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

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.

No Spark on a Husqvarna 250 WR

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 just bought a 1972 Husqvarna 250 WR. It has been sitting in a heated basement since 1975. It was never raced and is all original. It even still has the original tires. What it doesn't have is spark. I got a flywheel puller, but I have not removed the flywheel yet. Using a multimeter, I'm getting a reading of 4.32 ohms on the original coil. I'm not sure how to test the stator or if that is the correct next step? — Randy Kuser/via email

A: It sounds to me like the coil is fine, so next I would rotate the flywheel until I could see the points through one of the flywheel slots. They're bound to be corroded from sitting and may not be conducting properly. You can take a thin piece of card stock like a business card and pull it through the points to clean them a little bit. Spray a little contact cleaner on the points and switch to a clean strip of card stock and repeat until the card is clean. You may find you now have spark.

Motorcycle Lift Recommendations

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: Can you tell me what to look for in a good motorcycle lift for home maintenance? — David Geiger/via email

A: Thanks for a great question. Which of course raises other questions, because what lift you buy depends on what kind of work you'll mostly use it for. I usually see two different types of lifts, the platform lift and the parallelogram lift. If you have the room for it, you can't beat a platform lift. If your space is limited, the other type takes up less space and is usually light enough to lean up against the garage wall. I use both, depending on the work at hand. If I'm replacing old tires, the parallelogram lift allows me to remove both wheels at once, handy for me because I don't have tire changing equipment and take all my tire business to another local shop. If I'm working on a long-term revival, the platform lift gives me room to place parts removed from the machine and lets me raise the bike up high enough to work on it comfortably. I started out with a Harbor Freight lift over 10 years ago, and that lift is still being used at editor Backus' shop. I replaced it with a Titan air-operated lift because I got tired of pumping the Harbor Freight lift up manually several times a day when I was working on multiple bikes.

Most if not all the platform lifts will have a rear wheel drop-out for tire work. Most if not all the platform lifts will come with an adequate front wheel chock, but if you use them much you will want something better. I've got a Condor Pit Stop/Trailer Stop. It works perfectly.

Autolube Oil Mix Ratio Questions

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 1966 Yamaha 305 Big Bear. I had one of these when I was a teen and found it to be almost indestructible. I am wanting to reduce the oil mix ratio on the Autolube oil system. I have looked at several shop manuals and the factory only shows one setting. There is a pin that aligns with a mark on the pump and is adjusted with the throttle cable. I think that by using a synthetic 2-stroke oil (Amsoil) that I can reduce the oil mixture ratio, thereby reducing exhaust smoke and increase spark plug life, as well as improve overall performance. What are your thoughts on this, and what procedure would you recommend? — John Botts/Ponca City, Oklahoma

A: My usual solution to oil injection problems has been to bypass the pump if possible, and pre-mix to your desired ratio. The Yamaha manuals I have mention removal of the oil injection system as an option for competition and suggest a 40:1 gas/oil ratio. I have little experience here in changing the pump output, so I thought I'd get some expert advice from the folks at HVCcycle, 2-stroke specialists in Nebraska. Brad Obidowski from HVCcycle says: "Keep in mind the oil in the mix has to lubricate the crankcase main bearings too, so be careful you don't cause yourself engine problems chasing less smoke. Modern low ash oils burn better, leave less residue, smoke less, and protect better anyway. If you do decide to change the autolube pump, 0.012-0.015 inch is the standard shim gap. You need to reduce this to reduce the amount of oil. I's mostly guesswork once you deviate from the factory settings." He also mentions that trying to adjust the flow by modifying the cable pull could result in too little oil at higher rpms, causing problems. Reducing the amount the cable pulls will leave the output of the pump at an idle state longer, thus reducing the needed extra oil at cruising speed. Adjusting the shim stack keeps the oil delivery constant with the required throttle position and rpm range. My final advice would be to set it up as stock. Too many problems arise from getting the mix wrong.

