Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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7/13/2016

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.

Cylinder problems

Q: I recently purchased a 1968 Honda CL450 with just 782 miles on it. The cylinders are out of round, apparently. I had the lower end inspected and the shop told me it was nice and tight, and the pistons are fine, also. My question is, should I bore it, which will then require a new set of piston kits, or should I sleeve it, in which case I could then leave the top end alone except for new rings? Tim/via email

A: Either of those options would work, but I think boring the cylinders and fitting oversize pistons may be easier to do and probably less expensive than resleeving. Plus you get the added benefit of a little more oomph from more CCs. What makes you think the cylinders are out of round? Is it smoking excessively? You could try the test I suggest in the first letter to confirm the diagnosis. MC



6/29/2016

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.

Lots of smoke

Q: I am 63 years old. I have had my own little shop under my house for about 43 years. I have fixed just about every brand in those years. I bought a 1965 T100 Triumph 500 from a friend of mine about seven years ago. When I had a little extra cash I would throw it in the bike. I finally got it running. When I fired it up the left side cylinder smoked very badly. I rebuilt the whole engine. I had the head done by E & V Engines, new valve guides and valves, new pistons and rings at 0.20 over. I cannot figure out why it is smoking only on one side. I even put another set of new rings in it and it’s still smoking. I don’t know everything, but I think I put the engine together right. I hope you can help me. Larry Petras/Ohio

A: After talking with Larry, it seems as though he’s done about all he can to eliminate the common causes of smoking. All I could suggest was that maybe the left cylinder was not concentric and that was keeping the oil scraper from cleaning off the excess oil. I suggested he back off the valve adjusters so that they wouldn’t open, and then do a leakdown test at TDC, mid-stroke, and BDC to see if there was any change in the amount of air getting past the rings. Another possibility would be a crack in the head letting oil leak down from the overhead valves. Do any of our readers have other suggestions as to what the problem may be? MC



6/15/2016

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.

Chain and sprocket orientation

Q: I have several Japanese 2-strokes from the late 1960s and early 1970s and have an issue that has plagued me on countless motorcycles, both new and old, over the decades. I’ve never received an explanation that would seem to justify the sheer volume of instances I have run into.

 Every time I align a chain and front and rear sprockets, I find the chain will almost never run centered over the sprockets. Now, I’ve known for over 45 years that the little factory indents/alignment marks on the swingarm are generally useless for alignment purposes, so I have used all the alignment methods I have ever seen, from name-brand alignment tools (which work great, by the way) to measuring and equalizing the distance between the swingarm pivot and the axle shaft, the string method, etc. I always check the sprockets themselves to ensure they are flat as a pancake and not tweaked. Most recently, I had a piece of steel machined to be exactly straight and laid it up against the two sprockets of my current project, finding they were misaligned by 1.65mm. I then removed 1.65mm from the countershaft sprocket spacer as there was more than adequate clearance and got those two sprockets aligned within a gnat’s behind, but to no avail. For clarification, the sprockets and chain are new and correct factory OEM parts. The result is always the same: The right inner link of the chain rides up against the right outside edge of the sprocket. Thus, the chain is slightly to the left of center. I always make sure I have the correct play in the chain measuring it multiple ways, including with the shocks removed and the countershaft, swingarm shaft and rear axle all in the same plane.

Of course I am also aware that frames and mounting points, etc., were not always perfectly in alignment from the factory 40-plus years ago and can get out of whack from living a hard life over the years. Therefore I also do my best to ensure the frame is not tweaked before I ever start on a project and rectify any noted problems I find.

Out of curiosity, I recently visited my local multi-brand dealership and I nosed around the street bikes checking the chain alignment on every brand new street bike on the showroom floor. Every single bike I looked at but one had the exact same issue. The chain was to the left of center and riding on the right inner edge. Even the used bikes I looked at had the same issue. The only bikes in the dealership that didn’t have the issue were the dirt bikes. I’ve often wondered if the issue was that the front and rear sprockets were not vertically parallel and I don’t know how to check that. But after seeing all the new bikes with the exact same issue, well, I give. Chuck Floyd/via email

A: You’ve certainly put a lot of time and thought into this, and my answer is going to be so short you may be disappointed. Once you put any load on the gearbox the shaft deflects just enough to cause the chain to pull to the outside. It’s really that simple.  MC



6/1/2016

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.

Stalling problem

Q: I have a restored 1972 Triumph T100R that stalls at idle. My mechanic added a Boyer electronic ignition, but left the 12-volt coils in. It has original electrics other than that, including the alternator/stator. He tuned the new Amal carbs twice and adjusted the timing twice, to no avail. Finally, he said I just have to blip the throttle when coming to stops to prevent the stall. I am wondering if this is an electrical issue or a carburetor issue. The carbs are brand new from England. They have been synchronized carefully. Could the problem be the 12-volt coils? I have heard that the Boyer prefers 6-volt coils. It starts right up every time and idles. It’s just when I run the bike normally then come to a normal stop it dies, as if it runs out of fuel or the spark to the plugs dies. This has ruined an expensive and long-term restoration. The mechanic said he has done everything he can and that it’s my riding style. I don’t believe that, as I’ve had Triumphs all my life and none have done this. Bill/Rhode Island

A: You definitely need two 6-volt coils wired in series for the Boyer ignition to work properly. Since it fires both coils at the same time (known as wasted spark ignition as one spark occurs in a cylinder that’s on its exhaust stroke) there is a need for the two coils to present the same resistive load as one 12-volt coil. Your current setup is too resistive and I think it is keeping the ignition from firing consistently at low rpm. If you’re reluctant to take it back to the mechanic, you should be able to replace those coils yourself. Just make note of the way they are currently wired and get two 6-volt coils of the same physical size to put in their place. MC



5/18/2016

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.

