Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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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



4/6/2016

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.

Fouling spark plug

Q: My motorbike is a Bajaj Caliber. The spark plug on it is a light brown on long trips, but if I check the plug after a short journey or when it’s just been idling for a bit, the plug tip is black. Why is this and how can I overcome this problem? — Ricardo P./via email

A: If your plug is black and sooty at idle or low throttle settings, I’d try leaning out the idle mixture by 1/4 to 1/2 a turn. You may have to increase the idle speed if you do that, and you may find it stumbling a bit as you open the throttle. Oftentimes, I’ll adjust the idle a little rich so that acceleration is smoother as you open the throttle. If the plug is just black and not fouling, that may be the best compromise. (Note: A follow-up email from Ricardo says this worked.) MC 



3/23/2016

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.

Ethanol troubles

Q: As it’s very difficult to find ethanol-free gasoline these days, I’m curious as to your thoughts on the long-term effects of that concoction on daily riders? My last experience was with my not exactly vintage 1994 BMW R1100RS. Through 65,000 miles the effects of the less-than-ideal fuel was noticeable, with ventures into the tank to change out fuel filters and rubber hoses. We hear of additives to calm the effects, including Stabil and the like, but nothing is very confidence-inspiring. This bike was injected, so the injectors were a concern, along with every gasket and plastic part contacting the fuel. Then there is the “coat-the-tank” exercise that is commonly temporary and necessarily repeatable for steel-tanked bikes. So while I’d love to go back to the Honda CB500 four of my earlier days, I have my doubts. — Terry Meyers/via email

A: While it’s certain that ethanol in gasoline damages fiberglass tanks, the effects on the rest of the fuel system are more subtle. If your bike has a fiberglass tank, you should stay away from gasohol, as the ethanol dissolves fiberglass. Ask anyone with a vintage Bultaco and you’re sure to get an earful. It is becoming more difficult to get ethanol-free gasoline. Websites such as pure-gas.org show where you can buy ethanol-free gas in the U.S. A more expensive option is aviation gas, assuming the local airport will sell it to you. It may be technically illegal, as I don’t think avgas has highway taxes added to the price. The problem there is that you can’t travel and be certain of a good supply. That brings up my modus operandi, which is that any gas being burned right now is good enough. It’s when you let it sit in the tank for any length of time that problems stack up. You should make sure the fuel lines and any rubber parts in the carburetors or fuel system are alcohol resistant. For storage, I usually try to not leave a partially full tank of any fuel; the extra air space above the fuel invites condensation and rust. An ethanol treatment additive can help with the long-term effects of storage, too. MC



3/9/2016

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.

Ignition or carburetion

Q: I recently finished rebuilding my 1978 Triumph T140E. I installed a Boyer Bransden Mark III ignition and set the static timing. I installed the crankshaft plunger tool to confirm that the rotor mark on the alternator is at 38 degrees before top dead center (BTDC). On my rotor, which is keyed to the shaft, there are two marks 180 degrees opposite each other. I first found the TDC mark on the flywheel, then, with the bike in high gear, backed the wheel up with my finger on the plunger until it clicked into the 38 degrees BTDC hole (full advance). This made the pointer on the primary drive cover line exactly up with one of the marks on the rotor, which I marked with white paint. I felt confident this was 38 degrees BTDC. I then lined up the magnetic reluctor on the camshaft taper with the hole in the Boyer plate for clockwise timing and tightened it. It seems to have seated and be tight on the camshaft taper.

I can start the bike, though it seems to take an extraordinary amount of effort; many kicks, an occasional kickback or a backfire through the carburetor. Once started, it seems to skip at times at idle, and when ridden seems to lack pep, though it sounds OK. When I applied a timing gun to it, I had to move the plate far counterclockwise (I am not sure if this means I am advancing or retarding the spark) to get it to line up at high rpms. Then, when I shut the bike off and tried to start it again, I got a wicked stronger kickback through the kickstarter and more backfiring through the carb. I put it back to the original (static timing) setup, and got the same result I mentioned first. Once the engine is warm, it starts up much easier, often in just a kick or two.

What could make it so the stroboscopically set timing yields results are so different from the static timing and cause so much trouble when starting? This bike is a late 1978 T140E with new Amal MK I premier carbs replacing the old Mk IIs, set with 106/200 jets. The battery, wiring harness, coils (two 6-volt in series), plugs and plug wires are all new. Thanks for your advice. — Aram N./Denver, Colorado

A: Let me see if I can help with your timing issues. First off, moving the plate counter-clockwise when the rotor moves clockwise means you are advancing the spark. Too much of that will definitely lead to kickback when starting. Make sure you have the correct color coded leads from the timing plate connected to the black box; reversing them will lead to timing problems. Make sure your battery is fully charged; a failing battery can lead to timing problems. If at all possible, power the timing light from a separate battery source. That will eliminate ignition noise in the circuit as a source of bad readings. If the timing plug and the alternator rotor line up, I’d say your static timing is set correctly.

You mention that the bike starts much easier when warm. This leads me to believe your problem may be more carburetor than ignition. The skip at idle and lack of pep also indicates that. Backfiring through the carburetor when starting is usually caused by a lean condition. Make sure the idle circuit is clean; new Premiers have been known to have clogged idle passages. New Premiers also come with stay-up floats: Make sure your float levels are correct. Does a simple press on the tickler allow you to flood the carbs to start a cold engine or do you have to press them repeatedly to make it work? A possible complication is the recent rebuild; are you sure the cam timing isn’t off? I hope this helps. Let us know how things work. MC



2/24/2016

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, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Non-starter

Q: I have a 1980 Kawasaki 440 LTD motorcycle. Last September the starter stopped working and I took it to my bike guru here in Chino Valley, Arizona, who advised me to get another starter. My problem is locating a company that has a starter, either rebuilt or NOS for this motorcycle. Do you have any suggestions, or sources that you might recommend? I have the money and my mechanic is ready to get to work, but we need a working starter.  Mike/via email

A: My usual parts suppliers come up short in replacement starters for this model, but it looks like you can have Rick’s Motorsport Electrics rebuild your starter for $235. If you know of an automotive electric specialist in your area, you may be able to have it rebuilt there. Either way, good luck. Note: I got a follow up email from Mike, and he found a used starter at a bike parts yard in Phoenix.





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