains. The old plugs indicate rich running on the left, which I think may be due to no fire at idle. The bike runs great otherwise, and is a joy to ride. I’ve compensated by using the idle mixture set screws to maintain a slightly higher idle, but the right cylinder is carrying the load at idle. Do you have any ideas why this is happening after installing new Amals and the Pazon ignition? Emmett Fox/via email

A: Having chased this problem through all new equipment with no resolution must be maddening. It also makes it hard to diagnose, as you have already taken all of the easy answers out of this equation.

The first check is compression: If that cylinder is low, that could be the issue. The only other easy fix that I can think of would be to run a separate ground wire from the cylinder head (under a head steady bolt perhaps), directly back to the battery. I’ve read of poor grounding resulting in one cylinder firing in a wasted spark ignition where you’d think they would both have to fire due to the nature of the system. Adding a direct ground fixed that problem. Now the other possibility is that for some reason the left side isn’t getting the right mixture at idle to fire properly. Does the left side kick in if you pull the slide up on that carburetor only? If so, then you have a problem with fuel, not fire. I’ve also read enough about the new Amals to know that you can’t take it for granted that they are free of machining swarf as delivered from the factory. It’s worth your time to make sure the idle passages are clear and working. MC

Rear Brake Master Cylinder for a 1983 Kawasaki GPz750

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.

Finding a master cylinder

Q: I own a 1983 Kawasaki GPz 750, and I am in need of a rear brake master cylinder. I’ve already tried to find a rebuild kit; however, there is no part number listing for one from Kawasaki or the aftermarket. I’ve called quite a few salvage yards and have not had any success. Each time I ask what will work instead from either Kawasaki or the aftermarket, no one seems to know. So I pose the question to you: What from Kawasaki will work or what from the aftermarket will work? I’ve spent a number of years re-doing this bike and this is the last hurdle. I hope you guys can offer a suggestion or point me in a direction. Dennis Ventura/via email

A: The GPz was produced from 1982 to 1985, and yet there are no replacement kits for the rear master cylinder. I checked several sources including K&L and Kawasaki. Any readers out there with parts substitution advice? You may have to find a master cylinder you can adapt and install in place of the original. This is one of the many challenges of owning old bikes. MC

Rebuilding Ewarts Gas Taps

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.

Rebuilding fuel taps

Q: I’m trying to re-cork some old Ewarts push-pull gas taps. How do I get the old pins out? — Jim Koenig/via email

A: The best advice is probably to replace them with something else, but if you want to keep the originals, the first thing you want to do is buy several corks so you have a chance to select some good smooth ones and also in the event you split one installing it. The brass rod that holds the cork in place is peened over into the chrome tap pull, so you have to drill through the peening. Center punch the brass and use a small bit to drill just barely into the rod. Press or punch out the rod from the pull. While you are cleaning up the brass, boil a little water and sink the corks (I know, right?) in the water to soften and swell them. Once you have the brass cleaned and the corks soft, push a new cork onto the brass rod. Take it easy pushing it over the diameter change; this is where the cork will split if it has a mind to. If you haven’t drilled off too much of the brass rod, you can re-peen the end into the chrome pull, but a little Locktite bearing fit will also help hold the two together. A very little goes a long way, and you don’t want any on the cork. Carefully fit the cork back into the tap body. I’ve been warned against greasing them, but a very small amount of silicone grease on the very edge of the cork entering the tap helps ease the two parts together. MC