Cavalcade carburetors

Q: I have a 1988 Suzuki Cavalcade 1400 that spits back through the carburetors. I took the air cleaner off and could see small flashes of fire in each of the throttle throats when it would spit back. It only does it when idling or when the throttle is held at a steady speed. The spitting back quits when the choke is on. It does get better when the engine is warmed up. I don’t think it does it when accelerating or cruising at higher speeds. What do you think might be the problem? Morris/via email

A: Be careful, those backfires can take on a life of their own and really ruin your day. I have two ideas. I think that either the timing is off or the carburetors are set too lean. Lean settings were a common problem with many bikes from the 1980s. The fastest way to EPA and/or CARB certification was to set the idle so lean it hurts. Gasoline formulations have changed since then and modern fuels don’t burn as well when run lean. You say it gets better as it warms up? And gets better at bigger throttle openings? That’s a good indication the mixture is too lean at idle, either from clogged circuits or because of an air leak. I couldn’t locate a service manual, but you’ll need to get to the idle mixture adjustment screws, which can be difficult: They’re often sealed or adjustment-limited in 1980s bikes, again due to emissions regulations.

Update: Morris later informed me that he pulled the carbs off and found that the rubber intake pipes were cracked through, plus two of the four O-rings where they mount to the head were missing. I suggested that he also clean out the idle circuits while the carbs were off, if possible. Those passages are incredibly small and any gummy gasoline or rust flakes can easily clog them up. MC



5/4/2016

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.

More power

Q: I have a 1973 Hodaka Wombat that is all stock and in nice shape. It starts right up and runs well up to around 35mph, when it bogs down and won’t go any faster. I was told by a mechanic that the 125 should go to 50mph no problem. Is this normal for stock gearing, or might I have a clogged main jet or some electrical problem? I use premix 36:1. It has a working speedometer and lights. What is a realistic top speed for this bike and how can I get more top end? — Bill Baillie/Rhode Island

A: Two-stroke engines are very dependent on their exhaust for efficient running, so I’d probably start there. Make sure the baffles are in place and not clogged with carbon and oil. The next step I’d take would be to pull the carburetor and compare the jet sizes against the stock requirements. For a 1973 Wombat with a Mikuni VM24 SH-83A carburetor, the main jet should be a 180, the needle should be a 4J1 and the needle jet should be a 0-4. If you have a VM24 SH-83B carburetor, the numbers are 160, 4E1 and N-8. The needle clip should be in the third groove from the top for both and the float height should be set at 22.5mm for both. My Clymer manual calls for a 20:1 fuel-to-oil ratio.

How does it fail at the top end? Does it stumble and cough, or just die out? I spoke to my local Hodaka expert (who has a basement full of restored Hodakas), and he thinks you may be starving for fuel. First try raising the needle by lowering the needle clip one notch and see if you have any improvement, however minor. If you do you will know you are on the right track. You may be able to fix it by raising the needle, or it may take a larger main jet. You’ll have to experiment to see what works best. MC



4/20/2016

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.

Triumph/Lucas ET ignition 

Q: While most people have given up on the energy transfer (ET) system, those of us doing a restoration for AMCA judging must live with it, as the bike must be started and the system must be within specs. As I started with just a frame and cases, the statement to “reassemble as removed” will not apply. I believe the rotor location pin on the engine sprocket is the key to its placement and as I was advised to put it at TDC with the pin at 8 o’clock. I have done so, but I still question why. The factory service books do not advise this, as best I can tell. Tom Gunn’s notes from TRI-COR service school do not address it either. Can you advise me further? — Dave Goldman/via email

A: The energy transfer ignition is an odd duck. It basically fires the coils on the upstroke, for lack of a better term, where a standard battery/coil system fires on the downstroke, so to speak.

I’ll begin by explaining how a battery/coil system works, then explain how the ET system works. The battery/coil system charges the primary circuit of the coil from the alternator and then holds the primary voltage until the points open (dwell time). Once the points open, the magnetic field produced by the primary coil collapses and induces voltage in the secondary coil. This higher voltage is what jumps the spark gap in the engine and ignites the fuel/air mixture. This system has a rectifier to change the sine wave AC alternator output to DC and a battery to level out the voltage.

The ET system keeps the primary side grounded until the points open, and then the voltage flows through the primary coil, exciting the secondary coil to produce a spark. This system has no rectifier to change AC to DC and no battery to level out the voltage, so to produce the best spark, you must time the voltage output of the alternator (sine wave) to be highest when the points open. Those old ET alternators have two sets of coils, one for lighting (ha!) and one for ignition. The rotor is placed as it is in relation to TDC so that the sine wave output will be highest when the points are to be opened. This is also why the advance unit is restricted on an ET bike compared to a battery/coil bike. Outside of the peak alternator voltage, there isn’t enough energy output to fire the coils. MC





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