Pitted Master Cylinder Fixes

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: A couple of issues ago, I fielded a question about a pitted master cylinder on a Honda, where the part in question wasn't available as a replacement. I mentioned that I didn't know of any places that offered sleeves for Hondas, though I knew of plenty for British bikes. Several readers wrote back with places they knew of that offered that service. Proof, if any were needed, that motorcycle gearheads are the best people. Here's a sampling. Thanks to everyone who wrote in with solutions to the problem. — Keith Fellenstein

A: I had a similar situation on my 1980 Suzuki GS1000 even though it is used regularly. The infamous pitted bore, and since the bike is pretty much made out of unobtainium I had it sleeved. In my case I used White Post Restorations. They installed a brass sleeve of the original bore size and now it's better than new with no more corrosion issues. — Floyd Webb/via email

A: In your response regarding the CBX master cylinder, you said you didn't know of any companies that provide sleeving service for Hondas or any other brand master cylinders. I have run into this issue on several of the vintage metric bikes I work on. There is a company in Minneapolis, Minnesota, that can sleeve pretty much any metric master cylinder as long as it's within the dimensions of the special European stainless steel tubing they stock. They bore out the cylinder, press in the stainless sleeve and then hone out the inner diameter to match the original inner diameter so OEM or aftermarket stock cylinder components will fit right in. Contact Brake & Equipment Warehouse. — Earl Johnson/via email

Triumph Tiger Gauge Vibration

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 1977 Triumph Tiger. I have a recurring problem with both the tachometer and speedometer. At higher speeds (50mph-plus) that generate greater vibration, the entire gauge begins to rotate within the black rubber housing that holds the gauge. As it rotates, the lighting fixture/bulb comes loose and then falls out of the gauge. I then have to remove the gauge and rubber housing from the chrome bracket that holds them, remove the gauge from the rubber housing and then re-seat the gauge so that the opening for the bulb lines up with its matched opening on the rubber housing. You may very well have heard of this before. Any ideas how I can prevent this from happening (besides keeping my speeds under 50mph)? Thanks for your help and for your terrific columns in Motorcycle Classics. — Ron/via email

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A: In addition to the vibration, you have the torque reaction of the instrument against the rotation of the cable, too. A number of fixes come to mind, but probably the easiest one would be some double-sided tape or foam installed between each of the instruments and the cup. It wouldn't require much to hold it still against the vibration.

Triumph T120 Tiger Spark 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 have restored my 1971 Triumph TR6R T120 Tiger from top to bottom. The engine and electrics were professionally done, while I stuck to the other things. I’ve had the bike out half a dozen times and all seemed fine. Recently, while riding my Tiger, which now has 168 miles on it after the rebuild, my engine decided to run on one cylinder. I limped home. The coils are original Lucas 17M12. I checked for spark at the plugs first, the wires secondly, and got spark on the left side (as I sit on the bike) but not the right side. The bike has a new Pazon ignition in it. I then switched the wires to the opposite, and also did the same with the plugs and the coils. I got the same results on the right side — no spark. I took an ohm reading on both of the coils and got 4.7 on the primary side, and 5.36 and 5.3 on the secondary sides. I also changed gas. Upon start-up after all of this, the bike ran fine for about 30 seconds and then the right cylinder stopped running again. Am I on the right track to assume that I need to replace the coils? Both sparks are orange/light yellow when they fire. Are the coil ohm readings correct/within specifications, or does it indicate that they need to be replaced? The book says 3 ohms minimum and 3-4 ohms maximum for primary resistance, but nothing about the secondary resistance. Maybe I’ve answered my own question, but I’d like to hear from an expert if I am on the right track. — Burt Horner/via email

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A: The biggest problem I can see is you are running two 12-volt coils in series in a wasted spark ignition system that calls for two 6-volt coils in series. Since the Pazon charges and fires both coils every time, you are giving it too much of a load to deal with. Switch to two 6-volt coils in series or get one dual output coil of 3 ohm primary resistance and I think your problems will disappear. Update: I got an email back from Burt, and after changing to 6-volt coils and chasing down a grounding problem, he’s on the road again.